Vectorcardiograms (Frank system) were recorded simultaneously with His bundle electrograms during atrial stimulation in 3 patients with intermittent preexcitation Wolff-Parkinson-White (WPW) syndrome. In 2 cases with classic WPW, type A, loops were obtained during (1) exclusive conduction through the normal pathway, (2) coexisting accessory bundle and normal pathway conduction, and (3) exclusive accessory pathway conduction. Combination beats (resulting from ventricular depolarization through both pathways) showed an initial delay associated with anteriorly placed QRS loops and maximal vectors. When exclusive accessory bundle conduction occurred, a rightward and anteriorly oriented terminal delay was added to the initial slowing. This terminal delay was not ascribed to right bundle branch block but to the specific pattern of activation of an impulse apparently propagating from the posterosuperior wall of the left ventricle. In fact, these vectorcardiograms were similar to those recorded from patients with ectopic impulses originating at the posterosuperior left ventricular wall. When exclusive conduction through the normal pathway was associated with right bundle branch block, the prolonged St-V interval coexisted with a loop showing only terminal conduction disturbances. The loops seen during exclusive accessory bundle conduction in the patient with WPW, type B, had a leftward, posterior and superior orientation. The spatial delay was diffuse, although more marked toward the end of depolarization. This terminal (leftward) conduction defect was not attributed to right bundle branch block. The sequence of ventricular activation (as recorded at the body surface) was similar to that occurring during right ventricular apical pacing. Resemblance between vectorcardiograms showing exclusive accessory bundle conduction and those produced by direct stimulation of specific ventricular sites suggests, but certainly does not prove, that the electrical impulse is propagated from equivalent sites.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine