title: Effects of pacing site on QRS morphology in Wolff-Parkinson-White syndrome, with special reference to 'pseudo-tachycardia-dependent block in accessory pathway and 'atrial gap'.
abstract: 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 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.
mesh_terms: D001283:Atrioventricular Node / Q000503:physiopathology; D002036:Bundle of His / Q000503:physiopathology; D004562:Electrocardiography; D006325:Heart Atria / Q000503:physiopathology; D006327:Heart Block / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D010138:Pacemaker, Artificial / Q000379:methods*; D013610:Tachycardia / Q000150:complications; D014927:Wolff-Parkinson-White Syndrome / Q000503:physiopathology*