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What is branch vessel STEMI ? How common it is , among STEMI population ? Can you afford to manage it less aggressively ?

Posted Feb 03 2010 9:34am

STEMI is the major cardiac emergency .The acute mortality is about 20% (Both prehospital and in CCU )  STEMI occurs whenever a coronary artery is occluded  suddenly in toto .We traditionally believe that STEMI occurs only in the major  epicardial vessels. (LAD/LCX/RCA .)

The total length of   coronary tree is much  longer than the length of the three vessels put together.The diagonals , the ramus, the OMs ,the septals  run for varied  distances. The caliber of these vessels can be quite large.It is estimated the diameter  of   first diagonal ,   the first OM  or the   ramus can be as big as LAD proper in 30% of CAD population . Law of statistics tells us sudden occlusion can occur any where in the coronary tree in  ACS prone patients.

What is the real incidence of side branch STEMI ?

The  dogmatic answer is   ” We do not know”

Will we ever know ?

How will a  Diagonal / OM /Ramus   or PDA   STEMI  behave ?

It is surprising this question is not addressed by us  for  so long . Some may even question  the existence of  such an entity(Side branch STEMI ). This is most likely ,  reflect our ignorance on the issue . We know  bifurcation lesions at  the   side branch  origin is very common . Further , thrombus can migrate from a main stem to a side  branch  immediately after formation .

Clinical presentation of side branch STEMI

  • Acute presentation is identical  to  that of a major main branch STEMI . The  pain  can be severe , the primary arrhythmic threat is real . Ischemic VF , once initiated does not  modify it’s  character  according to the  quantum of insult .
  • ECG is the major variable.  You ,  don’t expect gross , ST elevation in many leads as one would see in LAD MI /RCA MI.
  • The  age old teaching that  an ECG can be entirely normal in acute MI ,  could actually imply the side branch STEMIs . When a small D2 or D3  gets occluded the ECG may not pick up the ST shifts .
  • The commonest site of atherosclerosis apart from proximal LAD is the bifurcation of PDA in RCA.  STEMI due to PDA occlusion is  the most  difficult thing to recognise. Many of them have very subtle ECG and clinical findings.
  • There has been reports of acute complete heart blocks with isolated AV nodal infarcts. Here sudden cardiac deaths are reported

It is very much possible ,  many of the  side branch  MIs   may be wrongly diagnosed as unstable angina by us , for the simple reason the myocardial necrosis is not large enough to produce ST elevation .They may actually respond to thrombolysis ,  as there is total occlusion in the coronary artery.  Since, they do not manifest ST elevation there is a lost opportunity here  . This ,   probably  is the population in TIMI 3B  trial that showed some ( statistically   insignificant ) benefit for   thrombolysis in NSTEMI.

Is primary PCI justified in side branch STEMI ?

May not be . The chances of side branch STEMI   to result in LV dysfunction and progressive adverse remodeling is considerably less . The hazards of primary PCI for exceeds the risks of  MI  due to a   septal  or diagonal branch lesion .

Final message

  • STEMI due to   branch coronary artery  occlusion is a less recognised entity among ACS.
  • Cardiologists ,  need to  look into this  issue with little more seriousness as it could represent a new  intermediate risk  category   among the much  flaunted  classification  of  acute coronary syndrome. Triaging and risk stratification of  ACS  needs  a revamp.
  • It is possible  many of the UA  patients  ,  may in fact represent total occlusion of side branches.
  • There is a  definite  case  for showing less aggression in these patient  subsets  ,  provided we are sure  about  the location of lesion.

Counter point

* Identifying  a side branch STEMI with confidence  may be very difficult at bed side in an emergency . Implication of wrongly  calling a STEMI  as benign  can be  dangerous . So it will be argued ,  one need not do this exercise of traiging STEMI into main branch or side branch .

Image courtesey

Coronary tree : http://www.southcharlestoncardiology.com/64cta.html

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