The AFORMED phenomenon: A proposed etiology

The alternating failure of response of mechanical to electrical depolarization (AFORMED) phenomenon was first described >lO years ago.l Although the physiologic effects and clinical significance of electromechanical dissociation have been studied, the cause of the phenomenon has not been investigated. This report describes our observations, which may help elucidate the etiology of this phenomenon. We observed the AFORMED phenomenon in 3 open-chest mongrel dogs during experiments unrelated to this phenomenon. 1:n these experiments, 20to 25-kg dogs were anesthetized with sodium pentobarbital, cuffed endotracheal tubes were inserted, and the dogs were placed on a positive-pressure, volume-regulated Harvard respirator. The lungs were periodically hyperinflated to prevent atelectasis. The chest was opened through a median sternotomy. A fluid-filled NIH catheter was placed in the ascending aorta by retrograde arterial catheterization of the femoral artery. A Carolina Medical Electronics perivascular flow probe was positioned around the pulmonary artery to measure the pulmonary artery flow. A Millar Micro-tip pressure transducer (model PC!-761) was inserted into the pulmonary trunk through a stab incision in right ventricular outflow tract for continuous recording of pulmonary artery pressure. Hypoxemia was induced by administering 14% oxygen and the effects of various receptor blockers were studied to elucidate the mechanism of hypoxic pulmonary hypertension. Each AFORMED episode occurred during the tachycardia phase that followed successful resuscitation of cardiac arrest. (Cardiac arres’t occurred in some dogs during hypoxic phase of the experiment.) The electrocardiogram, aortic pressure and pulmonary artery flow were recorded continuously during the AFORMED episodes. Rapid intravenous administration of 2.0 ml of 10% calcium gluconate promptly abolished the AFORMED phenomenon, but it reappeared 10 to 15 minutes later. There was a consistent but short-lived response to calcium in each dog and in each episode of the AFORMED phenomenon. Intravenous lanatoside-C abolished the phenomenon after a 30-minute latent period. There were no recurrences of AFORMED after administering