Rate dependent left bundle branch block: does it have any effect on the myocardial perfusion SPECT.

Dear Sir, the recent issue of Nuclear Medicine Review published an interesting study by Gholamrezanezhad et al. regarding rate dependent left bundle branch block and its effect on myocardial perfusion SPECT [1]. They reported four cases with rate dependent LBBB during exercise stress for myocardial perfusion imaging. Myocardial perfusion SPECT imaging showed no evidence of reversible perfusion defects in three of the patients. They concluded that “maybe it is possible to continue exercise tolerance test (ETT) for those patients undergoing myocardial perfusion scintigraphy and developing rate dependent LBBB”. As the authors themselves mentioned in their study, the number of cases in their case report was not statistically enough to draw any definite conclusion. We would like to report a case with rate dependent LBBB during ETT who developed perfusion defects in the septal wall which disappeared on the Dipyridamole stress imaging. The case was a 45 year old female patient with history of atypical chest pain since 2 years ago. Her rest ECG was normal. The patient had inconclusive ETT one month before. She was referred to our department for myocardial perfusion SPECT for diagnosis of possible coronary artery disease (CAD). Baseline blood pressure was 130/90 mmHg and baseline heart rate was 70. Five minutes after beginning of ETT (stage II of Bruce protocol and at heart rate of 147), the patient developed LBBB on the ECG monitoring (Figure 1). Rate dependent left bundle branch block: Does it have any effect on the myocardial perfusion SPECT