Related Experiment Videos
Myocardial infarction in dogs with chronic hypertension and left ventricular hypertrophy
Insights
Chronic hypertension and left ventricular hypertrophy do not impair coronary collateral flow or increase myocardial necrosis after coronary occlusion. These findings suggest nonatherosclerotic factors do not worsen heart attack outcomes in hypertension.
Area of Science:
- Cardiovascular Physiology
- Hypertension Research
- Myocardial Infarction Studies
Background:
- Chronic hypertension elevates risks for myocardial infarction (MI), morbidity, and mortality.
- Nonatherosclerotic coronary circulation abnormalities, like reduced vascular capacity and capillary density, may contribute to hypertension-related MI.
- Investigating these nonatherosclerotic factors is crucial for understanding MI pathophysiology in hypertension.
Purpose of the Study:
- To evaluate the impact of chronic hypertension and left ventricular hypertrophy on coronary circulation abnormalities.
- To assess the effects of these nonatherosclerotic factors on collateral blood flow and myocardial necrosis following sudden coronary occlusion.
- To determine if hypertension limits collateral recruitment or exacerbates necrosis in ischemic heart tissue.
Main Methods:
- Sudden coronary occlusion was induced in chronically hypertensive dogs and control dogs.
- Myocardial blood flow was measured using tracer microspheres before and after occlusion (5 min, 49 h).
- Histological analysis quantified the extent of myocardial infarction and necrosis in relation to ischemia.
Main Results:
- Hypertensive dogs exhibited significantly greater left ventricular mass and ischemic area compared to controls.
- Coronary occlusion reduced blood flow similarly in both groups.
- Collateral flow increased comparably, and the degree of necrosis per unit of ischemia was similar between hypertensive and control dogs over 48 hours.
Conclusions:
- Chronic hypertension and associated left ventricular hypertrophy did not impede coronary collateral supply in this canine model.
- These nonatherosclerotic abnormalities did not increase myocardial necrosis for a given level of ischemia.
- Findings suggest that impaired collateral function and increased necrosis are not primary drivers of worsened outcomes in hypertensive MI, independent of atherosclerosis.
Abstract:
Chronic hypertension increases the risk of myocardial infarction and the morbidity and mortality associated with it. Although accelerated atherosclerosis is partially responsible, other abnormalities in the coronary circulation associated with hypertension, such as decreased coronary vascular capacity and capillary density, could also contribute. To evaluate the effects of these nonatherosclerotic abnormalities, we produced sudden coronary occlusion in nine chronically hypertensive dogs. The mean aortic pressure and left ventricular mass were about 50% greater in hypertensive dogs than in the nine controls. Before occlusion and 5 min and 49 h after occlusion, myocardial blood flow was measured with tracer microspheres. Also, the extent of infarction in selected myocardial segments was quantified histologically. We found that coronary occlusion reduced flows to a similar extent, and that, over a 48-h period, collateral flow increased to a similar extent in the two groups. In addition, the amount of necrosis associated with a given degree of ischemia was similar in the two groups. Although the extent of the left ventricle that became ischemic was greater in the hypertensive dogs (28 +/- 2 vs. 18 +/- 4%; P < 0.05), chronic hypertension and left ventricular hypertrophy did not limit the recruitment of collateral supply or increase the amount of necrosis associated with a given degree of ischemia.