Third-degree AV Block - ECG

The third-degree AV block means a total block of the atrioventricular transmission and therefore it causes a total division of atrial and ventricular function. The electric signals are properly formed in the atria but they can not be transmitted to the ventricles. The ventricles work in their own rhythm that is very slow resulting in bradycardia. Both the P waves and QRS complexes are regular but each other totally uncoordinated. Some P waves are “hidden” within the QRS complexes. It is advisable to mark the visible P waves by a pencil to better see their regular occurrence.


Third-degree AV Block - ECG
Third-degree AV block – The P waves are marked by red arrows and the QRS complexes by blue ones. In this case, no P waves are hidden within the QRS complexes but some of them merge with the T wave.

Conclusion: Third-degree AV block may be caused by a cardiac ischemia and it can occur after a myocardial infarction. Because there is usually present severe bradycardia, the AV third-degree AV block is not well tolerated causing symptoms of heart failure and collapses. The best solution is the implantation of a pacemaker


Jiri Stefanek, MD  Author of texts: Jiri Stefanek, MD
 Sources: basic text sources