Download Update 11 - Update in Anaesthesia - WFSA

Update in Anaesthesia 29Figure 16: Ventricular FibrillationDISTURBANCES OF CONDUCTIONThe wave of cardiac excitation which spreads from thesinoatrial node to the ventricles via the conductionpathways may be delayed or blocked at any point.First Degree Block (figure 17)There is a delay in the conduction from the sinoatrial nodeto the ventricles, and this appears as a prolongation of thePR interval ie greater than 0.2 seconds. It is normallybenign but may progress to second degree block - usuallyof the Mobitz type I. First degree heart block is not usuallya problem during anaesthesia.Second Degree Block - Mobitz Type I (Wenkebach)(figure 18)There is progressive lengthening of the PR interval andthen failure of conduction of an atrial beat. This is followedby a conducted beat with a short PR interval and then thecycle repeats itself. This occurs commonly after an inferiormyocardial infarction, and tends to be self limiting. It doesnot normally require treatment although a 2:1 type blockmay develop with haemodynamic instability.Second Degree Block - Mobitz Type II (figure 19)If excitation intermittently fails to pass through the AVnode or the bundle of HIS, this is the Mobitz type IIphenomenon. Most beats are conducted normally butoccasionally there is an atrial contraction without asubsequent ventricular contraction. This often progressesto complete heart block and if recognised preoperativelywill need expert assessment..Second Degree Block - 2:1 TypeThere may be alternate conducted and non-conductedFigure 17: 1st degree heart blockFigure 18: 2nd Degree Block - The Wenkebach phenomenon