Atrioventricular Dissociation during Ventricular Fibrillatio
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Atrioventricular (AV) dissociation is a condition whereby the atria and the ventricles activate independently of each other. The normal activation—sinus node followed by the atria, AV node, and then the His-Purkinje system causing ventricular activation—is no longer observed. AV dissociation may occur when a subsidiary pacemaker in the AV node or the ventricle overtakes the sinus node for impulse initiation due to slowing of the sinus node, or it may occur when a subsidiary site beats faster than the sinus node, such as in ventricular tachycardia. The causes of AV dissociation are important to understand as they impact the treatment plan.

A 50-year-old woman with a history of bicaval cardiac transplantation presented to the emergency department with a 1-week history of dyspnea, fatigue, and weight gain. A transthoracic echocardiogram showed newly reduced left ventricular systolic function, and an endomyocardial biopsy confirmed acute cellular rejection of the transplanted heart. Her hemodynamic status deteriorated, thereby prompting initiation of venoarterial extracorporeal membrane oxygenation. Sustained ventricular fibrillation developed, with a loss of right and left ventricular contractility, as indicated by a nonpulsatile pulmonary arterial waveform and systemic arterial waveform.

A regular pulsatile central venouswaveform was observed. Repeat transthoracic echocardiography confirmed near ventricular standstill with a left ventricular thrombus and preserved right atrial contractility with tricuspid valve opening (corresponding to the central venous waveform). This observation, coupled with concomitant mitral valve opening, indicated atrioventricular dissociation during ventricular fibrillation. Premature closure of the atrioventricular valves immediately after atrial contraction was also observed. The patient had worsening multiorgan failure and died 1 week after presentation.