Effect of myocardial perfusion on end-systolic radial strain at the apex

According to the literature, subendocardial strain is more susceptible to reduced perfusion than mid-myocardial and sub-epicardial strains. The aim of this study was to compare radial strain in these 3 layers under various levels of flow reduction, using our previously described system with miniature high-frequency transducers sutured to the epicardial surface. The blood flow in the left anterior descending coronary artery (LAD) was controlled under three flow conditions: no flow reduction, 25% flow reduction and 75% flow reduction. The myocardial wall was divided into 3 equally sized layers. Tissue velocities were estimated from the RF signals using a phase shift Doppler estimator, finding the average phase shift between 3 successive RF lines. A 4^th order Butterworth filter was applied to the velocity estimates in both temporal and spatial directions, and radial strain rate and strain were calculated. The results showed that strain decreased by 16.4±7.2% in the sub-endocardium, while it decreased by 7.9±4.9% and 7.7±6.8%, respectively, in the mid- and sub-epicardial layers at 25% flow reduction. At 75% flow reduction, the strain was reduced by 28.1±7.7% compared to baseline in the sub-endocardial and mid-layers, while it was reduced by a similar amount in the mid-myocardium and subepicardium, 26.9±6.5% and 26.8±10.7%, respectively.