[Definition and significance of the area at risk in myocardial infarct and the ischemic border zone in acute myocardial infarct].

Abstract

Early localisation of infarction, estimation of infarct size and visualisation of metabolic and structural changes is of great importance for the management of acute myocardial infarction. This paper is based on an experimental model using a combination of in-vivo and in-vitro methods that allow the evaluation of the area at risk of infarction, the border zone and its changes over time. The purpose of the study was to characterize the topography and the time course of the border zone. The border zone forms an approximately 2 mm wide margin at the lateral edges of the infarct, with increasing width of the border zone along the subepicardium. Increasing duration of ischemia is associated with a dynamic sequence of events, not only within the area at risk of infarction but also in the peri-ischemic border zone, leading to an expansion of the subepicardial margin due to improved collateral blood flow over time. The area at risk of infarction is characterized by early distinct metabolic changes that were visualized as soon as 90 to 120 seconds following coronary artery occlusion. After 6 hours of occlusion almost the entire area at risk shows signs of irreversible injury due to severe hypoperfusion. The border zone, in contrast, is characterized by only moderate metabolic changes due to greater collateral perfusion (45 to 80% of the regional blood flow in the non-ischemic vascular bed). Several interventions were chosen and evaluated for their effects on the dynamic course of events within the area at risk of infarction and in the border zone. Interventions that have strong myocardial protective effects such as the combination of alpha- and beta-blockade, the application of specific O2-carriers (Perfluorocarbons) and pressure controlled retrograde perfusion via the coronary sinus ("PICSO"), not only reduce infarct size by 20 to 40% of the myocardium at risk of infarction, but also induce substantial topographic, functional and metabolic changes within the border zone.