Partial atrial standstill in sick sinus syndrome; intraatrial and AV nodal block with short PR interval.

Standstill and inexcitability (quiescence) of the high right atrium could be demonstrated in a patient with sinus node dysfunction and bradycardia--tachycardia syndrome. The onset of P wave in surface electrocardiogram did not represent the beginning of atrial excitation but followed 130 msec the high right atrial and 50 msec the low right atrial deflection, leading thereby to a short PR interval which gave misinformation on the atrioventricular conduction. A pacemaker implant with right ventricular stimulation freed the patient of his previous complaints. 4 wk after the implantation the demand unit was inhibited for 5 h by external stimulation. Continuous ECG monitoring, esophageal ECG recording and fluoroscopic study could not reveal any atrial activity. The conditions for atrial pacemaker implantation are discussed.