Intramural Outflow Tract Ventricular Arrhythmia With Preferential Conduction Mimicking a Left Ventricular Summit Origin.

BACKGROUND

Intramural ventricular arrhythmias with preferential conduction are challenging to ablate because the breakout site may be remote from the true site of origin.

CASE SUMMARY: A 61-year-old man presented with drug-refractory premature ventricular contractions after failed catheter ablation. Electrocardiography suggested an epicardial outflow tract origin. Endocardial mapping identified a prepotential at the left-right coronary cusp junction with a perfect pace map but an extremely long stimulus-to-QRS latency, indicating activation via a preferential conduction pathway. Coronary venous mapping with a microelectrode catheter revealed an earlier prepotential within a septal perforator vein, consistent with an intramural source. Because endocardial ablation was ineffective, selective retrograde venous ethanol ablation using a double-balloon technique was performed, resulting in immediate and durable elimination of premature ventricular contractions without complications.

DISCUSSION: Recognition of intramural substrates with preferential conduction is essential for selecting effective ablation strategies.

TAKE-HOME MESSAGES: Intramural ventricular arrhythmia with preferential conduction can be difficult to ablate because the breakout site from the conduction pathway may be remote from the true site of origin, leading to misleading electrocardiographic and endocardial mapping findings. Coronary venous mapping can identify intramural substrates and guide selective therapies, such as double-balloon-assisted ethanol ablation, when conventional endocardial ablation fails.