The relationship between the directions of myocardial bridges and of the branches of the coronary arteries in the human heart

Plaque morphology and distribution in patients with and without myocardial bridge - an intravascular ultrasound study

BACKGROUND

Myocardial bridging (MB) is a common congenital cardiovascular anomaly. There are reported associations of MB with different clinical presentations like effort angina, acute coronary syndromes (ACS) and sudden cardiac death. Acceleration of atherosclerosis in proximal vessel is reported in patients with MB, while bridged segments are reported to be free of atherosclerosis.

METHODS

We assessed patients who underwent intravascular ultrasound (IVUS) guided percutaneous intervention (PCI) of left anterior descending (LAD) artery. Plaque characteristics derived from IVUS analysis were compared between those who displayed myocardial bridge versus those who did not harbour the anomaly.

RESULTS

One hundred and forty-seven (147) patients underwent IVUS guided PCI. Incidence of MB was 44/147 (29.9%). Mean age of patients who had MB {+} was higher (62.1 ± 10.3 vs. 57.8 ± 11.2 (p = .03). 142/147 (96.6%) patients presented with ACS. ST elevation myocardial infarction (STEMI) was the most common presenting diagnosis (110/147 to 74.8%). There were no differences in qualitative plaque characteristics - attenuated plaque, calcification or calcium score between two groups. Plaque burden and length of the lesion in the proximal vessel were not different. Among patients with MB {+}, atheromatous extension to segments underlying the bridge was seen in 31/44 (70.5%) cases.

CONCLUSIONS

In a series of patients who presented with advanced clinical atherosclerosis, plaque characteristics were not different in patients who harboured myocardial bridge vs. those who did not have the anomaly. Atheromatous involvement was seen extending into bridged segment contrary to previous reports.

Morphological Features on Myocardial Bridges at the Anterior Interventricular Artery

Are described morphological features of myocardial bridges at the anterior interventricular artery obtained from the analysis of 274 cases with 312 myocardial bridges detected by angioCT performed over a period of 3.5 years on a total of 2857 subjects. CT examinations were performed on 1496 females, aged 56-79 years, and 1361 male subjects aged 34-74 years. At the level of the anterior interventricular artery we encountered 231 cases with myocardial bridges (84.31% of the total number of cases), being 267 myocardial bridges (85.58% of the total bridges analyzed). In the case of single myocardial bridges of the anterior interventricular artery, in 65 cases (33.33% of the 195 cases) they were located in the upper third of the artery, 32 cases were female (31.68% of female myocardial bridges) and 33 in male sex (35.11% of male myocardial bridges). In 129 cases (66.67%) were located in the middle third of the artery, 69 cases were female (63.30% female myocardial bridges) and 60 cases in male (64.89% of male myocardial bridges). In one case with three myocardial bridges, the inferior myocardial bridge was located in the lower third of the anterior interventricular artery. The length of the myocardial bridge was between 11.9 and 73.1 mm, for the female gender being 11.9-28.7 mm, and male 9.4-73.1 mm. The thickness of the myocardial bridge was found between 0.9-5.7 mm, for the female gender being 0.9-5.2 mm, and for the male the thickness was 1.7-5.7 mm. The caliber of the tunneling artery was found between 1.2-2.5 mm in female gender, for the male gender 1.3-4 mm.

Myocardial Bridging: A Meta-Analysis of Prevalence

The main objective of this article was to analyze prevalence data about myocardial bridging (MB) in published studies. To this purpose, we performed a meta-analysis of studies published in English literature that contained data about the prevalence of MB and its anatomical characteristics. The overall prevalence was 19% (CI: 17-21%); autopsy studies revealed an overall prevalence of 42% (CI: 30-55%), CT studies 22% (CI: 18-25%), and coronary angiography 6% (CI: 5-8%). Most bridges were located on the left anterior descending artery (82% overall, 63% on autopsy studies), had a mean thickness of 2.47 mm and a mean length of 19.3 mm. In conclusion, autopsy studies should be the gold standard in evaluating the actual prevalence of myocardial bridges, while in vivo high-resolution CT scanning should be preferred to coronary angiography studies.

Different Accumulation of Elements in Proximal and Distal Parts of the Left Anterior Descending Artery Beneath the Myocardial Bridge

To elucidate the action of the myocardial bridge (MB) on the coronary artery, the authors first prepared the hearts with the MB located in the middle one third of the left anterior descending (LAD) artery and then investigated element accumulation in the LAD artery of the hearts with the MB by direct chemical analysis. Eighty-four formalin-fixed adult Thai hearts were dissected and the MBs were found in 39 of 84 hearts with a total of 44 MBs. The 37 MBs were located in the middle one third of the LAD artery. To examine the action of the MB on element accumulation in the LAD artery, the hearts with the MB which was located in the middle one third of the LAD artery and was longer than 1.5 cm were used as Materials. The left main coronary (LMC) and LAD arteries were removed from these hearts successively and the isolated arteries were divided into eight to ten segments. After incineration of arteries with nitric acid and perchloric acid, seven element contents of Ca, P, S, Mg, Zn, Fe, and Na were determined by inductively coupled plasma-atomic emission spectrometry. To examine the endothelial changes of the LAD artery, the inner surface of segments of the LAD artery was observed by scanning electron microscopy. It was found that the extent of accumulation of Ca, P, Zn, and Na was not uniform throughout the LAD artery and was higher in the proximal part than in the distal part with regard to the LAD artery beneath the MB (the tunneled LAD artery). The extent of accumulation of Ca, P, Zn, and Na in the proximal part of the tunneled LAD artery was similar to that in the segments proximal to the MB, whereas the extent of accumulation of Ca, P, Zn, and Na in the distal part of the tunneled LAD artery was similar to that in the segments distal to the MB.

Morphological aspects of myocardial bridges

Although some myocardial bridges can be asymptomatic, their presence often causes coronary disease either through direct compression of the "tunnel" segment or through stimulation and accelerated development of atherosclerosis in the segment proximally to the myocardial bridge. The studied material contained 30 human hearts received from the Department of Anatomy. The hearts were preserved 3 to 5 days in 10% formalin solution. Thereafter, the fatty tissue was removed and arterial blood vessels prepared by careful dissection with special reference to the presence of the myocardial bridges. Length and thickness of the bridges were measured by the precise electronic caliper. The angle between the myocardial bridge fibre axis and other axis of the crossed blood vessel was measured by a goniometer. The presence of the bridges was confirmed in 53.33% of the researched material, most frequently (43.33%) above the anterior interventricular branch. The mean length of the bridges was 14.64 ± 9.03 mm and the mean thickness was 1.23 ± 1.32 mm. Myocardial bridge fibres pass over the descending blood vessel at the angle of 10-90 degrees. The results obtained on a limited sample suggest that the muscular index of myocardial bridge is the highest for bridges located on RIA, but that the difference is not significant in relation to bridges located on other branches. The results obtained suggest that bridges located on other branches, not only those on RIA, could have a great contractive power and, consequently, a great compressive force, which would be exerted on the wall of a crossed blood vessel.

Myocardial bridges in domestic pig--morphological aspects

The morphology of myocardial bridges (MB) in the heart of the domestic pig remain an open issue. Despite numerous analyses of the subject, many controversies still exist. Opinions also differ when the influence of the MB on haemodynamic processes in the coronal vessel system is concerned. In the examined group of 150 domestic pig's hearts, the length of the detected MB varied from 1.8 to 39.7 mm while their thickness amounted to 0.8 - 4.7 mm. Both the longest and the thickest bridges were connected with the posterior interventricular branch. It was noticed that the MB muscle bands cross the long axis of the vessels located in the grooves mostly at almost a right angle. Three forms of perivascular space were educed using the criterion of the distance of the vessel from the surrounding muscularis externa.

Distribution of myocardial bridges in domestic pig

Localisation and morphology of myocardial bridges in the heart of domestic pig remain an open issue. Since these structures significantly influence haemodynamics in the coronary arteries, their occurance may lead to numerous pathologies. In the examined group of 150 domestic pig's hearts, myocardial bridges were diagnosed in 47.3% of the material, mostly in males. In majority of cases the bridges were present above the posterior interventricular branch of the right coronary artery, less often above the anterior interventricular branch of the left coronary artery, and seldom above other blood vessels. The presence of myocardial bridges usually referred to the medial and initial segments of the arteries examined.

Frequency of myocardial bridges and dynamic compression of epicardial coronary arteries: a comparison between computed tomography and invasive coronary angiography

BACKGROUND

The objective of the present study was to describe the relative frequency of myocardial bridging and dynamic compression of the coronary arteries as assessed by CT angiography and conventional angiography.

METHODS AND RESULTS

A total of 311 patients (208 men, 103 women; mean age 63 years) who received both 64-section CT angiography and conventional angiography were reviewed retrospectively for myocardial bridging of the left anterior descending coronary artery. Myocardial bridging was considered when the left anterior descending coronary artery was within the interventricular gorge and was classified as either myocardial bridging with partial encasement or myocardial bridging with full encasement, according to the extent of vessel encasement by the myocardium. The length, location, and depth of myocardial bridging were correlated with the presence, length, and degree of dynamic compression observed at conventional angiography. Among the 300 patients studied (11 were excluded), myocardial bridging was observed at CT angiography in 174 (58%) as partial encasement (n=57) or full encasement (n=117). Conventional angiography revealed dynamic compression in 40 patients (13.3%; partial encasement in 1 patient and full encasement in 39). The length of the dynamic compression was considerably longer than the respective tunneled segment in all patients. Total length correlated (P=0.003) with the dynamic compression, but depth did not (P=0.283).

CONCLUSIONS

The frequency of myocardial bridging observed by CT angiography was 58%, and conventional angiography revealed dynamic compression in 13.3% of total patients. Dynamic compression occurred almost exclusively (97.5% of the time) in patients with full encasement of the left anterior descending coronary artery, regardless of the presence of overlying muscle.

Detection of myocardial bridging by 64-row computed tomography angiography of the coronaries

INTRODUCTION

Myocardial bridging is a congenital condition in which a section of coronary artery is surrounded by myocardium. Historically, myocardial bridging has been diagnosed by catheter angiography. This study investigates the effectiveness of electrocardiogram-gated 64-slice multidetector computed tomography in detecting myocardial bridging.

MATERIALS AND METHODS

We retrospectively reviewed 167 consecutive patients referred for coronary computed tomography angiography between January 4, 2005, and May 24, 2006. We recorded the number of coronary segments exhibiting myocardial bridging and described the location of each according to the American Heart Association classification system. Association of bridging with factors influencing image quality (body mass index and heart rate) was analyzed.

RESULTS

Of 152 eligible participants, 49 (32%) showed myocardial bridging. The mid-left anterior descending coronary artery (segment 7) was the most common location accounting for 69% of positive cases. Body mass index and heart rate did not affect detection rates.

CONCLUSION

Electrocardiogram-gated 64-slice multidetector computed tomography is a feasible, noninvasive method of detecting myocardial bridging which may offer higher sensitivity than catheter angiography for this diagnosis.

The relationship of myocardial bridges to coronary artery dominance in the adult human heart

Myocardial bridging is recognized as an anatomical variation of the human coronary circulation in which an epicardial artery lies in the myocardium for part of its course. Thus, the vessel is 'bridged' by myocardium. The anterior interventricular branch of the left coronary artery has been reported as the most common site of myocardial bridges but other locations have been reported. The purpose of this study was to provide more definitive information on the vessels with myocardial bridges, the length and depth of the bridged segment, and the relationship between the presence of bridges and coronary dominance. Two hundred formalin-fixed human hearts were examined. Myocardial bridges were found in 69 (34.5%) of the hearts with a total of 81 bridges. One bridge was found in 59 of these hearts and multiple bridges were observed in ten (eight with double bridges and two with triple bridges). Bridges were most often found over the anterior interventricular artery (35 hearts). Bridges were also found over the diagonal branch of the left coronary artery (14), over the left marginal branch (five) and over the inferior interventricular branch of the left coronary artery (six). Bridges were also found over the right coronary artery (15 hearts), over the right marginal branch (four) and over the inferior interventricular branch of the right coronary artery (two). The presence of bridges appeared to be related to coronary dominance, especially in the left coronary circulation. Forty-six (66.6%) of the hearts with bridges were left dominant. Forty-two of these had bridges over the left coronary circulation and four over the right coronary circulation. Seventeen hearts (24.6%) were right dominant. Eleven of these had bridges over the right coronary circulation and six over the left coronary circulation. The remaining six hearts were co-dominant with four having bridges over the left coronary circulation and two over the right coronary circulation. The mean length of the bridges was 31 mm and the mean depth was 12 mm. The possible clinical implications of myocardial bridging may vary from protection against atherosclerosis to systolic vessel compression and resultant myocardial ischaemia.

The investigation of perivasculary space under the myocardial bridge in different species

Our purpose in this study was to investigate the perivasculary space under the myocardial bridges (MB) in dog, sheep, goat and human hearts. A total of 160 hearts were studied, and perivasculary space under the myocardial bridges was examined under microscope. The specimens belonged to 25 dogs, 100 sheep, 25 goats and 10 humans. Special attention was paid to evaluate the distance between the MB and coronary arteries (CA), CA and underlying myocardium (UM) and to find the relation of concomitant vein number accompanying the CA and MB. 219 myocardial bridges were found in total of hearts, and specimens from these bridges were examined under microscope. There were large variations in distance between the MB and CA (0-714 microm) and distance between CA and UM (0-309 microm). The myocardial bridges were classified into three groups in terms of the number of veins accompanying CA, the bridges with no concomitant veins with one concomitant vein and with two concomitant veins. This suggests that the distance between the MB and CA is crucial to determine how much force is on the CA. The environment surrounding the CA may be a crucial factor in determining whether the MB influences the induction of heart disorders or not.

Orientation of intracoronary ultrasonography: looking beyond the artery

Over the past 5 years intravascular ultrasound imaging has achieved many technical advancements both in catheter design and image quality. In addition to improved image quality that provides clear display of the endovascular structure, efficient signal penetration permits the viewing of structures beyond the artery by highlighting the perivascular structures. These perivascular landmarks, which are unique within a particular coronary segment, help provide both axial and spatial orientation during multiple imaging runs throughout a coronary artery. Orientation on the basis of veins and pericardium assists the operator to appreciate the full three-dimensional view of a particular coronary segment. This article describes several of the common perivascular structures that may be viewed from different arteries routinely imaged during coronary procedures.