Incidentally Detected Myocardial Bridging of the Left Circumflex Coronary Artery in a Young Male

INTRODUCTION Myocardial bridging (MB) is known to be usually present since birth but generally manifests in the 20–30 years' age group and has an association with physical exertion.[1,2] The phenomenon of the intramyocardial course of the coronary artery usually goes unnoticed since blood flow through the coronaries primarily happens during diastole.[2-4] The incidence of MB depends on the methodology to detect its variant. Based on certain autopsy series, its incidence rate has been noted to reach 80%.[2,3] The mechanism and pathophysiology for the symptomatology of MB have been linked to atherosclerosis.[1] The compression of the coronary artery by an MB during systole can lead to significant ischaemia in the presence or absence of concomitant atherosclerosis.[3-5] Angiography reveals that MB shows obliteration of the epicardial artery during systole. Since the blood flow is maintained during the diastole, the condition usually presents itself during stressful events such as tachycardia.[1,2] CASE REPORT A 22-year-old male had a history of road traffic accidents and died due to intracranial haemorrhage and brain damage. The patient was not a known case of diabetes mellitus or hypertension or coronary heart disease. He was examined by a doctor in the Forensic Medicine Department at All India Institute of Medical Sciences, Rishikesh. An autopsy was performed, and on examination, the heart had a very firm consistency with thickening of the left ventricular wall with the decrease in chamber size. The whole heart was sent for histopathological analysis to the Pathology Department. The whole heart specimen weighed 254 g and measured 14 cm × 8.5 cm × 6.5 cm. The right ventricular wall measured 1.6 cm in thickness. Interventricular septa was 1.7 cm in thickness. On serial slicing, no areas of infarction were identified and appeared grossly unremarkable. There were no vegetations on the valves (bicuspid, tricuspid and semilunar). Right coronary artery and left anterior descending coronary artery (LAD) showed normal epicardial course [Figure 1a]; however, the left circumflex artery revealed 1 cm of intramyocardial course (MB or tunnelled segment) [Figure 1b]. No atheromatous changes were identified grossly. Sections were given from the right atrioventricular junction, right ventricular wall, left atrioventricular junction, left ventricular wall, left circumflex artery, LAD artery, right coronary artery, mitral valve, tricuspid valve, semilunar valve, interventricular septum, aortic stump and pulmonary artery. Microscopy from LAD showed an epicardial course with atherosclerotic changes with 40% blockage of the lumen and mild myxoid degeneration [Figure 1c]. Sections from the left circumflex artery showed features of a myocardial bridge covering the entire circumference of the artery and forming a tunnel [Figure 1d]. Microscopy from the left ventricular wall muscles showed patchy areas of fibrosis. Sections from valves show unremarkable histology.Figure 1: (a) Gross dissection shows the left anterior descending (LAD) coronary artery with the ordinary epicardial course (green arrow). (b) Gross image demonstrating left circumflex coronary artery with myocardial bridging (covered by 360° by myocardial muscle fibers) (red arrow). (c) Microscopy image (Masson's trichrome stain, ×2) showing LAD coronary artery shows atherosclerotic changes with luminal narrowing along with medial myxoid degeneration of arterial wall. (d) Photomicrograph of the left circumflex coronary artery shows 360° encircled by the myocardial muscle fibers (H and E, ×4)DISCUSSION The most commonly affected artery is the LAD coronary (70% in necropsy series), and very frequently, multiple bridges may be found in the heart affecting the same vessel or separate ones. Usually, the mid-segment of the LAD is affected.[2,3] The MBs of LAD arteries have been categorised according to the anatomy into superficial and deep.[5] MBs can be categorised into benign and pathological based on the length of the tunnelled segment. In general, when the segment measures 20–30 mm, it is called pathological and may present with ischaemia, infarction, arrhythmias and sudden death, but a shorter bridge may also cause ischaemic death, according to a few reports.[3,4] The other arteries which may also be affected by an MB are the right coronary, left circumflex, diagonal and marginal branches.[2] The part of the artery proximal to the MB may show features of atherosclerosis, while the segment under the MB might be relatively spared.[4,5] Provocation tests gave a better result in the detection of MB than angiography. Numerous new techniques such as coronary computed tomography, angiography and intravascular ultrasound have proved useful in ruling out the other causes for the same.[1-3] Intracoronary Doppler proves to be a useful tool to assess the anterograde flow of blood in patients with MB. The clinical features that may be associated with MB are (a) Chest pain: The most common symptom of MB is chest pain, which can be described as a squeezing, pressure-like sensation. The pain is typically brought on by physical activity and may be relieved by rest. (b) Shortness of breath: Some people with MB may experience shortness of breath, especially during exertion. (c) Palpitations: In some cases, MB can cause palpitations or a sensation of rapid or irregular heartbeats. (d) Fatigue: Fatigue or a general feeling of weakness may also be present in people with MB. (e) Arrhythmias: MB has been associated with the development of arrhythmias or abnormal heart rhythms. (f) Syncope: Rarely, MB can lead to syncope, or fainting, particularly during physical activity.[5-7] It is important to note that many people with MB may not experience any symptoms at all, and the condition is often discovered incidentally during imaging studies done for other reasons. Acute coronary syndromes, arrhythmias (including supraventricular tachycardia and ventricular tachycardia), exercise-induced atrioventricular conduction blocks, transient ventricular dysfunction and sudden death have all been reported as clinical complications of myocardial bridges.[3-5] The histopathological differential diagnosis of MB includes (a) Atherosclerosis: A condition characterised by the buildup of plaques within the arterial wall, which can cause stenosis or occlusion of the lumen. It may be associated with MB. (b) Fibromuscular dysplasia: A condition characterised by abnormal growth of the arterial wall, leading to stenosis or aneurysm formation. It may also be associated with MB. (c) Arteritis: An inflammation of the arterial wall that can cause stenosis or occlusion. It can be caused by infectious, autoimmune or other systemic diseases. (d) Vascular Ehlers–Danlos syndrome: A genetic disorder characterised by abnormalities in the connective tissue of the arterial wall. It can cause aneurysm formation and rupture. (e) Coronary artery dissection: A rare condition, in which the arterial wall splits apart, causing a separation between the layers of the arterial wall. It can cause acute myocardial infarction. (f) Takayasu arteritis: A type of arteritis that affects the aorta and its branches. It can cause stenosis or occlusion of the arterial lumen and may be associated with MB.[7-9] The histopathological features of MB include (a) Compression of the arterial lumen: MB occurs when a segment of a coronary artery tunnels through the heart muscle, which can cause compression of the arterial lumen. This compression can be observed histologically as a narrowing of the lumen diameter. (b) Thickening of the arterial wall: The arterial wall in the area of the myocardial bridge may be thicker than normal, which can be due to the hypertrophy of the smooth muscle cells and/or the deposition of collagen and extracellular matrix proteins. (c) Intimal thickening: The intima is the innermost layer of the arterial wall, and in MB, it may be thickened due to smooth muscle cell hypertrophy, collagen deposition or other pathological changes. (d) Luminal fibrous ridge: In some cases, a luminal fibrous ridge may be observed in the area of the myocardial bridge, which is a fibrous tissue mass that protrudes into the arterial lumen and can cause further narrowing of the arterial diameter. (e) Myocardial changes: The heart muscle underlying the myocardial bridge may show signs of compression, such as fibrosis or ischaemic changes. (f) Inflammatory changes: Inflammatory cells may be present in the arterial wall and/or in the surrounding tissues, indicating an ongoing immune response. (g) Vascular changes: The vasa vasorum, which are small blood vessels that supply the arterial wall with nutrients and oxygen, may be enlarged in the area of the myocardial bridge. Histopathological examination of the arterial wall is essential for the diagnosis of MB and can provide important information about the underlying pathological changes.[3-5,7-9] To summarise, MB is a difficult diagnosis to make because it can affect anyone of any age. It is possible that the patient will remain symptom-free. The most common way to diagnose this puzzling condition is through necropsy or autopsy examinations. Although uncommon, MB should be considered when treating a young patient with chest discomfort and other signs. Authors' contributions All Authors Contributed equally in the preparation of this manuscript. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for his images and other clinical information to be reported in the journal. The patient understands that name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest. Declaration of generative AI and AI-assisted technologies in the writing process During the preparation of this work, the author(s) used (mention the name of tool/service used) in order to (mention the reason for using AI tool). After using this tool/service, the author(s) reviewed and edited the content as needed and take(s) full responsibility for the content of the publication.