What are the different types of cardiac pacemakers?

Types of Cardiac Pacemakers

Cardiac pacemakers are fundamentally categorized into two main varieties: single-chamber pacemakers (for use in either atrium or ventricle) and dual-chamber pacemakers (for use in both atrial and ventricular chambers), with modern devices offering multiprogrammable capabilities and optional rate-responsive features 1.

Primary Classification by Chamber

Single-Chamber Pacemakers

Single-chamber devices pace and sense in one cardiac chamber only:

• Atrial (AAI/AAIR): Paces the atrium, inhibited by sensed atrial activity. The "R" designation indicates rate-responsive capability 2, 3
• Ventricular (VVI/VVIR): The classic ventricular pacing mode, inhibited by sensed spontaneous ventricular activity 1, 2

Dual-Chamber Pacemakers

Dual-chamber devices can pace and sense in both chambers, usually programmable to single-chamber modes as well 1:

• DDD/DDDR: Paces both chambers, senses both chambers, with atrial tracking capability. Every atrial event within programmed limits is followed by a ventricular event 2
• VDD: Ventricular pacing synchronized with sensed atrial activity, inhibited by sensed ventricular activity. Does not provide atrial pacing 1
• DVI/DVIR: Paces both chambers at a preselected rate, inhibited by ventricular but not atrial complexes 1
• DDI/DDIR: Dual-chamber pacing and sensing, inhibited by sensed events in both chambers, but without atrial tracking 1

Rate-Responsive (Adaptive Rate) Pacemakers

Many modern pacemakers incorporate sensors that respond to variables other than P waves to increase pacing rate 1. These adaptive rate pacemakers utilize sensors responding to:

Electrical phenomena:

• Impedance variations (respiratory rate, minute ventilation, right ventricular stroke volume, dP/dt and dV/dt)
• Intracardiac potentials (stimulus to T wave intervals, evoked potentials) 1

Important caveat: While some believe single-chamber adaptive rate pacemakers are equivalent to standard dual-chamber pacemakers, at slow heart rates it is almost always desirable to maintain AV synchrony. Long-term absence of AV synchrony increases the incidence of atrial fibrillation and stroke and may reduce patient life expectancy, particularly in patients with impaired ventricular function 1.

Key Programming Features

Virtually all modern pacemakers are multiprogrammable, making them adaptable to changing clinical situations 1. They provide:

• Telemetry of stored and variable data
• Information about pacemaker function and clinical performance
• Optimization of pacemaker function to avoid reoperation and extend battery life 1

Selection Considerations

When choosing between pacemaker types, consider 1:

1. The cardiac conduction abnormality
2. Nature and severity of comorbidities
3. Presence of coronary heart disease and angina pectoris
4. Degree of left ventricular dysfunction
5. Impact of present and future drug therapy
6. Level of anticipated activity
7. Availability of support services and follow-up clinics
8. Expertise of implant teams
9. Costs

Critical distinction: For sinus node dysfunction with intact AV conduction, dual-chamber pacing (DDD) or single-chamber atrial pacing (AAI) is recommended over single-chamber ventricular pacing (VVI) 3. For AV node disease, dual-chamber pacing is recommended 3.