Improved Myocardial Protection during a Prolonged Cross-Clamp Period

Severe coronary stenoses limit delivery of cardioplegic solution to ischemic regions in patients undergoing bypass operations. A prospective randomized trial was undertaken to determine whether the construction of proximal as well as distal anastomoses during a prolonged cross-clamp period would provide more uniform cardiac cooling and better myocardial protection. Ninety-one consecutive patients undergoing elective coronary bypass operations were randomized into two groups. The long cross-clamp technique was used in 46 patients (Group 1), and a proximal anastomosis was constructed after each distal anastomosis. The short cross-clamp technique was employed in 45 patients (Group 2), and distal anastomoses were constructed during aortic occlusion. Cardiopulmonary bypass time was identical, but the cross-clamp period was longer in Group 1 (59 ± 15 minutes versus 46 ± 17 minutes in Group 2; p < 0.001). The mean temperature in the most ischemic region was colder with the long cross-clamp technique (12.5 ± 3.1°C in Group 1 versus 14.8 ± 3.2°C in Group 2; p < 0.01). The total amount of the myocardial isoenzyme of serum creatine kinase released was greater in Group 2 than in Group 1 (332 ± 34 IU/L per hour in Group 1 versus 469 ± 45 IU/L per hour in Group 2). Thirty-six patients had coronary sinus catheters inserted (18 patients in each group). Myocardial lactate extraction returned to normal sooner in the patients who had a long cross-clamp period; time to a normal lactate extraction was 0.8 ± 0.8 hours in Group 1 versus 2.2 ± 2.1 hours in Group 2 ( p < 0.001). Volume loading and atrial pacing 2 to 4 hours postoperatively produced a similar hemodynamic response in the two groups, but myocardial lactate extraction increased in Group 1 and decreased in Group 2 ( p < 0.05). The construction of proximal as well as distal anastomoses during a prolonged cross-clamp period produced more uniform cooling and improved myocardial protection.