[Identification of the sinus potential in man by endocavitary electrocardiography. Identification criteria,...

The potential of the sinus node was recorded in 24 patients by endocavitary electrocardiography using the same equipment as for usual electrophysiological investigation. The sinus node potential is a slow wave which starts progressively, has a rounded peak and precedes the endocavitary atrial activation and the surface P wave, and is relayed at an acute angle to the high amplitude deflection of atrial depolarisation. In some specially selected recordings it is easy to confirm the sinus origin of this slow wave where its preatrial position may be defined by the fixed relation of the S-P interval and by the variability of the T-S interval. Usually it is necessary to use technical manoeuvres (vagal stimulation, premature atrial stimulation) to demonstrate the preatrial behaviour of a potential thought to be of sinus origin. The variability of the sinus potential and the apparent sinoatrial conduction time, is suggestive of a physiological instability of the intrasinus pacemaker. The sinoatrial conduction time measured directly does not seem to exceed 140 ms in normal subjects.