Usefulness of the subendocardial myocardial velocity gradient in low-dose dobutamine stress echocardiography

The subendocardial side of myocardium makes a major contribution to left ventricular (LV) contraction and is very susceptible to ischemia. In this study we sought to quantify regional wall motion during low-dose dobutamine stress echocardiography (DSE) by using the myocardial velocity gradient (MVG) derived from tissue Doppler imaging (TDI). We then compared the usefulness of subendocardial MVG with that of transmural MVG in detecting subtle wall motion abnormalities. Fourteen patients (single vessel disease = 6; normal coronary arteries = 8) underwent low-dose DSE (10 microg/ kg per min). M-Mode TDI of the LV posterior wall was recorded using a Toshiba SSA-380A combined with custom computer software, and analyzed for both subendocardial and transmural MVG. Visual estimation and transmural MVG failed to clearly demonstrate the differing responses between the nonischemic (systole: 3.0 +/- 0.8/s to 4.9 +/- 1.9/s, not significant; diastole: -4.3 +/- 1.3/s to -5.7 +/- 1.4/s, not significant; mean +/- SD, P versus ischemic segments) and ischemic (systole: 3.3 +/- 1.2/s to 3.8 +/- 1.0/s; diastole: -5.4 +/- 2.0/s to -5.3 +/- 1.1/s) segments during low-dose DSE. Subendocardial MVG demonstrated a significant change in the nonischemic segments (systole: 4.1 +/- 1.0/s to 7.7 +/- 2.2/s, P = 0.012; diastole: -6.5 +/-1.8/s to -11.3 +/- 2.2/s, P = 0.001), whereas the response remained unchanged in the ischemic segments (systole: 4.6 +/-2.4/s to 4.8 +/- 1.2/s; diastole: -7.0 +/- 1.9/s to -7.3 +/- 1.1/s). Subendocardial MVG, particularly diastolic subendocardial MVG, may serve as a useful indicator of subtle ischemic changes in wall motion induced by low-dose DSE.