Conduction block after cardioplegic arrest: prevention by augmented atrial hypothermia

Atrioventricular conduction abnormalities have become more frequent since the reintroduction of cardioplegic techniques for myocardial preservation during cardiac surgery. An animal model was developed to clarify the role of atrial septal hypothermia in the preservation of the primary site of postoperative conduction delay, the AV node. In our study, 10 animals served as the control group. They were subjected to 40 min of cardioplegic arrest during which the heart was protected with multidose cold potassium cardioplegia. Atrial septal temperatures averaged 27.4 degrees +/- 1.2 degrees C during cardioplegic arrest. We treated 10 additional animals (study group) similarly, except that atrial hypothermia was augmented by intracavitary or specialized topical techniques, which resulted in an average atrial septal temperature of 20.8 degrees +/- 3.3 degrees C (p less than .05). Detailed electrophysiologic studies of both groups were performed at 37 degrees C before and after cardioplegic arrest. Significant prolongation of AV nodal, and to a lesser extent His-Purkinje, conduction times was noted in the control group, but no conduction abnormalities occurred in the study group receiving augmented atrial hypothermia. Thus, conduction block in the specialized conduction system after cardioplegic arrest appears to be related to the adequacy of hypothermic preservation of the atrial septum and can be prevented by augmented atrial hypothermia.