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Structural basis of regional dysfunction in acutely ischemic myocardium
R Mazhari1, J H Omens, J W Covell
1Department of Bioengineering, The Whitaker Institute for Biomedical Engineering, University of California San Diego, 92093-0412, USA.
Cardiovascular Research
|August 18, 2000
Summary
Altered mechanical stresses, not intermediate contractility, explain the functional border zone in ischemic hearts. Regional wall stress, not anatomy, dictates the border zone width, especially during left anterior descending (LAD) artery occlusion.
Area of Science:
- Cardiovascular Physiology
- Myocardial Mechanics
- Ischemic Heart Disease
Background:
- The functional border zone, characterized by impaired systolic function in normally perfused myocardium adjacent to ischemia, is traditionally attributed to mechanical interactions across perfusion boundaries.
- Understanding the factors influencing this zone is crucial for developing targeted therapies for ischemic heart disease.
Purpose of the Study:
- To investigate how segment orientation and the specific coronary artery involved (left anterior descending vs. left circumflex) affect regional strains within the functional border zone.
- To determine if altered mechanical stresses, resulting from a step transition in contractility, can adequately explain the observed functional border zone.
Main Methods:
- Acquired regional epicardial strain distributions in anesthetized canines using radiopaque markers to measure displacements.
- Correlated strain data with local myofiber angles and regional blood flows.
- Developed a detailed three-dimensional computational model simulating myocardial perfusion and activation.
Main Results:
- The functional border zone for fiber strain was narrower than for cross-fiber strain.
- A significantly wider border zone was observed for left anterior descending (LAD) occlusion compared to left circumflex (LCx) occlusion (1.23 cm vs. 0.45 cm).
- The computational model accurately replicated these findings, demonstrating elevated stresses in the border zone without a transitional contractility zone.
Conclusions:
- Increased wall stresses, rather than a transitional zone of intermediate contractility, are responsible for abnormal regional mechanics in the acute ischemic border zone.
- Perfusion is more closely linked to fiber strain than cross-fiber strain.
- The wider functional border zone observed during LAD occlusion is primarily driven by higher regional wall stresses, not anatomical differences.