How is myocardial bridging confirmed?

Confirming the Presence of Myocardial Bridging

Coronary angiography remains the gold standard for confirming myocardial bridging, demonstrating the characteristic systolic compression ("milking effect") of the coronary artery during the cardiac cycle. 1, 2

Primary Diagnostic Approach

Invasive Coronary Angiography

• Angiography directly visualizes the pathognomonic "milking effect" - transient systolic compression of the coronary artery that relaxes in diastole, confirming the diagnosis 1, 2
• The systolic compression can be accentuated by intracoronary nitroglycerin injection to enhance visualization 1
• This remains the definitive diagnostic method despite technological advances, as it provides both anatomic and dynamic functional information 2, 3
• Intravascular ultrasound (IVUS) during angiography reveals the characteristic "half-moon" sign and quantifies the extent of phasic arterial compression 1

Non-Invasive Anatomic Confirmation

• Cardiac CT angiography clearly demonstrates the intramural course of the coronary artery, the overlying muscular bands, and surrounding tissues - even in asymptomatic patients without systolic compression 3
• CT provides superior anatomic detail including the length and depth of the intramyocardial course, which are critical prognostic factors (vessels >3 mm deep create greatest vulnerability) 1
• Cardiac MR angiography is preferred in younger patients due to radiation concerns and can demonstrate the anatomic features using specific coronary sequences 1

Functional Assessment After Anatomic Diagnosis

Once myocardial bridging is anatomically confirmed, functional testing is essential to determine clinical significance and guide management:

Stress Testing for Ischemia Detection

• ECG exercise testing, dobutamine stress echocardiography, or myocardial perfusion scintigraphy should be performed to evaluate for inducible ischemia in all symptomatic patients 4, 5, 6
• Nuclear scintigraphy and stress echocardiography detect exercise-induced ischemia that determines whether the bridge is clinically significant 1
• These functional studies guide patient management and sports participation decisions 1, 4

Advanced Hemodynamic Assessment

• Fractional flow reserve (FFR) assessment at baseline and with pharmacological stress quantifies the hemodynamic significance of the bridge 1
• Intracoronary Doppler studies reveal diastolic flow abnormalities that contribute to ischemia 7
• Quantitative coronary angiography demonstrates delayed and incomplete vessel diameter recovery during mid-to-late diastole in symptomatic patients 5

Diagnostic Algorithm by Clinical Context

In Patients with Hypertrophic Cardiomyopathy

• Coronary angiography (CT or invasive) is recommended before surgical myectomy in HCM patients at risk for coronary atherosclerosis 1
• Myocardial bridging occurs in 30-50% of HCM patients and may be demonstrated by specific coronary CMR sequences 1, 4, 5
• The 2024 AHA/ACC HCM guidelines recommend coronary angiography in HCM patients with symptoms or evidence of myocardial ischemia 1

In Athletes and Young Patients

• Initial echocardiographic evaluation should identify coronary ostia from the parasternal short-axis view 1
• If coronary ostia cannot be demonstrated from their proper Valsalva sinus, proceed to CT or CMR angiography based on age and risk profile 1
• CT is recommended by the European Society of Cardiology, while the American Heart Association prefers CMR angiography in younger individuals due to radiation concerns 1

Critical Diagnostic Pitfalls

• Angiography detects only 0.5-4.5% of myocardial bridges versus 15-85% at autopsy, indicating most bridges are clinically silent and only symptomatic bridges produce visible systolic compression 5
• Standard echocardiography has limited ability to directly visualize myocardial bridging; its primary role is assessing LV function and identifying coronary ostia 1
• Do not rely on symptoms alone - the diagnosis requires objective demonstration of either the anatomic abnormality or its functional consequences 1, 7