Paroxysmal Supraventricular Tachycardias due to Accessory AV Pathways (Preexcitation Syndromes)

Key Features

• Two classic features of Wolff-Parkinson-White (WPW) pattern on ECG

  • Short PR interval

  • Wide, slurred QRS complex due to manifest preexcitation (delta wave)

• Most patients with WPW pattern do not have clinical history of arrhythmia but have a higher risk of sudden cardiac death due to rapidly conducted atrial fibrillation through the accessory pathway

• Risk factors

  • Age younger than 20

  • History of tachycardia

  • Rapid conduction properties at electrophysiologic testing

Clinical Findings

• Accessory pathways occur in 0.1–0.3% of the population and facilitate reentrant arrhythmias

• Orthodromic reentrant tachycardia

  • Accounts for ~ 90% of atrioventricular reciprocating tachycardia (AVRT) episodes

  • Characterized by conduction antegrade down the AV node and retrograde up the accessory pathway, resulting in a narrow QRS complex (unless an underlying bundle branch block or interventricular conduction delay is present)

• Antidromic reentrant tachycardia

  • Conducts antegrade down the accessory pathway and retrograde through the AV node

  • Results in a wide QRS complex

• Atrial fibrillation or flutter with antegrade conduction down the accessory pathway and a rapid ventricular response seen in up to 30% of patients with Wolff-Parkinson-White syndrome

Diagnosis

• Some patients have a delta wave found incidentally on ECG

• Exercise treadmill testing useful in determining if preexcitation is lost at rapid rates

• Electrophysiologic testing with possible catheter ablation useful to ensure patients are not at an increased risk for syncope or sudden death

  • Patients found to have the shortest preexcited R-R interval (SPERRI) during atrial fibrillation of ≤ 250 msec or inducible supraventricular tachycardia are at increased risk for sudden cardiac death

  • Should undergo catheter ablation

Treatment

• For narrow-complex reentrant rhythms involving a bypass tract (orthodromic AVRT)

  • Vagal maneuvers

  • Intravenous adenosine

  • Intravenous verapamil

• For wide-complex tachycardia in the presence of an accessory pathway, be it reentrant-type (antidromic AVRT) or atrial fibrillation with antegrade conduction down the bypass tract

  • Intravenous class Ia (procainamide) and class III (ibutilide) antiarrhythmic agents

    • Medications of choice

    • Increase the refractoriness of the bypass tract

  • If hemodynamic compromise is present, electrical cardioversion is warranted

  • Agents such as calcium channel blockers and beta-blockers should be avoided because of increased risk of ventricular fibrillation

• Agents such as calcium channel blockers, and beta-blockers should be avoided

• Amiodarone can be effective in refractory cases

• If hemodynamic compromise is present, electrical cardioversion is warranted

• Radiofrequency ablation is the procedure of choice for long-term management of patients with accessory pathways and recurrent symptoms

• For patients not a candidate for catheter ablation, class Ic or class III antiarrhythmic medication may be considered