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Excerpt
We read with great interest the article “False-Positive Results Obtained with Stress Myocardial SPECT in Patients with Right Bundle Branch Block”(1). In 1992, we published an article on reversible Tl-201 perfusion defects in a patient with incomplete right bundle branch block (RBBB) and angiographically normal coronary arteries (2). Tl-201 chloride scintigraphy showed stress-induced transient defects in the septal and inferoapical areas. The differences in findings in our patient and those reported by Küçük and colleagues include the location of the left ventricle lesions and the reversibility of the lesions. Our patient’s lesions were located in the septal and inferoapical segments and were reversible, whereas 7 of 31 (23%) of Küçük and colleagues’ patients with RBBB had perfusion defects involving the inferior wall (n = 5 patients) and the inferolateral wall (n = 2 patients). These seven patients’ defects appeared to be irreversible according to their report (1).
Left bundle branch block (LBBB) is known to cause decreased blood flow and therefore decreased tracer uptake in the region of the interventricular septum, especially during exercise as a result of asynchronous systole (3). The most common LBBB defect is related to tachycardia and is noted during exercise, with improvement on resting images. Therefore, the lesions appeared as reversible defects. Twenty to fifty percent of patients with LBBB can have transient defects in the septum during exercise perfusion imaging in the absence of left coronary artery disease. To resolve such false-positive findings, these patients are candidates for pharmacologic stress with dipyridamole or adenosine as a substitute for physical exercise (3,4). Did these seven patients undergo dipyridamole or adenosine stress testing? If the results of Tl-201 SPECT in these patients were within normal limits after dipyridamole or adenosine was administered, the mechanism of the ventricular defect in patients with RBBB might explain the cause of LBBB in relation to the tachycardia.
