ECG Conduction Blocks
ECG Library summary of the different types of conduction disturbance, with links to read more about each type of conduction block Conduction Blocks First-degree block First-degree block PR interval >200 msec (1 large square) Second-degree block Mobitz Type I (Wenckebach Block): progressive prolongation of the PR interval before the missed QRS complex Mobitz Type II (Hay Block): absence of progressive prolongation of the PR interval before the missed QRS complex Fixed ratio blocks (e.g. 2:1, 3:1): constant relationship between P waves and QRS complexes (e.g. 2:1 = 2 P waves for each QRS complex). High grade AV block: 2nd degree AV block with a high P:QRS ratio, producing a very slow ventricular rate Third-degree block Third-degree block: absence of any relationship between P waves of sinus origin and QRS complexes (AV dissociation) Fascicular Blocks Left anteriorfascicular block (LAFB) Left axis deviation qR complexes in leads I, aVL rS complexes in leads II, III, aVF Prolonged R wave peak time in aVL > 45ms Left posterior fascicular block (LPFB) Right axis deviation rS complexes in leads I, aVL qR complexes in leads II, III, aVF Prolonged R wave peak time in aVF Right bundle branch block QRS > 120 ms Dominant R wave in V1 RSR’ pattern (“M”) in V1 with wide, slurred S wave (“W”) in V6 (=MaRRoW) Left bundle branch block QRS > 120 ms Dominant S wave in V1 Deep S wave (“W”) in V1 with broad R wave (“M”) in V6 (=WiLLiaM) Bifascicular block RBBB plus either LAFB or LPFB Trifascicular block Bifascicular block plus 3rd degree AV block Interventricular conduction disturbance QRS > 100 ms, not due to LBBB or RBBB. Most important causes are hyperkalaemia or tricyclic antidepressant poisoning Advanced Reading Online ...