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Effects of afterload elevation on the ischemic myocardium in isolated, paced canine heart with partial coronary
Y Maruyama1, S Isoyama, K Ashikawa
1First Department of Internal Medicine, Tohoku University School of Medicine, Sendai, Japan.
Insights
Elevating afterload pressure in a canine heart model with coronary stenosis improved myocardial ischemia and function by increasing coronary blood supply. However, combining afterload and preload elevation negated these benefits.
Area of Science:
- Cardiology
- Physiology
- Myocardial Ischemia Research
Background:
- Partial coronary stenosis significantly impairs myocardial function and increases ischemic markers.
- Understanding the impact of hemodynamic changes on ischemic myocardium is crucial for therapeutic strategies.
Purpose of the Study:
- To investigate the effects of afterload and preload manipulation on ischemic myocardium in a canine model.
- To determine the influence of altered cardiac loading conditions on myocardial function and injury markers.
Main Methods:
- Utilized an isolated, paced canine heart model with induced partial left circumflex coronary stenosis.
- Reduced coronary blood flow to one-third of baseline values to create ischemia.
- Manipulated afterload and preload independently and in combination, monitoring hemodynamic and electrocardiographic parameters.
Main Results:
- Afterload elevation with constant preload decreased myocardial carbon dioxide (CO2) tension and improved ST-segment deviation, indicating reduced ischemic injury.
- Mechanical function, assessed by the relationship between mean aortic pressure and systolic shortening, improved with increased afterload.
- Combined afterload and preload elevation failed to improve ischemic injury markers or mechanical function, despite increased coronary flow.
Conclusions:
- Elevating afterload pressure under constant preload can ameliorate ischemia caused by coronary stenosis by enhancing coronary blood supply.
- Increased preload can counteract the beneficial effects of afterload elevation on ischemic myocardium.
- Hemodynamic management strategies require careful consideration of both afterload and preload to optimize outcomes in myocardial ischemia.
Abstract:
The effect of afterload elevation on the ischemic myocardium was examined in an isolated, paced canine heart with a partial coronary stenosis. The coronary blood flow of the left circumflex coronary artery was reduced to approximately one-third of the values before stenosis. The left circumflex coronary stenosis produced a decrease in global ventricular function, a decrease in systolic shortening and deviation of the ST-segment of the epicardial electrocardiogram and an increase in myocardial carbon dioxide (CO2) tension of the ischemic region. Then, afterload elevation with constant preload decreased the myocardial CO2 tension and improved the ST-segment deviation of the ischemic myocardium. Mechanical function, estimated by the relation between mean aortic pressure and systolic shortening, also improved with elevation of mean aortic pressure. In contrast, afterload elevation combined with preload elevation did not improve ischemic injury, as estimated by myocardial CO2 tension, and did not improve ST-segment deviation or mechanical function despite an increase in left circumflex coronary flow. These results suggest that the elevation of afterload pressure under constant preload improves ischemia produced by a partial coronary stenosis due to increased coronary blood supply; however, the preload elevation counterbalances the beneficial effects of afterload elevation.