Pacemaker nomenclature

Advanced, Basic Sciences

Pacemakers and intra-cardiac defibrillators share a similar nomenclature which was developed as a way to standardize programming across the world. For both devices, the first letter indicates the chamber(s) paced, the second indicates the chamber(s) sensed, and the third letter indicates the response(s) to sensing. For example, a programming of VVO indicates that the ventricle is paced, the ventricle is sensed, and there is no response to sensing. Table 1 and 2 are the Generic Pacemaker and Defibrillator Codes respectively. 

See Table 1


AAI: atrial-only antibradycardia pacing in which any failure of the atrium to produce an intrinsic event, within the appropriate time window (determined by the lower rate limit), will result in an atrial pacing pulse emission. There is no ventricular sensing; thus a premature ventricular event will not likely reset the pacing timer. 

AOO: asynchronous atrial-only pacing in which the pacing device emits a pacing pulse, regardless of the underlying cardiac rhythm. 

DDD: dual-chamber antibradycardia pacing function in which every atrial event, within programmed limits, will be followed by a ventricular event. The DDD mode implies dual chamber pacing with atrial tracking. In the absence of intrinsic activity in the atrium, it

will be paced, and, after any sensed or paced atrial event, an intrinsic ventricular event must appear before the expiration of the atrioventricular (A-V) timer or the ventricle will be paced. 

DDI: dual-chamber behavior in which the atrial activity is tracked into the ventricle only when the atrial event is created by the antibradycardia pacing function of the generator. In the DDI mode, the ventricle is paced only when no intrinsic ventricular activity

is present. 

DOO: asynchronous A-V sequential pacing without regard to underlying cardiac rhythm. VOO: asynchronous ventricular-only pacing without regard to the underlying cardiac rhythm. 

VVI: ventricular-only antibradycardia pacing in which any failure of the ventricle to produce an intrinsic event, within the appropriate time window (determined by the lower rate limit), will result in a ventricular pacing pulse emission. There is no atrial sensing; thus, there can be no A-V synchrony in a patient with a VVI pacemaker and any intrinsic atrial activity.

* NBG: N refers to NASPE, B refers to BPEG, and G refers to generic.

See Table 2

* For robust identification, Position IV is expanded into its complete NBG code. For example, a biventricular pacing defibrillator with ventricular shock and antitachycardia pacing functionality would be identified as VVE-DDDRV, assuming that the pacing section was programmed DDDRV. Currently, no hemodynamic sensors have been approved for tachycardia detection (Position III).

Table 1: General Pacemaker Codes (NBG*): NASPE/BPEG Revised (2002) at

Table 2: General Defibrillator Codes (NBG): NASPE/BPEG at


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Abdullah S. Terkawi, MD