Altered load dependence of postischemic myocardium

Area of Science:

• Cardiovascular Physiology
• Cardiac Metabolism
• Myocardial Ischemia Research

Background:

• Intermittent myocardial ischemia causes "stunned" myocardium with impaired contractile function.
• The impact of loading conditions on postischemic myocardium's contraction remains unclear.
• Understanding load dependence is crucial for managing coronary artery disease.

Purpose of the Study:

• To investigate how loading conditions affect systolic function in postischemic myocardium.
• To compare the response of stunned myocardium to changes in preload and afterload.
• To elucidate the mechanisms behind regional wall motion abnormalities in stunned myocardium.

Main Methods:

• Utilized anesthetized dogs with implanted piezoelectric crystals to measure myocardial wall thickening.
• Assessed systolic wall thickening under nine combinations of left atrial pressure (preload) and mean arterial pressure (afterload).
• Measurements were taken before and after a 10-minute coronary occlusion followed by 1-hour reperfusion.

Main Results:

• Ischemia and reperfusion reduced test zone wall thickening by 36 +/- 3%.
• Postischemic myocardium exhibited a diminished response to increased preload.
• The response of the test zone to afterload changes was unaltered, but interactions caused apparent abnormalities.

Conclusions:

• Load dependence of postischemic myocardium differs significantly from normal myocardium.
• Altered responses to preload and interactions with surrounding tissue affect systolic function.
• Clinical assessments of regional contraction in stunned myocardium require consideration of these load-dependent differences.