Quantification of the myocardial response to low-dose dobutamine using tissue Doppler echocardiographic measures of velocity and velocity gradient.

Low-dose dobutamine echocardiography has been clinically useful in myocardial viability studies, although routine visual assessment of wall motion is subjective. The objective was to quantify the incremental myocardial response to low-dose dobutamine infusion using a new semiautomated tissue Doppler (TD) analysis system and to compare these data with routine echocardiographic measures in the same subjects. Twelve subjects had TD and routine echocardiographic studies at baseline and during 10-minute stages of dobutamine infusion at 1, 2, 3, and 5 microg/kg/min. Color TD video data were converted to a digital velocity matrix (4.5 velocity data points/mm at 500 Hz) for analysis of mitral annular velocity, endocardial velocity, and velocity gradient at each stage. Posterior wall percent thickening and ejection fraction were calculated from the routine images. Mitral annular peak systolic velocity significantly increased with only 1 microg/kg/min of dobutamine from 69 +/- 9 to 77 +/- 7 mm/s (p <0.05 vs baseline), and further incremental increases occurred with each subsequent dose. Anteroseptal and posterior wall peak endocardial velocity increased with 2 microg/kg/min of dobutamine from 33 +/- 7 to 46 +/- 15 mm/s and 50 +/- 9 to 61 +/- 10 mm/s, respectively (p <0.01 vs baseline) and further increased with 5 microg/kg/min (p <0.0001 vs 3 microg/kg/min). Posterior wall peak systolic gradient also increased with 2 microg/kg/min of dobutamine from 3.1 +/- 0.6 to 5.4 +/- 1.6 s(-1) (p <0.05 vs baseline). Routine measures of percent wall thickening or ejection fraction did not detect increases until the 3 microg/kg/min dose. TD can detect subtle alterations in contractility induced by low-dose dobutamine and has the potential to quantify regional ventricular function objectively.