Methods
Quantification of the Myocardial Response to Low-Dose Dobutamine Using Tissue Doppler Echocardiographic Measures of Velocity and Velocity Gradient

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Abstract

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 μg/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 μg/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 μg/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 μg/kg/min (p <0.0001 vs 3 μg/kg/min). Posterior wall peak systolic gradient also increased with 2 μg/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 μg/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.

Section snippets

Methods

Twelve normal volunteers (10 men and 2 women, age 34 ± 5 years), with no history of cardiovascular disease and normal routine 2-dimensional and Doppler echocardiograms were selected for study. The protocol was approved by the Institutional Review Board for Biomedical Research and all subjects gave written informed consent. Echocardiographic data were acquired with a 3.75-MHz, phased-array transducer and a TD ultrasound system (SSA-380A, Toshiba Corp., Tochigi, Japan) described elsewhere in

Endocardial Time-Velocity Plots:

Examples of endocardial time-velocity plots at each stage of dobutamine appear in Fig. 4, with group mean results of peak systolic velocity shown in Fig. 5. Significant increases from baseline in peak systolic endocardial velocity occurred with 2 μg/kg/min of dobutamine infusion in both anteroseptum and posterior walls. Further highly significant increases occurred with 5 μg/kg/min compared with all previous stages, demonstrating a dose-response relation (p <0.0001 vs 3 μg/kg/min dose).

Discussion

This study demonstrates that measures of myocardial velocity and velocity gradient using color-coded TD echocardiography can be applied to assess noninvasively alterations in LV function induced by pharmacologic inotropic modulation. Significant changes in TD indexes of global and regional function were consistently detected with infusions of very low doses of dobutamine in normal subjects. Alterations in mitral annular velocity were detected with a dose of only 1 μg/kg/min, and endocardial

References (30)

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