This study investigates whether subendocardial ischemia can be detected by measuring multilayer radial systolic strain from epicardial tissue Doppler imaging.
In 10 anesthetized open-chest pigs an extracorporeal shunt from the proximal brachiocephalic to the left anterior descending coronary artery was constricted in steps. Color microsphere injections and short axis Tissue Velocity Imaging (TVI) recordings were performed with open shunt, with a non-significant stenosis, and with 2 steps of shunt flow reduction.
With open shunt and no transmural flow gradient, there was a gradient of peak ejection strain with high values subendocardially for both 4 and 2 layer measurements. For 2 layer measurement strain was 56.0+/-10.5% subendocardially and 22.0+/-5.2% subepicardially. A non-significant stenosis, not altering transmural flow distribution, reduced strain to 40.3+/-5.4% in the endocardial half-layer. With reduced shunt flow resulting in subendocardial ischemia, peak ejection strain decreased further, primarily in inner wall layers, and postsystolic strain became evident. At severe stenosis (52.4+/-1.8% shunt flow reduction) strain was reduced to 3.8+/-3.6% in the subendocardium and 0.0+/-2.6% in the subepicardium.
Evaluation of myocardial function with multilayer radial systolic strain has a potential for detecting subendocardial ischemia.
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