A segment of the epicardial coronary artery embedded in the overlying myocardial tissue is known as myocardial bridging. Myocardial bridging is often an incidental finding in adults, whereas childhood myocardial bridging is almost always associated with hypertrophic cardiomyopathy or left ventricular hypertrophy.Reference Yetman, McCrindle, McDonald, Freedom and Gow 1 Moreover, isolated myocardial bridgings have been found at autopsy in adolescents who had a cardiac arrest during strenuous physical activity.Reference Corrado, Thiene, Cocco and Frescura 2 However, after new diagnostic modalities such as quantitative coronary angiography, intravascular ultrasound, and intracoronary Doppler flow velocity measurements became available, the number of newly diagnosed asymptomatic patients with myocardial bridging also increased.Reference Bourassa, Butriaru, Lesperance and Tardif 3
Discrete membranous subaortic stenosis can never be seen at birth, but different members of the same family might be affected. Although the genetic basis of discrete subaortic stenosis is still unknown, familial incidences suggest a multi-factorial model of inheritance in association with environmental factors. Apart from isolated cases, subaortic stenosis might also be associated with other anomalies.Reference Abdallah, Toomey, O'Riordan, Davidson and Marks 4
Here, we describe the case of a 13-year-old asymptomatic girl who was diagnosed with myocardial bridging during her follow-up for discrete subaortic stenosis.
Case report
A 13-year-old asymptomatic girl was being followed up for the diagnosis of mild discrete subaortic stenosis. Her family history revealed an 11-year-old brother who was being followed up for mild discrete subaortic stenosis and died suddenly during exercise. He was also asymptomatic and had no signs of ischaemia on follow-up visits. Her 16-year-old brother is also being followed up for mild subaortic stenosis and is asymptomatic.
Her physical examination revealed a 2/6 sytolic murmur, best heard at the second and third left intercostal area, with no additional pathological findings. The electrocardiographies on follow-up were normal, without any ischaemic findings, but negative T waves in lead V5–V6 were determined recently. Transthoracic echocardiography revealed mild discrete subaortic stenosis with a left ventricular–aortic systolic pressure gradient of 25 mmHg. The 24-hour electrocardiography evaluation was also normal. An exercise stress test, which was normal 3 years ago, revealed a 1 mm ST segment depression without any symptom on recent examination.
Owing to a family history of sudden cardiac death and ischaemic findings on the exercise test, a computed tomography angiography of the heart was performed. It revealed that a segment in the middle part of the left anterior descending artery was embedded in the myocardium. On the basis of these findings, the patient underwent cardiac catheter angiography. After the diagonal 2 division of the left anterior descending artery, a short segment of myocardial bridging with a 70–80% narrowing was observed. Just 1 cm distal to this segment, another myocardial bridging of 20 mm length with a positive milking effect of 100% systolic compression was also seen (Figs 1 and 2; Supplementary videos: 1, 2). The myocardial fractional flow reserve was 0.80 with 120 mcg adenosine. The systolic gradient between the left ventricle outlet and the ascending aorta was 15 mmHg. To reveal the ischaemic effect of myocardial bridging, myocardial perfusion scintigraphy was performed. The scan revealed anterior and anteroseptal ischaemia at the apical part of the left ventricle.
Figure 1 The left anterior descending coronary artery before systolic compression.
Figure 2 Systolic compression of the left anterior descending coronary artery.
β-Blocker therapy was initiated. Thereafter, she was operated upon successfully for myocardial bridging and discrete subaortic stenosis. The post-operative echocardiogram was normal, and the exercise stress test showed no signs of ischaemia.
Discussion
Coronary arteries and their major branches lie on the surface of the heart. When a band of myocardial muscle fibres overlies a segment of the coronary artery, which results in mechanical stenosis secondary to systolic compression, a condition termed as myocardial bridging occurs. The incidence of myocardial bridging in the general population is between <5% and 86% in different series, according to the method used to determine the bridging.Reference Mohlenkamp, Hort Wge and Erbel 5 Such a wide discrepancy suggests that only a minority of patients with myocardial bridging are in fact at risk of clinical symptoms and cardiac events.
Myocardial bridging is usually seen in the setting of hypertrophic cardiomyopathy or left ventricular hypertrophy and is rarely reported in an otherwise structurally normal heart. The incidence of myocardial bridging among children with hypertrophic cardiomyopathy on coronary angiography varies between 28% and 40%.Reference Yetman, McCrindle, McDonald, Freedom and Gow 1 , Reference Mohiddin, Begley, Shih and Fananapazir 6 As selective coronary angiography is not a routine procedure for children, the exact incidence of myocardial bridging among healthy children and patients, other than those having hypertrophic cardiomyopathy, is not known. Yet, symptomatic myocardial bridging probably occurs in a small subgroup of children, in whom ischaemic symptoms can be linked directly to their myocardial bridging. Sharma reported symptomatic myocardial bridgings in children. All patients included his study had significant symptoms of chest pain or syncope with exertion or cardiac arrest, supported by the evidence of coronary ischaemia linked to myocardial bridging, which ultimately resolved after mechanical decompression in short-term follow-up. Further, all his patients had hypertrophic cardiomyopathy or left ventricle hypertrophy, in contradistinction to our patient.Reference Sharma, Hellenbrand, Kleinman and Mosca 7
Myocardial bridgings are most commonly located over the middle segment of the left anterior descending coronary artery and may occasionally involve the diagonal branches, the posterior descending right coronary artery, and the marginal branch of the circumflex artery.Reference Bourassa, Butriaru, Lesperance and Tardif 3 In our patient, two different parts of the left anterior descending artery followed an intramural course, causing a 70–80% and 100% narrowing during systole, respectively. Over 90% systolic compression of the tunnelled coronary segment with an ongoing diastolic compression of at least 50% characterises a significant myocardial bridging, as was seen in our case.Reference Mohlenkamp, Hort Wge and Erbel 5 It is surprising that our patient never displayed symptoms, even during tremendous exercise.
Discrete subaortic stenosis can be seen in different members of the same family. The genetic basis of this disease is still indefinite. Some authors propose an autosomal recessive condition, whereas others propose an autosomal dominant inheritance pattern.Reference Petsas, Anastassiades, Constantinou and Antonopoulos 8 A multi-factorial model of inheritance, in association with environmental factors, may be involved in the pathogenesis. A familial incidence of discrete subaortic stenosis, although very rare, signifies the screening of family members.Reference Fatimi, Ahman, Javed, Shamim and Ahmad 9 In our case, three members of the same family had mild subaortic stenosis.
Myocardial bridging is usually a benign condition with a long-term survival but can also cause myocardial ischaemia, myocardial infarction, exercise-induced tachycardia, conduction disturbances, and sudden death. Our patient was symptom-free in her daily life but had ischaemic findings during the exercise stress test. We estimate that her brother who died suddenly during exercise also had myocardial bridging with discrete subaortic stenosis. Therefore, we recommended her elderly brother to undergo coronary angiography, although he is asymptomatic.
In patients with myocardial bridging, medical or surgical management remains controversial. To date, however, there is no convincing evidence that surgery improves morbidity or mortality in patients with bridging.Reference Downar, Williams, McDonald, Wigle and McCrindle 10 Nitrates, β-blockers, and calcium channel blockers could be used for symptomatic relief. Surgery could be the choice for severe cases. Although our patient was asymptomatic but had a myocardial bridging segment of 100% narrowing, surgical decompression was performed. After surgery, she remained asymptomatic, and the signs of ischaemia on the exercise test resolved.
Our case is different from those reported in the literature, as our patient had neither left ventricular hypertrophy nor hypertrophic cardiomyopathy on echocardiography but had severe myocardial bridging on angiography. This case is also unique as the myocardial bridging was concomitant with familial subaortic stenosis.
Acknowledgements
We are grateful to Professor Dr Tevfik Gurmen for his kind contribution to the coronary angiography evaluation of the patient.
Financial Support
This research received no specific grant from any funding agency, commercial or not-for-profit sectors.
Conflicts of Interest
None.
Ethical Standards
Informed consent was obtained from parents of the patients before performing catheter angiography, and the study was reviewed and approved by the Ethical Committee of Cerrahpasa Medical Faculty, Istanbul University.
