Atrial standstill secondary to atrial inexcitability (atrial quiescence). Recognition and treatment following open-heart surgery.

SUMMARY Atrial standstill secondary to atrial inexcitability or atrial quiescence was diagnosed in 11 patients and atrial standstill, in which atrial excitability was still present though depressed, was diagnosed in two patients during the immediate period following open-heart surgery. Atrial quiescence was successfully treated in six patients and atrial standstill with depressed excitability in both patients by the infusion of small doses of isoproterenol. Atrial quiescence was not treated in the other five patients and reverted spontaneously within 24 hours after surgery. It is suggested that atrial quiescence results from relative depolarization of the atrial membrane and that the success of therapy with isoproterenol results from hyperpolarization of the atrial membrane by this drug. A TRIAL STANDSTILL secondary to atri-al inexcitability or atrial quiescence is a rhythm in which there are no P waves in the ECG, an atrial electrogram (EG) cannot be recorded from electrodes either in contact with the atria or within the atrial chambers, and the atria cannot be paced by electrical stimuli delivered through electrodes in contact with the atria. During this rhythm, the Isoproterenol Atrial membrane potential Atrial pacing Open-heart surgery [lity ventricles are usually depolarized from an A-V junctional pacemaker. Although, as summarized by Rosenbaum and Levine,' there are several descriptions of absence of spontaneous atrial activity in the experimental animal, Sir Thomas Lewis2 was the first to describe such a rhythm in patients. Since then, there have been many other reports, recently summarized Pinas4 were the first to report the association of the absence of spontaneous atrial activity with the inability to pace, the heart with electrical stimuli delivered through electrodes in contact with the atria. Since then there have been four additional reports.3 4, 6, 7 Studies on isolated peffused cardiac tis-sue8' 9 have demonstrated that inexcitability is associated with a low (<55 mv) membrane resting potential. In many instances, infusion