Case B7. Third Degree AV Block with Junctional Escape Rhythm. St Emlyn’s ECG Library

Third degree heart block stemlyns, ECG Library, #FOAMed, St. Emlyn’s ECG Library.

The EGG was recorded from a 75 year old man admitted for insertion of a permanent pacemaker. He had a history of brief episodes of loss of consciousness during which he went pale and collapsed. He recovered consciousness rapidly after these episodes with amnesia for the event.


Rhythm: The ECG shows P waves at a rate of 85 per minute. The QRS complexes occur at a rate of 42 per minute. Inspection of the rhythm strip shows that there is no relationship between the P waves and the QRS complexes; atrial and ventricular depolarization are occurring independently from separate pacemakers- atrioventricular dissociation is present. Morphology: The 12 lead ECG shows a narrow QRS complex escape rhythm (.10 seconds or less). The QRS complexes appear broad in VI, V2 and V3, but this is due to distortion of the terminal part of the S waves by a P wave.


It was known from a previous recording that the QRS morphology recorded here was identical to that when the patient was in sinus rhythm. This demonstrates that the pacemaker iniuating ventricular depolarization is a ‘high’ or proximal one situated above the bifurcation of the bundle of His into right and left bundle branches ie it is a junctional pacemaker. The symptoms described are typical of Adams Stokes attacks caused by abrupt loss of cardiac output and hence cerebral perfusion. Recovery is rapid when the cardiac rhythm is restored. When complete heart block is associated with Stokes Adams attacks patients are at high risk of sudden death and should be treated by permanent pacing. Pacing is also usually indicated if syncope has not occurred as the risk of sudden death remains high. Pacing restores life expectancy to ‘normal’ in elderly patients.


Cite this article as: Simon Carley, "Case B7. Third Degree AV Block with Junctional Escape Rhythm. St Emlyn’s ECG Library," in St.Emlyn's, November 3, 2018,

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