Transmural Left Ventricular Shear Strain Alterations Adjacent to and Remote from Infarcted Myocardium

Allen Cheng1, Frank Langer1, Tom C. Nguyen1, Marcin Malinowski1, Daniel B. Ennis2, George T. Daughters1,3, Neil B. Ingels, Jr.1,3, D. Craig Miller1
Departments of 1Cardiovascular and Thoracic Surgery and 2Radiology, Stanford University School of Medicine, Stanford, and 3Laboratory of Cardiovascular Physiology and Biophysics, Research Institute of the Palo Alto Medical Foundation, Palo Alto, California, USA
 

Background and aim of the study: In some patients, dysfunction in a localized infarct region spreads throughout the left ventricle to aggravate mitral regurgitation and produce deleterious global left ventricular (LV) remodeling. Alterations in transmural strains could be a trigger for this process, as these changes can produce apoptosis and extracellular matrix disruption. The hypothesis was tested that localized infarction perturbs transmural strain patterns not only in adjacent regions but also at remote sites.
Methods: Transmural radiopaque beadsets were inserted surgically into the anterior basal and lateral equatorial LV walls of 25 sheep; additional markers were used to silhouette the left ventricle. One week thereafter, 10 sheep had posterior wall infarction from (obtuse marginal occlusion, INFARCT) and 15 had no infarction (SHAM). Four-dimensional marker dynamics were studied with biplane videofluoroscopy eight weeks later. Fractional area shrinkage, LV volumes and transmural circumferential, longitudinal and radial systolic strains were analyzed.

Results: Compared to SHAM, INFARCT greatly increased longitudinal-radial shear (midwall: 0.07 ± 0.07 versus 0.14 ± 0.06; subendocardium: 0.03 ± 0.07 versus 0.20 ± 0.08) in the inner half of the lateral LV wall and increased circumferential-radial shear (midwall: 0.03 ± 0.05 versus 0.10 ± 0.04; subepicardium: 0.02 ± 0.05 versus 0.12 ± 0.10) increased in the outer half of the LATERAL wall. In the ANTERIOR wall, INFARCT also increased longitudinal-radial shear (midwall: 0.01 ± 0.05 versus 0.12 ± 0.04; subendocardium: 0.04 ± 0.09 versus 0.25 ± 0.20) in the inner layers.
Conclusion: Increased transmural shear strains were found not only in an adjacent region, but also at a site remote from a localized infarction. This perturbation could trigger remodeling processes that promote the progression of ischemic cardiomyopathy. A better understanding of this process is important for the future development of surgical therapies to reverse destructive LV remodeling.
The Journal of Heart Valve Disease 2006;15:209-218
 
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