Myocardial bridge is an anomaly characterized by intramyocardial paths of an epicardial coronary artery segment. It was found during autopsies in 1737 and described angiographically in 1960. Typical angiographic aspect of myocardial bridge is systolic narrowing of the artery, alternatively with returning to normal during the diastolic phase of the cardiac cycle. Describing image: “milking effect” or “step up-step down.” This entity is more common than previously thought with angiographic incidence of about 15% but can reach 60% in some studies, being present in 1/3 of adults. Appears most commonly in middle segment of LAD (anterior interventricular artery), rarely on LCX (circumflex artery) and RCA (right coronary artery).
Although it has been considered to be a variant of normal coronary anatomy it was shown that it may have potential clinical relevance.
The pathophysiological mechanism of clinical manifestations is linked on the one hand to a tendency for patients with myocardial bridge to develop atherosclerosis, muscle and, on the other hand can be linked with systolic compression mechanism itself. It has been shown that coronary artery intima beneath the bridge undergoes specific morphological changes of arterial endothelium, also vasoactive agents (endothelin-1, angiotensin-convertase, endothelial nitric oxide-synthase, eNOS) expression were lower and below bridge atherosclerotic process is more diminished or absent. Instead data from studies suggest that myocardial bridging is frequently associated with the development of atherosclerosis in the proximal segments of the involved coronary artery.
As systole contributes only with 15% of coronary flow and the bridge is a systolic phenomenon, the clinical relevance appears only in particular situations such as tachycardia. Tachycardia can cause myocardial ischemia and arrhythmias by a shortened diastolic phase and increased systolic flow increased.
In terms of clinical manifestations: angina pectoris, myocardial infarction, AV block, supraventricular and ventricular tachycardia, sudden death. Given the high prevalence of myocardial bridging, however among patients these complications are rare. Patients may complain of typical chest pain accompanied by ECG changes during effort test, myocardial scintigraphy at effort. Coronary angiography, MS-CT, cardiac MRI can show the bridge. IVUS and intracoronary Doppler studies have shown that there is a degree of compression during the diastolic phase, accompanied by hemodynamic changes characteristic mainly in early diastolic phase.
The management is primarily based on drugs: beta-blockers and calcium-blockers as first-line therapy, these drugs group reduce the heart rate, increase diastolic interval and lower systolic compression. Nitrates are avoided. In selected cases at severely symptomatic patients, suspected to be at high risk, the involved coronary artery requires surgical approach.
A particular aspect to be noted in young patients with AMI with ST-segment elevation (with clinical presentation, ECG, enzyme) when coronary angiography reveals no coronary atherosclerotic lesions, but no obvious myocardial bridge. After 5-7 days repeating the invasive exploration may highlight the presence of myocardial bridge that during the acute episode was not visible due to acute kinetic disorder.
Myocardial bridges are usually clinically apparent in young men. Given the relatively high epidemiological prevalence, clinical suspicion should be considered in all cases of typical or atypical chest pain in young patients with low probability of atherosclerosis disease and no cardiovascular risk factors.
Traditionally myocardial bridges were considered benign, but multiple studies have demonstrated the potential of clinical complications that can be dangerous including myocardial ischemia and MI, coronary spasm, rupture of interventricular septum, supraventricular and ventricular arrhythmias, sudden death.
The prognosis of patients with myocardial bridge is not as benign as previously thought, and once detected, it should be treated and monitored actively.