Reciprocating tachycardia using bilateral anomalous pathways: electrophysiologic and clinical implications

Area of Science:

• Electrophysiology
• Cardiology
• Cardiac Electrophysiology

Background:

• Supraventricular tachycardia (SVT) can be disabling and challenging to manage.
• Accessory pathways, such as Kent bundles, are implicated in various cardiac arrhythmias.
• Bilateral accessory pathways, involving both right and left sides, present unique electrophysiologic considerations.

Observation:

• A patient with disabling SVT exhibited electrophysiologic evidence of both right and left Kent bundles.
• Tachycardia acceleration occurred via sequential antegrade and retrograde conduction over these pathways.
• Spontaneous block in the right Kent bundle led to slowed tachycardia and right bundle branch block (RBBB).

Findings:

• Antegrade conduction through the left bundle branch followed by early retrograde atrial activation via the left Kent bundle shortened the ventriculoatrial (VA) interval.
• The coexistence of bilateral Kent bundles can be suspected when a shortened VA interval and RBBB pattern are observed in patients with right-sided preexcitation.
• Bilateral accessory pathways can possess distinct electrophysiologic properties.

Implications:

• This finding aids in diagnosing bilateral accessory pathways, particularly when electrocardiographic (ECG) findings include a shortened VA interval and RBBB.
• Understanding different electrophysiologic properties of bilateral pathways is crucial for effective antiarrhythmic drug selection.
• Unequal responses to antiarrhythmic therapies may be anticipated in patients with bilateral accessory pathways.