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). 1 This syndrome represents an important cause of morbidity that can significantly impact quality of life in patients with cardiac pacemakers.

Definition and Pathophysiology

Pacemaker syndrome includes:

1. Episodic alternating AV synchrony and asynchrony
2. Inadequate cardiac output associated with ventriculoatrial (VA) conduction
3. Patient awareness of beat-to-beat variations due to absence of AV synchrony or fixed asynchrony in cardiac contractile sequence 1

These hemodynamic disturbances manifest through several mechanisms:

• Cannon A waves (atrial contraction against closed AV valves)
• V waves transmitted to the atria or pulmonary veins
• Bundle branch block patterns of ventricular contraction with paced beats 1

Clinical Manifestations

Patients with pacemaker syndrome may experience:

• Light-headedness or syncope
• Fatigue
• Chest discomfort
• Dyspnea
• Cough
• Confusion
• Presyncope 1

These symptoms result from adverse hemodynamics caused by the loss of AV synchrony and occurrence of ventriculoatrial conduction or atrial contraction against closed AV valves 1.

Incidence and Risk Factors

The Mode Selection Trial (MOST) found that approximately 18.3% of patients with sinus node dysfunction treated with ventricular-based (VVIR) pacing developed pacemaker syndrome, with most cases occurring early (13.8% at 6 months, 16.0% at 1 year, increasing to 19.7% at 4 years) 2.

Risk factors associated with pacemaker syndrome include:

• Lower sinus rate
• Higher programmed pacemaker rate
• Higher percentage of paced beats
• Presence of retrograde VA conduction 2

Diagnosis

Diagnosis of pacemaker syndrome requires:

1. Development of congestive signs and symptoms associated with retrograde conduction during VVIR pacing, OR
2. A ≥20 mm Hg reduction of systolic blood pressure during VVIR pacing associated with reproducible symptoms of weakness, lightheadedness, or syncope 2

Transesophageal pulsed Doppler echocardiography can be used to assess pulmonary venous flow, which shows marked augmentation of the normally small pulmonary venous z wave ("cannon z waves") in patients with pacemaker syndrome 3.

Prevention and Management

The primary approach to preventing pacemaker syndrome is to maintain proper AV synchrony through appropriate pacing mode selection:

• For sinus node dysfunction: Atrial-based pacing (AAI or DDD) is preferred 1
• For AV block: Dual-chamber pacing (DDD) is recommended 1, 4

When pacemaker syndrome develops in patients with VVI pacing, reprogramming to dual-chamber pacing (DDD) mode can significantly improve quality of life 2. This change restores AV synchrony and abolishes the hemodynamic disturbances associated with the syndrome.

Expanded Concept: Beyond VVI Pacing

While pacemaker syndrome is most commonly associated with VVI pacing, it can occur in other contexts:

1. Pseudopacemaker syndrome: Can occur in patients with marked first-degree AV block without a pacemaker, when the P wave is too close to the preceding QRS complex, producing similar hemodynamic disturbances 5

2. Rare occurrences in atrial and dual-chamber pacing: Although uncommon, pacemaker syndrome can sometimes be seen with other pacing modes 4

Clinical Implications

The high incidence of pacemaker syndrome in patients with ventricular-based pacing (nearly 20% in MOST) suggests that:

1. Prediction of which patients will develop pacemaker syndrome is difficult
2. The most effective prevention strategy is to implant atrial-based pacemakers in all patients when possible 2
3. Regular monitoring for symptoms of pacemaker syndrome is essential in all patients with cardiac pacemakers

Proper pacemaker mode selection and programming are crucial for preventing this iatrogenic condition and optimizing patient outcomes.