Assessment of hibernating myocardium by dobutamine stimulation in a canine model.

OBJECTIVES

The purpose of this study was to 1) develop an animal model of hibernating myocardium, and 2) evaluate the ability of dobutamine stimulation to detect hibernating myocardium using both qualitative and quantitative assessment of regional myocardial function.

BACKGROUND

Left ventricular dysfunction may be due to chronic ischemia with or without myocardial infarction and may improve after coronary blood flow is enhanced by revascularization procedures. This condition has been coined "hibernating myocardium" and variably defined in recent years. The results of recent clinical studies suggest that dobutamine echocardiography may be useful for detecting viable myocardium in patients with left ventricular dysfunction.

METHODS

Twenty-one dogs underwent initial operation. Sonomicrometer crystals were implanted, and baseline measurements of segment shortening and wall thickening (by echocardiography) were made. A coronary artery was ligated; the chest was closed; and measurements were repeated. Dobutamine was incrementally infused with determination of wall thickening and segment shortening at baseline and on days 3 and 7 and weeks 2 and 4 after coronary artery occlusion. Finally, the chest was reopened; the ligated vessel was bypassed; and measurements were repeated.

RESULTS

Of the 10 dogs that completed the entire protocol, 7 had varying degrees of nontransmural myocardial infarction (group 1), and 3 had complete transmural myocardial infarction (group 2). In group 1, baseline function was significantly impaired compared with preligation function but increased during dobutamine infusion. When reperfused after 4 weeks, both wall thickening and segment shortening increased significantly. In group 2, significant changes were not seen during the dobutamine studies or after reperfusion. Myocardial perfusion during dobutamine infusion increased in group 1 but did not change in group 2.

CONCLUSIONS

We demonstrated improvement in chronically dysfunctional myocardium after restoration of previously interrupted myocardial blood flow in dogs after nontransmural myocardial infarction, thus validating a canine model of hibernating myocardium. As assessed by two independent methods, dobutamine infusion identified hibernating myocardium in an animal model.