Clinical and quantitative birefringence assessment of 100 patients with aortic clamping periods in excess of 120 minutes after hypothermic cardioplegic arrest.

At St. Thomas' Hospital the first 100 patients with prolonged aortic cross-clamp times in excess of 120 minutes have been analyzed clinically (low cardiac output and mortality) and 49 of these patients from which left and right ventricular biopsies were taken, have been analyzed by quantitative birefringence (biophysical measurement of myocardial deterioration). A total of 8 patients died (8%) and 11 had low cardiac output syndrome (11%). The patients were divided into those given only a single infusion (n = 18) and those given hourly infusions (n = 82) of hypothermic cardioplegic solution. These were then subdivided into those with single (n = 37) or multiple (n = 63) corrective surgical procedures. In the patients who had a single corrective surgical procedure there was no difference at all, but in those patients who had multiple corrective surgical procedures, hourly infusion reduced low cardiac output from 12.5% to 9.4% in multiple valve patients and from 50% to 19% in bypass graft combined with valve replacement patients. In this latter group mortality fell from 50% to 4.8% but there were only 2 patients given a single infusion. There was no statistically significant advantage in hourly infusions compared with single infusions, either clinically or cytochemically. Twenty-six patients had aortic cross-clamp periods in excess of 150 minutes. Mortality and low cardiac output increased compared with the 120 to 150 minute group, rising from 3% to 19% and from 7% to 23% respectively. As a result of these analyses, surgical practice has been changed to 30-minute reinfusion intervals with currently improved results.