Pacemaker Panic

aka ECG Exigency 012

You grab the chart of the next patient to be seen, the triage note states that he has a permanent pacemaker in situ.


Q1. What is a pacemaker and what are its components?

A pacemaker is a device that administers electrical energy to the heart to stimulate contraction and regulate its rhythm.  Pacemakers may be permanent or temporary (e.g. transcutaneous, transvenous or epicardial wires).

The essential components of a pacemaker are:

  • Pulse generator (the power source)
  • Output circuit
  • Sensing circuit
  • Timing circuit
  • Pacing leads

Its important to remember these components when trouble-shooting problems with pacemakers…

The patient’s nurse hands you the patient’s rhythm strip:

pacemaker 1
Click to enlarge

Q2. What is the pacing mode in this case?


Q3. What does this pacing mode mean?

These three letters represent a pacing code (the NBG Pacemaker Code). Each letter has a specific meaning depending on its position. A fourth and a fifth letter may also be used to indicate that the pacemaker is programmable or anti-tachyarrhythmia functions.

This is what DDD actually means:

1st letter: Chamber paced — dual chamber (atrial and ventricle)
2nd letter: Chamber sensed — dual chamber (atrial and ventricle)
3rd letter: Pacemaker response to a sensed event — dual response (can trigger or inhibit)

Thus a pacemaker functioning in DDD mode can pace either or both the atria and ventricles. It can sense and respond to endogenous electrical activity from either the atria or the ventricles. Spontaneous atrial and ventricular activity will inhibit atrial and ventricular pacing. If there is atrial activity without ventricular activity, then only ventricular pacing will be triggered.

Q4. Is the pacemaker functioning correctly? If not, in what way?

The pacemaker is functioning correctly.

Click to enlarge

There is an atrial pacing spike (A) followed by a ventricular pacing spike (B) after an appropriate delay to allow for AV conduction. This pattern is also seen elsewhere in the rhythm strip, and in each case the pacing spike is capturing (it is appropriately followed by either an atrial or ventricular complex).

There are two instances where the pacemaker senses endogenous atrial activity (C). This inhibits the delivery of an atrial pacing spike, but after an appropriate delay (to allow for AV conduction) a ventricular pacing spike is delivered (as no endogenous ventricular activity is detected).

The pacemaker also appropriately sensed endogenous ventricular activity in the form of a ventricular ectopic (D) (aka a PVC or premature ventricular contraction). No pacing spikes were delivered, indicating appropriate inhibition.

Q5. If this patient develops ventricular fibrillation, is it safe to defibrillate him?


Be sure to keep the paddles or gel pads away from the pacemaker when performing defibrillation — antero-posterior placement is preferable.

How far? As far away as possible… At least 10 cm.

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  1. says

    When you say "anteroposterior" placement is preferable, do you mean that the patient has to be rolled on her side to defibrillate? Is that a common position for defibrillation and how do you accomplish it (pillows & blankets so everyone can stay clear?)