Low recruitment, insufficient funding

The proposed clinical trial is relevant to public health because it is expected to expand the differential diagnosis and provide an evidence--based therapy for the large population of patients with angina in the absence of obstructive CAD who currently remain undiagnosed and untreated. It, therefore, upholds an important part of the mission of the The National Heart, Lung, and Blood Institute (NHLBI), which is to promote the treatment of heart disease and enhance the health of all individuals so that they can live longer and more fulfilling lives.

Angina in the absence of obstructive coronary artery disease (CAD) affects millions, resulting in a reduced quality of life and a burden on the health care system. Previous work has focused on endothelial and microvascular dysfunction as causes of angina in these patients, but even when these etiologies are tested for, nearly half of patients remain undiagnosed, and proven therapies are lacking. The long--term goal of this research proposal is to improve the lives of patients with angina in the absence of obstructive CAD. These patients have been found to have a disproportionate prevalence of myocardial bridges (MBs) (60% vs. 30% in the general population).

MBs are known to cause angina, and the mechanism by which they do so is also known, but MBs have not been actively studied in the context of patients with angina in the absence of obstructive CAD. Medical therapies for symptomatic MBs, including beta blockers and calcium channel blocker have been suggested, but have never been appropriately tested, and may not be better than placebo. The overall objective of this research proposal is to demonstrate that MBs are an important and treatable cause of angina in patients with non--obstructive CAD.

The investigator will conduct the first--ever randomized, double--blind, placebo--controlled trial of medical therapy in patients with angina and an MB. The rationale is that a proven treatment would significantly expand the paradigm by which patients with angina in the absence of obstructive CAD are evaluated and treated. Our central hypothesis is that beta blockers and calcium channel blockers are effective treatments for reducing angina in patients with an MB compared with placebo. Guided by strong preliminary data, this hypothesis will be tested by pursuing two specific aims: 1) Determine the efficacy of beta blockers and calcium channel blockers in treating patients with angina and an MB and 2) Identify predictors of efficacy of beta blockers and calcium channel blockers in treating patients with angina and an MB. For Aim #1, the investigator will randomize a total of 360 adult patients with angina and an MB into one of three treatment arms: beta blocker (nebivolol), calcium channel blocker (diltiazem), or placebo (1:1:1).

Efficacy will be determined after 30 days on the study drug by a change in angina, as assessed by the Seattle Angina Questionnaire (SAQ). The investigator will also evaluate changes in exercise capacity, as well as drug adherence and side effects. For Aim #2, the investigator will evaluate MB muscle index (MMI, a product of MB length x depth) by coronary computed tomography angiography, as well as male sex, as predictors of efficacy. Randomization will be stratified on sex, ensuring a balance of women and men in each arm. The proposed research is innovative because it shifts the current clinical perspective on angina in the absence of obstructive CAD by considering myocardial bridging as a potential etiology.

It is also significant because it will substantially increase the number of patients with angina in the absence of obstructive CAD that clinicians are able to diagnose and treat, ultimately leading to improvements in quality of life and a reduction in health care costs.

Inclusion Criteria

1. Age ≥18 years
2. Stable angina (typical or atypical, based on Diamond criteria (35))
3. Exercise stress echocardiogram or exercise stress test (with beta blocker or calcium channel blocker held) performed within six months of enrollment
4. CCTA or invasive coronary angiogram confirming the presence of an MB
5. Absence of obstructive CAD, as demonstrated by no ischemia on stress testing and no significant obstructive CAD (coronary stenosis <50%) on CCTA or invasive coronary angiogram

Exclusion Criteria:

1. Asymptomatic
2. Status--post heart transplant
3. Presence of another likely explanation of chest pain, such as pulmonary hypertension, hypertrophic obstructive cardiomyopathy, or aortic stenosis
4. Presence of an acute coronary syndrome (unstable angina, NSTEMI, or STEMI), Tako--tsubo, or cardiogenic shock
5. An abnormal left ventricular ejection fraction (EF<55%)
6. History of a severe adverse reaction to beta blockers or calcium channel blockers (prior minor intolerance or ineffectiveness not exclusion)
7. Use of existing medication that has an unsafe drug--drug interaction with beta blockers or calcium channel blockers
8. Refusal to take beta blockers or calcium channel blockers
9. Resting systolic blood pressure <100 mmHg or heart rate <50 beats per minute
10. Inability to provide an informed consent, including an inability to speak, read, or understand English or Spanish
11. A hearing impairment that won't allow for a typical verbal conversation or a visual impairment that won't allow for reading of the written consent
12. A potentially vulnerable subject (including pregnant women, prisoners, economically and educationally disadvantaged, decisionally impaired, and institutionalized individuals)

Up to 6 months

Early termination led to a small number of subjects analyzed.