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 usefu l diagnostic tool in the evaluation of patients with implantable cardi overter defibrillators. Visual analysis of local electrogram morpholog ic features has been demonstrated to be useful in distinguishing ventr icular tachycardia from supraventricular rhythm. The effect of bundle branch block (BBB) aberration during supraventricular tachycardia on l ocal 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 p roduce 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 intermi ttent BBB during electrophysiologic evaluation of documented or suspec ted supraventricular tachycardia. Local electrogram recordings from ca theters placed in the right ventricular apex and coronary sinus during supraventricular tachycardia with BBB aberrancy were compared with re cordings 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 blind ed observers defined the paired electrograms as the same or distinctly different. During right BBB a change in electrogram morphologic featu res was demonstrated in 11 (85%) of 13 recordings from the right ventr icular apex and in only 1 (8%) of 12 recordings from the coronary sinu s. In contrast, during left BBB a change in electrogram morphologic fe atures was seen in 6 (100%) of 6 recordings from the coronary sinus an d in only 1 (8%) of 13 recordings from the right ventricular apex. The se results demonstrate that when the described recording techniques ar e used, a change in local ventricular electrogram morphologic features during BBB is predominantly manifest in recording sites ipsilateral t o the BBB, whereas recording sites contralateral to the BBB are relati vely unaffected. This information may have implications regarding inte rpretation of stored electrograms when an attempt is made to establish a rhythm diagnosis leading to implantable cardioverter defibrillator therapy.