Author + information
- Received December 15, 1986
- Revision received April 8, 1987
- Accepted May 1, 1987
- Published online November 1, 1987.
- ↵*Address for reprints: Maleah Grover-McKay, MD, Cardiology Section (111C), Veterans Administration Medical Center, 5901 East Seventh Street, Long Beach, California 90822.
The onset and resolution of electrical and functional measures of regional myocardial ischemia were examined in nine conscious dogs during control exercise and exercise after beta-receptor blockade. The dogs had been instrumented with an ameroid constrictor and were studied when no regional dysfunction was evident at rest, although severe coronary stenosis or coronary occlusion with collateral circulation development was present. ST segment elevation was measured on subendocardial electrograms, and regional wall motion was studied by sonomicrometry. During control exercise, subendocardial myocardial blood flow in the ischemic zone, normalized to blood flow in the nonischemic zone, decreased. Subendocardial ST elevation increased slowly, was significantly different from control standing values by 2.5 minutes of exercise and returned quickly to control values within 5 minutes after exercise. Percent systolic wall thickening decreased rapidly, was significantly depressed by 1 minute of exercise and did not return to control values until 30 minutes after exercise.
A second, identical exercise stress was performed on the same day after a single oral dose (1 mg/kg body weight) of atenolol. In the ischemic zone during exercise after atenolol compared with control exercise, normalized subendocardial myocardial blood flow was improved and significantly less ST elevation occurred, but the onset and resolution of ST elevation were not altered. Systolic wall dysfunction during exercise was significantly less after atenolol, and function returned toward preexercise values by 1 minute after exercise, even more rapidly than ST segment resolution.
It is concluded that during and after severe exercise-induced ischemia, alterations in regional electrical and mechanical events were dissociated in time so that regional dysfunction began earlier, and during the recovery phase regional contractile dysfunction persisted long after resolution of ST segment elevation. With exercise after beta-receptor blockade, ischemia was milder, and this temporal dissociation between mechanical and electrical abnormalities during recovery disappeared. These findings suggest that contractile dysfunction is a better marker of severe regional ischemia than are electrocardiographic events during and after exercise.
- Received December 15, 1986.
- Revision received April 8, 1987.
- Accepted May 1, 1987.
- American College of Cardiology Foundation