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Reductions in regional myocardial function at rest in conscious dogs with chronically reduced regional coronary
1Department of Medicine, State University of New York at Buffalo 14215.
Insights
Regional heart function recovery after coronary artery occlusion is prolonged in dogs, suggesting complex adaptations beyond reduced blood flow. This study provides insights into cardiac response to gradual ischemia.
Area of Science:
- Cardiovascular Physiology
- Cardiac Function Analysis
- Ischemic Heart Disease Models
Background:
- Assessing regional subendocardial function is crucial for understanding cardiac response to coronary artery disease.
- Limited collateralization models are essential for studying the effects of coronary artery occlusion.
Purpose of the Study:
- To examine the temporal response of regional subendocardial function in dogs after circumflex ameroid occluder implantation.
- To investigate the relationship between regional coronary pressure, flow, and function during gradual coronary occlusion.
Main Methods:
- Conscious, chronically instrumented dogs were used with a circumflex ameroid occluder.
- Sonomicrometry measured regional function in circumflex and left anterior descending coronary artery beds.
- Epicardial anastomoses were ligated to limit collateralization.
Main Results:
- Regional function in the circumflex bed depressed significantly after occlusion (68% of control).
- Coronary pressure decreased to 60 mm Hg, with partial recovery of function over 2-4 weeks.
- Dissociation between subendocardial flow and function observed before, but not after, occlusion.
Conclusions:
- Gradual coronary occlusion leads to prolonged reductions in regional cardiac function.
- These functional changes are not solely due to subendocardial infarction or critical reduction in resting flow.
- Cardiac functional adaptations to developing ischemia are complex and not fully explained by acute pressure/flow changes.
Abstract:
We have examined the temporal response of regional subendocardial function in conscious chronically instrumented dogs following implantation of a circumflex ameroid occluder. Collateralization was limited by ligation of epicardial anastamoses between the circumflex and adjacent coronary arteries at the time of instrumentation. Sonomicrometrically measured regional function in the circumflex coronary artery became depressed relative to that in the left anterior descending coronary artery bed under resting conditions with the onset of an aortic-circumflex pressure gradient of 15 +/- 2.9 mm Hg (mean +/- SEM). At the time of total ameroid occlusion, the ratio of circumflex to left anterior descending coronary artery function fell to 68 +/- 8% of control, with mean circumflex coronary pressure decreasing to 60 +/- 1.6 mm Hg. Following ameroid occlusion, distal coronary pressure increased, and circumflex function recovered towards control but remained depressed relative to that in the left anterior descending coronary artery for 2-4 weeks. Measurements of regional subendocardial perfusion suggested a dissociation between subendocardial flow and function prior to but not following coronary occlusion by the ameroid. We conclude that this model results in reductions in regional function that are relatively prolonged and are not readily attributable to subendocardial infarction or a critical reduction in resting coronary flow. The data suggest that functional adaptations in response to gradually developing coronary occlusion are more complex than those associated with acute reductions in coronary artery pressure and flow.