Supraventricular Tachycardias

Atrial (supraventricular) tachycardias
The term "supraventricular arrhythmia" refers to a diverse group of abnormal rhythms ranging from chronic atrial fibrillation to paroxysmal sinus tachycardia due to reentry within the sinus node. Supraventricular tachycardia can be broadly defined as any tachycardia requiring the atrium or the atrioventricular (AV) node, either in whole or in part, for its perpetuation. The atrial arrhythmias vary considerably in their rate and regularity, their clinical manifestations and the setting in which they occur. These rhythms are characteristically abrupt in onset and termination and are often seen in patients who do not have evidence of organic heart disease. Although these disturbances in rhythm are generally benign, in patients with organic heart disease a rapid supraventricular rhythm may produce significant hemodynamic complications. In some patients with pre-excitation syndromes and antegrade conduction down an accessory pathway, there is a risk of sudden death.

The overall rates vary from 150 to 250 beats/minute; the most common range is 160 to 200 beats/minute. Atrial tachycardia may be conducted on a I:I basis into the ventricles, producing similar atrial and ventricular rates or second-degree AV block. Regular or irregular conduction ratios may occur, or phasic aberrant ventricular conduction may be noted, leading to a series of bizarre QRS complexes. AV block of varying degree may coexist with atrial tachycardia, particularly in digitalis intoxication. Concomitant AV block facilitates recognition and polarity of the P wave. When all P waves have a uniform morphology, the term unifocal atrial tachycardia is used.

This rhythm disturbance appears to be most common in women, but may occur in either sex. It is frequently observed in anxious young people and in those who are physically fatigued, consume large amounts of coffee, use alcohol or smoke heavily. It is also noted occasionally (but is uncommon) with myocardial ischemia and in the setting of acute MI. Atrial tachycardia occurs in some patients with myocardial diseases during systemic arterial hypoxia and in some patients with serious mitral valve disease.

Mechanisms of supraventricular tachycardia
Slow-fast form — In this common form of AV nodal reentry tachycardia, a reentrant circuit is composed of a slow pathway with a short refractory period (RP) and a fast pathway with a long RP. A premature beat is required to initiate tachycardia, and the tachycardia uses the slow pathway for antegrade conduction and the fast pathway for retrograde conduction.

Fast-slow form — In this unusual form of AV nodal reentrant tachycardia, sometimes referred to as "incessant tachycardia," the slow pathway has a long RP and the fast pathway has a short RP. A premature beat is not necessary to initiate tachycardia; a normally timed sinus beat may initiate it.

Types of atrial tachycardia include:

SA node reentry
Intra-atrial reentry
Automatic atrial
AV node reentry
AV reentry

A trial flutter and atrial fibrillation are discussed in another section.

Summary of ECG criteria

150 to 250 beats/minute.
QRS: normal duration unless bundle branch block is present.
P waves: When P waves are identifiable, the P wave morphology is often different from sinus P wave morphology, and the P wave may precede, coincide with or follow the QRS complex.

Figure 4. ECG of Atrial Rhythm Disturbances

Paroxysmal supraventricular tachycardia
Paroxysmal supraventricular tachycardia (PSVT) most commonly occurs secondary to AV nodal re-entrant tachycardia or macro re-entry in patients with WPW syndrome. The presence of intermittent PSVT does not necessarily constitute an indication for treatment, although some patients develop angina, shortness of breath and/or syncope during the rapid supraventricular tachycardia. Others are concerned by the "palpitations" and these concerns may constitute an indication for suppression of the arrhythmia in patients. It should be emphasized that certain maneuvers that produce vagal stimulation may convert these tachycardias to sinus rhythm. In particular, carotid sinus massage, pressure on the eyeballs, the Valsalva maneuver and/or the dive reflex may convert atrial tachycardia to sinus rhythm. Sedation and withdrawal from excesses of coffee, tobacco, alcohol and fatigue may also be corrective. If the rhythm disturbance occurs in association with the WPW syndrome, pharmacologic intervention or catheter ablation may be necessary to control the recurrent episodes of PSVT.

This content is reviewed regularly. Last updated 11/24/08.