Health knowledge made personal
Join this community!
› Share page:
Go
Search posts:

Can you diagnose AV dissociation without looking at ECG ?

Posted Sep 09 2009 10:23pm

AV dissociation is  common clinical situation that can occur  during both    bradyarrhythmias  and tachyarrhythmias .

Bradycardias

  • Complete heart block
  • During pacemaker rhythms

Tachycardias

  • Accelerated junctional  rhythm
  • Idioventricular  rhythm
  • Ventricular  tachycardia

AV dissociation is essentially an  ECG diagnosis. But it is associated with some  clinical  signs   ,which can be detected by an astute physician in the bedside. At rapid heart rates  it may be really difficult at times to recognise theses findings, but a  cardiology fellow should look for these whenever they encounter AV dissociation  in ECG.

  1. Varying pulse volume
  2. Varying korotkoff  sounds during BP measurement.
  3. Cannon a waves in JVP
  4. Varying intensity of first heart sound on auscultation
  5. Mitral regurtitant murmur may be heard
  6. Hypotension in compromised hearts

What is the mechanism of clinical signs of AV dissociation ?

During AV dissociation , the atrial and ventricular contractions occur  out of phase  and the sequential contraction  is lost. So atrial contractions  might  occur with a closed AV valves .  This result in reflux of blood into the neck resulting in cannon waves . It may be visible only in few beats as the retrograde conduction VA conduction , is highly variable.

Further , only some atrial beats contribute for ventricular filling some do not.This results  in varying LV volumes and this  could result in changing pulse volume.Occasionally the ventricular and atrial   contraction occur simultaneously  .When this happens ,  some amount of blood  reguritates through the open tricuspid valve and mitral valve  which result in MR or TR .

Clinical utility

This could be important , in differentiating  the perennial  issue   of decoding the   wide qrs  VT from  SVT with  aberrancy .A rapid clinical assessment  here could  aid in the diagnosis  of VT  by  identifying  AV dissociation  . An experienced cardiologists will realise even in a given  ECG  with VT  identifying or ruling out  AV dissociation is not always a  pleasant excercise !

In this era of  high tech gadget  oriented cardiology is it not too much  to call for clinical   recognition of  this  entity ?

Definitely not, if  we know Wencke bach  recognised  the classical type 1 2nd degree  AV block in late 19th century even before the ECG machine was  invented ,

Simply by looking at the neck , by carefully observing progressive prolongation of  distance between a and c waves and subsequent dropping of c waves . Amazing isn’t it ?

Post a comment
Write a comment:

Related Searches