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Alterations in lateral left ventricular wall transmural strains during acute circumflex and anterior descending
Frank Langer1, Filiberto Rodriguez, Allen Cheng
1Department of Cardiothoracic Surgery, Stanford University School of Medicine, Stanford, California 94305-5247, USA.
Insights
Myocardial strain patterns differ based on the location of ischemia. Acute proximal-left anterior descending (pLAD) occlusion alters lateral wall shear, while proximal-circumflex (pCX) occlusion increases it, reflecting mechanical interactions between ischemic and nonischemic heart regions.
Area of Science:
- Cardiovascular Physiology
- Biomechanical Engineering
- Cardiac Imaging
Background:
- Previous studies noted increased circumferential-radial shear in acute midcircumflex ischemia in open-chest animals.
- This study investigated transmural strains in closed-chest animal models during acute proximal-circumflex (pCX) and proximal-left anterior descending (pLAD) occlusions.
Purpose of the Study:
- To analyze transmural myocardial strains in response to acute coronary artery occlusions.
- To understand the mechanical interactions between ischemic and nonischemic myocardial regions.
Main Methods:
- Radiopaque markers and transmural bead columns were used in six sheep for regional systolic fractional area shortening and transmural strain analysis.
- Three-dimensional marker coordinates were obtained via biplane videofluoroscopy during 1-minute pLAD and pCX occlusions.
- Systolic strains were assessed along circumferential, longitudinal, and radial axes and transformed into fiber strains.
Main Results:
- Both pLAD and pCX occlusions induced similar hemodynamic changes.
- pCX occlusion led to decreased transmural circumferential strain and fiber shortening in the ischemic region, with increased circumferential-radial shear in the lateral wall.
- pLAD occlusion showed normal strains adjacent to ischemia, with reversed lateral wall circumferential-radial shear and decreased longitudinal-radial shear.
Conclusions:
- Altered mechanical interactions between ischemic and nonischemic myocardium explain the observed shear strain changes.
- The direction of circumferential-radial shear deformation is dependent on the location of the adjacent ischemic territory.
- Findings highlight the distinct mechanical responses to different coronary occlusion locations.
Background:
Increased circumferential-radial shear in the midlateral left ventricle adjacent to ischemic myocardium has been observed during acute midcircumflex ischemia in open-chest animals. Extending this work, we studied transmural strains in closed-chest animals during acute proximal-circumflex (pCX) and proximal-left anterior descending (pLAD) occlusions.
Methods:
Six sheep had radiopaque markers implanted to silhouette the left ventricle and measure regional systolic fractional area shortening; three transmural bead columns were inserted into the midlateral wall for transmural myocardial strain analysis. After 8 weeks, three-dimensional marker coordinates were obtained using biplane videofluoroscopy, both before and during separate 1-minute pLAD and pCX balloon occlusions. Systolic strains were assessed along circumferential, longitudinal, and radial axes, and then transformed into fiber strains using quantitative microstructural measurements.
Results:
Acute pLAD occlusion and pCX occlusion caused similar hemodynamic insults. Systolic fractional area shortening revealed that the beads were in the ischemic territory during pCX occlusion, but adjacent to the ischemic myocardium during pLAD occlusion. Transmural circumferential strain and fiber shortening fell in the ischemic region during pCX occlusion, but remained normal when adjacent to the ischemic myocardium during pLAD occlusion. Circumferential-radial shear strain increased in the lateral left ventricle during pCX occlusion, but reversed in this same region during pLAD occlusion. Longitudinal-radial shear also decreased during pLAD occlusion.
Conclusions:
Reversal of lateral wall circumferential-radial shear and decreased longitudinal-radial shear during acute pLAD occlusion reflects altered mechanical interaction between ischemic and nonischemic myocardium. Increased circumferential-radial shear during pCX occlusion also reflects mechanical interaction. The direction of circumferential-radial shear deformation depends on the location of the adjacent ischemic territory.
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