From the Guidelines
Single chamber pacemakers are recommended for patients with bradycardia, sick sinus syndrome, or heart block who only need pacing in one chamber, particularly the elderly or those with permanent atrial fibrillation. The most common type is the ventricular pacemaker (VVI mode), which senses activity in the ventricle and paces it when necessary 1. For patients with intact AV node conduction but sinus node dysfunction, an atrial pacemaker (AAI mode) may be used.
Key Considerations
- The procedure to implant a single chamber pacemaker is minimally invasive, usually performed under local anesthesia with conscious sedation, and typically takes 1-2 hours.
- Recovery involves limiting arm movement on the implant side for about a month and avoiding strong magnetic fields.
- Regular follow-up appointments are essential to check battery life (which lasts 7-10 years) and ensure proper functioning.
- While dual-chamber pacemakers are often preferred for maintaining AV synchrony, single chamber devices are simpler, have fewer complications, and are appropriate for many patients.
Clinical Guidelines
- According to the 2012 HRS/ACCF expert consensus statement, single-chamber ventricular pacing (VVI) may be considered in instances where frequent pacing is not expected or the patient has significant comorbidities that are likely to influence survival and clinical outcomes (Level of Evidence: C) 1.
- The statement also recommends dual-chamber pacing (DDD) or single-chamber atrial pacing (AAI) over single-chamber ventricular pacing (VVI) in patients with sinus node dysfunction and intact AV conduction (Level of Evidence: A) 1.
Patient Selection
- Single chamber pacemakers are suitable for patients with specific clinical situations that limit the benefits of dual-chamber pacing, such as sedentary patients, those with significant medical comorbidities likely to impact clinical outcomes, and those in whom technical issues preclude or increase the risk of placing an atrial lead 1.
- They are also appropriate for patients with permanent or longstanding persistent atrial fibrillation in whom efforts to restore or maintain sinus rhythm are not planned 1.
From the Research
Single Chamber PM and Atrial Fibrillation
- Single chamber pacemakers (PM) are often used to treat sinus node dysfunction (SND), which can co-exist with atrial fibrillation (AF) 2, 3.
- Studies have shown that SND affects up to one in five patients with AF, and the pathophysiological derangements associated with AF can lead to anatomic and electrical changes in the region of the sinoatrial node 2.
- The relationship between SND and AF is complex, and may involve common factors and mechanisms such as ion channel remodeling, gap junction abnormalities, and structural remodeling 3.
Treatment Approaches
- Catheter ablation, including pulmonary vein isolation, may be effective in reducing episodes of tachybrady syndrome and sinus pauses in patients with AF and SND 2, 4.
- Permanent pacing, including single chamber PM, may be used to manage SND, but the optimal pacing strategy for reducing the risk of AF is unclear 2, 4.
- Ganglionated plexus (GP) ablation may also be effective in achieving a dual therapeutic effect on both SND and AF by acting on common mechanisms 3.
Underlying Mechanisms
- Ion channel remodeling, including alterations in the "funny" current (If) and Ca2+ clock, can contribute to the development of AF and SND 3, 5.
- Gap junction abnormalities, including decreased expression of connexins (Cxs), can also play a role in the pathogenesis of AF and SND 3, 5.
- Structural remodeling, including fibrosis and cardiac amyloidosis (CA), can further increase the susceptibility to sustained reentry and SAN dysfunction 3, 5.