What do the letters of the pacemaker pacing codes indicate?

Updated: Oct 11, 2019
  • Author: Daniel M Beyerbach, MD, PhD; Chief Editor: Jeffrey N Rottman, MD  more...
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A typical pacing code consists of 3-5 letters. The first letter indicates the chamber(s) paced, as follows:

  • A - Atrial pacing

  • V - Ventricular pacing

  • D - Dual-chamber (atrial and ventricular) pacing

The second letter indicates the chamber in which electrical activity is sensed, as follows:

  • A, V, or D

  • O is used when pacemaker discharge is not dependent on sensing electrical activity.

The third letter refers to the response to a sensed electric signal, as follows:

  • T - Triggering of pacing function

  • I - Inhibition of pacing function

  • D - Dual response (ie, any spontaneous atrial and ventricular activity will inhibit atrial and ventricular pacing, and lone atrial activity will trigger a paced ventricular response)

  • O - No response to an underlying electric signal (usually related to the absence of associated sensing function)

The fourth letter represents rate modulation, as follows:

  • R - Rate-response ("physiologic") pacing

  • O - No programmability or rate modulation

The fifth letter represents multisite pacing, as follows:

  • A - Atrial

  • V - Ventricular

  • D - Dual (pacing + shock)

Although the first 3 letters of the pacing code are used most commonly, a 5-position code is currently in use.

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