Collateral perfusion through overlapping vessels reduces canine right ventricular ischemic injury from positive end-expiratory pressure.

OBJECTIVE: To test, in a canine model of right ventricular ischemia with 15 cm H2O positive end-expiratory pressure, whether collateral perfusion through overlapping vessels from the left ventricle to the right ventricular free wall can reduce infarct size. DESIGN: Randomized, prospective, controlled, experimental study in dogs. SETTING: Anesthesia research laboratory of an academic medical center. SUBJECTS: Twenty microfilaria-free mongrel dogs. INTERVENTIONS: Anesthetized, closed-chest dogs were managed with the application of 15 cm H2O positive end-expiratory pressure. The right coronary artery was ligated (90 mins) with occlusion (n = 10) and without occlusion (n = 10) of overlapping vessels. MEASUREMENTS AND MAIN RESULTS: Myocardial blood flow (using radioactive microspheres) was measured in the area at risk (gentian violet) and in the area of necrosis (triphenyltetrazolium chloride). With right coronary and overlapping vessel occlusion, blood flow in the area at risk decreased from 80.1 +/- 14.0 to 9.0 +/- 1.7 mL/min/100 g after 5 mins of ischemia (p = .0001) and remained depressed at 8.7 +/- 1.8 mL/min/100 g after 75 mins of ischemia. With right coronary occlusion alone, blood flow decreased after 5 mins of ischemia from 64.8 +/- 5.4 to 14.3 +/- 1.9 mL/min/100 g (p = .0001 compared with baseline), which was 60% greater than the group with occluded collateral vessels (p = .0055). Moreover, after 75 mins of ischemia, blood flow in the area at risk increased further to 28.9 +/- 5.4 mL/min/100 g with patent overlapping vessels (p = .0001 compared with 5-min value). The patency of overlapping vessels during right ventricular free wall ischemia reduced the area at risk from 68.5 +/- 2.4% to 38.6 +/- 5.1% (p = .0001) and the area of necrosis/area at risk from 58.1 +/- 8.4% to 16.9 +/- 3.6% (p = .0007). CONCLUSIONS: Despite 15 cm H2O positive end-expiratory pressure, perfusion through overlapping vessels improved peri-ischemic blood flow in the area at risk, thereby reducing the size of the risk area and the amount of right ventricular free wall necrosis.

Positive end-expiratory pressure potentiates the severity of canine right ventricular ischemia-reperfusion injury.

Positive end-expiratory pressure (PEEP) increases right ventricular (RV) afterload and oxygen demands. However, whether increased RV oxygen demands with high levels of PEEP can potentiate the severity of RV ischemic damage is unknown. In 20 anesthetized, closed-chest dogs randomly assigned to 0 cmH2O PEEP (ZEEP; n = 10) or 15 cmH2O PEEP (PEEP; n = 10), RV blood flow (radioactive microspheres) and segmental shortening (ultrasonic crystals) were determined during 90 min ischemia and 120 min reperfusion while mean aortic pressure was maintained above 90 mmHg. The in vivo RV area at risk (gentian violet) and area of necrosis (triphenyltetrazolium chloride) were assessed. After application of 15 cmH2O PEEP, pulmonary vascular resistance increased by 75% (P less than 0.05). During ischemia, the RV rate-pressure product remained greater with PEEP (2,403 +/- 174 mmHg.beat.min-1) than with ZEEP (1,909 +/- 94 mmHg.beat.min-1; P less than 0.05), indicating higher oxygen demands with PEEP. The area at risk from ischemia relative to RV free wall tended to be greater with PEEP (68.5 +/- 2.4%) than with ZEEP (60.0 +/- 3.9%; P = 0.08), and collateral blood flow in this risk zone was significantly lower during ischemia with PEEP (9.0 +/- 1.7 ml.min-1 x 100 g-1) than with ZEEP (18.3 +/- 3.6 ml.min-1 x 100 g-1; P less than 0.05). Accordingly, PEEP extended RV necrosis in the area at risk from 21.8 +/- 5.3% (ZEEP) to 58.1 +/- 8.4% (PEEP; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)