Persistence of regional left ventricular dysfunction after exercise-induced myocardial ischemia

To determine whether regional myocardial dysfunction occurring after exercise-induced ischemia might be caused by continued abnormalities of myocardial blood flow in the post-exercise period, nine dogs were instrumented with ultrasonic microcrystals for determination of circumferential segment shortening, circumflex artery electromagnetic flow probes, and hydraulic coronary artery occluders. Dogs performed treadmill exercise during partial inflation of the coronary artery occluder. When the stenosis was maintained after exercise (persistent stenosis), subendocardial hypoperfusion was noted 1 min after exercise (subendocardial flow = 0.79 ± 0.42 ml/min per g vs. 1.39 ± 0.43 ml/min per g control), and this was associated with continued dysfunction in the ischemic zone (segment shortening 45.4 ± 36.9% of resting control). When the stenosis was released immediately after exercise (temporary stenosis), however, flow was markedly increased 1 min post-exercise (mean transmural flow 4.24 ± 1.22 ml/min per g; subendocardial flow 4.18 ± 1.52 ml/min per g), and this was associated with a transient increase in segment shortening to 104.5 ± 9.3% of resting control. 5 min after exercise, however, moderate reductions in ischemic segment shortening were noted after both temporary stenosis and persistent stenosis runs, and these persisted for 30 min post-exercise. It is concluded that regional left ventricular dysfunction may persist for a significant period of time after exercise-induced ischemia. Furthermore, early after exercise, dysfunction is related to persistent abnormalities of myocardial blood flow, whereas late after exercise it is independent of primary reductions in myocardial blood flow.