P waves and P loops in coronary sinus and left atrial rhythms

Abstract

P-wave and P-loop changes during transvenous pacing of specific locations in the coronary sinus and left atrium were studied in dogs and in man. During coronary sinus rhythm, the diagnostic criteria for P-wave changes were always met. In addition, inversion of the P wave in Lead V 6 was consistently obtained. The P loop was always directed cephalad. “Dome-dart” P waves in V 1 were present in one of 14 patient studies. Pacing the left atrial appendage produced less consistent P-wave changes; “domedart” P waves in V 1 were present in 3 of 7 dog studies and in one of 3 patients. The P vector was directed caudad, rightward, and ventrad. Pacing the inferior left atrium in close proximity to the coronary sinus produced P-wave and P-loop changes which were identical with and indistinguishable from those of coronary sinus rhythm. It is suggested that a common site of impulse formation or a common intra-atrial conduction pathway is utilized. Confirmatory evidence was obtained from intra-atrial electrograms. Additional evidence was obtained from Bachman bundle potential recordings, which indicated a reversal of atrial activation during left atrial rhythm.