Optimal viability evaluation by a simplified rest redistribution thallium-201 & contractility assessment with low dose dobutamine combined protocol

Abstract

Background: There is overlap in myocardial viability information by rest thallium-201 (Tl) uptake and contractile reserve under low dose dobutamine (LDD). In this study, we investigate a new protocol that involves acquisition of the delayed rest redistribution (RR) Tl images under LDD to help provide combined Tl uptake & contractile reserve viability information in a single study. Methods: 41 patients (27 men), mean age 67±11 with myocardial infarction underwent routine RR gated SPECT Tl myocardial imaging. LDD (10 ug/kg/min) infusion was maintained during delayed images acquisition. Segmental Tl types were semiquantitatively classified into normal, fixed (mild, moderate, severe, or absent) & reversible defects, & subclassified by wall motion (WM)/ thickening (WT) changes between early resting & delayed LDD gated images into normal, fixed or improved dysfunctional (contractile reserve present) segments. Results: The mean left ventricular ejection fraction was 30% at rest & 34% with LDD (p < .001). In dysfunctional myocardium, improved WM &/or WT abnormalities under LDD were significantly higher (p < .001) in reversible (56/97) & in fixed (76/158) than normal segments (3/80). Out of 215 fixed Tl uptake defects, 33 showed no appreciable uptake to evaluate WM/WT. In the remaining 182 fixed defects, 158 were dysfunctional. Improved WM/WT in dysfunctional segments was significantly higher (p < .05) in mild (30/56) & in moderate (35/65) than severe (11/37) fixed defects. Quantitative analysis showed significant (p < .001) WT increase between rest & LDD in all Tl uptake types. However, WT was higher in normal than fixed or reversible Tl defects both at rest (p < .001) & with LDD (p < .001). Conclusion: Comprehensive myocardial viability evaluation can be routinely performed using this new protocol that simultaneously provides Tl uptake & contractile reserve information in a single examination. Moreover, this protocol requires no additional time or radioactivity over the usual RR Tl protocol. Further comparison to post revascularization functional outcome is needed for validation.