Efficacy of Medical Therapy in Women and Men With Angina and Myocardial Bridging

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.