Myocardial Bridges on Coronary Computed Tomography Angiography　― Correlation With Intravascular Ultrasound and Fractional Flow Reserve ―

Abstract

Background: Myocardial bridges (MB) are commonly seen on coronary CT angiography (CCTA) in asymptomatic individuals, but in patients with recurrent typical angina symptoms, yet no obstructive coronary artery disease (CAD), evaluation of their potential hemodynamic significance is clinically relevant. The aim of this study was to compare CCTA to invasive coronary angiography (ICA), including intravascular ultrasound (IVUS), to confirm MB morphology and estimate their functional significance in symptomatic patients. Methods and Results:We retrospectively identified 59 patients from our clinical databases between 2009 and 2014 in whom the suspicion for MB was raised by symptoms of recurrent typical angina in the absence of significant obstructive CAD on ICA. All patients underwent CCTA, ICA and IVUS. MB length and depth by CCTA agreed well with length (0.6±23.7 mm) and depth (CT coverage) as seen on IVUS. The product of CT length and depth (CT coverage), (MB muscle index (MMI)), ≥31 predicted an abnormal diastolic fractional flow reserve (dFFR) ≤0.76 with a sensitivity and specificity of 74% and 62% respectively (area under the curve=0.722). Conclusions:In patients with recurrent symptoms of typical angina yet no obstructive CAD, clinicians should consider dynamic ischemia from an MB in the differential diagnosis. The product of length and depth (i.e., MMI) by CCTA may provide some noninvasive insight into the hemodynamic significance of a myocardial bridge, as compared with invasive assessment with dFFR.

The Myocardial Bridge: Potential Influences on the Coronary Artery Vasculature

“…40 Furthermore, cardiac CT can easily assess the length and thickness of MB over the coronary artery. 42 Exercise echocardiography has recently been reported as an effective noninvasive modality for assessing MB; this method cannot assess or identify the presence of MB but can suggest the presence of MB by revealing the specific characteristic of focal buckling of the septum with apical sparing during the end-systolic and early-diastolic phases. 43,44 By contrast, echocardiography, particularly, more advanced echocardiography, may be useful for the noninvasive assessment of the hemodynamic significance of MB.…”

Myocardial bridge: an unrecognized cause of chest pain in pulmonary arterial hypertension

“…Developed at Stanford University, this is a non-invasive index of hemodynamic compromise of an MB, which is defined by the product of the length and depth of the MB. 1 The MMI of our patient was 39. An MMI of ≥31 indicates a 71% sensitivity and a 62% specificity for detecting a hemodynamically significant MB, as determined by an invasive assessment of diastolic fractional flow reserve (dFFR) of < 0.76.…”

“…Therefore, diastolic FFR with dobutamine challenge is currently the technique of choice to evaluate for hemodynamically significant myocardial bridging. 1,7 The medical management of hemodynamically significant MBs consists primarily of beta blockers and calcium channel blockers, which reduce contractility, increase diastolic filling time, and can contribute vasodilatory properties. 10 It is well-known that patients with MBs can develop coronary endothelial dysfunction, which may further contribute to symptoms.…”

“…Therefore, diastolic FFR with dobutamine challenge is currently the technique of choice to evaluate for hemodynamically significant myocardial bridging. 1,7…”

“…An MMI of ≥31 indicates a 71% sensitivity and a 62% specificity for detecting a hemodynamically significant MB, as determined by an invasive assessment of diastolic fractional flow reserve (dFFR) of < 0.76. 1 An invasive coronary angiogram was then performed, which excluded atherosclerotic CAD and confirmed the CT finding of an MB in the mid LAD. Invasive stress testing with dobutamine to determine the dFFR was not undertaken, albeit the risk of such an evaluation in patients with severe PAH and the development of hypotension and arrhythmias is relatively low.…”