Myocardial contraction patterns in non-ischaemic and ischaemic regions during acute coronary insufficiency
S Birkeland1, J Westby, K Matre
1Department of Surgery, University of Bergen, Haukeland Hospital, Norway.
Insights
Coronary insufficiency significantly alters myocardial contraction patterns, with the most pronounced changes occurring along the cardiac major axis. This research highlights how blood flow reduction impacts heart muscle movement during ischemia.
Area of Science:
- Cardiovascular Physiology
- Cardiac Mechanics
- Myocardial Blood Flow
Background:
- Coronary insufficiency, a state of reduced blood flow to the heart muscle, can profoundly affect cardiac function.
- Understanding the specific patterns of myocardial contraction during ischemia is crucial for diagnosing and treating heart conditions.
Purpose of the Study:
- To investigate the impact of coronary artery occlusion on myocardial contraction patterns in different cardiac axes.
- To correlate changes in myocardial blood flow with alterations in regional and global cardiac mechanics.
Main Methods:
- Utilized echocardiography to assess myocardial contraction patterns in apical long axis and cross-oriented segments.
- Employed radiolabeled microspheres to quantify myocardial tissue blood flow during induced coronary insufficiency in cats.
- Performed circumflex and left coronary artery occlusions to simulate varying degrees of ischemia.
Main Results:
- Circumflex artery occlusion led to hyperkinesis, with increased ejection shortening in longitudinal (61%) and circumferential (17%) segments.
- Subsequent left coronary artery underperfusion significantly reduced subendocardial blood flow (up to 75%) without affecting subepicardial flow.
- Reduced subendocardial flow correlated with decreased global major axis shortening (77%) and longitudinal segment shortening (36%), while midwall circumferential segments remained unchanged.
Conclusions:
- Myocardial contraction changes during coronary insufficiency are most prominent along the cardiac major axis.
- Regional differences in myocardial blood flow significantly influence regional and global myocardial contraction patterns.
- The study provides insights into the mechanical consequences of ischemia on the left ventricle's contractile behavior.
Abstract:
The effect of coronary insufficiency on the myocardial contraction pattern was studied in 11 thoracotomized cats using apical long axis echocardiograms and cross-oriented segments in the anterior midwall. Myocardial tissue blood flow was studied using radiolabelled microspheres. After circumflex coronary artery occlusion, ejection shortening increased on average 17% for circumferential segments (P < 0.05) and 61% for longitudinal segments (P < 0.001). Hyperkinesis was also validated as augmented anterior endocardial wall motion and wall thickening. Circumflex occlusion increased end-systolic sphericity of the left ventricle (P < 0.05). Subsequent underperfusion of the left coronary artery, in two discrete steps, decreased subendocardial blood flow by, on average, 36% (P < 0.001) and 75% (P < 0.001) vs the post-occlusion value, while subepicardial flow did not change. While subendocardial blood flow decreased by 36%, systolic shortening of the global major axis decreased, by, on average, 77% (P < 0.001), shortening of the longitudinal segments by 36% (P < 0.001), and systolic shortening of the minor axis by 18% (P < 0.05), whereas shortening of midwall circumferential segments did not change. This study shows that changes in myocardial contraction in both non-ischaemic and ischaemic regions during coronary insufficiency are most pronounced in the direction of the cardiac major axis.
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