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CLINICAL RESEARCH: CARDIAC IMAGING

Impact of scar thickness on the assessment of viability using dobutamine echocardiography and thallium single-photon emission computed tomography

A comparison with contrast-enhanced magnetic resonance imaging

^* University of Queensland, Brisbane, Australia

Manuscript received July 9, 2003; revised manuscript received August 16, 2003, accepted September 9, 2003.

^* Reprint requests and correspondence: Prof. Thomas H. Marwick, University of Queensland Department of Medicine, Princess Alexandra Hospital, Ipswich Road, Brisbane, Qld 4012, Australia.
tmarwick{at}soms.uq.edu.au

OBJECTIVES: We sought to determine whether the transmural extent of scar (TES) explains discordances between dobutamine echocardiography (DbE) and thallium single-photon emission computed tomography (Tl-SPECT) in the detection of viable myocardium (VM).

BACKGROUND: Discrepancies between DbE and Tl-SPECT are often attributed to differences between contractile reserve and membrane integrity, but may also reflect a disproportionate influence of nontransmural scar on thickening at DbE.

METHODS: Sixty patients (age 62 ± 12 years; 10 women and 50 men) with postinfarction left ventricular dysfunction underwent standard rest-late redistribution Tl-SPECT and DbE. Viable myocardium was identified when dysfunctional segments showed Tl activity >60% on the late-redistribution image or by low-dose augmentation at DbE. Contrast-enhanced magnetic resonance imaging (ceMRI) was used to divide TES into five groups: 0%, <25%, 26% to 50%, 51% to 75%, and >75% of the wall thickness replaced by scar.

RESULTS: As TES increased, both the mean Tl uptake and change in wall motion score decreased significantly (both p < 0.001). However, the presence of subendocardial scar was insufficient to prevent thickening; >50% of segments still showed contractile function with TES of 25% to 75%, although residual function was uncommon with TES >75%. The relationship of both tests to increasing TES was similar, but Tl-SPECT identified VM more frequently than DbE in all groups. Among segments without scar or with small amounts of scar (<25% TES), >50% were viable by SPECT.

CONCLUSIONS: Both contractile reserve and perfusion are sensitive to the extent of scar. However, contractile reserve may be impaired in the face of no or minor scar, and thickening may still occur with extensive scar.

Abbreviations and Acronyms   2DE = two-dimensional echocardiogram/ echocardiographic   ceMRI = contrast-enhanced magnetic resonance imaging   DbE = dobutamine echocardiography   LV = left ventricle/ventricular   TES = transmural extent of scar   Tl-SPECT = thallium single-photon emission computed tomography   VM = viable myocardium

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