Reentrant Supraventricular Tachycardias (SVT) Including Wolff-Parkinson-White Syndrome

The reentry pathway (see figure ) in supraventricular tachycardia may be

AV nodal reentrant tachycardia occurs most often in otherwise healthy patients. It is most commonly triggered by an atrial premature beat Atrial premature beats Various rhythms result from supraventricular foci (usually in the atria). Diagnosis is by electrocardiography. Many are asymptomatic and require no treatment. (See also Overview of Arrhythmias... read more .

Accessory pathway reentrant tachycardia involves tracts of conducting tissue that partially or totally bypass normal AV connections (bypass tracts). They run most commonly from the atria directly to the ventricles and less commonly from the atrium to a portion of the conduction system or from a portion of the conduction system to the ventricle. They can be triggered by atrial premature beats or ventricular premature beats Ventricular Premature Beats (VPB) Ventricular premature beats (VPB) are single ventricular impulses caused by reentry within the ventricle or abnormal automaticity of ventricular cells. They are extremely common in both healthy... read more .

Most patients present during young adulthood or middle age. They typically have episodes of sudden-onset, sudden-offset, rapid, regular palpitations often associated with symptoms of hemodynamic compromise (eg, dyspnea, chest discomfort, light-headedness). Attacks may last only a few seconds or persist for several hours (rarely, > 12 hours).

Infants present with episodic breathlessness, lethargy, feeding problems, or rapid precordial pulsations. If the episode of tachycardia is protracted, infants may present with heart failure Heart failure Congenital heart disease is the most common congenital anomaly, occurring in almost 1% of live births ( 1). Among birth defects, congenital heart disease is the leading cause of infant mortality... read more .

Examination is usually unremarkable except for a heart rate of 160 to 240 beats/minute.

Diagnosis of supraventricular tachycardia is by ECG Electrocardiography The standard electrocardiogram (ECG) provides 12 different vector views of the heart’s electrical activity as reflected by electrical potential differences between positive and negative electrodes... read more showing rapid, regular tachycardia. Previous tracings, if available, are reviewed for ECG signs of manifest WPW syndrome Classic Wolff-Parkinson-White (WPW) syndrome .

P waves vary. In most cases of AV node reentry, retrograde P waves are in the terminal portion of the QRS complex (often producing a pseudo-R′ deflection in lead V1); about one third occur just after the QRS complex, and very few occur before. P waves always follow the QRS complex in orthodromic reciprocating tachycardia of WPW syndrome.

QRS complex is narrow except with coexisting bundle branch block, antidromic tachycardia, or dual accessory connection reciprocating tachycardia. Wide-complex tachycardia must be distinguished from ventricular tachycardia (see table and figures Classic Wolff-Parkinson-White syndrome Classic Wolff-Parkinson-White (WPW) syndrome and Narrow QRS tachycardia Narrow QRS tachycardia: Orthodromic reciprocating tachycardia using an accessory pathway in Wolff-Parkinson-White syndrome ).

Many episodes stop spontaneously before treatment.

Vagotonic maneuvers (eg, Valsalva maneuver, unilateral carotid sinus massage, ice water facial immersion, swallowing of ice-cold water), particularly if used early, may terminate the tachyarrhythmia; some patients use these maneuvers at home.

AV node blockers are used if vagotonic maneuvers are ineffective and the QRS complex is narrow (indicating orthodromic conduction) and regular (indicating the episode is not atrial fibrillation); blocking conduction through the AV node for one beat interrupts the reentrant cycle. Adenosine is the first choice. Dose is 6 mg by rapid IV bolus (0.05 to 0.1 mg/kg in children), followed by a 20-mL saline bolus. If this dosage is ineffective, 2 subsequent 12-mg doses are given every 5 minutes. Adenosine sometimes causes a brief (2- to 3-second) period of cardiac standstill, which may distress patient and physician. Verapamil 5 mg IV or diltiazem 0.25 to 0.35 mg/kg IV are alternatives.

For a regular, wide QRS complex tachycardia known to be an antidromic reciprocating tachycardia not involving double accessory pathways (which must be identified by the history; they cannot be established acutely), AV nodal blockers may also be effective. However, if the mechanism of the tachycardia is unknown and ventricular tachycardia has not been excluded, AV nodal blockers should be avoided because they may worsen ventricular tachycardias. In such cases (or those in which drugs are ineffective), IV procainamide or amiodarone can be used. Alternatively, synchronized cardioversion Cardiac Resynchronization Therapy (CRT) The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more with 50 joules (0.5 to 2 joules/kg for children) is quick and safe and may be preferred to these more toxic drugs.

When episodes of AV nodal reentrant tachycardia are frequent or bothersome, options include long-term antiarrhythmics or transvenous catheter ablation Ablation for Cardiac Arrhythmia The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more . Generally, ablation is recommended, but if it is not acceptable, drug prophylaxis usually begins with digoxin and proceeds, as required, to beta-blockers, nondihydropyridine calcium channel blockers, or both, then to one or more class Ia, class Ic, or class III antiarrhythmics (see table Antiarrhythmic Drugs Antiarrhythmic Drugs (Vaughan Williams Classification) ). However, postadolescent patients with manifest Wolff-Parkinson-White syndrome (in whom atrial fibrillation becomes more likely) should not receive digoxin or a nondihydropyridine calcium channel blocker alone (see also Atrial Fibrillation and Wolff-Parkinson-White Syndrome Atrial Fibrillation and Wolff-Parkinson-White Syndrome (WPW) In Wolff-Parkinson-White syndrome, antegrade conduction occurs over an accessory pathway. If atrial fibrillation, develops this is a medical emergency as very rapid ventricular rates can develop... read more ).