Effects of diastolic synchronized retroperfusion on regional coronary blood flow in experimental myocardial ischemia

Coronary venous retroperfusion has previously been suggested as a potential mode of treatment of myocardial ischemia. This study was designed to examine the actual changes in regional myocardial blood flow that occur with diastolic synchronized retroperfusion of the coronary sinus. Coronary sinus retroperfusion consisted of (1) diastolic augmentation of delivery of arterial blood into the acutely ischemic myocardium, and (2) systolic facilitation of coronary venous drainage. This was achieved using a gas-actuated electrocardiogram-synchronized retroperfusion pump that propels arterial blood during diastole through an autoinflatable bladder catheter. Hemodynamic data and measurements of ischemic tissue injury (S-T segment mapping) and regional myocardial blood flow (radioactive microsphere technique) were obtained before and after 1 and 2 hours of coronary arterial occlusion. Experiments were performed in 19 open chest dogs: Retroperfusion was instituted after the 1st hour of coronary occlusion and maintained for the subsequent hour in 8 dogs and the results were compared with those obtained in 6 randomly selected untreated dogs. In five additional dogs, the fraction of microspheres escaping myocardial entrapment in either an anterograde or a retrograde direction was determined. In both treated and untreated dogs, changes in hemodynamics, S-T segment mapping and regional myocardial blood flow showed the same trend up to 1 hour of coronary occlusion. Synchronized retroperfusion resulted in a minor but significant decrease in heart rate and an increase in stroke volume. As early as 15 minutes after the start of synchronized retroperfusion, there was a significant decrease in S-T segment elevation (from 5.95 ± 1.01 to 3.09 ± 0.58 mV [mean ± standard error of the mean], p <0.01) that was maintained for the subsequent hour; in the control series, S-T segment elevation was unaffected. After 1 hour of retroperfusion, regional transmural flow increased in the nonischemic zone from 0.84 ± 0.07 to 1.05 ± 0.10 ml/min per g (p <0.05) with an unchanged $\text{endocardial}\text{epicardial}$ flow ratio (1.10 ± 0.04 and 1.11 ± 0.04 before and 1 hour after treatment, respectively). In the ischemic zone, 1 hour of retroperfusion increased transmural flow by 59.3 percent (from 0.32 ± 0.05 to 0.51 ± 0.04 ml/min per g, p <0.05) with a greater increase in endocardial flow (from 0.19 ± 0.02 to 0.35 ± 0.03 ml/min per g, p <0.05) than in epicardial flow (from 0.43 ± 0.05 to 0.59 ± 0.06 ml/min per g, p <0.01) leading to a significant increase in $\text{endocardial}\text{epicardial}$ flow ratio (from 0.46 ± 0.05 to 0.64 ± 0.07, p <0.01).These experimental data show that retroperfused arterial blood reaches the ischemic as well as the nonischemic zones and is favorably redistributed toward the endocardium. Thus, diastolic synchronized retroperfusion is capable of restoring nutritional blood flow to approximately 50 percent of normal control flow. This improvement in myocardial perfusion might be of value in delaying irreversible myocardial ischemia.