Coronary Anomalies and Myocardial Bridging

Definition and classification

Coronary anomalies are congenital abnormalities involving the origin, course, distribution, or termination of the coronary arteries. They include anomalous aortic origin of a coronary artery (AAOCA), coronary fistulae, and myocardial bridging. Although many are clinically silent, some produce myocardial ischaemia, ventricular arrhythmias, myocardial infarction, or sudden cardiac death.

Myocardial bridging is an anatomical variant in which a segment of an epicardial coronary artery passes through the myocardium rather than remaining on the epicardial surface. The intramyocardial segment is termed the tunnelled artery. The left anterior descending artery (LAD) is most commonly involved.

The reported prevalence depends substantially on the diagnostic method. Myocardial bridging has been identified in approximately 0.5–12% of angiographic series and up to 5–75% of CT series; other angiographic descriptions report rates of approximately 5–10%, while fewer than 5% of otherwise normal angiograms demonstrate bridging. The wide range reflects differences in ascertainment and imaging technique.

Coronary fistulae represent abnormal communications between a coronary artery and a cardiac chamber or vessel. Other congenital anomalies include anomalous origin of a coronary artery from the pulmonary artery and anomalous origin of one coronary artery from the opposite aortic sinus.

Pathophysiology

Myocardial bridging

During systole, contraction of the overlying myocardium compresses the tunnelled coronary segment, producing an apparent angiographic narrowing. The narrowing generally improves or disappears during diastole, distinguishing myocardial bridging from a fixed coronary stenosis. However, intravascular ultrasound has shown that delayed opening of the bridged segment may extend into diastole, so the physiological effect is not limited to systole.

Exercise may amplify the abnormality through increased myocardial contractility and heart rate. Coronary compression and a Venturi or “suction” effect have been proposed as mechanisms of inducible ischaemia. The functional impact depends on the bridge’s thickness, length, depth, and location, as well as related biomechanical and fluid-dynamic factors. Increased thickness and length, and a more proximal vessel location, are associated with greater clinical risk.

Most bridges do not cause important haemodynamic disturbance. Nevertheless, clinically significant bridging has been associated with exertional angina, myocardial ischaemia, myocardial infarction, ventricular arrhythmias, impaired left ventricular function, myocardial stunning, and sudden cardiac death. It may also be associated with early death after cardiac transplantation.

Myocardial bridging is not itself an atherosclerotic lesion, but it may cause local coronary injury over time. Atherosclerotic disease appears more likely to develop in the arterial segment proximal to the bridge, particularly in older adults. Consequently, an adult with bridging and a substantial proximal atherosclerotic burden should be considered and treated in the same broad category as a patient with coronary artery disease when clinically appropriate.

Other coronary anomalies

Anomalous coronary origin and course can impair coronary perfusion, particularly during vigorous exercise. In AAOCA, high-risk anatomical features include an interarterial course between the aorta and pulmonary artery, a slit-like orifice, a high coronary origin, acute-angle take-off, and an intramural course. An anomalous left coronary artery is less common but more malignant than an anomalous right coronary artery.

Anomalous origin of a coronary artery from the pulmonary artery can result in reduced coronary oxygen content, coronary steal, and myocardial ischaemia. Coronary fistulae create an abnormal connection between a coronary artery and a cardiac chamber or vessel.

Clinical presentation and symptoms

Most myocardial bridges are clinically silent and are discovered incidentally during coronary angiography or CT, sometimes after an abnormal exercise ECG. Symptoms and complications are more likely when the bridge is anatomically substantial or when associated coronary disease or another cardiac disorder is present.

Possible presentations include:

• Exertional angina or chest discomfort

• Exercise-induced myocardial ischaemia

• Syncope, particularly when exertional

• Myocardial infarction

• Ventricular arrhythmias

• Sudden cardiac death

• Depressed left ventricular function

• Myocardial stunning

The relationship between symptoms and bridging must be established functionally, because the anatomical finding alone does not prove that the bridge is clinically significant.

AAOCA is particularly important in younger individuals and during or after vigorous exercise because of its association with sudden cardiac death. Syncope suspected to result from ventricular arrhythmia, angina after exclusion of other causes, and a history of cardiac arrest are concerning presentations.

Evaluation and physical examination

Assessment should establish two separate elements:

• The anatomical characteristics of the coronary anomaly.

• Whether it produces inducible myocardial ischaemia.

For myocardial bridging, anatomical assessment should document the number of bridges, the length and depth of each tunnelled segment, and the location within the coronary tree. The presence of associated hypertrophic cardiomyopathy or other cardiac disease should also be considered.

The history should specifically address:

• Exertional chest pain

• Exercise tolerance

• Syncope or near-syncope

• Palpitations

• Previous myocardial infarction

• Exercise-related cardiac arrest

• Family history of premature coronary disease or sudden death

• Conventional risk factors for coronary artery disease

The source material does not provide a specific set of physical examination findings characteristic of myocardial bridging or other coronary anomalies. Examination should therefore be directed toward identifying associated structural heart disease, ventricular dysfunction, and features suggesting alternative explanations for symptoms.

Diagnostic evaluation

Electrocardiography and exercise testing

An abnormal exercise ECG may lead to the discovery of myocardial bridging, but an anatomical bridge should not be assumed to be clinically important solely because it is present.

A positive inotropic and positive chronotropic stress test is described as the best approach for demonstrating myocardial ischaemia related to myocardial bridging. Functional stress assessment is therefore central to the evaluation of symptomatic patients and those in whom the anatomical finding appears substantial.

In patients with coronary anomalies more broadly, non-pharmacological functional testing is recommended to confirm or exclude myocardial ischaemia. Exercise-based cardiac stress imaging is specifically recommended in patients with AAOCA with an interarterial course, in addition to cardiopulmonary exercise testing.

Coronary angiography

Invasive coronary angiography can demonstrate the characteristic dynamic narrowing of a bridged segment: systolic compression with reduction or disappearance of the narrowing during diastole. Bridging may otherwise be mistaken for a fixed coronary stenosis or may produce a filling defect.

Coronary angiography may also be used to define anomalous coronary anatomy, although CT or MRI-based assessment is recommended as alternative approaches for evaluating anomalous coronary arteries. Invasive physiological assessment may be useful when the clinical significance of a bridge is uncertain; functional consequences can be characterized with intracoronary Doppler measurements.

Coronary CT

Coronary CT is particularly valuable for defining coronary anatomy. In the assessment of coronary anomalies, CT is superior for demonstrating:

• An intramural course

• A slit-like coronary origin

• An acute-angle take-off

• Myocardial bridging

• Coronary plaque

CT angiography is also important in assessing high-risk anatomy in AAOCA, especially when considering intervention in asymptomatic patients.

Cardiac magnetic resonance

Cardiac magnetic resonance can assess coronary anomalies and myocardial ischaemia using stress perfusion. It also provides information about ventricular structure and function and can characterize myocardial fibrosis or scar.

For adults with congenital heart disease, CMR may be used for assessment of coronary anomalies and coronary artery disease, although CT is superior for several specific coronary anatomical features, including myocardial bridging and plaque assessment.

Myocardial perfusion imaging

The functional consequences of myocardial bridging may be evaluated with myocardial perfusion imaging. Non-pharmacological functional imaging—including nuclear imaging, stress echocardiography, or stress CMR with physical stress—is recommended in patients with coronary anomalies to confirm or exclude myocardial ischaemia.

Biomarkers and laboratory findings

The source material does not describe characteristic blood-test abnormalities or specific biomarkers for myocardial bridging or coronary anomalies. Biomarker assessment should therefore be determined by the clinical presentation, particularly when myocardial infarction or acute myocardial injury is suspected, but no specific biomarker strategy is provided here.

Management

General principles

Management is guided by symptoms, objective evidence of ischaemia, coronary anatomy, associated disease, and the presence of complications such as ventricular arrhythmia or myocardial infarction.

An anatomically identified myocardial bridge without associated disease and without inducible ischaemia generally has a good prognosis and does not ordinarily require intervention. The majority of bridges are clinically silent.

Patients with symptoms or demonstrated ischaemia require treatment directed at reducing the physiological consequences of the bridge. In older adults, the proximal coronary segment should be assessed for atherosclerotic disease, because proximal plaque burden may be associated with the bridge and may determine the need for coronary artery disease management.

Medical treatment

Beta-blockers should be used when myocardial bridging is symptomatic or when myocardial ischaemia has been established. The source material does not specify a preferred agent, dose, titration schedule, or target heart rate.

The rationale for beta-blocker treatment is consistent with reducing the exercise-related physiological burden of the bridge by addressing the positive chronotropic and inotropic conditions under which ischaemia is most likely to occur. Treatment should be individualized according to symptoms, ventricular function, blood pressure, and coexisting disease.

No other drug class, dose, or specific pharmacological regimen is provided in the source material for myocardial bridging or coronary anomalies.

Surgical treatment

Surgical repair may be considered in selected patients with symptomatic or functionally significant myocardial bridging, particularly when symptoms or ischaemia persist despite medical treatment. The source material does not define a specific operative technique or provide selection criteria beyond the presence of clinically significant disease.

For AAOCA, surgery is recommended in patients with:

• Cardiac arrest

• Syncope suspected to be due to ventricular arrhythmias

• Angina when other causes have been excluded

Surgery should be considered in asymptomatic patients with evidence of myocardial ischaemia or with anomalous origin of the left coronary artery and high-risk anatomy.

Coronary stenting

Coronary stenting is discouraged for myocardial bridging. The source material does not provide procedural outcomes or a detailed explanation for this recommendation, but stenting should not be regarded as the routine alternative to medical or surgical management.

Guideline recommendations

The principal recommendations relevant to coronary anomalies and myocardial bridging are summarized below.

High-risk anatomy in AAOCA includes an interarterial course, slit-like orifice, high orifice, acute-angle take-off, and an intramural course, including its length.

For myocardial bridging specifically, beta-blockers are recommended when symptoms or ischaemia are present, surgical repair may be considered in selected cases, and coronary stenting is discouraged. A bridge without inducible ischaemia and without associated disease generally carries a good prognosis.

Prognosis and follow-up

The prognosis of myocardial bridging is usually favourable when there is no associated cardiac disease and no inducible myocardial ischaemia. Most bridges remain clinically silent.

Risk is increased by:

• Greater bridge thickness

• Greater bridge length

• A proximal coronary location

• Demonstrated inducible ischaemia

• Coexisting coronary atherosclerosis, particularly proximal to the bridge

• Associated cardiomyopathy

• Ventricular arrhythmias

Clinically significant myocardial bridging has been associated with myocardial infarction, ventricular arrhythmias, myocardial dysfunction, myocardial stunning, and sudden cardiac death, although these complications are uncommon relative to the frequency of the anatomical finding.

Follow-up should be proportionate to symptoms, ischaemia, anatomy, and associated disease. Patients without symptoms or inducible ischaemia generally require no intervention beyond appropriate clinical assessment. Symptomatic patients and those with documented ischaemia require reassessment of symptoms and functional status after treatment. Patients with significant coronary anomalies, high-risk AAOCA anatomy, or previous surgery require ongoing clinical and functional evaluation; exercise stress imaging is specifically indicated after surgery in patients with a history of aborted cardiac arrest.