Decreased coronary flow can occur during repair of total anomalous pulmonary venous connection: The importance of preferential myocardial hypothermia in an infant pig model

Operative mortality for total anomalous pulmonary venous connection (TAPVC) has improved from 40% to 13% due to improved techniques. This paper documents heretofore unrecognized decreased left ventricular coronary flow during the repair stage of TAPVC and shows how preferential myocardial hypothermia (PMH) can cool the heart during the ischemic stage of the operation. Blood flow distribution (15 μ microspheres) was measured in thirteen 2-week-old pigs (3 kg each). Determinations were made before cardiopulmonary bypass (CPB), 2 minutes after CPB, 15 minutes into the sham stage (Group I) or the repair stage (Group II) and 20 minutes after CPB. The repair stage was 30 minutes of heart retraction to simulate repair of TAPVC. PMH was accomplished by CPB and cooled perfusate (4°C) that resulted in profound myocardial (16°C) and moderate systemic (27°C) hypothermia. Group I (N = 5) was the control and Group II (N = 8) had heart retraction to simulate repair of TAPVC. PMH caused a redistribution of blood flow favoring the heart. This was measured as per cent cardiac output from pre-bypass controls (23.2% ± 2.7) to bypass flows (43.6% ± 5.8) (P < 0.05) that resulted in myocardial (16°C ± 0.1) and systemic (27°C ± 0.1) cooling. During CPB, left ventricular, septal, and right ventricular flow (cc/100 g/min) did not change in Group I (sham animals), but decreased in Group II when the heart was retracted to simulate repair of TAPVC. PMH caused redistribution of flow favoring the heart that results in selective cooling. During the repair of TAPVC, retraction of the heart causes decreased left and right ventricular flow, and may cause irreparable damage if myocardial hypothermia is not employed.