In a patient with a Wolff Parkinson White (WPW) syndrome type A mid right atrial stimulation at a rate of 73/min produced a lesser degree of ventricular pre excitation than when a slower sinus rhythm was present. This paradoxical effect was not related to tachycardia dependent block in the accessory pathway because pre excitation again increased at faster pacing rates. It was partly the result of a (proportionally) greater prolongation of intra atrial conduction time to the accessory pathway than to the atrioventricular node and partly of a faster atrioventricular nodal conduction time. The latter, in turn, could be attributed either to later than normal arrival of excitation at the atrioventricular node, at a time when this structure was more recovered, or to a change in the site or mode of entry into the atrioventricular node. A gap in the atria was present because at a St1 St2 interval shorter than that at which A2 had been blocked in the accessory pathway conduction was again possible, but with longer A1-A2 intervals. Finally, at similar, short, coupling intervals the impulse penetrated the atrioventricular node from the mid right atrium but not from the coronary sinus. The unusual findings in this case support a recent assumption that in patients with WPW type A atrial stimulation should be performed from the coronary sinus to minimize the potential sources of error which can be produced by intra atrial delay.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine