European Journal of Cardiovascular Medicine

Myocardial bridging is a congenital anomaly, where a segment of an epicardial coronary artery is covered by myocardial fibres for a variable distance and the underlying arterial segment is described as a mural coronary artery or a tunnelled artery. The history of myocardial bridges dates back to 1737 when it was first recognized by Reyman and then by Black in 1805. The first detailed post mortem examination of myocardial bridges was done by Geiringer in 1951 and the first radiological description was given by Portmann and Iwig in 1960. The bridged segment of the coronary artery is susceptible to various pathophysiological mechanisms leading to myocardial ischemia, especially when associated with other cardiovascular diseases. The myocardial bridges were initially thought to be innocent bystanders in the development of acute coronary syndromes. But in the last two decades, the outlook has changed with the increasing incidence of sudden cardiac deaths in young athletes, where myocardial bridges were the only finding at autopsy. The mechanism by which the myocardial bridges induce clinical symptoms is uncertain, but among the proposed are vasospasm, thrombus formation, endothelial dysfunction and impaired coronary flow reserve. Most important of these is the dynamic systolic compression of the tunnelled artery with sustained early diastolic diameter reduction.

The major arteries and their main branches run subepicardially or they may be overlapped by the lips of myocardium. But the major coronary branches are intra myocardial. The myocardium in that case forms myocardial bridges. Recently it has been discussed that the muscular bridges are regarded as a cause for myocardial ischemia. Selective angiography reveals that during systole, the muscular bridge exercises a milking effect over the underlying coronary artery segment.

The aim of this study is to provide more information on the incidence of myocardial bridges, arterial preponderance for myocardial bridging, the length of the bridged segment as this discovery is important for patients who complain of angina symptoms without any coronary arterial stenosis. In such cases ischemia may be caused by muscular bridge. Myocardial bridges may complicate coronary artery bypass surgery.

The study was carried out on 40 embalmed heart specimens preserved in the Department of Anatomy, Dr. PSIMS, chinnavutapalli, Gannavaram Mandalam, Krishna District and Andhra Medical College, Visakhapatnam. These heart specimens were collected from cadavers of 40-65 age groups. The specimens were numbered and preserved in 10% formalin solution. The specimens were observed for the presence of myocardial bridges; its length and the artery covered by this myocardial bridge was noted.

In the present study two myocardial bridges were noticed which accounts for about 5% of the total cases as shown in fig 1.

In one case, the myocardial bridge was covering the beginning of the Anterior interventricular artery. The myocardial bridge measured 3.5cm in length. From below the bridge the lower part of the Anterior interventricular artery emerged and traversed on the surface of the Anterior interventricular septum (Fig 2).

Fig No. 2- Myocardial Bridge covering AIVA

AIVA - Anterior Interventricular Artery   MB - Myocardial Bridge

The second myocardial bridge was noticed bridging the lower part of the left marginal artery (Fig 3). In this case also the myocardial bridge was long. It is difficult to detect the presence of myocardial bridges and may only be found during surgery which may complicate the course of the intervention.

Fig No. 3: Myocardial Bridge covering the lower part of Marginal Artery

(Left lateral view of heart)

AIVA - Anterior Interventricular Artery

MA -Marginal Artery

CxA - Circumflex Artery

MB - Myocardial Bridge

PT - Pulmonary Trunk.

The main coronary arteries and their major branches run subepicardially and they will be overlapped by lips of myocardium. Occasionally during their course they penetrate the myocardium and run through the myocardium. The possible reasons for their occurrence could be as follows:

Embryological Consideration:

Embryologically, there are two theories for the development of myocardial bridges.

1. The myocardial bridges are primary structures, which are isolated from the rest of the myocardium by the sudden, intra myocardial course taken by the coronary artery.
2. The myocardial bridges are secondary structures, which are formed by the migration of the myocytes over the sub-epicardial coronary artery.

 Comparative Anatomy: The coronary arteries are classified into three types with respect to the presence or absence of the myocardial bridges.

Type I: Coronary arteries are intra myocardial as seen in rodents, goats and sheep.

Type II: Coronary arteries are predominantly sub epicardial; myocardial bridges are occasionally present as in humans, gorilla and carnivores.

Type III: Coronary arteries are always sub epicardial as seen in horses and pigs.

Myocardial Bridges/ Coronary Mural/ Submerged Artery: This phenomenon was first described by Reyman (1737) and has received a number of names: myocardial bridge, the portion of the myocardium that covers the artery (Tandler 1912; Polacek 1961; Angelini et al, 1983), and the coronary mural (Geiringer 1951) or submerged artery (Hadziselimovic 1982) the portion of the artery that is covered by the myocardium. Table I shows the percentages of myocardial bridge detected using a range of techniques. Dissection is the technique that offers the highest frequency, surpassing 50% of cases in some series. The most frequent location is above the anterior interventricular artery, especially in its middle third, followed by the left marginal artery. Noble et al (1976) described the milking effect of the myocardial bridges on the coronary arteries. Sometimes, the contraction of myocardial bridges may reduce the caliber of the artery by more than 75%, and so in situations requiring a substantial oxygen supply to the myocardial cells, the electrocardiogram may present anomalies compatible with ischemia and lactate production. This is the basis for the hypothesis that the myocardial bridges may be the cause of myocardial ischemia (Noble et al, 1976; Voelker et al, 1988). The morphometric characteristics of the nuclei of the fibers of the myocardial bridges are different from those of the adjacent myocardial cells, leading Reig et al (1990) to suggest that the fibers of the myocardial bridges were less functional than those in the rest of the myocardium. The myocardial bridges are a risk factor for certain surgical interventions, in particular aorto-coronary bypasses that affect the anterior interventricular artery. This is because the submerged portion of the artery is only a few millimeters from the right ventricle, and there is a risk of perforation during the surgical maneuvers to identify the artery. In addition, in cases that involves the handling of the right infundibulum –for instance, to repair congenital tronco-conal cardiopathies or to replace cardiac valves– a conal artery, or the initial portion of an acute marginal artery, partially covered by a myocardial bridge, may be sectioned. Presumably, too, only a part of the myocardial bridges produces a systolic contraction that can be detected by coronary angiography, and so on many occasions the myocardial bridge may only be found during surgery, which may complicate the course of the intervention.

In the present case only in 5% of cases the myocardial bridges were noted. Edward et al observed 276 cases and noticed myocardial bridges in 5.4% of cases. Angelini et al studied 1100 hearts and noticed myocardial bridges in 5.5% cases. Binia et al studied 600 hearts and noticed myocardial bridges in 4% of cases. The present findings of the bridges tallied with findings of Edward et al, Angelini et al and Binia et al.

Table 19. Characteristics of myocardial bridges in published series

In the present study only two myocardial bridges were noticed. From the present study, we infer that the presence of myocardial bridges in an unsuspected population is relatively higher. The definitive role of these bridges in acute coronary syndromes is yet uncertain. But owing to its higher rate of detection in those with myocardial ischemia, it is better to screen for the bridges along with other causative factors and treat the patients prophylactically. CT Coronary Angiography is found to be the investigation of choice in detection of these myocardial bridges.

The myocardial bridges may cause milking effect on the vessels. They are risk factors for certain surgical interventions and cardiac surgeries. Hence a knowledge of the presence and extent of these myocardial bridges is considered important for the cardiologists in treating the patients with acute coronary symptoms.

FUNDING: Nil

CONFLICT OF INTEREST: None Declared

1. Reyman HC. Dissertation de vasis cordis propriis. Haller Bibl Anat 1737;2:366.
2. Black S. A case of angina pectoris with dissection. Memoirs Med Soc Lond 1805;6:41
3. Geiringer E. The mural coronary. Am Heart J 1951;41(3):359-68
4. Porstmann W, Iwig J. Intramural coronary vessels in the angiogram. Fortschr Geb Rontgenstr Nuklearmed 1960;92:129-33.
5. Polacek P, Kralove H. Relation of myocardial bridges and loops on the coronary arteries to coronary occlusion. Am Heart J 1961;61(1):44-52.
6. Angelini P, Trivellato M, Donis J, et al. Myocardial bridges: a review. Prog Cardiovasc Dis 1983;26(1):75- 88
7. Noble J, Bourassa MG, Petitclerc R and Dyrda I. Myocardial bridging and milking effect of the left anterior descending coronary artery: Normal variant or obstruction? Am J Cardiol. 1976; 37: 993-999.
8. Voelker W, Ickrath O, Mauser M, Schick KD, Karsch KR. Anterior wall infarct in an angiographically demonstrated muscle bridge of the ramus interventricularis anterior. Dtsch Med Wochenschr. 1988; 113: 551- 554.
9. Reig J, Ruiz C, Moragas A. Morphometrical analysis of myocardial bridges in children with ventricular hypertrophy. Ped Cardiol. 1990; 11:186-190.
10. Edwards JC, Burnsides C, Lansing AI, et al. Arteriosclerosis in the intramural and extramural portions of coronary arteries in the human heart. Circulation 1956;13(2):235-41.
11. Irvin RG. The angiographic prevalence of myocardial bridging in man. Chest. 1982; 81: 198-202
12. Reig J, Petit M. Main trunk of the left coronary artery: Anatomic study of the parameters of clinical interest. Clinical Anatomy. 2004; 17: 6-13
13. Suganya saminathan J. Evolution Med. Dent. Sci./eISSN- 2278-4802, pISSN- 2278-4748 Jan. 14, 2019;133-136.