PATIHOPHYSIOLOGY AND NATURAL HISTORY PREEXCITATION Recordings of basal ventricular preexcitation from electrode catheters in patients with accessory atrioventricular connections

To determnine the effects of ventricular preexcitation via accessory atrioventricular connections (ACs) on the sequence of basal ventricular activation, electrophysiologic study records of 22 patients with AC were reviewed. In each, AC site was confirmed by mapping done at operation. Local ventricular preexcitation (VP), defined as earlier timing of a local ventricular electrogram relative to the surface electrocardiographic QRS onset in preexcited compared with in normal QRS complexes, was assessed at the coronary sinus and at the ventricular septal summit recorded from the His bundle site. Five patients with concealed AC did not have VP. VP patterns with manifest AC were similar during average fusion QRS complexes and maximum ventricular preexcitation. Left free wall and left crux AC produced VP apparent on the ventricular electrogram recorded at the coronary sinus alone. With anteroseptal AC, VP was noted only at the ventricular septal summit. Posteroseptal AC produced VP that was apparent on the ventricular electrogram recorded at the coronary sinus and on the electrogram of the ventricular septal summit. Right free wall AC preexcited neither of these basal ventricular regions. The observation of VP patterns may help in localizing AC and may be particularly useful in patients without retrograde AC function at electrophysiologic study. Circulation 69, No. 2, 233-241, 1984. WHEN ATRIOVENTRICULAR conduction is normal the basal regions of the heart are activated relatively late in the overall process of ventricular depolarization.1 However, in patients with Wolff-ParkinsonWhite syndrome, ventricular preexcitation advances activation of a variable portion of basal ventricular tissue. Electrophysiologic studies in these patients usually include observation of local ventricular electrograms of two basal areas the posterobasal left ventricle, recorded from the coronary sinus, and the ventricular septal summit, recorded from the His bundle catheter site. This investigation examines the patterns of altered basal ventricular activation during manifest preexcitation, as reflected in alterations in the From the Cardiac Arrhythmia Study Unit, Division of Cardiology, Stanford University Medical Center, and Division of Cardiology, University of California San Francisco, San Francisco. Address for correspondence: L. Brent Mitchell, M.D., F. R. C. P. (C), Division of Cardiology, University of Calgary and Foothills Hospital, 1403 29th St., N.W., Calgary, Alberta, Canada T2N 2T9. Received for publication Jan. 13, 1983; revision accepted Oct. 20, 1983. This work was completed during Dr. Mason's tenure as a scholar of Brotman Foundation, Los Angeles, and during Dr. Mitchell's tenure as a fellow of the Canadian Heart Association. *Present address: Division of Cardiology, Foothills Hospital, University of Calgary, Calgary, Alberta, Canada. Vol. 69, No. 2, February 1984 timing of local electrograms recorded from these two ventricular sites. In addition to the physiologic insight such information provides, the pattern of local ventricular preexcitation varies with the position of the responsible accessory atrioventricular connection and therefore helps to locate the site of the pathway. Since bundle branch block (BBB) alters the sequence of ventricular activation, we also assessed its confounding effects on indexes of local ventricular preexcitation.