Postextrasystolic potentiation of regional mechanical performance during prolonged myocardial ischemia in the dog.

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Abstract
The effects of postextrasystolic potentiation (PESP) on the contractile performance of central ischemic and border zones and of nonishcemic myocardium were studied in 14 open-chest dogs subjected to a 4 h left anterior descending coronary artery ligation followed by 1 h of reperfusion. Intrinsic mechanical function during right ventricular pacing (134 .+-. 3 beats/min) was compared with function in beats after single, closely coupled (179 .+-. 3 ms) extrasystoles throughout ischemia and reperfusion. Regional myocardial blood flow using radioactive microspheres and infarct size using tetrazolium blue staining were also measured in these segments. PESP was capable of augmenting border zone segment performance to control levels throughout 4 h of ischemia. PESP significantly augmented central ischemic zone segment function throughout ischemia, but not to control levels. After prolonged ischemia, reperfusion improved both regional intrinsic and potentiated mechanical performance in border and ischemic zones. At 4 h of ischemia, myocardial blood flow decreased 52% (to 60 ml/100 g per min) in the border zone and 78% (to 28 ml/100 g per min) in the ischemic zone. Infarct size (the percentage necrosis of the transmural segment) measured 55 .+-. 10% and 74 .+-. 7% in border and ischemic zones, respectively. In the open-chest dog, PESP elicited considerable contractile reserve in border and ischemic zones during prolonged ischemia, and despite profound ischemic injury, both intrinsic and potentiated mechanical function in the ischemic zone could be improved after reperfusion.

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