Differential electrical activity of the atria during cardioplegic arrest in pigs

To elucidate the electrical interrelationship of the atria during cardioplegic arrest, simultaneous bipolar right atrial (RA) and left atrial (LA) electrograms and myocardial temperatures of all four chambers of the heart were recorded in 10 pigs during an hour of aortic clamping. Five pigs (Group 1) underwent single venous cannulation; in 5 others (Group 2), snared double caval cannulation, RA venting, and intracavitary RA irrigation with cold saline solution were employed. Myocardial protection was provided by systemic hypothermia (28 degrees C) and intermittent intraaortic administration of cold (4 degrees C) hyperkalemic (20 mEq/L) crystalloid cardioplegic solution. Single RA cannulation was associated with sustained RA activity during cardioplegic arrest and with the warmest mean myocardial temperatures. Electrical activity was infrequent in the left atrium, which was often silent while RA impulses continued to be observed. Four Group 1 pigs exhibited high-grade RA-LA block, whereas in 2 animals completely asynchronous RA-LA electrical activity occurred. Isolated LA activity was not encountered. The combined methods used in Group 2 pigs significantly reduced mean myocardial temperatures. Both RA and LA impulses were practically abolished, and their mean durations decreased 96% and 85%, respectively. It is concluded that the pattern of electrical activity differs in the two atria during cardioplegic arrest when a single venous cannula is employed. Intracavitary RA irrigation with cold saline solution in the presence of snared caval cannulas provides improved myocardial hypothermia and effectively eliminates both RA and LA activity in the course of cold crystalloid cardioplegia.