Role of dipyridamole thallium-201 imaging in left bundle branch block

Exercise thallium-201 imaging is of limited diagnostic accuracy in patients with left bundle branch block (LBBB), because decreased septal activity often occurs in the absence of left anterior descending artery disease.^1-3 A combination of tachycardia, shortened diastolic relaxation time and asynchronous contraction are considered to be responsible for this phenomenon.^1,2 Recently, it has been suggested that dipyridamole thallium-201 scintigraphy significantly improves specificity in patients with LBBB by assessing coronary flow reserve at lower heart rates.⁴ Relatively few patients in the latter report, however, had angiographic correlation. Accordingly, this study compares this technique with angiographic findings in a larger group of patients with LBBB at rest.