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Organic vs Benign Left bundle branch block

Posted Oct 29 2010 10:00am

LBBB is a common ECG abnormality .The ECG is so classical , no one ever misses the diagnosis. But , what we miss  often is the significance of it .

What is the cause of LBBB in a given patient is much more important than the LBBB itself !

Though the commonest cause of LBBB is a benign one (Pure electrical defect without any valvular , myocardial or ischemic heart disease ) , it is prudent to rule out organic LBBB   . The term  organic  here refers to structural or ischemic etiology .

LBBB  & STEMI

To diagnose STEMI in LBBB we have the much famed  Sgarbosa criteria .It is a too popular to forget in spite of  it’s limited utility . Applying it in an emergency is not easy exercise . Clinical prediction , cardiac enzymes are  safe and could be more accurate. Thanks to  ACC guidelines  , it has simplified our task .You  are encouraged to thrombolyse all cases of  new  onset LBBB* if clinical picture is strongly  suggestive of ACS.(*The term  “presumably new” onset LBBB  was included  , implying  it is better to err on the safe side )


LBBB & NSTEMI

No one knows how to recognise NSTEMI in LBBB. Logic would say, primary ST depression might occur. How sensitive it is , and which  lead to look for is not known.

LBBB in DCM

Here is an  ECG of a patient who came to our OPD  absolutely asymptomatic for a routine review . He is been diagnosed as a case of  dilated  cardiomyopathy with 30% EF and  no evidence of  ongoing  ischemia.If the history is not known he would have been  diagnosed as a ACS.

To diagnose cardiomyopathy in LBBB we have no specific criteria. But  we have found the following useful

  • Extreme left axis deviation > Minus 45-60 degrees/AVR positivity
  • Low voltage QRS , especially in limb leads
  • ST depression is more flatish  than  the typical  secondary ST/T changes of LBBB
  • QRS notching or slurring either in the r wave or s wave.
  • Atrial abnormalites as evidence by wide P waves.
  • Associated VPDs

Further inputs are welcome to differentiate organic from benign LBBB

Counter point : When we have  facility to do  bedside  echo , why should we  scratch our heads ?

Do not waste time , do a spot echo  . . .

Echo can be very useful in ruling out cardiomyopathies and old MI.But  remember , echocardiography is  unpredictable to detect acute septal MI in the presence of LBBB  , as  paradoxical motion of IVS tend to mask the  ischemic wall motion defect .A simple clue is normal systolic wall thickening will be observed in benign LBBB ,  in spite of  paradoxical  motion .This thickening appears as  post systolic beaking  that  face posteriorly . In STEMI and LBBB thinning or absence of thickening is expected.


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