Effect of bundle branch block on local electrogram morphologic features: implications for arrhythmia diagnosis by stored electrogram analysis.

Analysis of stored local ventricular electrogram recordings is a useful diagnostic tool in the evaluation of patients with implantable cardioverter defibrillators. Visual analysis of local electrogram morphologic features has been demonstrated to be useful in distinguishing ventricular tachycardia from supraventricular rhythm. The effect of bundle branch block (BBB) aberration during supraventricular tachycardia on local electrogram morphologic features is not entirely clear. Erroneous diagnoses resulting from a change in electrogram morphologic features with BBB may occur. To determine whether the development of BBB can produce a change in local electrogram morphologic features and whether this change is dependent on the site of recording, we retrospectively reviewed local electrogram recordings from 23 patients who had intermittent BBB during electrophysiologic evaluation of documented or suspected supraventricular tachycardia. Local electrogram recordings from catheters placed in the right ventricular apex and coronary sinus during supraventricular tachycardia with BBB aberrancy were compared with recordings during narrow complex supraventricular tachycardia or normal sinus rhythm. Bipolar recordings were made with a 5 mm interelectrode distance with filter settings at 40 to 400 Hz. Three independent blinded observers defined the paired electrograms as the same or distinctly different. During right BBB a change in electrogram morphologic features was demonstrated in 11 (85%) of 13 recordings from the right ventricular apex and in only 1 (8%) of 12 recordings from the coronary sinus. In contrast, during left BBB a change in electrogram morphologic features was seen in 6 (100%) of 6 recordings from the coronary sinus and in only 1 (8%) of 13 recordings from the right ventricular apex. These results demonstrate that when the described recording techniques are used, a change in local ventricular electrogram morphologic features BBB is predominantly manifest in recording sites ipsilateral to the BBB, whereas recording sites contralateral to the BBB are relatively unaffected. This information may have implications regarding interpretation of stored electrograms when an attempt is made to establish a rhythm diagnosis leading to implantable cardioverter defibrillator therapy.