Which test for CAD should be used in patients with left bundle branch block?
ABSTRACT
Exercise stress electrocardiography is unreliable as a test for obstructive coronary artery disease (CAD) if the patient has left bundle branch block. The authors provide an algorithm for using alternative tests: exercise stress echocardiography, dobutamine echocardiography, computed tomographic (CT) angiography, and nuclear myocardial perfusion imaging.
KEY POINTS
- Although current guidelines recommend exercise stress echocardiography, it cannot reliably detect significant obstructive CAD in patients who have left bundle branch block at rest.
- CT angiography is the first-line imaging test for these patients if they are under age 65. For those 65 and older, the first-line test is either pharmacologic stress nuclear myocardial perfusion imaging with coronary vasodilators or dobutamine stress echocardiography.
- For patients who cannot tolerate CT contrast due to renal impairment or who have a true contrast allergy, pharmacologic nuclear myocardial perfusion imaging using coronary vasodilators and dobutamine stress echocardiography can be alternatives.
CURRENT GUIDELINES
Exercise stress echocardiography
American College of Cardiology Foundation/American Heart Association guidelines for diagnosis and management of patients with stable ischemic heart disease recommend exercise stress echocardiography for patients with an intermediate to high pretest probability of ischemic heart disease who have an uninterpretable electrocardiogram and at least moderate physical functioning or no disabling comorbidity (class 1 indication, level of evidence B).11
Current American Society of Echocardiography guidelines also support exercise stress echocardiography as an appropriate test for suspected obstructive CAD in patients with resting left bundle branch block.27 However, this recommendation is based on limited data.
Pharmacologic stress nuclear myocardial perfusion imaging
American Society of Nuclear Cardiology guidelines endorse pharmacologic stress nuclear myocardial perfusion imaging using coronary vasodilators for evaluating suspected obstructive CAD in patients with resting left bundle branch block.28,29
THE POSSIBLE HARMS OF TESTING
Although current guidelines recommend it, recent data show that exercise stress echocardiography has poor specificity and diagnostic accuracy for significant obstructive CAD in patients with resting left bundle branch block. And performing this test in patients with left bundle branch block may result in further downstream investigations.
Based on limited data from a small number of studies published more than 15 years ago, dobutamine stress echocardiography has moderate sensitivity and specificity for significant CAD in patients with resting left bundle branch block. However, this test does not provide functional information about the patient’s exercise performance.
Pharmacologic stress nuclear myocardial perfusion imaging using coronary vasodilators is an appropriate investigation strategy. However, radiation exposure is a limitation.30
CT angiography can assess for significant obstructive CAD in patients with resting left bundle branch block. However, its diagnostic accuracy can be affected by coronary calcification in older patients. Additionally, each scan is associated with a small amount of radiation exposure,31 and a small number of patients will have a true contrast allergy.32
CLINICAL BOTTOM LINE
For patients with typical ischemic symptoms and new left bundle branch block on electrocardiography, specialist cardiology consultation should be sought, with consideration given to proceeding directly to coronary angiography. For stable outpatients, we propose the following diagnostic approach (Figure 3).
Exercise stress echocardiography is recommended by current guidelines, but it cannot reliably detect significant obstructive CAD in patients with resting left bundle branch block—its specificity and diagnostic accuracy are poor.14,15 Alternative imaging strategies include CT angiography, pharmacologic nuclear myocardial perfusion imaging using coronary vasodilators, and dobutamine stress echocardiography.
For investigating suspected obstructive CAD in patients with resting left bundle branch block, we propose CT angiography as the first-line imaging test for patients under age 65 and pharmacologic stress nuclear myocardial perfusion imaging using coronary vasodilators or dobutamine stress echocardiography for those age 65 and older. For patients who cannot tolerate contrast due to renal impairment or who have a true contrast allergy, pharmacologic nuclear myocardial perfusion imaging using coronary vasodilators and dobutamine stress echocardiography may be used as alternatives.
