European Journal of Cardiovascular Medicine

In  India,  the  prevalence  of  cardiovascular  diseases  has  been  rising  significantly,  making them  the  leading  cause  of  mortality,  particularly  among  individuals  in  their  most productive  midlife  years. This  trend  contrasts  with  developed  nations,  where  mortality due  to  cardiovascular  conditions  occurs  more  frequently  at  older  ages.

One  particular  anatomical  variant  associated  with  ischemic  heart  disease  is  the myocardial  bridge. A  myocardial  bridge  occurs  when  a  segment  of  an  epicardial  coronary artery  follows  an  intramuscular  course,  becoming  partially  embedded  within  the  overlying  myocardial  tissue  instead  of  running  along  the  surface  of  the  heart. This  phenomenon  was  first  noted  during  autopsies  by Reyman  in  17371. However,  it  was  not until  1951  that  Geiringer2  formally  described  these  structures  as  " myocardial bridges."

The  presence  of  a  myocardial  bridge  can  have  significant  clinical  implications. Under normal  conditions,  these  bridges  may  remain  asymptomatic  and  are  often  discovered incidentally  during  autopsies,  with  studies  reporting  their  presence  in  up  to  25%  of individuals  who  have  died  from  unrelated  causes. However,  in  certain  physiological  and pathological  conditions,  myocardial  bridges  can  contribute  to  myocardial  ischemia. This risk  is  particularly  elevated  in  individuals   with a  left-dominant  coronary  circulation  and in  those  with  multiple  myocardial  bridges.

Additionally, the co-existence of atherosclerosis and myocardial bridging can further exacerbate ischemic symptoms, particularly during periods of increased myocardial demand, such as physical exertion or emotional stress. The compression of the tunnelled coronary segment during systole can lead to altered blood flow dynamics, predisposing individuals to myocardial ischemia, angina, or even acute coronary syndromes.

Given  the  potential  clinical  significance  of  myocardial  bridges,  understanding  their anatomical   characteristics—including  their  location,  number,  length  and  depth (whether superficial  or  deep)— is  crucial. Furthermore,  assessing  their  correlation  with  coronary dominance  can  aid  in  identifying  individuals  who  may  be  at  a  heightened  risk  of ischemic  heart  disease.

With  this  background  in  mind,  a  detailed  anatomical  study  of  myocardial  bridges  has been  undertaken  to  enhance  our  understanding  of  their  structural  variations  and  clinical implications. This  knowledge  may  contribute  to  improved  risk  stratification  and  the development  of  targeted  diagnostic  and  therapeutic  approaches  for  affected  individuals.

The  study  undertaken  was  a  cadaveric  dissection  based  study, where  adult  human  hearts  were  collected  from  the  bodies   provided   for   dissection   to   the   undergraduate  students  in   the   department   of   Anatomy,   Assam   Medical   College   and  Hospital,   Dibrugarh. The  ethical  clearance  for  the  study  was  obtained  from  the  Institutional   Ethical Committee  (human). Total  100  human  hearts  of  different  age  groups  and  of  either  sex were  studied. Specimen with gross congenital malformations were excluded from the study. The  specimens  were  properly  washed  and  preserved  in  10%  formalin  for  dissection  at  a  convenient  time. The  hearts  were  meticulously  dissected  to  see  the location  of  myocardial  bridge  along  both  coronary  arteries  and  their  main  branches. Required  dimensions  of  myocardial  bridges  were  examined  with  the  help  of  vernier calliper  and  depending  on  the  posterior  interventricular  artery  the  coronary  dominance was  determined.

Aim

1. To find  the  incidence  of  myocardial  bridges  over  the  coronary arteries
2. To find  the  correlation  between  coronary  dominance  and  myocardial  bridges

Table 1: Showing total number of specimens and myocardial bridges

Table 2: Showing total no. of myocardial bridges

Myocardial bridges  were  observed  to  be  more  in  left  coronary  artery (52%)  than  right coronary  artery (10%).  Overall incidence of myocardial bridges was found to be 62%. (Table 1 and 2)

Table 3: Showing no. of myocardial bridges over different coronary arteries

Left  anterior  descending  artery  had  maximum  number  of  bridges (64.5%),  more  so  in its  middle  segment (Table 3 and 4) . Myocardial bridges were not seen on right marginal artery.

Table 4: Showing no. of myocardial bridges over Left Anterior Descending Artery

Table 5: Incidence of Single and Double myocardial Bridges

Table-6: Showing Total Dominance Pattern

Right  coronary  artery  dominance  was  seen  in  most  of  the  cases  irrespective  of  age and  sex

Table-7: Showing number and percentage of myocardial bridges and coronary dominance

In  the  present  study  the  overall  incidence  of  myocardial  bridge  is  52%  which  is comparable  to  studies  conducted  by  Lujinovic A. et al (2013) 3: 53.33%,  M.P  Wakchaure (2019) 4: 54%  and  Gunjan  Rai  et al (2020) 5: 53.06%.  However  this  prevalence  was  higher than  other  studies: 5%,   0.61%  reported  in  the  literature6,7  but  high  incidence  of  92.5% was  reported  by  P.Moula et al (2023)8. Consistent  with  the  literature  in  earlier  studies Lujinovic A. et al (2013) 3,  Narayanan VK et al (2017) 9,  the  middle  segment  of  left  anterior descending  artery  was  the  most  common  location  for  myocardial  bridge  in  the  present study  but  Vanildo et al (2002) 10  also  reported  a  high  incidence  of 88.66%  over  the  same artery.13 %  incidence  of  myocardial  bridges  was  observed  on   the 1st  segment  of  right  coronary artery  in  the  present  study  whereas  a  higher  incidence  of  100%  was  reported  by  Firdaus  Shaikh et al (2022) 11 In  the  present  study,  left  anterior  descending  branch  had  maximum  number  of  single and  double  bridges (Table 5, Fig 3 ). No  triple  or  quadruple   bridges were  found  unlike  in  a study  conducted  by  Ballesteros et al (2009) 12.

Right  dominance  pattern  was  observed  by  most  of  the  literatures  reviewed. Comparing the  overall  pattern  of  coronary  dominance (table 6)  the  hearts  with  bridges  expressed a  very  different pattern (table 7) . In  the  present  study  maximum  incidence  of  myocardial bridges  was  observed  over  the  left  coronary  artery  in  case  of  right  coronary  dominance as  (63.5%). This  incidence  is  higher  to  that  reported  by  Bharambe et al (2008) 13 and comparable  to  that  reported  by  Firdaus Shaikh et al (2022) 11. The authors  added  that  in such  cases  the  obstruction  of  left  coronary  artery  by  myocardial  bridge  could  be overcome  by  the  wider  distribution  of  right  coronary  artery  with  less  incidence  of myocardial  suffering  and  infarcts.  Moreover, the  obstruction  of  the  dominant  artery  by the  effect  of  myocardial  bridge  could  result  in  bad  effect  due  to  larger  mass  of myocardium  being  supplied  by  the  dominant  artery. Loukas M (2006) 14  reported  a  higher incidence  of  myocardial  bridges  over  the  left  coronary  circulation (60.8%)  in  left  coronary artery  dominance  than  the  present  study. Clinically,  this  may  suggest  that  bridges  could be  less  frequent  in  populations  with  the  more  usual  spread  of  arterial  dominance.  In case  of  codominance  the  incidence  of  myocardial  bridges  over left  coronary  artery  and right  coronary  artery  is  almost  similar  with  the findings  of  Bharambe et al (2008) 13  and Firdaus  Shaikh et al (2022) 11

 In  literature,  the  length  of  myocardial  bridge  varied  from  3.6 mm  to  more  than  50 mm15. Bridges  may  be  superficial (<2 mm)  or deep (>2mm)  depending  on  the  depth  of  the myocardial  bridge16.  In  our  study  most  of  the  myocardial  bridges  were  of  superficial type  which  correlates  with  the  findings  of  Ashraf (2014) 17.  Geiringer2 reported the smallest length of 5mm. In  our  study  we  observed  the minimum  length  and  thickness  4 mm X 1mm  was  over  left  anterior  descending  artery .The  maximum  length  and  thickness  30mm x 4mm  was  also  over  left  anterior  descending  artery  but  Narayanan VK et al (2017) 9  noticed  the  largest  and  deep  bridges  over  the  diagonal  artery  with  an average  measurement  of 45 mm x 20 mm. As  the  length  of  coronary  arterial  narrowing markedly  influences  coronary  haemodynamics (Feldman et al. 1978) 18,  so  relatively  long bridges   are  observed  in   symptomatic patients (Bourasa et al. 2003) 19

Although  an  intriguing  area  of  research,  the  clinical  significance  of  myocardial  bridges is  uncertain  as  it  remains  clinically  silent  or  acts  as  a  contributing  factor  in  the development  of  myocardial  infarction  that  requires  surgical  interventions.  Social  factors, change  of  food  habits and  sedentary  life  style  has  already  increased  the  load  on  heart muscles  and  addition  of  anatomical  factors  such as  dominance  pattern  of  the  coronary artery  and  myocardial  bridges  makes  the  heart  more  susceptible  to  ischaemia  (Hurt’s “The Heart”, 10th Edition) 20

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