What does the NBG (NASPE/BPEG Generic) pacemaker code represent and how is it interpreted?

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NBG Pacemaker Code: Structure and Interpretation

The NBG (NASPE/BPEG Generic) pacemaker code is a standardized 5-position letter system that describes pacemaker function, where each position indicates: (I) chamber(s) paced, (II) chamber(s) sensed, (III) response to sensing, (IV) rate modulation capability, and (V) multisite pacing location. 1, 2

Code Structure and Position Meanings

Position I: Chamber(s) Paced

  • A = Atrium paced 3
  • V = Ventricle paced 3
  • D = Dual (both atrium and ventricle paced) 3
  • O = None (no pacing) 3

Position II: Chamber(s) Sensed

  • A = Atrium sensed 3
  • V = Ventricle sensed 3
  • D = Dual (both chambers sensed) 3
  • O = None (no sensing) 3

Position III: Response to Sensing

  • I = Inhibited (pacing output suppressed by sensed event) 3
  • T = Triggered (pacing output delivered in response to sensed event) 3
  • D = Dual (both inhibited and triggered responses) 3
  • O = None (asynchronous, no response to sensing) 3

Position IV: Rate Modulation

  • R = Rate modulation present (adaptive-rate pacing using physiologic sensors) 1, 2
  • O = None (fixed rate only) 2

Position V: Multisite Pacing

  • A = Atrium (multisite atrial pacing) 2
  • V = Ventricle (multisite ventricular pacing) 2
  • D = Dual (multisite pacing in both chambers) 2
  • O = None (single site pacing per chamber) 2

Common Pacemaker Mode Examples

AAI Mode

  • Atrial-only antibradycardia pacing where the atrium is paced if no intrinsic atrial event occurs within the programmed time window 3
  • No ventricular sensing occurs, so premature ventricular events do not reset the pacing timer 3
  • Appropriate for sinus node dysfunction with intact AV conduction 3

VVI Mode

  • Ventricular-only antibradycardia pacing where the ventricle is paced if no intrinsic ventricular event occurs 3
  • No atrial sensing, therefore no AV synchrony is maintained 3
  • Used when atrial contribution is not hemodynamically significant, such as in persistent atrial fibrillation 3

DDD Mode

  • Dual-chamber antibradycardia pacing with atrial tracking capability 3
  • Every atrial event (within programmed limits) is followed by a ventricular event 3
  • If no intrinsic atrial activity occurs, the atrium is paced; after any sensed or paced atrial event, the ventricle must depolarize before the AV timer expires or it will be paced 3
  • Can track rapid atrial rates to the ventricles, potentially causing tachycardia 4

DDI Mode

  • Dual-chamber pacing and sensing where atrial activity is tracked only when created by the pacemaker's antibradycardia function 3
  • The ventricle is paced only when no intrinsic ventricular activity is present 3
  • Provides AV synchrony at slow rates without atrial tracking, unlike DDD 3

VDD Mode

  • Ventricular pacing synchronized with sensed atrial activity, inhibited by sensed ventricular activity 3
  • Does not provide atrial pacing capability 3
  • Appropriate when adequate atrial rates and intracavitary atrial signals are present with complete AV block 3

Asynchronous Modes (AOO, VOO, DOO)

  • AOO: Asynchronous atrial-only pacing without regard to underlying rhythm 3
  • VOO: Asynchronous ventricular-only pacing without regard to underlying rhythm 3
  • DOO: Asynchronous AV sequential pacing without regard to underlying rhythm 3
  • Used perioperatively when electromagnetic interference is anticipated 3, 5

Rate-Responsive Variants

AAIR, VVIR, DDDR Modes

  • The "R" in position IV indicates rate modulation capability using physiologic sensors 1, 2
  • Sensors respond to physical activity, minute ventilation, or other physiologic variables to adjust pacing rate 3
  • VVIR is particularly contraindicated with retrograde VA conduction or when rapid rates aggravate angina or heart failure 3
  • Appropriate for patients with chronotropic incompetence and anticipated moderate to high physical activity levels 3, 4

Critical Clinical Considerations

Pacemaker Syndrome Risk

  • VVI pacing can cause pacemaker syndrome due to loss of AV synchrony, retrograde VA conduction, and cannon A waves 3
  • Symptoms include lightheadedness, syncope, inadequate cardiac output, and patient awareness of beat-to-beat variations 3
  • Known pacemaker syndrome is a Class III contraindication for VVI mode 3

Pacemaker-Mediated Tachycardia

  • DDD pacemakers can create endless-loop tachycardia by tracking retrograde P waves 4
  • Prevention requires extending post-ventricular atrial refractory period (PVARP) or using automatic PMT termination algorithms 4
  • Patients with accessory pathways capable of rapid anterograde conduction should not receive atrial-tracking pacemakers 4

Electromagnetic Interference Management

  • For procedures involving electrocautery, reprogram to asynchronous mode (VOO or DOO) in pacemaker-dependent patients 3, 5
  • Use bipolar electrocautery systems preferentially to minimize electromagnetic interference 5
  • Interrogate the device post-procedure to verify sensing/pacing thresholds remain intact 5

References

3
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

4
Guideline

Tachycardia Mechanisms and Management in Pacemaker Patients

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

5
Guideline

Pacemaker Safety During Biopsy Procedures

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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