No shortcuts with left bundle branch block and myocardial perfusion imaging: Lesson learnt with dobutamine cardiac PET

Abstract

Left bundle branch block (LBBB) is a relatively frequent electrical abnormality seen in the setting of coronary artery disease (CAD), cardiomyopathies, primary electrical disease of the heart, hypertension, or valvular heart disease. Non-invasive evaluation of coronary disease with functional testing in patients with pre-existing LBBB continues to pose diagnostic challenges for clinicians. False-positive perfusion abnormalities have been well described using exercise single-photon emission computed tomography myocardial perfusion imaging (SPECT MPI). The diagnostic use of dobutamine (Dob) as a pharmacologic stressor SPECT in patients with LBBB has been evaluated in only one study to our knowledge. Interestingly this study suggested that there is no difference in perfusion defects with Dob SPECT when compared to adenosine despite higher heart rates with Dob. Furthermore the authors of this study concluded that both Dob and adenosine were equally specific in detection of left anterior descending stenosis. Nevertheless, most guidelines do not recommend Dob as an option in SPECT for LBBB given concerns similar to exercise, namely tachycardia which could result in false-positive septal perfusion defects. Cardiac positron emission tomography myocardial perfusion imaging (PET MPI) has been proposed to be a better modality for avoiding false positives in patient with LBBB compared to SPECT. PET MPI has higher spatial resolution and strengths of quantitative blood flow analysis and lower incidence of septal perfusion defects in patients with LBBB. The use of Dob in PET for LBBB has not been formally studied and it is unclear if the superior aspects of PET technology can help avoid false-positive perfusion defects. We illustrate a case of Dob PET, with marked false-positive results in a patient with left bundle branch block. We briefly discuss the challenges of perfusion imaging in LBBB and highlight avoidance of Dob in LBBB regardless of SPECT or PET.