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Posts Tagged ‘kieth and flack’

Sinus node which orchestrtes the rhythm of life  gets it’s blood supply by a small blood vessel arising from either RCA or LCX. (55 :45%) . The  course of sinus node  branch  is highly variable .

There are three distinct pattern observed.

  1. Posterior encircling  of  SVC .(50%)*
  2. Anterior  encircling  of  SVC(40%)
  3. Form a  “garland like ” anastomosis  on either side of SVC (10%)

* Some refer to as clockwise and counterclockwise course.

SA node is a spindle shaped structure with a length up to 20mm . Extending from cranial to caudal aspect.The pecularity of the blood supply to SA nodal artery is  , it enters the SA node either in it’s superior aspect or inferior aspect never  in  the mid part. There can be water shed area in the either ends depeding upon the entry.This can have  electrophysiological and  pathological significance .

The other consistent feature is that ,  the major trunk of SA node artery courses through the central core of SA node.In fact , many times pathologists recognise ther SA node ,  with the help of   this arterial course.

Is there a collateral blood supply to SA node ?

It is not common  . Rarely  atrial branches of LCX /RCA  can have extensive anastomosis with SA nodal branches .The hemodynamic significance  of which is  not known. 

Ischemic SA nodal disease has become an important entity . As the cardiologists are preoccupied with opening  occluded coronary arteries  in cath labs , it  is not  surprising to note, there is little  ongoing  research  in the anatomy and physiology of SA nodal  blood supply.

We have to go back in time to get some great articles on the  subject

At this point of time ,  we should realise  the 1ooth anniversary of  SA nodediscovery passed of silently  .  Kieth and Flack  found the SA node with bare eyes  in the year 1907 , when none of the present-day investigations  including ECG and X RAY were  not even conceptualised !

With  tributes to those humble pathologists like  M.J Davies, R.H .Anderson, T.N. James,M. Lev ,J.L.Titus  who   followed   the foot steps  of  Kieth and Flack ,

Here is a  link to one of the great articles on the blood supply to SA node

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC514694/pdf/brheartj00203-0035.pdf

Related point : How do you  recognise  the  SA nodal artery in coronary angiogram ?

During RCA angiogram it is many times confusing  to identify the SA nodal branch . In RAO and LAO views the plane of exit  of SA nodal branch from RCA  will be determined by the  course  it is going to take .(Anterior vs posterior encircling pattern). The conal branch  which is often the first branch of RCA  ,  also behaves aberrantly  many  times. So, we can’t have a rule of thumb in identifying SA nodal branch .

When SA node branch originates from LCX it has to take a long route but once it reaches the SVC/RA junction it takes  one of the above described course. It is not clear whether LCX  fully understands it’s responsibility  , when RCA ignores it 45 % of times .  There is reason to suspect the commitment and dedication of LCX  because it rarely supply  the SA node by a   seperate branch.  It is often the left atrial CX  that comes to the rescue  and give a twig to the  SA node .

Considering the complexity of SA nodal blood supply  , one can understand  why some develop premature sinus node failure. One can never determine with evidence , how much of SA node destruction is due to ischemia and how much is due to age related degeneration and fibrosis.

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