Summary of the different types of conduction disturbance. Follow the links to read more about each type.
- PR interval >200 msec (1 large square)
Second-degree block (occasional absence of QRS and T after a P wave of sinus origin)
- Type I (Wenckebach’s) – progressive prolongation of the PR interval before the missed QRS complex
- Type II (Mobitz II) – 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.
- Absence of any relationship between P waves of sinus origin and QRS complexes (AV dissociation).
Left anterior fascicular block (LAFB)
- Left axis deviation, Q waves in leads I and aVL, and a small R in lead III, in the absence of LVH.
Left posterior fascicular block (LPFB)
- Right axis deviation, a small R in lead I, and a small Q in lead III, in the absence of RVH
- QRS > 120 ms, dominant R wave in V1, RSR’ pattern (“M”) in V1 with wide S wave (“W”) in V6 (=MaRRoW)
- QRS > 120 ms, dominant S wave in V1, deep S wave (“W”) in V1 with slurred R wave (“M”) in V6 (=WiLLiaM)
- Bifascicular block with evidence of either first or second-degree AV block
Interventricular conduction disturbance
- QRS > 100 ms, not due to LBBB or RBBB. Most important causes are hyperkalaemia or tricyclic antidepressant poisoning
Further Reading
- ECG BASICS – Waves, Intervals, Segments and Clinical Interpretation
- ECG CLINICAL CASES – Your favourite ECG’s placed in clinical context with a challenging Q&A approach
- ECG and Cardiology Eponymous Syndromes – Cheats guide to eponymous emancipation
- ECG Reference Sites on the WEB – the best of the rest
Author Credits
About Mike Cadogan
