Myocardial blood flow imaging in patients with a left bundle branch block or ventricular-paced rhythm: “And therein, as the Bard would tell us, lies the rub”

Abstract

Nuclear-based imaging has been for more than a decade the cornerstone of noninvasive evaluation of myocardial perfusion in symptomatic patients. Ischemia assessment is of importance for guiding referral to invasive coronary angiography (ICA) and subsequent revascularization strategies. Although numerous trials such as the FAME, COURAGE and more recently the ISCHEMIA trial have indisputable demonstrated that stent placement shows no benefit in myocardial infarctions and cardiac death among stable coronary artery disease (CAD) patients, percutaneous coronary interventions (PCI) provide more and quicker symptom relief than optimal medical therapy. This therapeutic benefit of PCI may not be neglected and overlooked by clinicians by blindly staring at outcome data. Germane to this, it has to be said that the role of ischemia as a therapeutic target for prevention of future disease burden may still be a pivotal one. The recently published ISCHEMIA trial investigated the role of medical therapy versus revascularization in a large cohort of patients with moderate to severe ischemia, a patient category neglected in previous studies. Despite this laudable achievement, paradoxically only 25% of included patients fulfilled the criterion of severe ischemia. Importantly, the definition of myocardial perfusionbased ischemia was mainly determined by the extent of ischemia and as such disregarding the depth of ischemia, which may be a potential important prognostic precursor for future cardiac events when treated conservatively. Therefore, functional imaging continues to have a pivotal role in selecting patients who likely will benefit from revascularization. However, diagnosis of ischemia in patients with a left bundle branch block (LBBB) or ventricular-paced rhythm (VPR) poses a diagnostic challenge raising the question which imaging technique is the most accurate for this task. And therein, as the Bard would tell us, lies the rub. The present guidelines do not advocate one functional test over another in symptomatic patients with an intermediate pretest likelihood. The choice for a specific functional test is based on local availability and expertise. It is noteworthy to point out that a large body of evidence shows cardiac positron emission tomography (PET) to exhibit a higher diagnostic accuracy than conventional single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) for detection of CAD in stable chest pain patients. In earlier studies, in which ICA served as the reference standard, PET mainly excelled in reducing the number of false-positives due to its high spatial resolution and the use of a CT-based attenuation correction. An interesting and challenging group of patients are those with a LBBB or VPR. In these patients vasodilator stress imaging is advised. Of note, a LBBB may result from a sequela of ischemic heart disease, congenital heart Reprint requests: Ibrahim Danad, MD, PhD, Department of Cardiology, Amsterdam University Medical Center, Location VU University Medical Center, De Boelelaan 1117, 1081 HV Amsterdam, The Netherlands; [email protected] J Nucl Cardiol 2021;28:989–91. 1071-3581/$34.00 Copyright 2021 American Society of Nuclear Cardiology.