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Posts Tagged ‘hemiblocks’

The bundle of his divides into two

  • Anterior fascicle
  • Posterior fascicle
  • Middle septal  fascicle*

Middle fascicle * Many  dispute  it’s presence .  One may wonder , how  can anatomy be  under  dispute  ? If you cut a heart you should be able to clear the dispute .  But medicine is not that simple . . . What you do not see may be more important than what we see.

The anterior  fascicular block (LAFB) is one of the common conduction disorder. It ‘s significance :  Can  be a  benign  or a  dangerous entity depending upon the clinical situation .The  problem with  LAFB  is , it is diagnosed primarily by the axis shift it inflicts on the QRS complex.

In a strict sense, it is not a ideal way .There is  a tendency to label all significant left axis (> -60*) deviations  as LAFB. This  practice has made diagnosing LAFB very common in elderly, hypertensives, etc. In these situations it may not mean anything ,  except to suggest a  delay in conduction in  left anterior  fascicle.

If we filter out all these  benign  axis shift  ECGs  , the true organic pathological LAFB  may  not be that common .

Organic , LAFB occurs in the following situations.

  • Degenerative  blocks (Part of Lev & Lenegre’s disease)
  • Aortic valve disease .
  • Hypertensive heart disease
  • Post MI (Either alone or part of bifascicular or trifascicular block )
  • In association with dilated cardiomyopathy

Even in degenerative  , ischemic conduction defects LAFB is far more common than LPFB why ?

The traditional explanations are

  1. Anterior fascicle is relatively sub epicardial in location
  2. It is a  long and thin  structure prone to damage easily
  3. Exposed to the mechanical   stress of   LVOT **
  4. Anterior fascicle has  only a single blood supply(LAD)

** Which experiences  the peak LV  pressure  at > 100mhg and a dp/dt  up to  2000mmhg  (While,  the posterior fasicle is located  away  in the inflow portion of LV  , which is exposed  to low pressure – at best 10mmhg filling pressure )

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