Dissociation between epicardial and transmural function during acute myocardial ischemia

Area of Science:

• Cardiovascular Physiology
• Myocardial Ischemia Research
• Cardiac Function Assessment

Background:

• Assessing myocardial function is crucial for understanding ischemia.
• Epicardial function is often used as a surrogate for transmural function.
• Regional differences in myocardial blood flow and function are not fully understood.

Purpose of the Study:

• To investigate the relationship between epicardial function and transmural function during varying degrees of coronary inflow restriction.
• To compare epicardial segment shortening with systolic wall thickening as measures of myocardial function.
• To determine if regional variability exists in the epicardial response to non-transmural ischemia.

Main Methods:

• Utilized sonomicrometers to measure epicardial and transmural function in anesthetized open-chest dogs.
• Induced three levels of coronary inflow restriction by monitoring systolic wall thickening.
• Assessed myocardial blood flow using microspheres in dogs with induced ischemia in anterior-apical or posterior-basal regions.

Main Results:

• Epicardial segment shortening underestimated transmural dysfunction, particularly in the posterior-basal region, at moderate ischemia levels (35% and 80% reduction in systolic wall thickening).
• Subepicardial blood flow was minimally affected at lower ischemia levels, while deep myocardial blood flow decreased significantly.
• Anterior epicardial segment shortening decreased significantly, whereas posterior-basal epicardial segment shortening remained unaffected at moderate ischemia levels, indicating regional variability.

Conclusions:

• Epicardial function measurements can significantly underestimate the severity of transmural myocardial ischemia.
• Regional differences in myocardial perfusion and function exist, impacting the reliability of epicardial measurements.
• Further research is needed to refine methods for assessing transmural cardiac function during ischemia.