Atrial electrical activity and its suppression during cardioplegic arrest in pigs

Right atrial electrical activity and myocardial temperatures of all four chambers were monitored during a 1 hour period of cardioplegic arrest in 20 pigs subjected to different methods of venous cannulation and cardiac cooling. Myocardial protection was provided by systemic hypothermia (28° C) and intermittent intra-aortic administration of cold (4° C) hyperkalemic (20 mEq/L) crystalloid cardioplegia. The use of a single right atrial cannula for venous drainage was associated with sustained atrial activity (50 ± 5.5 minutes) during cardioplegic arrest and the warmest right atrial (27° ± 0.2° C) and right ventricular (20.5caval cannulation with snaring and right atrial venting decreased right atrial and ventricular temperatures marginally (25.3° ± 0.5° C and 19.1 ± 0.4° C, respectively, p < 0.05) but did not significantly alter the duration of atrial electrical activity (42.2 ± 2.5 minutes, p > 0.05). Addition of an extracavitary right atrial drip of cold (4° C) saline, 750 ml for the 1 hour aortic clamping period, reduced right atrial temperature (22.8° ± 0.4° C) and activity (24.8 ± 6.3 minutes) to a significant extent. Intracavitary irrigation of the right atrium with cold saline, in the presence of snared double caval cannulas, decreased right atrial and ventricular temperatures most dramatically (17.0° ± 0.5° C and 17.5° ± 0.3° C, respectively, p < 0.05), reduced the duration of atrial electrical activity by 84% (to 8 ± 3.9 minutes, p < 0.01), and diminished the total number of atrial contractions per hour of aortic clamping by 88%. It is concluded that intracavitary right atrial cooling with separate snared caval cannulation is the most effective method of ensuring atrial inactivity and prolonged right heart hypothermia during cardioplegic arrest.