Post-Stress Left Ventricular Contractile Dysfunction: Does It Represent Persistent Myocardial Ischemia or Stunning?

Exercise-induced left ventricular regional wall motion abnormalities among patients with coronary artery disease indicate myocardial ischemia due to significant coronary artery narrowing. Recovery of such stress-induced wall motion abnormalities is thought to occur within minutes after the termination of exercise. However, in some patients, persistent contractile dysfunction has been observed up to 90 minutes into recovery. Whether persistent regional wall motion abnormalities after exercise are due to stunned myocardium (prolonged but reversible postischemic dysfunction despite restoration of blood flow) or persistent ischemia due to coronary vasoconstriction (prolonged postischemic dysfunction due to persistent reduction of regional blood flow) is not well established. It is possible that persistent but reversible left ventricular dysfunction post-exercise may represent persistent reduction in regional blood flow and/or altered regional metabolic state. In this protocol, we intend to elucidate the mechanisms of prolonged but reversible post-exercise left ventricular contractile dysfunction. Results of this study may provide insight into the post-exercise cardiovascular physiology among patients with coronary artery disease. In addition, clinical implications can be drawn regarding patient safety and timing of discharge from the exercise laboratory, as well as timing of post-exercise myocardial perfusion studies. We propose to evaluate left ventricular regional wall motion by gated blood pool tomographic (SPECT) imaging at rest, during maximal exercise, 15 and 30 minutes after termination of exercise. Myocardial perfusion (O-15 water) and metabolic (F-18 deoxyglucose) studies will be performed utilizing positron emission tomography (PET). Absolute regional myocardial blood flow (ml/min/gm) will be assessed at rest, during maximal exercise, 15 and 30 minutes post-exercise along with myocardial fluorodeoxyglucose utilization 45 to 90 minutes post-exercise. Patients afflicted with conditions that limit their capacity to perform an adequate exercise study will undergo pharmacological stress study with dobutamine. Normal subjects will also be studied in order to create a control database.