Tachycardia with VA dissociation: an unusual tachycardia mechanism.

摘要

A 56-year-old man with a history of congestive heart failure and a biventricular ICD was referred for assessment of frequent episodes of antitachycardia pacing and occasional shocks for tachycardia. An EP study was performed for further assessment. During catheter manipulation in the right ventricle, tachycardia was observed. At baseline, the AH interval was 100 msec and the HV interval was 50 msec at 58 bpm. Preexcitation was not demonstrated with atrial pacing, and VA conduction was absent at all cycle lengths tested. Tachycardia was easily reproduced by ventricular and atrial pacing. What is the differential diagnosis of the tachycardia?Intracardiac tracings are shown in Figure 3. Administration of 6 mg of intravenous adenosine consistently resulted in termination of the tachycardia. Attempts to entrain the tachycardia by right atrial pacing were unsuccessful. Catheter manipulation in the right ventricle during tachycardia resulted in transient right bundle branch block (RBBB) with delayed activation recorded at the RV apex. A premature ventricular beat was introduced at a time when the His bundle was refractory, demonstrated in Figure 4. What is the mechanism of the tachycardia determined at EP study?