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Paramedics of the Australian Capital Territory Ambulance Service during a training regime

A paramedic is a healthcare professional that works in emergency medical situations. Paramedics provide advanced levels of care for medical emergencies and trauma.^[1] The majority of paramedics are based in the field in ambulances, emergency response vehicles, or in specialist mobile units such as cycle response. Paramedics provide out-of-hospital treatment and some diagnostic services,^[2][3] although some may undertake hospital-based roles, such as in the treatment of minor injuries.

History of paramedics[link]

Early history[link]

Throughout the evolution of paramedic care, there has been an ongoing association with military conflict. One of the first indications of a formal process for managing injured people dates from the Imperial Legions of Rome, where aging Centurions, no longer able to fight, were given the task of organizing the removal of the wounded from the battlefield and providing some form of care. Such individuals, although not physicians, were probably among the world's earliest surgeons by default, being required to suture wounds and complete amputations. A similar situation existed in the Crusades, with the Knights Hospitallers of the Order of St. John of Jerusalem filling a similar function; this organisation continued, and evolved into what is now known throughout the Commonwealth of Nations as the St. John Ambulance.

Early ambulance services[link]

While civilian communities had organized ways to deal with the care and transportation of the sick and dying as far back as the bubonic plague in London between 1598 and 1665, such arrangements were typically temporary. In time, however, these arrangements began to formalize and become permanent. During the American Civil War, Jonathan Letterman devised a system of mobile field hospitals employing the first uses of the principles of triage. After returning home, some veterans began to attempt to apply what had they had seen on the battlefield to their own communities, and commenced the creation of volunteer life-saving squads and ambulance corps.

German Red Cross paramedics training in 1931

These early developments in formalised ambulance services were decided at local levels, and this led to services being provided by diverse operators such as the local hospital, police, fire brigade, or even funeral directors who often possessed the only local transport allowing a passenger to lie down. In most cases these ambulances were operated by drivers and attendants with little or no medical training, and it was some time before formal training began to appear in some units. An early example was the members of the Toronto Police Ambulance Service receiving a mandatory five days of training from St. John as early as 1889.^[4]

Prior to World War I motorized ambulances started to be developed, but once they proved their effectiveness on the battlefield during the war the concept spread rapidly to civilian systems. In terms of advanced skills, once again the military led the way. During World War II and the Korean War battlefield medics administered painkilling narcotics by injection in emergency situations, and pharmacists' mates on warships were permitted to do even more without the guidance of a physician. The Korean War also marked the first widespread use of helicopters to evacuate the wounded from forward positions to medical units, leading to the rise of the term "medivac". These innovations would not find their way into the civilian sphere for nearly twenty more years.

Pre-hospital emergency care[link]

By the early 1960s experiments in improving care had begun in some civilian centres. One early experiment involved the provision of pre-hospital cardiac care by physicians in Belfast, Northern Ireland, in 1966.^[5] This was repeated in Toronto, Canada in 1968 using a single ambulance called Cardiac One, which was staffed by a regular ambulance crew, along with a hospital intern to perform the advanced procedures. While both of these experiments had certain levels of success, the technology had not yet reached a sufficiently advanced level to be fully effective; for example, the Toronto portable defibrillator and heart monitor was powered by lead-acid car batteries, and weighed around 45 kilograms (99 lb).

Paramedics caring for a collapsed woman in New York

In 1966 a report called Accidental Death and Disability: The Neglected Disease of Modern Society—commonly known as The White Paper—was published in the United States. This paper presented data showing that soldiers who were seriously wounded on the battlefields during the Vietnam War had a better survival rate than individuals who were seriously injured in motor vehicle accidents on California's freeways.^[6] Key factors allowing the victim to survive the journey to definitive care such as a hospital were stated to be comprehensive trauma care, rapid transport to designated trauma facilities, and the presence of medical corpsman who were trained to perform certain critical advanced medical procedures such as fluid replacement and airway management.

As a result of the The White Paper the Federal government moved to develop minimum standards for ambulance attendant training, ambulance equipment and vehicle design. These new standards were incorporated into Federal Highway Safety legislation and the state were advised to either adopt these standards into state laws or risk a reduction in Federal highway safety fundings. The "White Paper" also prompted the inception of a number of emergency medical service (EMS) pilot units across the US including paramedic programs. The success of these units led to a rapid transition to make them fully operational, with the first paramedic program being in Miami, Florida.

New York City's Saint Vincent's Hospital developed America's first Mobile Coronary Care Unit (MCCU) under the medical direction of William Grace, MD and was based on Dr. Frank Pantridge's Belfast, Northern Ireland MCCU project. In 1967 Eugene Nagle, MD and Jim Hirschmann, MD helped pioneer America's first EKG telemetry transmission to a hospital and then in 1968, a functional paramedic program in conjunction with the City of Miami Fire Department. In 1969. the City of Columbus Fire Services joined together with the Ohio State University Medical Center and developed the "HEARTMOBILE" paramedic program under the medical direction of James Warren, MD and Richard Lewis, MD. In 1969. the Haywood County (NC) Volunteer Rescue Squad developed a paramedic program under the medical direction of Ralph Fleicher, MD. In 1969, the initial Los Angeles paramedic training program was instituted in conjunction with Harbor General Hospital under the medical direction of Michael Criley, MD and James Lewis, MD. In 1969, the Seattle "Medic 1" paramedic program was developed in conjunction with the Harborview Medical Center under the medical direction of Leonard, Cobb. The Marietta (GA) initial paramedic project was instituted in the Fall of 1970 in conjunction with Kennestone Hospital and Metro Ambulance Service, Inc. under the medical direction of Luther Fortson, MD. The Los Angeles county and city established paramedic programs following the passage of The Wedworth-Townsend Act in 1970. This was followed by other cities and states passing their own paramedic bills, leading to the formation of services across the US. Many other countries also followed suit, with paramedic units quickly being formed around the world.

In the military, however, the required telemetry and miniaturization technologies were more advanced, particularly due to initiatives such as the space program, but it would take several more years before these technologies drifted through to civilian applications. In North America, physicians were judged to be too expensive to be used in the pre-hospital setting, although such initiatives were implemented, and sometimes still operate, in European countries and Latin America.

Public notability[link]

While doing background research at Los Angeles' UCLA Harbor Medical Center for a proposed new show about doctors, television producer Robert A. Cinader, working for Jack Webb, happened to encounter "firemen who spoke like doctors and worked with them".^{[citation needed]} This concept developed into the television series Emergency!, which ran from 1972 to 1979, portraying the exploits of this new profession called paramedics. The show gained popularity with emergency services personnel, the medical community, and the general public. When the show first aired in 1972, there were just six paramedic units operating in three pilot programs in the whole of the US, and the term paramedic was essentially unknown. By the time the program ended in 1979, there were paramedics operating in all fifty states. The show's technical advisor, James O. Page, was a pioneer of paramedicine and responsible for the UCLA paramedic program; he would go on to help establish paramedic programs throughout the US, and was the founding publisher of the Journal of Emergency Medical Services (JEMS). The JEMS magazine creation resulted from Page's previous purchase of the "PARAMEDICS International" magazine.

Evolution and growth[link]

Throughout the 1970s and 80s, the paramedic field continued to evolve, with a shift in emphasis from patient transport to treatment both on scene and en-route to hospitals. This led to some services changing their descriptions from "ambulance services" to "emergency medical services".

Bicycle paramedics in Los Angeles indicate the changing nature of the job

The training, knowledge-base, and skill sets of both paramedics and emergency medical technicians (EMTs) were typically determined by local medical directors, what it was felt the community needed, and what was affordable. There were also large differences between localities in the amount and type of training required, and how it would be provided. This ranged from in-service training in local systems, through community colleges, and up to university level education. This emphasis on increasing qualifications has followed the progression of other health professions such as nursing, which also progressed from on the job training to university level qualifications.

The variations in educational approaches and standards required for paramedics has led to large differences in the required qualifications between locations—both within individual countries and from country to country. This has led to many countries passing laws to protect the title of "paramedic" (or its local equivalent) from use by anyone except those qualified and experienced to a defined standard. This usually means that paramedics must be registered with the appropriate body in their country, for example all paramedics in the United Kingdom must by registered with the Health Professions Council in order to call themselves a paramedic. In the United States, a similar system is operated by the National Registry of Emergency Medical Technicians (NREMT), although this is only accepted by forty of the fifty states.

As paramedicine has evolved a great deal of both the curriculum and skill set has existed in a state of flux. Requirements often originated and evolved at the local level, and were based upon the preferences of physician advisers and medical directors. Recommended treatments would change regularly, often changing more like a fashion than a scientific discipline. Associated technologies also rapidly evolved and changed, with medical equipment manufacturers having to adapt equipment that worked adequately the hospital environment to be able to cope with the less controlled pre-hospital environment.

Physicians began to take more interest in paramedics from a research perspective as well. By about 1990, the fluctuating trends began to diminish, being replaced by outcomes-based research. This research then drove further evolution of the practice of both paramedics and the emergency physicians who oversaw their work, with changes to procedures and protocols occurring only after significant research demonstrated their need and effectiveness (an example being ALS). Such changes affected everything from simple procedures, such as CPR, to changes in drug protocols. As the profession grew, some paramedics went on to become not just research participants, but researchers in their own right, with their own projects and journal publications.

Changes in procedures also included the manner in which the work of paramedics was overseen and managed. In the early days medical control and oversight was direct and immediate, with paramedics calling into a local hospital and receiving orders for every individual procedure or drug. While this still occurs in some jurisdictions, it has become increasingly rare, with physicians building an increasing confidence and trust in the work of paramedics. Day-to-day operations largely moved from direct and immediate medical control to pre-written protocols or standing orders, with the paramedic typically seeking advice after the options in the standing orders had been exhausted.

Canada[link]

First responders from St. John Ambulance and local fire departments assist paramedics during an exercise in Canada

While the evolution of paramedicine described above is focused largely on the US, many other countries followed a similar pattern, although often with significant variations. Canada, for example, attempted a pilot paramedic training program at Queen's University, Kingston, Ontario, in 1972. The program, which intended to upgrade the then mandatory 160 hours of training for ambulance attendants, was found to be too costly and premature. The program was abandoned after two years, and it was more than a decade before the legislative authority for its graduates to practice was put into place. An alternative program which provided 1,400 hours of training at the community college level prior to commencing employment was then tried, and made mandatory in 1977, with formal certification examinations being introduced in 1978. Similar programs occurred at roughly the same time in Alberta and British Columbia, with other Canadian provinces gradually following, but with their own education and certification requirements. Advanced Care Paramedics were not introduced until 1984, when Toronto trained its first group internally, before the process spread across the country. By 2010 the Ontario system involved a two year community college based program, including both hospital and field clinical components, prior to designation as a Primary Care Paramedic, although it is starting to head towards a university degree-based program. Some services, such as Toronto EMS, continue to train advanced care paramedics internally.

United Kingdom[link]

In the United Kingdom, ambulances became largely municipal services shortly after the end of World War II. Training was frequently conducted internally, although national levels of coordination led to more standardization of staff training. As of 2010 public ambulance services were operated by regional entities, most often trusts, under the authority of the National Health Service, with significant standardization of training and skills. The UK model utilizes two levels of ambulance staff, internally trained Ambulance Technicians, which are similar to EMTs in the US, and paramedics with advanced life support skills. Initially paramedics were mainly trained internally, with experienced ambulance technicians often progressing to the role of paramedic. Increasingly, however, university qualifications are being expected for paramedics, with the entry level being an Honours Bachelor of Science degree in Pre-Hospital or Paramedic Care. Some British paramedics have gone on to become Paramedic Practitioners, a role that practices independently in the pre-hospital environment in a capacity similar to that of a nurse practitioner, but with more of an acute care orientation.

Current practice[link]

Paramedicine continues to grow and evolve into a formal profession in its own right, complete with its own standards and body of knowledge, and in many locations paramedics have formed their own professional bodies. The early technicians with limited training, performing a small and specific set of procedures, has become a profession requiring a university qualification in countries such as Australia, South Africa, and the UK, and increasingly in Canada. In some locations paramedics are evolving into a second tier medical practitioner and being granted the legal status of self-regulated health professionals. This requires them to meet set standards of education and proficiency, deals with complaints regarding individual practitioners, and will usually involve government regulation.

In the United States, paramedic training is considered vocational. Paramedics are not required to obtain a first professional degree for licensure in any of the fifty states. Paramedic education programs typically follow the US Department of Transportation’s Emergency Medical Technician-Paramedic: National Standard Curriculum. While many regionally accredited colleges and universities offer paramedic programs only a handful require a formal degree component prior to completion. Course minimum required hours vary from state to state but range between 700 – 1300 didactic and clinical hours. Calendar length can vary from between six months to upwards of two years.

The disparity of educational requirements and lack of an academic degree contribute to overall lower wages and less respect amongst other allied health care providers.

Structure of employment[link]

Firefighter paramedics assist a simulated burn victim during a US Navy mass casualty drill

Paramedics are employed by a variety of different organizations, and the services provided by paramedics may occur under differing organizational structures, depending on the part of the world. A new and evolving role for paramedics involves the expansion of their practice into the provision of relatively basic primary health care and assessment services.

Some paramedics have begun to specialize their practice, frequently in association with the environment in which they will work. Some early examples of this involved aviation medicine and the use of helicopters, and the transfer of critical care patients between facilities. While some jurisdictions still use physicians, nurses, and technicians for transporting patients, increasingly this role falls to specialized senior and experienced paramedics. Other areas of specialization include such roles as tactical paramedics working in police units, marine paramedics, hazardous materials (Hazmat) teams, Heavy Urban Search and Rescue, and paramedics on offshore oil platforms, oil and mineral exploration teams, and in the military.

The majority of paramedics are employed by the municipal emergency medical service for their area, although this employer could be itself be working under a number of models, including a specific autonomous public ambulance service, a fire department, a hospital based service or a private company working under contract. There are also legions of paramedics who volunteer for backcountry rescue teams, small town rescue squads, and the like.

The provision of municipal ambulance services, and paramedics, can vary by area, even within the same country or state. For instance, in Canada, the province of British Columbia operates a province-wide service (the British Columbia Ambulance Service) whereas in Ontario, the service is provided by each municipality, either as a distinct service, linked to the fire brigade, or contracted out to a third party.

Paramedic skills[link]

Common skills[link]

While there are varying degrees of training and expectations around the world, a general set of skills shared by essentially all paramedics and EMTs includes:

• Spinal injury management, including immobilization and safe transport
• Fracture management, including assessment, splinting, and use of traction splints where appropriate
• Obstetrics, including assessment, assisting with uncomplicated childbirth, and recognition of and procedures for obstetrical emergencies such as breech presentation, cord presentation, and placental abruption
• Management of burns, including classification, estimate of surface area, recognition of more serious burns, and treatment
• Advanced airway management techniques including surgical airways.
• Triage of patients in a mass casualty incident
• Assessment and evaluation of general incident scene safety
• Effective verbal and written reporting skills (charting)
• Routine medical equipment maintenance procedures
• Routine radio operating procedures
• Emergency vehicle operation

Medications administered[link]

Paramedics in most jurisdictions administer a variety of emergency medications. The specific medications they are permitted to administer vary widely, based on local standards of care and legal restrictions, and physician or medical director preferences. For an accurate description of permitted drugs or procedures in a given location, it is necessary to contact that jurisdiction directly. A representative list of medications may commonly include:

A paramedic preparing an intravenous infusion for a patient

• Analgesic medications such as aspirin, ketorolac, paracetamol and Tylenol used to relieve pain or decrease nausea and vomiting
• Narcotics like morphine, pethidine, fentanyl, and dilaudid, used to treat severe pain, such as with burns and fractures
• Adenosine, calcium channel blockers Diltiazem and Verapamil used to slow down excessively high heart rates
• Parasympatholytic drug such as Atropine, used to speed up slow bradycardia heart rates
• Sympathomimetics such as dopamine, dobutamine used for severe hypotension (low blood pressure) and cardiogenic shock
• D50W (a solution of 50% dextrose in water), used to treat hypoglycemia (low blood sugar)
• Sedatives like midazolam, lorazepam, and etomidate, used to reduce the irritability or agitation of patients
• Paralytics such as succinylcholine, rocuronium, and vecuronium, used when an emergency procedure such as rapid sequence induction (RSI) is required
• Antipsychotics like haloperidol or ziprasidone, used to sedate combative patients
• Respiratory medications such as salbutamol, Ipratropium bromide and methylprednisolone, used to treat conditions such as asthma and acute bronchitis
• Cardiac medications such as nitroglycerin, aspirin, and morphine, fentanyl used to treat cardiac ailments such as angina and heart attacks
• Antiarrhythmics such as amiodarone, lidocaine and magnesium sulfate used to treat cardiac arrhythmias such as ventricular tachycardia and ventricular fibrillation
• Ondansetron used for nausea and vomiting
• Naloxone used to treat opioid drug overdose

Skills by certification level[link]

As described above, many jurisdictions have different levels of paramedic training, leading to variations in what procedures different paramedics may perform depending upon their qualifications. Three common general divisions of paramedic training are the basic technician, general paramedic or advanced technician, and advanced paramedic. Common skills that these three certification levels may practice are summarized in the table below. The skills for the higher levels automatically also assume those listed for lower levels.

Medicolegal authority[link]

The medicolegal framework for paramedics is highly dependant on the overall structure of emergency medical services in the territory where they are working.

Paramedics load an injured woman into a helicopter ambulance after a head-on collision in Canada

In places where paramedics are recognized health care professionals registered with an appropriate body, they can conduct all procedures authorised for their profession, including the administration of prescription medication, and are personally answerable to a regulator. For example, in the United Kingdom, the Health Professions Council regulates paramedics and can censure or strike a paramedic from the register. In some cases paramedics may gain further qualifications to extend their status to that of a paramedic practitioner, which provides the right to prescribe, rather than just administer, medication.

In other places paramedics operate as a direct extension of a physician medical director, and practice as an extension of the medical director's license to practice medicine. The authority to practice in this semi-autonomous manner is granted in the form of standing order protocols (off-line medical control), and, in some cases, direct physician consultation via phone or radio (on-line medical control). Under this paradigm, paramedics effectively assume the role of out-of-hospital field agents to regional emergency physicians, with independent clinical decision-making authority that is typically enjoyed only by expert clinicians within the hospital setting. In some locations paramedics are only permitted to practice many advanced skills while assisting a physician who is physically present, except for immediately life-threatening emergencies.

In entertainment[link]

• Emergency! was a popular 1970s television series which centered on the work of paramedics in the Los Angeles County Fire Department, and the staff at the fictional Rampart Emergency Hospital. Emergency! has been widely credited with inspiring many municipalities in the United States to develop their own paramedic programs, and acted as an inspiration for many individuals to enter the fields of emergency medicine.^{[citation needed]} The show rated well for its entire production run (1972–79), as well as in syndicated reruns, and inspired a related cartoon series.
• Mother, Jugs & Speed is a 1976 comedy film, starring Bill Cosby, Raquel Welch, and Harvey Keitel. The film depicts a private ambulance company struggling to survive in Los Angeles, and gives an indication of the state of the ambulance industry just prior to its increased professionalism.
• Trauma Center is a 1983 American television medical drama focussing on the McKee Hospital Trauma Center, and two paramedics who had to rescue or save injured people before delivering them to the trauma center.
• Casualty is a long-running British BBC television series (1986–present), depicting the fictional Holby City Hospital's Accident and Emergency Department, and the related paramedics. Casualty has inspired the spin-off series, Holby City, and a number of made-for-television films.
• Paramedics is a 1988 American comedy film focussing on a group of paramedics in a US city.
• Paramedic: On the Front Lines of Medicine, is a 1988 autobiographical account of a paramedic's first year on the job by Peter Canning. A sequel, Rescue 471: A Paramedic's Stories was released in 2000.
• Bringing Out the Dead is a 1999 American drama film, directed by Martin Scorsese and starring Nicolas Cage, showing forty-eight hours in the life of a burnt-out paramedic in New York's Hell's Kitchen. The film is based on the novel of the same name by Joe Connelly, a former New York City paramedic.
• Paramedics is an American reality television show that originally screened from 1999 to 2001, and now runs intermittently on the Discovery Health Channel. The show features the life and work of emergency medical squads in major urban centers in the United States.
• Third Watch (1999–2005) is an American television drama, parts of which focussed on the firefighters and paramedics of the New York City Fire Department.
• Into the Breach: A Year of Life and Death with EMS is a 2002 book written by J. A. Karam, focussing on real-life stories of paramedics, emergency medical technicians, and heavy-rescue specialists fighting to control trauma and medical emergencies.
• Saved is a 2006 medical television drama centered on a fictional paramedic, his partner, and their chaotic lives on and off the job.
• Black Flies is a 2008 American novel written by Shannon Burke, based on his experiences working as a paramedic in Harlem, New York.
• Trauma is a 2009–10 American television drama series focussing on a group of San Francisco Fire Department paramedics working in conjunction with the fictional trauma center of San Francisco City Hospital.

• Denise Sherwood, from "Army Wives" was a paramedic, having been a nurse beforehand and a 911 dispatcher later on.

See also[link]

Paramedics by country

• Paramedics in Australia
• Paramedics in Canada
• Paramedics in France
• Paramedics in Germany
• Paramedics in Ireland
• Paramedics in Poland
• Paramedics in South Africa
• Paramedics in the United Kingdom
• Paramedics in the United States

Related fields

• Biophone
• Critical Care Emergency Medical Transport Program
• Flight medic
• Health care providers
• National Association of Emergency Medical Technicians
• National Registry of Emergency Medical Technicians

References[link]

• "National EMS Museum". http://www.emsmuseum.org/virtual-museum/history/articles/399743/. 
• American Heart Association (January 2006)
• Meisel, Zachary (2005-11-08). "Ding-a-Ling-a-Ling— Ambulances can be dangerous places.". Slate. Washington Post. Newsweek Interactive Co. LLC. http://www.slate.com/id/2129684/. Retrieved 2007-01-25. 
• "Tribute to R Adams Cowley, M.D.". University of Maryland Medical Center. http://www.umm.edu/shocktrauma/history.html. Retrieved 2005-12-30. 
• US DOT "National Scope of Practice Model". National Highway Traffic Safety Administration. Archived from the original on 2007-06-28. http://web.archive.org/web/20070628202306/http://nhtsa.gov/staticfiles/DOT/NHTSA/Communication+&+Consumer+Information/Articles/Associated+Files/EMSScope.pdf. Retrieved 2007-04-16. 

External links[link]

Look up paramedic in Wiktionary, the free dictionary.

Wikimedia Commons has media related to: Paramedic

• Paramedic Emblem
• National EMS Museum
• National Registry of Emergency Medical Technicians
• National Association of Emergency Medical Technicians
• NHTSA Emergency Medical Services National Page
• Paramedic Study Guide

Myocardial infarction
Classification and external resources
Diagram of a myocardial infarction (2) of the tip of the anterior wall of the heart (an apical infarct) after occlusion (1) of a branch of the left coronary artery (LCA), right coronary artery = RCA
ICD-10	I21-I22
ICD-9	410
DiseasesDB	8664
MedlinePlus	000195
eMedicine	med/1567 emerg/327 ped/2520
MeSH	D009203

Myocardial infarction (MI) or acute myocardial infarction (AMI), commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die. This is most commonly due to occlusion (blockage) of a coronary artery following the rupture of a vulnerable atherosclerotic plaque, which is an unstable collection of lipids (cholesterol and fatty acids) and white blood cells (especially macrophages) in the wall of an artery. The resulting ischemia (restriction in blood supply) and ensuing oxygen shortage, if left untreated for a sufficient period of time, can cause damage or death (infarction) of heart muscle tissue (myocardium).

Classical symptoms of acute myocardial infarction include sudden chest pain (typically radiating to the left arm or left side of the neck), shortness of breath, nausea, vomiting, palpitations, sweating, and anxiety (often described as a sense of impending doom).^[1] Women may experience fewer typical symptoms than men, most commonly shortness of breath, weakness, a feeling of indigestion, and fatigue.^[2] A sizeable proportion of myocardial infarctions (22–64%)^[3] are "silent", that is without chest pain or other symptoms.

Among the diagnostic tests available to detect heart muscle damage are an electrocardiogram (ECG), echocardiography, cardiac MRI and various blood tests. The most often used blood markers are the creatine kinase-MB (CK-MB) fraction and the troponin levels. Immediate treatment for suspected acute myocardial infarction includes oxygen, aspirin, and sublingual nitroglycerin.^[4]

Most cases of myocardial infarction with ST elevation on ECG (STEMI) are treated with reperfusion therapy, such as percutaneous coronary intervention (PCI) or thrombolysis.^[5] Non-ST elevation myocardial infarction (NSTEMI) may be managed with medication, although PCI may be required if the patient's risk warrants it.^[6] People who have multiple blockages of their coronary arteries, particularly if they also have diabetes mellitus, may benefit from bypass surgery (CABG),^[7][8]. The European Society of Cardiology guidelines in 2011 proposed treating the blockage causing the myocardial infarction by PCI and performing CABG later when the patient is more stable.^[7] Rarely CABG may be preferred in the acute phase of myocardial infarction, for example when PCI has failed or is contraindicated.^[7]

Ischemic heart disease (which includes myocardial infarction, angina pectoris and heart failure when preceded by myocardial infarction) was the leading cause of death for both men and women worldwide in 2004.^[9] Important risk factors are previous cardiovascular disease, older age, tobacco smoking, high blood levels of certain lipids (low-density lipoprotein cholesterol, triglycerides) and low levels of high density lipoprotein (HDL) cholesterol, diabetes, high blood pressure, lack of physical activity and obesity, chronic kidney disease, excessive alcohol consumption, the abuse of illicit drugs (such as cocaine and amphetamines), and chronic high stress levels.^[10][11][12]

Classification[link]

There are two basic types of acute myocardial infarction based on pathology:

• Transmural: associated with atherosclerosis involving a major coronary artery. It can be subclassified into anterior, posterior, inferior, lateral or septal. Transmural infarcts extend through the whole thickness of the heart muscle and are usually a result of complete occlusion of the area's blood supply.^[13]
• Subendocardial: involving a small area in the subendocardial wall of the left ventricle, ventricular septum, or papillary muscles. The subendocardial area is particularly susceptible to ischemia.^[13]

In the clinical context, a myocardial infarction can be further subclassified into a ST elevation MI (STEMI) versus a non-ST elevation MI (non-STEMI) based on ECG changes.^[14]

The phrase heart attack is sometimes used incorrectly to describe sudden cardiac death, which may or may not be the result of acute myocardial infarction. A heart attack is different from, but can be the cause of cardiac arrest, which is the stopping of the heartbeat, and cardiac arrhythmia, an abnormal heartbeat. It is also distinct from heart failure, in which the pumping action of the heart is impaired; however severe myocardial infarction may lead to heart failure.^[7]

A 2007 consensus document classifies myocardial infarction into five main types:^[15]

• Type 1 – Spontaneous myocardial infarction related to ischaemia due to a primary coronary event such as plaque erosion and/or rupture, fissuring, or dissection
• Type 2 – Myocardial infarction secondary to ischaemia due to either increased oxygen demand or decreased supply, e.g. coronary artery spasm, coronary embolism, anaemia, arrhythmias, hypertension, or hypotension
• Type 3 – Sudden unexpected cardiac death, including cardiac arrest, often with symptoms suggestive of myocardial ischaemia, accompanied by new ST elevation, or new LBBB, or evidence of fresh thrombus in a coronary artery by angiography and/or at autopsy, but death occurring before blood samples could be obtained, or at a time before the appearance of cardiac biomarkers in the blood
• Type 4 – Associated with coronary angioplasty or stents:
  • Type 4a – Myocardial infarction associated with PCI
  • Type 4b – Myocardial infarction associated with stent thrombosis as documented by angiography or at autopsy
• Type 5 – Myocardial infarction associated with CABG

Signs and symptoms[link]

Rough diagram of pain zones in myocardial infarction; dark red: most typical area, light red: other possible areas; view of the chest

Back view

The onset of symptoms in myocardial infarction (MI) is usually gradual, over several minutes, and rarely instantaneous.^[16] Chest pain is the most common symptom of acute myocardial infarction and is often described as a sensation of tightness, pressure, or squeezing. Chest pain due to ischemia (a lack of blood and hence oxygen supply) of the heart muscle is termed angina pectoris. Pain radiates most often to the left arm, but may also radiate to the lower jaw, neck, right arm, back, and epigastrium,^[7][17] where it may mimic heartburn. Levine's sign, in which the patient localizes the chest pain by clenching their fist over the sternum, has classically been thought to be predictive of cardiac chest pain, although a prospective observational study showed that it had a poor positive predictive value.^[18]

Shortness of breath (dyspnea) occurs when the damage to the heart limits the output of the left ventricle, causing left ventricular failure and consequent pulmonary edema. Other symptoms include diaphoresis (an excessive form of sweating),^[1] weakness, light-headedness, nausea, vomiting, and palpitations. These symptoms are likely induced by a massive surge of catecholamines from the sympathetic nervous system^[19] which occurs in response to pain and the hemodynamic abnormalities that result from cardiac dysfunction. Loss of consciousness (due to inadequate cerebral perfusion and cardiogenic shock) and sudden death (frequently due to the development of ventricular fibrillation) can occur in myocardial infarctions.^[7]

Women and older patients report atypical symptoms more frequently than their male and younger counterparts.^[20] Women also report more numerous symptoms compared with men (2.6 on average vs 1.8 symptoms in men).^[20] The most common symptoms of MI in women include dyspnea (shortness of breath), weakness, and fatigue. Fatigue, sleep disturbances, and dyspnea have been reported as frequently occurring symptoms that may manifest as long as one month before the actual clinically manifested ischemic event. In women, chest pain may be less predictive of coronary ischemia than in men.^[21]

At least one-fourth of all myocardial infarctions are silent, without chest pain or other symptoms, ^[22][3] with silent myocardial infarcations being more common in younger people. These cases can be discovered later on electrocardiograms, using blood enzyme tests or at autopsy without a prior history of related complaints. Estimates of the prevalence of silent myocardial infarctions vary between 22 and 64% ^[3]. A silent course is more common in the elderly^[3], in patients with diabetes mellitus^[23] and after heart transplantation, probably because the donor heart is not fully innervated by the nervous system of the recipient.^[24] In people with diabetes, differences in pain threshold, autonomic neuropathy, and psychological factors have been cited as possible explanations for the lack of symptoms.^[23]

Any group of symptoms compatible with a sudden interruption of the blood flow to the heart are called an acute coronary syndrome.^[25]

The differential diagnosis includes other catastrophic causes of chest pain, such as pulmonary embolism, aortic dissection, pericardial effusion causing cardiac tamponade, tension pneumothorax, and esophageal rupture. Other non-catastrophic differentials include gastroesophageal reflux and Tietze's syndrome.^[26]

Causes[link]

Heart attack rates are higher in association with intense exertion, be it psychological stress or physical exertion, especially if the exertion is more intense than the individual usually performs.^[27] The period of intense exercise and subsequent recovery is associated with about a 6-fold higher myocardial infarction rate (compared with other more relaxed time frames) for people who are physically very fit.^[27] For those in poor physical condition, the rate differential is over 35-fold higher.^[27] One observed mechanism for this phenomenon is the increased arterial pulse pressure stretching and relaxation of arteries with each heart beat, which, as has been observed with intravascular ultrasound, increases mechanical "shear stress" on atheromas and the likelihood of plaque rupture.^[27]

Acute severe infection, such as pneumonia, can trigger myocardial infarction. A more controversial link is that between Chlamydophila pneumoniae infection and atherosclerosis.^[28] While this intracellular organism has been demonstrated in atherosclerotic plaques, evidence is inconclusive as to whether it can be considered a causative factor.^[28] Treatment with antibiotics in patients with proven atherosclerosis has not demonstrated a decreased risk of heart attacks or other coronary vascular diseases.^[29]

There is an association of an increased incidence of a heart attack in the morning hours, more specifically around 9 a.m.^[30][31][32] Some investigators have noticed that the ability of platelets to aggregate varies according to a circadian rhythm, although they have not proven causation.^[33]

Risk factors[link]

Myocardial infarction results from atherosclerosis.^[7] Risk factors for myocardial infarction include:

• Age^[10]
• Gender: At any given age men are more at risk than women, particularly before the menopause,^[27] but because in general women live longer than men ischemic heart disease causes slightly more total deaths in women.^[10]
• Diabetes mellitus type 1 or Diabetes mellitus type 2 ^[34]
• High blood pressure^[35]
• Dyslipidemia/hypercholesterolemia (abnormal levels of lipoproteins in the blood), particularly high low-density lipoprotein, low high-density lipoprotein and high triglycerides^[35]
• Tobacco smoking, including secondhand smoke^[35]
• Short term exposure to air pollution including: carbon monoxide, nitrogen dioxide, and sulfur dioxide but not ozone.^[36]
• Family history of ischaemic heart disease or myocardial infarction particularly if one has a first-degree relative (father, brother, mother, sister) who suffered a 'premature' myocardial infarction (defined as occurring at or younger than age 55 years (men) or 65 (women).^[10]
• Obesity^[37] (defined by a body mass index of more than 30 kg/m², or alternatively by waist circumference or waist-hip ratio).
• Lack of physical activity.^[10]
• Psychosocial factors including, low socio-economic status, social isolation, negative emotions and stress increase the risk of myocardial infarction and are associated with worse outcomes after myocardial infarction. Socioeconomic factors such as a shorter education and lower income (particularly in women), and unmarried cohabitation are also correlated with a higher risk of MI.^[38]
• Alcohol — Studies show that prolonged exposure to high quantities of alcohol can increase the risk of heart attack.
• Oral contraceptive pill – women who use combined oral contraceptive pills have a modestly increased risk of myocardial infarction, especially in the presence of other risk factors, such as smoking.^[39]
• Hyperhomocysteinemia (high homocysteine)in homocysteinuria is associated with premature atherosclerosis^[40], whether elevated homocysteine in the normal range is causal is contentious.^[41]

Inflammation is known to be an important step in the process of atherosclerotic plaque formation.^[42] C-reactive protein (CRP) is a sensitive but non-specific marker for inflammation. Elevated CRP blood levels, especially measured with high-sensitivity assays, can predict the risk of MI, as well as stroke and development of diabetes.^[42] Moreover, some drugs for MI might also reduce CRP levels.^[42] The use of high-sensitivity CRP assays as a means of screening the general population is advised against, but it may be used optionally at the physician's discretion in patients who already present with other risk factors or known coronary artery disease.^[43] Whether CRP plays a direct role in atherosclerosis remains uncertain.^[42] Inflammation in periodontal disease may be linked to coronary heart disease, and, since periodontitis is very common, this could have great consequences for public health.^[44] Serological studies measuring antibody levels against typical periodontitis-causing bacteria found that such antibodies were more present in subjects with coronary heart disease.^[45] Periodontitis tends to increase blood levels of CRP, fibrinogen and cytokines;^[46] thus, periodontitis may mediate its effect on MI risk via other risk factors.^[47] Preclinical research suggests that periodontal bacteria can promote aggregation of platelets and promote the formation of foam cells.^[48][49] A role for specific periodontal bacteria has been suggested but remains to be established.^[50] There is some evidence that influenza may trigger an acute myocardial infarction.^[51]

Baldness, hair greying, a diagonal earlobe crease (Frank's sign^[52]) and possibly other skin features have been suggested as independent risk factors for MI.^[53] Their role remains controversial; a common denominator of these signs and the risk of MI is supposed, possibly genetic.^[54]

Calcium deposition is another part of atherosclerotic plaque formation. Calcium deposits in the coronary arteries can be detected with CT scans. Several studies have shown that coronary calcium can provide predictive information beyond that of classical risk factors.^[55][56][57]

Many of these risk factors are modifiable, so many heart attacks can be prevented by maintaining a healthier lifestyle. Physical activity, for example, is associated with a lower risk profile.^[58] Non-modifiable risk factors include age, sex, and family history of an early heart attack, which is thought of as reflecting a genetic predisposition.^[27] To understand epidemiological study results, it is important to note that many factors associated with MI mediate their risk via other factors. For example, the effect of education is partially based on its effect on income and marital status.^[38]

The European Society of Cardiology and the European Association for Cardiovascular Prevention and Rehabilitation have developed an interactive tool for prediction and managing the risk of heart attack and stroke in Europe. HeartScore is aimed at supporting clinicians in optimising individual cardiovascular risk reduction. The Heartscore Programme is available in 12 languages and offers web-based or PC version.^[59]

Pathophysiology[link]

A myocardial infarction occurs when an atherosclerotic plaque slowly builds up in the inner lining of a coronary artery and then suddenly ruptures, causing catastrophic thrombus formation, totally occluding the artery and preventing blood flow downstream.

Drawing of the heart showing anterior left ventricle wall infarction

Acute myocardial infarction refers to two subtypes of acute coronary syndrome, namely non-ST-elevated myocardial infarction and ST-elevated myocardial infarction, which are most frequently (but not always) a manifestation of coronary artery disease.^[14] The most common triggering event is the disruption of an atherosclerotic plaque in an epicardial coronary artery, which leads to a clotting cascade, sometimes resulting in total occlusion of the artery.^[60][61] Atherosclerosis is the gradual buildup of cholesterol and fibrous tissue in plaques in the wall of arteries (in this case, the coronary arteries), typically over decades.^[62] Blood stream column irregularities visible on angiography reflect artery lumen narrowing as a result of decades of advancing atherosclerosis.^[63] Plaques can become unstable, rupture, and additionally promote a thrombus (blood clot) that occludes the artery; this can occur in minutes. When a severe enough plaque rupture occurs in the coronary vasculature, it leads to myocardial infarction (necrosis of downstream myocardium).^[60][61]

If impaired blood flow to the heart lasts long enough, it triggers a process called the ischemic cascade; the heart cells in the territory of the occluded coronary artery die (chiefly through necrosis) and do not grow back. A collagen scar forms in its place. Recent studies indicate that another form of cell death called apoptosis also plays a role in the process of tissue damage subsequent to myocardial infarction.^[64] As a result, the patient's heart will be permanently damaged. This myocardial scarring also puts the patient at risk for potentially life threatening arrhythmias, and may result in the formation of a ventricular aneurysm that can rupture with catastrophic consequences.

Injured heart tissue conducts electrical impulses more slowly than normal heart tissue. The difference in conduction velocity between injured and uninjured tissue can trigger re-entry or a feedback loop that is believed to be the cause of many lethal arrhythmias. The most serious of these arrhythmias is ventricular fibrillation (V-Fib/VF), an extremely fast and chaotic heart rhythm that is the leading cause of sudden cardiac death. Another life-threatening arrhythmia is ventricular tachycardia (V-Tach/VT), which may or may not cause sudden cardiac death. However, ventricular tachycardia usually results in rapid heart rates that prevent the heart from pumping blood effectively. Cardiac output and blood pressure may fall to dangerous levels, which can lead to further coronary ischemia and extension of the infarct.

The cardiac defibrillator is a device that was specifically designed to terminate these potentially fatal arrhythmias. The device works by delivering an electrical shock to the patient in order to depolarize a critical mass of the heart muscle, in effect "rebooting" the heart. This therapy is time dependent, and the odds of successful defibrillation decline rapidly after the onset of cardiopulmonary arrest.

Diagnosis[link]

The diagnosis of myocardial infarction can be made after assessing patient's complaints and physical status. ECG changes, coronary angiogram and levels of cardiac markers help to confirm the diagnosis. ECG gives valuable clues to identify the site of myocardial damage while coronary angiogram allows visualization of narrowing or obstructions in the heart vessels.^[65] At autopsy, a pathologist can diagnose a myocardial infarction based on anatomopathological findings.

A chest radiograph and routine blood tests may indicate complications or precipitating causes and are often performed upon arrival to an emergency department. New regional wall motion abnormalities on an echocardiogram are also suggestive of a myocardial infarction. Echo may be performed in equivocal cases by the on-call cardiologist.^[66] In stable patients whose symptoms have resolved by the time of evaluation, Technetium (99mTc) sestamibi (i.e. a "MIBI scan") or thallium-201 chloride can be used in nuclear medicine to visualize areas of reduced blood flow in conjunction with physiologic or pharmacologic stress.^[66][67] Thallium may also be used to determine viability of tissue, distinguishing whether non-functional myocardium is actually dead or merely in a state of hibernation or of being stunned.^[68]

WHO criteria^[69] formulated in 1979 have classically been used to diagnose MI; a patient is diagnosed with myocardial infarction if two (probable) or three (definite) of the following criteria are satisfied:

1. Clinical history of ischaemic type chest pain lasting for more than 20 minutes
2. Changes in serial ECG tracings
3. Rise and fall of serum cardiac biomarkers such as creatine kinase-MB fraction and troponin

The WHO criteria were refined in 2000 to give more prominence to cardiac biomarkers.^[70] According to the new guidelines, a cardiac troponin rise accompanied by either typical symptoms, pathological Q waves, ST elevation or depression, or coronary intervention is diagnostic of MI.

Prevention[link]

The risk of a recurrent myocardial infarction decreases with strict blood pressure management and lifestyle changes, chiefly smoking cessation, regular exercise, a sensible diet for those with heart disease, and limitation of alcohol intake. People are usually commenced on several long-term medications post-MI, with the aim of preventing secondary cardiovascular events such as further myocardial infarctions, congestive heart failure or cerebrovascular accident (CVA). Unless contraindicated, such medications may include:^[71][72]

• Antiplatelet drug therapy such as aspirin and/or clopidogrel should be continued to reduce the risk of plaque rupture and recurrent myocardial infarction. Aspirin is first-line, owing to its low cost and comparable efficacy, with clopidogrel reserved for patients intolerant of aspirin. The combination of clopidogrel and aspirin may further reduce risk of cardiovascular events, however the risk of hemorrhage is increased.^[73]
• Beta blocker therapy such as metoprolol or carvedilol should be commenced.^[74] These have been particularly beneficial in high-risk patients such as those with left ventricular dysfunction and/or continuing cardiac ischaemia.^[75] β-Blockers decrease mortality and morbidity. They also improve symptoms of cardiac ischemia in NSTEMI.
• ACE inhibitor therapy should be commenced 24–48 hours post-MI in hemodynamically stable patients, particularly in patients with a history of MI, diabetes mellitus, hypertension, anterior location of infarct (as assessed by ECG), and/or evidence of left ventricular dysfunction. ACE inhibitors reduce mortality, the development of heart failure, and decrease ventricular remodelling post-MI.^[76]
• Statin therapy has been shown to reduce mortality and morbidity post-MI.^[77][78] The effects of statins may be more than their LDL lowering effects. The general consensus is that statins have plaque stabilization and multiple other ("pleiotropic") effects that may prevent myocardial infarction in addition to their effects on blood lipids.^[79]
• The aldosterone antagonist agent eplerenone has been shown to further reduce risk of cardiovascular death post-MI in patients with heart failure and left ventricular dysfunction, when used in conjunction with standard therapies above.^[80] Spironolactone is another option that is sometimes preferable to eplerenone due to cost.
• Evidence supports the consumption of polyunsaturated fats instead of saturated fats as a measure of decreasing coronary heart disease.^[81] Omega-3 fatty acids, commonly found in fish, have been shown to reduce mortality post-MI.^[82] While the mechanism by which these fatty acids decrease mortality is unknown, it has been postulated that the survival benefit is due to electrical stabilization and the prevention of ventricular fibrillation.^[83] However, further studies in a high-risk subset have not shown a clear-cut decrease in potentially fatal arrhythmias due to omega-3 fatty acids.^[84][85]

Blood donation may reduce the risk of heart disease for men,^[86] but the link has not been firmly established.

A Cochrane review found that giving heparin to people with heart conditions like unstable angina and some forms of heart attacks reduces the risk of having another heart attack. However, heparin also increases the chance of suffering from minor bleeding.^[87]

Management[link]

An MI requires immediate medical attention. Treatment attempts to salvage as much myocardium as possible and to prevent further complications, hence the phrase "time is muscle".^[88] Oxygen, aspirin, and nitroglycerin may be administered. Morphine was classically used if nitroglycerin was not effective; however, it may increase mortality in the setting of NSTEMI.^[89] A 2009 and 2010 review of high flow oxygen in myocardial infarction found increased mortality and infarct size, calling into question the recommendation about its routine use.^[90][91] Other analgesics such as nitrous oxide are of unknown benefit.^[6] Percutaneous coronary intervention (PCI) or fibrinolysis are recommended in those with an STEMI.

Prognosis[link]

The prognosis post myocardial infarction varies greatly, depending on a person's health, the extent of the heart damage and the treatment given. For the period 2005–2008 in the United States, the median mortality at 30 days was 16.6% with a range from 10.9% to 24.9% depending on the hospital.^[92] Using variables available in the emergency room, people with a higher risk of adverse outcome can be identified. One study found that 0.4% of patients with a low-risk profile died after 90 days, whereas in high-risk people it was 21.1%.^[93]

Some of the more reproduced risk-stratifying factors include: age, hemodynamic parameters (such as heart failure, cardiac arrest on admission, systolic blood pressure, or Killip class of two or greater), ST-segment deviation, diabetes, serum creatinine, peripheral vascular disease and elevation of cardiac markers.^[93][94][95] Assessment of left ventricular ejection fraction may increase the predictive power.^[96] The prognostic importance of Q-waves is debated.^[97] Prognosis is significantly worsened if a mechanical complication such as papillary muscle or myocardial free wall rupture occurs.^[98] Morbidity and mortality from myocardial infarction has improved over the years due to better treatment.^[99]

Complications[link]

Complications may occur immediately following the heart attack (in the acute phase), or may need time to develop (a chronic problem). Acute complications may include heart failure if the damaged heart is no longer able to adequately pump blood around the body; aneurysm or rupture of the myocardium; mitral regurgitation, in particular if the infarction causes dysfunction of the papillary muscle; and arrhythmias, such as ventricular fibrillation, ventricular tachycardia, atrial fibrillation and heart block. Longer-term complications include heart failure, atrial fibrillation, and the increased risk of a second myocardial infarction.

Epidemiology[link]

Myocardial infarction is a common presentation of ischemic heart disease/coronary artery disease. The World Health Organization estimated in 2004, that 12.2% of worldwide deaths were from ischemic heart disease;^[9] with it being the leading cause of death in high or middle income countries and second only to lower respiratory infections in lower income countries.^[9] Worldwide more than 3 million people have STEMIs and 4 million have NSTEMIs a year.^[100]

Rates of death from ischemic heart disease have slowed or declined in most high income countries, although cardiovascular disease still accounted for 1 in 3 of all deaths in the USA in 2008.^[101] In contrast, ischemic heart disease is becoming a more common cause of death in the developing world. For example in India, ischemic heart disease had become the leading cause of death by 2004 accounting for 1.46 million deaths (14% of total deaths) and deaths due to ischemic heart disease were expected to double during 1985–2015.^[102] Globally it is predicted that disability adjusted life years (DALYs) lost to ischemic heart disease will account for 5.5% of total DALYs in 2030, making it the second most important cause of disability (after unipolar depressive disorder), as well as the leading cause of death by this date.^[9]

Legal implications[link]

At common law, in general a myocardial infarction is a disease, but may sometimes be an injury. This has implications for no-fault insurance schemes such as workers' compensation. In general, a heart attack is not covered;^[103] however, it may be a work-related injury if it results, for example, from unusual emotional stress or unusual exertion.^[104] In addition, in some jurisdictions, heart attacks suffered by persons in particular occupations such as police officers may be classified as line-of-duty injuries by statute or policy. In some countries or states, a person having suffered from a myocardial infarction may be prevented from participating in activity that puts other people's lives at risk, for example driving a car or flying an airplane.^[105]

Research[link]

Patients who receive stem cell treatment by coronary artery injections of stem cells derived from their own bone marrow after a myocardial infarction (MI) show improvements in left ventricular ejection fraction and end-diastolic volume not seen with placebo. The larger the initial infarct size, the greater the effect of the infusion. Clinical trials of progenitor cell infusion as a treatment approach to ST elevation MI are proceeding.^[106]

There are currently 3 biomaterial and tissue engineering approaches for the treatment of MI, but these are in an even earlier stage of medical research, so many questions and issues must be addressed before they can be applied to patients. The first involves polymeric left ventricular restraints in the prevention of heart failure. The second utilizes in vitro engineered cardiac tissue, which is subsequently implanted in vivo. The final approach entails injecting cells and/or a scaffold into the myocardium to create in situ engineered cardiac tissue.^[107]

References[link]

External links[link]

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