Discussion

Myocardial bridges, coronary artery segments coursing into the myocardium, can be asymptomatic variants but may need therapy when causing ischaemia.^{Reference Ishikawa, Kawawa, Kohda, Shimada and Ishii1} They almost exclusively affect the left anterior descending coronary artery and have rarely been reported in children^{Reference Kiess, Vollroth and Bakhtiary2} or in association with CHD.^{Reference Kiess, Vollroth and Bakhtiary2,Reference Zaidi and Gumina3}

Ischaemia related to myocardial bridges may be due to direct compression during cardiac systole as well as endothelial injury of the vessel proximal to the myocardial bridge due to abnormal haemodynamics resulting in coronary atherosclerosis and stenosis.^{Reference Ishikawa, Kawawa, Kohda, Shimada and Ishii1} The latter is probably the reason that myocardial bridges often become symptomatic later in life despite their presence since birth. Exercise-induced ischaemia is due to tachycardia, increasing myocardial oxygen requirement and decreasing diastolic coronary flow.^{Reference Pérez-Pomares, de la Pompa and Franco4} Myocardial bridges have been reported in myocardial diseases such as dilated, noncompaction^{Reference Imbalzano, Ceravolo, Di Stefano, Vatrano and Saitta5} and more commonly hypertrophic cardiomyopathy.^{Reference Basso, Thiene, Mackey-Bojack, Frigo, Corrado and Maron6} Although most patients with myocardial bridges remain asymptomatic, symptoms like angina, exertional chest pain, or dyspnoea may develop,^{Reference Rubinshtein, Gaspar, Lewis, Prasad, Peled and Halon7} and ventricular arrhythmia, myocardial infarction, syncope, and sudden death have been reported.^{Reference Ishikawa, Kawawa, Kohda, Shimada and Ishii1}

Myocardial bridges in children have been described usually in the presence of ventricular hypertrophy and hypertrophic cardiomyopathy, while ventricular fibrillation, syncope, and cardiac arrest have been reported as presenting symptoms more often in children.^{Reference Kiess, Vollroth and Bakhtiary2,Reference Sharma, Hellenbrand, Kleinman and Mosca8} Myocardial bridging in association with structural CHD has been reported only in a neonate with coarctation, ventricular septal defect, and parachute mitral valve^{Reference Kiess, Vollroth and Bakhtiary2} and an adult with transposition of the great arteries after Mustard procedure.^{Reference Zaidi and Gumina3} Our case and these two reports prove that myocardial bridges can exist in patients with CHD and may account for their symptomatology. This fact is important as symptoms of myocardial bridges may be mistakenly attributed to residual CHD thus delaying diagnosis and, also, because young patients with significant structural heart disease and dysfunction may be more susceptible to life-threatening complications of myocardial bridges, such as arrhythmias and sudden death.

Myocardial bridges are usually visualised with invasive coronary angiography showing the milking or squeezing of the affected coronary artery, but can also be depicted and possibly quantified using intracoronary ultrasound, MRI, and CT.^{Reference Zaidi and Gumina3} Multidetector CT offers increased detection rates of myocardial bridging due to its higher resolution as well as the direct depiction of the myocardial bridge muscle.^{Reference Ishikawa, Kawawa, Kohda, Shimada and Ishii1} Exercise stress testing, nuclear scintigraphy, coronary flow reserve evaluation by echocardiography, fractional flow reserve measurement, and myocardial perfusion imaging may be helpful in assessing the clinical relevance of myocardial bridging in affected patients.^{Reference Tang, Wang and Shi9}

No treatment is required for asymptomatic patients with incidental diagnosis of myocardial bridging as this condition usually has a benign course. Symptomatic patients with myocardial bridges generally respond well to β-blockers as ischaemia usually manifests during tachycardia and stress, while nitrates should be avoided as they may exacerbate symptoms. Patients refractory to medical therapy have been successfully treated with percutaneous coronary intervention with the risks of stent fracture and coronary perforation, as well as with surgical myotomy and unroofing,^{Reference Ishikawa, Kawawa, Kohda, Shimada and Ishii1} a procedure that has been reported successful even in children.^{Reference Sharma, Hellenbrand, Kleinman and Mosca8,Reference Seki, Ramesh Janai, Bakhtiary and Kostelka10}

In conclusion, myocardial bridging may exist in patients with CHD, as this case illustrates. Physicians should be aware of this possibility in the differential diagnosis of symptoms in CHD patients so that appropriate diagnostic and therapeutic strategies can be applied in this population.