The Mechanical Consequences of Anomalous Atrioventricular Excitation (WPW Syndrome)

Abstract

The clinical and ecg features of anomalous atrioventricular excitation (Wolff-Parkinson-White syndrome) have been extensively studied, but the mechanical consequences of this abnormality have received less attention. Since the sequence of ventricular contraction may provide important clues to the basic mechanism of the syndrome, 12 patients with anomalous atrioventricular excitation were studied by means of phonocardiograms, carotid stethograms, and in one instance by cardiac catheterization. In 3 cases studies were possible during both normal and anomalous excitation so mat the patient acted as his own control. In 5 instances mechanical abnormalities were detectable. These abnormalities were varied and consisted in one case of the early onset and completion of ejection in both ventricles and in one case of early completion of ejection in the left ventricle. This was demonstrated by comparing events during anomalous and normal excitation. In 3 cases there was delayed onset of contraction on the contralateral side and possibly on the homolateral side as well. The remaining 7 cases showed no mechanical abnormalities by the methods employed. These observations suggest that the effect of anomalous excitation on the mechanics of the heart is variable and that 2 mechanical varieties of the Wolff-Parkinson-White syndrome exist. In one there is demonstrable ventricular asynchrony, whereas in the other there is no evidence of such asynchrony. It may not be possible to distinguish between these 2 varieties by clinical and ecg methods, but the detection on auscultation of broad or paradoxic splitting of the second sound is suggestive. The variable mechanical effects may be ascribed to differences of transmission time through the A-V node and to the site of entrance of the excitatory impulse from the anomalous pathway.