The regional effect of retrograde cardioplegia in areas of evolving ischemia

Retrograde cardioplegia (RCP) is often used for myocardial protection during coronary bypass grafting, but the regional effect of RCP in areas of evolving ischemia is unknown. We examined the functional and metabolic indices of regional myocardial preservation following acute coronary occlusion with evolving ischemia in a canine model. Following the institution of 37 degrees C cardiopulmonary bypass in 14 dogs, the left anterior descending artery (LAD) was occluded for 15 min. The hearts were then subjected to 90 min of cardioplegic arrest (12 degrees C, 15 mL/kg every 30 min). Seven had antegrade cardioplegia (ACP) alone, while seven had ACP until arrest, then RCP. No topical cooling was used. The LAD occlusion was released after the first bolus of cardioplegia. Regional temperature and pH were measured in the LAD and circumflex (nonischemic) distributions. After 90 min of ischemia and 30 min of reperfusion, all dogs were weaned from bypass. Postischemic function was determined globally by the return of developed pressure (%dP/dt) and regionally by ultrasonic wall crystals. End-ischemic ATP preservation in the LAD distribution was assessed by HPLC (mm ATP/mg protein). Results show that regional functional and metabolic indices were better maintained with RCP in the ischemic LAD distribution. Although only moderate reduction of global function was seen with ACP, the severe reduction noted in LAD regional wall motion with ACP reflects poor regional protection that can be significantly improved in evolving ischemia with RCP.