Diagnostic Accuracy and Prognostic Significance of Quantitative Thallium-201 Scintigraphy in Patients with Left Bundle Branch Block

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Abstract
We evaluated the diagnostic and prognostic value of exercise thallium-201 (201T1) scintigraphy in 74 consecutive patients (mean age 56 ± 11 years) with left bundle branch block (LBBB) presenting for evaluation of possible coronary artery disease (CAD). Only 18 patients (24%) had a normal scintiscan by quantitative criteria. Catheterization was performed in 22 patients for clinical indications, and abnormal scans were observed in 20 (91%), 19 of whom had defects in the territory of the left anterior descending (LAD) coronary artery. Only 10 patients who underwent catheterization had significant CAD and all had abnormal scintiscans. Six other patients with nonischemic cardiomyopathy had abnormal scans, as did 4 of 6 normal patients. These 4 patients demonstrated delayed redistribution in LAD scan segments despite normal coronary angiograms. The entire cohort was separated based on the presence (group I, n = 38) or the absence (group II, n = 36) of catheterization or clinical evidence of heart disease. Abnormal scintiscans were seen in 95% of group I patients versus 56% of group II patients (p < 0.001). Group I patients had a higher prevalence of multivessel disease by 201T1 criteria (39 vs. 8%, p < 0.002), left ventricular dilatation (32 vs. 0%, p < 0.001) and increased lung 201T1 uptake (26 vs. 3%, p < 0.007). During 22 ± 16 months of follow-up, 11 patients from group I versus none from group II experienced sudden death, myocardial infarction or underwent coronary bypass surgery. When all 201T1-scintigraphic variables and the presence versus the absence of overt heart disease were entered into a stepwise discriminant function analysis, the only significant predictors of adverse outcome were clinically overt heart disease and increased lung 201T1 uptake. In conclusion, our data indicate that: (1) many patients with LBBB and either angiographically normal coronary arteries or no clinically manifest heart disease have abnormal 201T1 scintigrams, usually in the supply region of the LAD coronary artery; (2) focal perfusion defects can be observed in LBBB patients with nonischemic cardiomyopathy; (3) despite a 56% prevalence of focal perfusion abnormalities in LBBB patients without clinically overt heart disease, 2-year prognosis is excellent (0% event rate in this group), and (4) in patients with clinically manifest heart disease, only abnormal lung uptake of 201T1 provided significant additional independent prognostic information.

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