Tachycardia

Tachycardia comes from the Greek words tachys (rapid or accelerated) and kardia (of the heart). Tachycardia typically refers to a heart rate that exceeds the normal range for a resting heartrate (heartrate in an inactive or sleeping individual). It can be dangerous depending on the speed and type of rhythm.

Definition

The upper threshold of a normal human heart rate is based upon age. Tachycardia for different age groups is as listed below:

1–2 days: >159 beats per minute (bpm)

3–6 days: >166 bpm

1–3 weeks: >182 bpm

1–2 months: >179 bpm

3–5 months: >186 bpm

6–11 months: >169 bpm

1–2 years: >151 bpm

3–4 years: >137 bpm

5–7 years: >133 bpm

8–11 years: >130 bpm

12–15 years: >119 bpm

>15 years – adult: >100 bpm

When the heart beats excessively rapidly, the heart pumps less efficiently and provides less blood flow to the rest of the body, including the heart itself. The increased heart rate also leads to increased work and oxygen demand by the heart, which can lead to rate related ischemia.

Classification

showing a run of ventricular tachycardia (VT)]] An electrocardiogram (ECG) is used to classify the type of tachycardia. They may be classified into narrow and wide complex based on the QRS complex.

Ventricular

Ventricular tachycardia (VT or V-tach) is a potentially life-threatening cardiac arrhythmia that originates in the ventricles. It is usually a regular, wide complex tachycardia with a rate between 120 and 250 beats per minute. Ventricular tachycardia has the potential of degrading to the more serious ventricular fibrillation. Ventricular tachycardia is a common, and often lethal, complication of a myocardial infarction (heart attack).

Exercise-induced ventricular tachycardia is a phenomenon related to sudden deaths, especially in patients with severe heart disease (ischemia, acquired valvular heart and congenital heart disease) accompanied with left ventricular dysfunction.

Both of these rhythms normally last for only a few seconds to minutes (paroxysmal tachycardia), but if VT persists it is extremely dangerous, often leading to ventricular fibrillation.

Supraventricular

This is a type tachycardia that originates from above the ventricles, such as the atria. It is sometimes known as paroxysmal atrial tachycardia (PAT). Several types of supraventricular tachycardia are known to exist.

Atrial fibrillation

Atrial fibrillation is one of the most common cardiac arrhythmias. It is generally an irregular, narrow complex rhythm. However, it may show wide QRS complexes on the ECG if a bundle branch block is present. At high rates, the QRS complex may also become wide due to the Ashman phenomenon. It may be difficult to determine the rhythm's regularity when the rate exceeds 150 beats per minute. Depending on the patient's health and other variables such as medications taken for rate control, atrial fibrillation may cause heart rates that span from 50 to 250 beats per minute (or even higher if an accessory pathway is present). However, new onset atrial fibrillation tends to present with rates between 100 and 150 beats per minute.

AV nodal reentrant tachycardia (AVNRT)

AV nodal reentrant tachycardia is the most common reentrant tachycardia. It is a regular narrow complex tachycardia that usually responds well to the Valsalva maneuver or the drug adenosine. However, unstable patients sometimes require synchronized cardioversion. Definitive care may include catheter ablation.

AV reentrant tachycardia

AV reentrant tachycardia (AVRT) requires an accessory pathway for its maintenance. AVRT may involve orthodromic conduction (where the impulse travels down the AV node to the ventricles and back up to the atria through the accessory pathway) or antidromic conduction (which the impulse travels down the accessory pathway and back up to the atria through the AV node). Orthodromic conduction usually results in a narrow complex tachycardia, and antidromic conduction usually results in a wide complex tachycardia that often mimics ventricular tachycardia. Most antiarrhythmics are contraindicated in the emergency treatment of AVRT, because they may paradoxically increase conduction across the accessory pathway.

Junctional tachycardia

Junctional tachycardia is an automatic tachycardia originating in the AV junction. It tends to be a regular, narrow complex tachycardia and may be a sign of digitalis toxicity.

Management

The management of tachycardia depends its type (wide complex verses narrow complex), whether or not the person is stable or unstable, and if the instability is due to the tachycardia. Unstable means that either important organ functions are affected or cardiac arrest is about to occur.

Stable

In those who are stable treatment is determined by the exact ECG findings: wide verses narrow complex, regular verses irregular heart rate, and whether the QRS is monomorphic or polymorphic.

Unstable

In those who are unstable with a narrow complex tachycardia intravenous adenosine may be attempted. In all others immediate cardioversion is recommended.

References

External links

Dysautonomia Youth Network of America, Inc.

Postural Orthostatic Tachycardia Syndrome - overview from Dysautonomia Information Network

Heart Arrhythmias Respond to Ablation UCLA Healthcare

Heart Rate Calculator Heart Rate Calculator for Diagnosis of Tachycardia

Category:Cardiology Category:Symptoms and signs: Circulatory and respiratory systems