Myocardial contractility evaluated from cross-oriented segments during beta-adrenergic blockade or sympathetic nerve...

Area of Science:

• Cardiovascular Physiology
• Myocardial Mechanics
• Ischemic Heart Disease Research

Background:

• Characterizing the inotropic state of remaining myocardium is vital in models of left ventricular ischemia.
• Dysfunctional regions require accurate assessment of myocardial contractility for effective treatment strategies.

Purpose of the Study:

• To evaluate different indices of regional myocardial contractility in ischemic conditions.
• To identify the most reliable index for assessing left ventricular inotropic state in regional ischemia.

Main Methods:

• Studied 18 pentobarbitone-anesthetized open-chest cats with acute circumflex coronary artery occlusion.
• Investigated effects of sympathetic nerve stimulation and beta-adrenergic blockade on myocardial contractility.
• Evaluated contractility using pressure-length relationships of longitudinal and circumferential segments.

Main Results:

• End-systolic pressure-length relationship was insensitive to interventions in longitudinal segments.
• Circumferential end-systolic pressure-length relationship indicated low contractility; peak systolic shortening velocity indicated high contractility.
• The pressure-length loop area versus end-diastolic length relationship reflected both increased and decreased left ventricular inotropic states.

Conclusions:

• The pressure-length loop area versus end-diastolic length relationship is the optimal index for regional myocardial contractility in ischemic hearts.
• This index provides a comprehensive measure of contractility changes in dysfunctional myocardial regions.