This ECG trace was taken from a 68 year old man, one hour following aortic valve replacement for aortic stenosis. Atrial and ventricular epicardial pacing wires are in place, and the pacing mode is DDD.

a) . What problem is demonstrated?

b). Outline the steps that you could take to address the problem.

The problem is resolved, and normal DDD pacing resumes. One hour later another
ECG trace is taken.

c). What problem is demonstrated?

d). What precipitated the problem?

e). Outline the pathophysiological mechanism of this problem

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College Answer

a) . What problem is demonstrated?
•    Intermittent failure of ventricular capture.


b). Outline the steps that you could take to address the problem.
•     Increase the ventricular output
•     Check the connections to the pacemaker and pacing connector leads
•     Reverse the polarity of the pacing to the ventricle
•     Replace pacemaker box and pacing connector leads
•     Unipolar pacing, with a cutaneous pacing stitch. This may fix the problem if one lead is faulty.
•     Chronotropic therapy eg isoprenaline
•     Alternative pacing method: transcutaneous, transvenous
•    Open the chest and replace the epicardial wires

c). What problem is demonstrated?
•     Pacemaker mediated tachycardia

d). What precipitated the problem?
•    A ventricular ectopic

e). Outline the pathophysiological mechanism of this problem
•    The dual chamber pacemaker is forming part of a re-entry circuit. A ventricular ectopic has triggered retrograde conduction along the patient’s conducting system. The resulting P-wave has been sensed by the atrial lead of the pacemaker, and this has triggered ventricular pacing. The paced ventricular impulse has triggered retrograde conduction along the patient’s normal conducting system, and the cycle continues.

Discussion

Elaborate detail is given elsewhere to the troubleshooting of a temporary pacemaker circuit. None of the college answers are surprising or requiring of any additional research. Failure of capture, at least, is a common enough occurrence that most people would have some intuitive grasp of how to answer it in writing.

References