Can sick sinus syndrome (SSS) contribute to slow atrial fibrillation (AFib)?

Sick Sinus Syndrome Can Contribute to Slow Atrial Fibrillation

Yes, sick sinus syndrome (SSS) can contribute to slow atrial fibrillation, as SSS affects the heart's intrinsic pacemaker function and can result in bradycardic atrial fibrillation. This relationship is recognized in clinical guidelines and has important implications for diagnosis and management.

Pathophysiological Connection

• SSS represents a spectrum of sinus node dysfunction that includes:

  • Sinus bradycardia
  • Sinus pauses or arrest
  • Sinoatrial exit block
  • Chronotropic incompetence
  • Bradycardia-tachycardia syndrome 1

• The connection between SSS and slow atrial fibrillation occurs through several mechanisms:

  1. Shared pathophysiology: Both conditions often result from age-related degenerative changes in the cardiac conduction system 2
  2. Bradycardia-tachycardia syndrome: A specific form of SSS where bradycardia alternates with tachyarrhythmias, including atrial fibrillation 1
  3. Post-conversion pauses: After termination of atrial fibrillation, patients with SSS may experience prolonged sinus pauses due to suppressed sinus node automaticity 1

Diagnostic Considerations

• Electrocardiographic evidence must document both:

  • Bradycardia component (sinus bradycardia, sinus pause, or sinus node arrest)
  • Tachycardia component (which may include atrial fibrillation) 1

• Extended monitoring is often necessary to capture the relationship between SSS and atrial fibrillation:

  • 24-hour Holter monitoring
  • Event monitoring
  • Implantable loop recorder
  • Inpatient telemetry 1

• A temporal relationship between tachycardia and bradycardia is important, as tachycardia can suppress sinus node automaticity and cause sinus pauses 1

Clinical Implications

• Patients with SSS have a high incidence of developing atrial fibrillation:

  • 8.2% at initial diagnosis
  • Increasing to 15.8% during follow-up 2

• Atrial flutter is strongly associated with an increased risk of incident SSS, especially in patients with coexisting atrial fibrillation 3

• The combination of SSS and atrial fibrillation increases thromboembolic risk:

  • 15.2% risk of systemic embolism in unpaced SSS patients compared to 1.3% in age-matched controls 2

Management Considerations

• Pacing therapy: Permanent pacing is indicated when symptoms correlate with bradycardia 1

  • Dual-chamber pacing (DDDR) is preferred over single-chamber ventricular pacing
  • Atrial-based minimal ventricular pacing modes may be considered as alternatives

• Medication management:

  • Caution with bradycardia-inducing medications:
    • Beta-blockers
    • Non-dihydropyridine calcium channel blockers (especially verapamil and diltiazem)
    • Antiarrhythmic drugs 2, 4
  • Diltiazem is specifically contraindicated in patients with SSS except in the presence of a functioning ventricular pacemaker 4

• Anticoagulation: Should be considered in patients with SSS and atrial fibrillation due to increased thromboembolic risk 1

Important Clinical Pitfalls

• Medication-induced bradycardia: Always rule out extrinsic causes of bradycardia before diagnosing intrinsic SSS 1

• Pacemaker mode selection: VVI or VVIR pacing should be avoided in SSS as it may increase the risk of atrial fibrillation compared to atrial-based pacing 2, 1

• Monitoring after ablation: Patients with SSS and paroxysmal atrial fibrillation who undergo catheter ablation may still require pacemaker implantation (13.8% in one study), with SSS type 1 being a significant predictor 5

• Physiologic bradycardia: Distinguish normal physiologic bradycardia (as in trained athletes) from pathological SSS 1

By understanding the relationship between SSS and slow atrial fibrillation, clinicians can better diagnose and manage this complex cardiac condition, ultimately improving patient outcomes through appropriate pacing strategies and medication management.