Download Update 11 - Update in Anaesthesia - WFSA

30Update in AnaesthesiaFailure of conductionto ventriclesFigure 19: Second degree blockbeats, resulting in 2 P waves for every QRS complex -this is 2:1 block. A 3:1 block may also occur, with oneconducted beat and two non-conducted beats. This mayalso herald complete heart block, and in some situationsthe placing of a temporary transvenous pacing wire preoperativelywould be recommended.Complete Heart Block (figure 20)There is complete failure of conduction between the atriaand the ventricles. The ventricles are therefore excited bya slow escape mechanism from a focus within the ventricles.There is no relationship between the P waves and the QRScomplexes, and the QRS complexes are abnormallyshaped. This may occur occasionally as a transientphenomenon in theatre as a result of vagal stimulation, inwhich case it often responds to stopping surgery andintravenous atropine. When it occurs in association withacute inferior myocardial infarction, it is due to AV nodalischaemia and is often transient. Very rarely it may becongenital! However if it occurs with anterior myocardialinfarction it indicates more extensive damage including tothe HIS - Purkinje system. It may also occur as a chronicstate usually due to fibrosis around the bundle of HIS.Management Isoprenaline given by intravenous infusion can beused to increase the ventricular rate In the acute situation a temporary transvenouspacing wire may be required. A permanentpacemaker will be required in the longer term ifthe block is chronic and before contemplatingelective surgery.Bundle Branch Block (figure 21)If the electrical impulse from the SA and AV nodes reachesthe interventricular septum normally the PR interval willbe normal. However if there is a subsequent delay indepolarisation of the right or left bundle branches, therewill be a delay in depolarisation of part of the ventricularmuscle and the QRS complex will be wide and abnormal.A wide complex rhythm which is present at the start ofsurgery on initial attachment of the ECG monitor is usuallydue to bundle branch block (BBB), and is not an indicationfor cancelling the operation. However this does indicatethe importance of attaching the ECG monitor beforeinduction of anaesthesia, particularly where a preoperativeECG is not available. Any changes on the ECGduring anaesthesia and surgery can then easily be comparedto the patients ‘ normal’ ie pre-anaesthetic ECG tracing.The definition of which bundle is blocked can only beachieved by analysing a full 12 lead ECG. Two types ofBBB are recognised.Figure 20: Complete heart block