What is pacemaker syndrome?

Pacemaker Syndrome: Definition and Clinical Implications

Pacemaker syndrome is a clinical condition characterized by symptoms resulting from the loss of normal atrioventricular (AV) synchrony, most commonly occurring in patients with ventricular-based pacing (VVI mode), which significantly impacts quality of life and represents an important cause of morbidity. 1

Mechanisms and Pathophysiology

Pacemaker syndrome develops through several key mechanisms:

• Loss of AV synchrony: The primary pathophysiological mechanism involves improper timing between atrial and ventricular contractions 2
• Retrograde ventriculoatrial (VA) conduction: When the ventricle contracts before the atrium, blood can be forced backward into the atria 1
• Hemodynamic disturbances: These manifest through:
  • Cannon A waves (atrial contraction against closed AV valves)
  • Elevated venous pressure
  • Decreased cardiac output
  • Potential activation of vasodepressor reflexes 1, 2

Clinical Presentation

Patients with pacemaker syndrome typically present with:

• Light-headedness or syncope
• Fatigue and exercise intolerance
• Chest discomfort
• Dyspnea and cough
• Confusion
• Presyncope
• Signs of congestive heart failure 1

These symptoms occur due to:

1. Episodic alternating AV synchrony and asynchrony
2. Inadequate cardiac output associated with VA conduction
3. Patient awareness of beat-to-beat variations in cardiac contractile sequence 1

Incidence and Risk Factors

The Mode Selection Trial (MOST) found that:

• Approximately 18.3% of patients with sinus node dysfunction treated with VVIR pacing developed pacemaker syndrome
• Most cases occurred early (13.8% at 6 months, 16.0% at 1 year)
• Baseline predictors included lower sinus rate and higher programmed pacemaker rate
• Post-implantation predictors were higher percentage of paced beats, higher programmed low rate, and slower underlying sinus rate 3

Prevention and Management

The American College of Cardiology recommends:

• For sinus node dysfunction: Atrial-based pacing (AAI or DDD) is preferred to maintain proper AV synchrony 4, 1
• For AV block: Dual-chamber pacing (DDD) is recommended 1
• For established pacemaker syndrome: Reprogramming to dual-chamber pacing (DDD) mode can significantly improve quality of life 1, 3

Special Considerations

Pseudopacemaker Syndrome

• Can occur without a pacemaker in patients with marked first-degree AV block
• Produces similar hemodynamic disturbances as artificial pacemaker stimulation with retrograde VA conduction 5

Broader Definition

Some experts propose that pacemaker syndrome represents the clinical consequences of suboptimal AV synchrony or AV dyssynchrony, regardless of the pacing mode 6

Pitfalls and Caveats

1. Underdiagnosis: Pacemaker syndrome is often underdiagnosed as an iatrogenic disease 6
2. Difficult prediction: Because prediction of pacemaker syndrome is difficult, some experts suggest that the only way to prevent it is to implant atrial-based pacemakers in all patients 3
3. Not limited to VVI mode: While most common with ventricular pacing, pacemaker syndrome can rarely occur with atrial and dual-chamber pacing 2
4. Timing matters: Symptoms typically emerge when pacing begins, making the temporal relationship important for diagnosis 7

When evaluating patients with cardiac pacemakers who develop new symptoms, always consider pacemaker syndrome, especially if they have ventricular-based pacing systems.