Comparison of 2 Myocardial Velocity Gradient Assessment Methods During Dobutamine Infusion with Doppler Myocardial Imaging,☆☆

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Abstract

Myocardial velocity gradient (MVG) has been shown to be the best quantitative parameter for the detection of ischemic myocardium during dobutamine infusion with the use of Doppler myocardial imaging. MVG has been previously assessed 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 measurements throughout the cardiac cycle in the subendocardium parallel to the endocardial boundary to the left ventricular cavity and in the subepicardium parallel to the epicardial boundary (time-velocity plot method). This study was designed to compare MVG obtained from the thickness-velocity plot method and from the time-velocity plot method in quantifying dobutamine-induced changes in myocardial wall motion in 8 phases of the cardiac cycle on color M-mode Doppler myocardial imaging recordings of the left ventricular posterior wall performed in 8 conscious dogs at baseline and at steady state during dobutamine infusion (10 μg/kg per minute). For both methods, MVG was considered present if its mean value was significantly different from zero and if endocardial and epicardial velocities were significantly different. There was close agreement between the 2 methods. MVG was present during the preejection period, systole, rapid ventricular filling, and atrial contraction. Dobutamine induced a significant increase in MVG during the preejection 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 2.44 ± 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 showed that ejection and diastole were 11% and 28% decreased during dobutamine infusion, respectively, as heart rate was 31% increased. Thus according to our quantitative criteria, both MVG assessment procedures enabled objective interpretation of dobutamine effects on left ventricular wall motion. In addition, the time-velocity plot method provided automatic detection of peak velocity, timing, and duration of wall velocity changes over time. (J Am Soc Echocardiogr 1999;12:22-31.)

Section snippets

Animal Preparation

Eight chronically instrumented, conscious adult mongrel dogs weighing 22 to 28 kg were investigated. As previously reported,7 dogs were instrumented for the measurement of arterial pressure, LV pressure, and LV dP/dt. All experiments were conducted when the dogs were healthy, apyretic, and had been trained to lie quietly on the experiment table. Examinations were performed at steady state before and during dobutamine infusion (10 μg/kg per minute for 15 minutes). Data were continuously recorded

RESULTS

The feasibility of color M-mode DMI was 100%. There was a significant positive correlation between MVG obtained from the thickness-velocity plot method and from the time-velocity plot method (r = 0.82, P < .0001). There was a close agreement between the 2 MVG assessment methods. The bias (mean difference in MVG between the 2 methods) of all measurements was –0.17 ± 9.71 seconds-1 . MVG values obtained by the time-velocity plot method were significantly higher than those obtained by the

DISCUSSION

DMI has been shown to be reliable for addressing ventricular wall mechanical events related to cardiac function through measurements of wall velocities.4, 14, 15, 16, 17, 18 MVG was first described by McVeigh and Zerhouni19 with the use of magnetic resonance tagging and by Fleming et al20 with the use of color M-mode DMI. MVG has been shown to represent regional wall motion independent of overall cardiac translation in the chest.2, 3 In the current study, MVG was calculated on conscious dogs in

CONCLUSIONS

Our study showed that 2 complementary methods may be applied to MVG assessment and enabled objective interpretation of dobutamine effects on LV wall motion. For the first time, quantitative criteria have been used for assessing MVG, and its range values have been given in normal hearts at baseline and during dobutamine infusion. In addition to the thickness-velocity plot method, the time-velocity plot method only provides peak velocity during each cardiac phase, sequential changes in LV wall

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      Previous studies (Sabbah et al. 1981) proved that the subendocardium undergoes greater thickening and shortening than the epicardium; Sagar and colleagues found functional changes in the epi- and endocardium layers during ischaemia (Sagar et al. 1987). Myocardial gradient has been reported to be a good indicator of contractility defects in ischaemic segments (Garot et al. 1999; Pellerin et al. 1999). Other alternatives to evaluate myocardial contraction on M-mode grey-scale images have been explored, such as myocardial wall thickening and thinning (Guth et al. 1984; Jamal et al. 2001) obtained as the ratio between systole and diastole wall width.

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