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U Mehlhorn1, S J Allen, D L Adams
1Department of Anesthesiology, University of Texas-Houston Medical School 77030, USA.
Insights
Minimal myocardial contraction during cardiopulmonary bypass (CPB) or biventricular assistance helps maintain cardiac lymphatic function, preventing significant myocardial edema and preserving cardiac function.
Area of Science:
- Cardiovascular Surgery
- Cardiac Physiology
- Myocardial Protection
Background:
- Crystalloid and blood cardioplegia can cause cardiac dysfunction and myocardial edema due to impaired lymphatic flow from lack of contraction.
- Minimal myocardial contraction, induced by esmolol, has been explored as an alternative during coronary artery bypass operations.
- This study investigates if minimal contraction during circulatory support prevents myocardial edema by maintaining lymphatic function.
Purpose of the Study:
- To test the hypothesis that minimal myocardial contraction during circulatory support prevents myocardial edema.
- To assess the impact of minimal contraction on cardiac lymphatic function and myocardial water content.
- To evaluate left ventricular performance after circulatory support with minimal contraction.
Main Methods:
- Six dogs were placed on cardiopulmonary bypass (CPB) and six on a biventricular assist device.
- Myocardial lymph flow rate and water content were serially measured in both groups.
- Heart rate was minimized with esmolol during 1 hour of total circulatory support.
Main Results:
- Myocardial lymph flow was maintained during CPB and increased with biventricular assistance.
- Despite some water accumulation during support, edema resolved rapidly post-support.
- Myocardial water content was only slightly increased, and left ventricular function (preload recruitable stroke work) remained normal.
Conclusions:
- Minimal myocardial contraction supports lymphatic function, leading to minimal myocardial edema.
- This approach is associated with normal cardiac performance after circulatory support.
- Minimal myocardial contraction may offer a protective strategy, particularly for high-risk patients.
Background:
Both crystalloid and blood cardioplegia result in cardiac dysfunction associated with myocardial edema. This edema is partially due to the lack of myocardial contraction during cardioplegia, which stops myocardial lymph flow. As an alternative, acceptable surgical conditions have been created in patients undergoing coronary artery bypass operations with esmolol-induced minimal myocardial contraction. We hypothesized that minimal myocardial contraction during circulatory support using either standard cardiopulmonary bypass (CPB) or a biventricular assist device would prevent myocardial edema by maintaining cardiac lymphatic function and thus prevent cardiac dysfunction.
Methods:
We placed 6 dogs on CPB and 6 dogs on a biventricular assist device and serially measured myocardial lymph flow rate and myocardial water content in both groups and preload recruitable stroke work only in the CPB dogs. In all dogs we minimized heart rate with esmolol for 1 hour during total circulatory support.
Results:
Although myocardial lymph flow remained at baseline level during CPB and increased during biventricular assistance, myocardial water accumulation still occurred during circulatory support. However, as edema resolved rapidly after separation from circulatory support, myocardial water content was only slightly increased after CPB and biventricular assistance, and preload recruitable stroke work was normal.
Conclusions:
Our data suggest that minimal myocardial contraction during both CPB and biventricular assistance supports myocardial lymphatic function, resulting in minimal myocardial edema formation associated with normal left ventricular performance after circulatory support. The concept of minimal myocardial contraction may be a useful alternative for myocardial protection, especially in high-risk patients with compromised left ventricular function.