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Which test for CAD should be used in patients with left bundle branch block?

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Release date: March 1, 2018
Expiration date: February 28, 2019
Estimated time of completion: 1 hour

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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.


 

References

A 62-year-old woman with hypertension and type 2 diabetes mellitus has been experiencing shortness of breath on exertion and chest discomfort for 2 months. Her hypertension has been suboptimally controlled, and her most recent hemoglobin A1c measurement was 7.0%. She has never smoked and has no family history of premature coronary artery disease (CAD). She is otherwise well and walks for 30 minutes 3 times per week. A 12-lead electrocardiogram demonstrated normal sinus rhythm with left bundle branch block. Her physician suspects she has CAD. What testing does this patient need?

LIMITED DATA, GUIDELINES

For clinicians investigating suspected obstructive CAD in patients with left bundle branch block on resting electrocardiography, the data and guidelines are limited regarding the optimal noninvasive tests and how to interpret them.

Here, we present a practical review of the diagnostic utility of exercise stress electrocardiography, exercise stress echocardiography, dobutamine stress echocardiography, nuclear myocardial perfusion imaging, and computed tomographic (CT) angiography for assessing suspected obstructive CAD in patients with resting left bundle branch block.

WHAT IS LEFT BUNDLE BRANCH BLOCK?

In left bundle branch block, as the name implies, electrical conduction along the left bundle branch is blocked or delayed. Ventricular activation therefore begins in the right ventricle and the right side of the interventricular septum.1 Transseptal activation from the right ventricle to the left ventricle is slow, because it is transmyocardial.1 Left ventricular basal and posterolateral wall segments become activated last.1 Due to delay in the onset of left ventricular contraction, ventricular contraction is dyssynchronous. Classically, interventricular septal motion during systole has been described as paradoxical, with anterior septal motion.2–4

A 12-lead electrocardiogram from a 70-year-old woman with a 12-month history of progressive exertional dyspnea

Figure 1. A 12-lead electrocardiogram from a 70-year-old woman with a 12-month history of progressive exertional dyspnea demonstrates sinus rhythm with a ventricular rate of 88 beats per minute and a wide left bundle branch block (QRS duration 150 ms).

On electrocardiography, the QRS duration is widened (≥ 120 ms), with a distinctive morphology as shown in Figure 1. Left bundle branch block makes it difficult to accurately assess for dynamic ST-segment changes with exercise, rendering exercise stress electrocardiography a suboptimal test for obstructive CAD if left bundle branch block is present.

LEFT BUNDLE BRANCH BLOCK AND RISK OF DEATH

Although left bundle branch block can be an isolated finding, it can also be associated with underlying obstructive CAD5 or cardiomyopathy.6 When it occurs at rest, the risk of death from a cardiovascular event is 3 to 4 times higher.7 However, the exact incidence of significant obstructive CAD in asymptomatic patients with incidentally detected left bundle branch block is unknown.

Acute left bundle branch block accompanying acute myocardial infarction is associated with a high risk of death. Hindman et al,8 in a 1978 multicenter study, described 432 patients with acute myocardial infarction and left or right bundle branch block. In the 163 patients who had left bundle branch block, the in-hospital mortality rate was 24% and the 1-year mortality rate was 32%.

Freedman et al9 in 1987 reviewed 15,609 patients with chronic CAD who underwent coronary angiography, of whom 522 had left or right bundle branch block. During a follow-up of nearly 5 years, 2,386 patients died. The actuarial probability of death at 2 years in patients with left bundle branch block was more than 5 times that of patients without it (P < .0001).

During 18 years of observation in the Framingham study,10 55 participants developed left bundle branch block, at a mean age at onset of 62. Twenty-six (48%) of these participants developed clinically significant CAD or heart failure coincident with or subsequent to the onset of left bundle branch block. Fifty percent of the participants who developed left bundle branch block died of cardiovascular disease within 10 years of its onset.

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