Noninvasive assessment of myocardial stunning from short-term coronary occlusion using tagged magnetic resonance imaging

Brief myocardial ischemia of less than 20 min duration, followed by reperfu sion is known to cause transient contractile dysfunction, often termed myoc ardial stunning. Tagged magnetic resonance imaging offers a noninvasive met hod that can be used to quantify this regional mechanical dysfunction in st unned myocardium. To this end, a closed-chest canine model of myocardial st unning was created by short-term (similar to 20-min) coronary: occlusion, v ia inflation of an angioplasty balloon placed fluoroscopically in the left anterior descending (LAD) coronary followed by reperfusion. Changes in myoc ardial strain before occlusion during occlusion, and at 15 and 30 min after reperfusion were determined rising repeated-measures analysis of variance. After instrumentation but before coronary occlusion, global reductions in myocardial strain were observed relative to animals that did not undergo co ronary catheterization procedures. Declines of 46% and 49% in regional myoc ardial blood flow in the LAD and left circumflex bed, respectively: from pr einstrumentation levels occurred die to coronary angiography and placement of a deflated angioplasty balloon in the LAD for I hr. During LAD occlusion , maximum myocardial shortening was significantly reduced in the anterior a nd anteroseptal regions of the left ventricular apex (i.e., ischemic region ) but returned to baseline values by 30 min after reperfusion. No augmentat ion of myocardial function was observed in the nonischemic regions during o cclusion or reperfusion. Thus, this noninvasive technique to evaluate myoca rdial ischemia demonstrated a graded response in myocardial function to isc hemia and persistent regional dysfunction or "myocardial stunning" after sh ort-term coronary occlusion.