Relation Between Thallium Uptake and Contractile Response to Dobutamine

Abstract

Background Both thallium scintigraphy and dobutamine echocardiography have been used to assess myocardial viability. However, thallium uptake and the inotropic response to dobutamine are expressions of different cellular phenomena. The present study was undertaken to investigate the relation between the two methods in patients with chronic coronary artery disease and left ventricular dysfunction to derive insights into the mechanisms related to myocyte viability. Methods and Results Thirty patients (28 men and 2 women; age, 59±10 years) with chronic coronary artery disease and impaired left ventricular systolic function at rest (mean ejection fraction, 32±9%) were included in the study. Patients underwent transesophageal echocardiography during incremental doses of dobutamine from 2.5 to a maximum of 40 μg · kg −1 · min −1 and single photon emission computed tomographic thallium scintigraphy using a stress-redistribution-reinjection protocol. The left ventricle was divided into 16 segments for analysis of echocardiographic and thallium images. Segmental myocardial contractile function was graded as normal, hypokinesis, akinesis, or dyskinesis at each incremental dose of dobutamine. Thallium uptake in each myocardial segment was graded on a 5-point scale from 0 (absent) to 2 (normal) for each of the stress, redistribution, and reinjection images. A segment was considered viable if the assigned thallium score was 1 or higher (normal uptake or only mild to moderate defect) in any of the stress, redistribution, or reinjection images. Among 472 myocardial segments available for analysis, 311 had resting wall motion abnormalities, of which 56% (173/311) showed contractile improvement with dobutamine (usually first observed at ≤10 μg · kg −1 · min −1 ) and 84% (262/311) were considered viable by thallium scintigraphy ( P <.0001). Of the 262 segments considered viable by thallium, 167 (64%) had a contractile improvement with dobutamine; in contrast, only 6 of the 49 segments (12%) considered nonviable by thallium had a positive dobutamine response ( P <.0001). Furthermore, a positive inotropic response to dobutamine was significantly related to the magnitude of thallium uptake: the proportion of segments with a positive dobutamine response rose with increasing magnitude of thallium uptake ( P <.001). The disagreement between the two tests was related primarily to segments considered viable by thallium that did not show contractile improvement with dobutamine. Conclusions These findings demonstrate the existence of a relation between thallium uptake and the inotropic response to dobutamine in patients with chronic coronary artery disease and left ventricular dysfunction. However, the proportion of segments showing a positive response to dobutamine is significantly lower than those with thallium uptake, suggesting that the cellular mechanisms responsible for a positive inotropic response to adrenergic stimulation require a higher degree of myocyte functional integrity than those responsible for thallium uptake.