Comparison of 2 myocardial velocity gradient assessment methods during dobutamine infusion with Doppler myocardial imaging

Myocardial velocity gradient (MVG) has been shown to be the best quantitati ve parameter for the detection of ischemic myocardium during dobutamine inf usion with the use of Doppler myocardial imaging. MVG has been previously a ssessed by velocity measurements across the thickness of the myocardium at the time of visually selected maximal color brightness (thickness-velocity plot method). We hypothesized that MVG could be assessed by velocity measur ements throughout the cardiac cycle in the subendocardium parallel to the e ndocardial boundary to the left ventricular cavity and in the subepicardium parallel to the epicardial boundary (time-velocity plot method). This stud y was designed to compare MVG obtained from the thickness-velocity plot met hod and from the time-velocity plot method in quantifying dobutamine-induce d changes in myocardial wall motion in 8 phases of the cardiac cycle on col or M-mode Doppler myocardial imaging recordings of the left ventricular pos terior wall performed in 8 conscious dogs at baseline and at steady state d uring dobutamine infusion (10 mu g/kg per minute). For both methods, MVG wa s considered present if its mean value was significantly different from zer o and if endocardial and epicardial velocities were significantly different . There was close agreement between the 2 methods. MVG was present during t he preejection period, systole, rapid ventricular filling, and atrial contr action. Dobutamine induced significant increase in MVG during the preejecti on period (from 2.64 +/- 0.83 to 4.05 +/- 0.81 seconds(-1)), systole (from 2.14 +/- 0.59 to 6.08 +/- 2.20 seconds(-1) in early systole, from 1.90 +/- 1.06 to 5.31 +/- 2.95 seconds(-1) in mid systole, from 1.37 +/- 0.57 to 2.4 4 +/- 0.53 seconds(-1) in end systole), and rapid ventricular filling (from 3.06 +/- 1.12 to 7.82 +/- 2.58 seconds(-1)), related to a greater rise in endocardial than in epicardial velocities. The time-velocity plot method sh owed that ejection and diastole were 11% and 28% decreased during dobutamin e infusion, respectively, as heart rate was 31% increased. Thus according t o our quantitative criteria, both MVG assessment procedures enabled objecti ve interpretation of dobutamine effects on left ventricular wall motion. In addition, the time-velocity plot method provided automatic detection of pe ak velocity, timing, and duration of wall velocity changes over time.