Development of regional myocardial ischemia distal to a critical coronary stenosis during cardiopulmonary bypass: Comparison of the fibrillating vs. the beating nonworking states

The present study was designed to determine whether conversion to the beating, nonworking (BNW) heart would diminish fibrillation-induced regional ischemia distal to a critical coronary stenosis. Ten mongrel dogs were placed on total cardiopulmonary bypass with a critical stenosis applied to the left anterior descending coronary artery (LAD). The time on total bypass was divided into three equal 50-minute periods during which the hearts were maintained alternately in sinus rhythm or ventricular fibrillation. When BNW hearts were fibrillated, intramyocardial carbon dioxide tension (Pm_CO2 ) in the LAD supplied subendocardium rose from 73 ± 7 (±SEM) to 120 ± 14 mm Hg (p < 0.001), and intramyocardial oxygen tension (Pm_O2 ) fell from 24 ± 4 to 10 ± 2 mm Hg (p < 0.005). Regional arterial-coronary venous lactate difference (A-CV lac) fell from 13.8 ± 3.8 mg% (extraction) to -10.8 ± 3.2 mg% (production) (p < 0.005). When fibrillating hearts were converted to the BNW state, Pm_O2 rose from 12 ± 2 to 19 ± 4 mm Hg and Pm_CO2 decreased from 101 ± 9 to 85 ± 4 mm Hg. A-CV lac rose from -6.5 ± 2.6 mg% (production) to 10.4 ± 4.8 mg% (extraction) (p < 0.01). These results suggest that in a region of myocardium distal to a critical stenosis, ventricular fibrillation during bypass results in regional myocardial ischemia whereas the BNW state does not. This ischemia likely is due to the inability of flow in the stenosed coronary artery to increase in response to the increased oxygen demand of fibrillation. Furthermore, conversion to the BNW state can reverse the ischemia which develops in the fibrillating state.