For an adult with exertional chest pain, dyspnea, or exercise‑induced arrhythmias and coronary angiography showing a myocardial bridge, what cardiac magnetic resonance imaging (MRI) protocol—including high‑resolution cine, stress perfusion, and late gadolinium enhancement—should be used to assess its functional significance and guide management?

Cardiac MRI Protocol for Myocardial Bridge Assessment

Direct Recommendation

For adults with exertional chest pain, dyspnea, or exercise-induced arrhythmias and angiographically confirmed myocardial bridge, perform stress cardiac MRI with perfusion imaging and late gadolinium enhancement to determine functional significance, rather than relying on anatomic visualization alone. 1, 2

Structured Diagnostic Algorithm

Step 1: Confirm Anatomic Diagnosis (Already Completed)

• Coronary angiography has already demonstrated the characteristic "milking effect" (systolic compression with diastolic relaxation), confirming the myocardial bridge diagnosis 2
• The anatomic presence alone does not determine clinical significance, as 0.5-4.5% detection rate on angiography versus 15-85% at autopsy indicates most bridges are clinically silent 2

Step 2: Functional Assessment with Stress CMR (Primary Recommendation)

The 2024 ESC guidelines for chronic coronary syndromes recommend stress CMR perfusion imaging (Class I, Level B) to diagnose and quantify myocardial ischemia and estimate risk of major adverse cardiovascular events in patients with suspected chronic coronary syndrome. 1

Required CMR Protocol Components:

Stress Perfusion Imaging:

• Perform adenosine or dipyridamole vasodilatory stress perfusion imaging to detect exercise-induced ischemia in the territory supplied by the bridged artery 3, 4
• This directly answers whether the bridge causes hemodynamically significant flow limitation during increased myocardial oxygen demand 5, 6
• Stress perfusion CMR provides high diagnostic accuracy (sensitivity 80-90%) for detecting ischemia and has been validated against invasive fractional flow reserve 1, 4

Late Gadolinium Enhancement (LGE):

• Acquire LGE sequences to exclude myocardial scar or prior infarction in the distribution of the bridged artery 1, 3
• LGE can identify areas of fibrosis that may indicate prior ischemic injury from the bridge 1, 3
• The presence of LGE in an asymptomatic patient with myocardial bridge suggests prior hemodynamically significant compression 1

High-Resolution Cine Imaging:

• Obtain cine sequences to assess regional wall motion abnormalities in the territory of the bridged segment 1, 3
• Evaluate left ventricular systolic function and volumes, as depressed function may indicate chronic ischemia from the bridge 3, 6
• Assess for wall motion abnormalities during stress that resolve at rest (stunning pattern) 5, 6

Step 3: Interpretation Framework

Positive Functional Study (Bridge is Clinically Significant):

• Stress-induced perfusion defect in the territory of the bridged artery that normalizes at rest indicates flow-limiting compression 1, 3
• New or worsening regional wall motion abnormalities during stress in the bridged territory 3, 4
• Presence of LGE suggesting prior ischemic injury 1, 3
• Management: Consider beta-blocker therapy first; if symptoms persist despite optimal medical therapy, surgical unroofing or myotomy may be indicated 5, 6

Negative Functional Study (Bridge is Not Clinically Significant):

• Normal stress perfusion without inducible defects 1, 4
• No stress-induced wall motion abnormalities 3
• No LGE in the bridged territory 1, 3
• Management: Reassure patient; symptoms likely due to alternative etiology; avoid unnecessary revascularization 5, 6

Critical Advantages of CMR Over Alternative Modalities

Why CMR is Superior to Nuclear Imaging:

• CMR provides comprehensive tissue characterization (edema, fibrosis, hemorrhage) in addition to perfusion, allowing detection of non-coronary causes of chest pain 3, 7
• Higher spatial resolution than SPECT enables detection of subendocardial ischemia that may be missed by nuclear techniques 1, 3
• No radiation exposure, particularly important in younger patients with myocardial bridges 1, 4

Why Functional Testing is Essential:

• The European Heart Journal emphasizes that functional assessment (nuclear scintigraphy, stress echo, or CMR) is mandatory in all symptomatic patients with myocardial bridge to determine clinical significance (Class IIa recommendation) 1, 2
• Anatomic demonstration of the bridge by CT or angiography does not predict which patients will have ischemia or benefit from intervention 2, 5

Common Pitfalls to Avoid

Do Not Rely on Resting Imaging Alone:

• Resting echocardiography or resting CMR cannot detect the dynamic flow limitation that occurs during exercise or stress 2, 5
• The bridge compresses during systole, but ischemia manifests during increased demand (exercise), requiring stress testing 5, 6

Do Not Use Nitrates During Testing:

• Nitrates may worsen symptoms in myocardial bridge by increasing heart rate and contractility, exacerbating systolic compression 5, 6
• Beta-blockers are the preferred medical therapy as they reduce heart rate and contractility, decreasing compression 5, 6

Do Not Assume Symptoms are from the Bridge:

• CMR's comprehensive assessment can identify alternative diagnoses (myocarditis, cardiomyopathy, microvascular dysfunction) that may explain symptoms better than the incidentally found bridge 3, 7
• The 2024 ESC guidelines emphasize that stress CMR helps distinguish obstructive CAD from microvascular dysfunction, both of which can coexist with myocardial bridges 1

Alternative Functional Testing (If CMR Unavailable)

Nuclear Myocardial Perfusion Imaging:

• The 2024 ESC guidelines recommend stress SPECT or preferably PET perfusion imaging (Class I, Level B) as an alternative to CMR for diagnosing and quantifying ischemia 1
• PET provides quantitative myocardial blood flow measurement, which may be particularly useful in myocardial bridge assessment 1

Stress Echocardiography:

• Dobutamine stress echocardiography can detect inducible wall motion abnormalities in the bridged territory 1, 4
• Less sensitive than CMR or nuclear imaging for detecting subendocardial ischemia 4