Heterogeneous Onset of Myocardial Relaxation in Subendocardial and Subepicardial Layers Assessed With Tissue Strain Imaging: Comparison of Normal and Hypertrophied Myocardium

ObjectivesWe sought to investigate the existence of a time difference in myocardial relaxation between the subendocardium and subepicardium in patients with and without myocardial hypertrophy.BackgroundRegional differences in mechanical and electrical properties between the subendocardium and subepicardium have been described for the left ventricle in animals. However, this difference has not been well evaluated in clinical conditions.MethodsTime-to-peak radial strain with reference to the QRS complex was measured at the subendocardium and subepicardium at the mid-posterior wall of the left ventricle in 12 normal subjects, 14 patients with hypertensive heart disease, and 27 patients with aortic stenosis (16 with and 11 without strain electrocardiogram [ECG] pattern) using tissue Doppler-based strain imaging.ResultsTime-to-peak radial strain in the subepicardium (381 ± 60 ms) was shorter than that in the subendocardium (463 ± 29 ms; p < 0.001) in normal subjects, suggesting that the subepicardial relaxation precedes subendocardial relaxation. No significant difference was found between normal subjects and patients with hypertensive heart disease (388 ± 67 ms for the subepicardium; 455 ± 36 ms for the subendocardium in hypertensive heart disease). In cases with hypertrophied myocardium due to aortic stenosis, time-to-peak radial strain in the subendocardium was shortened and that in the subepicardium was prolonged. In 10 (63%) of 16 patients with aortic stenosis and strain ECG pattern, the timing of peak strain in the subendocardium (417 ± 63 ms) preceded that in the subepicardium (452 ± 62 ms).ConclusionsThere is heterogeneous onset of myocardial relaxation in the subendocardial and subepicardial layers at the mid-posterior wall of the left ventricle. Subepicardial myocardial relaxation precedes subendocardial relaxation in normal subjects. In contrast, there is inversion of the transmural sequence of myocardial relaxation between the subendocardium and subepicardium in some patients with aortic stenosis and strain ECG pattern.