SHORT-TERM SYNCHRONIZED RETROPERFUSION BEFORE REPERFUSION REDUCES INFARCT SIZE AFTER PROLONGED ISCHEMIA IN DOGS

Background. Previous studies have demonstrated that synchronized coron ary venous retroperfusion (SRP) can restore blood flow to the ischemic myocardium, resulting in infarct size reduction and improvement of th e left ventricular function. Despite the nutritive blood flow achieved by SRP being relatively limited, SRP has been shown to improve washou t of by-products from the ischemic myocardium. The aim of this study w as to investigate whether short-term SRP immediately prior to reperfus ion would attenuate the deteriorative phenomena following reperfusion. Methods and Results. Closed-chest anesthetized dogs underwent 3 hours of left anterior descending coronary artery (LAD) occlusion. The dogs were then randomized into two groups: (1) control group (n=9), in whi ch the occlusion was immediately followed by 3-hour reperfusion; or (2 ) SRP group (n=9), in which SRP was started 3 hours after occlusion an d maintained for 30 minutes with sustained occlusion followed by 2.5-h our reperfusion with simultaneous discontinuation of SRP. There were n o statistical differences between the groups in global hemodynamics an d degree of ischemia measured by radiolabeled microspheres. Myocardial infarct size (triphenyltetrazolium method) expressed as percentage of risk area was significantly smaller in the SRP group (24+/-7%, mean+/ -SEM) than in the control group (54+/-9%). The extent of myocardial he morrhage expressed as percentage of infarct size was also significantl y reduced in the SRP group (3+/-2%) compared with the control group (2 4+/-6%). The increase in end-diastolic wall thickness in the ischemic area after reperfusion assessed by two-dimensional echocardiography wa s significantly less in the SRP group. Blood flow measurements after r eperfusion demonstrated the occurrence of no-reflow phenomenon only in the control group. Histological examination revealed extensive myocar dial hemorrhages only in the control group, which extended into the no nnecrotic myocardium in four of nine hearts and extensive contraction band necrosis compared with the SRP group. Conclusions. Short-term SRP prior to reperfusion can reduce infarct size, myocardial hemorrhage, wall swelling, and no-reflow phenomenon. The mechanism of this benefic ial effect is not clear but might be due to gradual reperfusion and wa shout of by-products from the ischemic myocardium before fully oxygena ted arterial blood reperfusion.