Pseudo-Wenckebach due to Low Upper Rate Limit
Report:
Sinus rhythm 92-96/min 0.5
Conducted sinus capture beat (penultimate QRS) 0.5
First degree AV block (PR 0.24”) 0.5
Second degree AV block (last cycle) with ventricular pacemaker escape beat 0.5
Atrial-sensing ventricular pacemaker 1
4:3 pseudo-Wenckebach sequences 3
Fusion beats 2
Failure to sense (last two P waves) - atrial undersensing 2
Comment:
The overall ventricular rate is about 73/min, due to Wenckebach “conduction” of sinus rhythm 92 – 96/min, engendered by the pacemaker’s upper rate limit of 80/min. This is uncommonly low limit, but may be useful if the patient develops angina in faster paced (but not necessarily native) rhythm. This was the case here; she was in fact on thyroxin 100 mcg daily for myxœdema. Another situation where rate limitation may be useful is mitral stenosis.
This patient’s problem were elsewhere: she was dehydrated and on Persantin SR 200 mg BD, with marked postural hypotension. This was addressed and the symptoms resolved.
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