Sick sinus syndrome

Sick sinus syndrome (SSS) refers to the dysfunction of the sinoatrial node and is responsible for several types of arrhythmia. It comprises bradyarrhythmias (e.g., sinus bradycardia, sinoatrial pauses, blocks, and arrest), and may alternate with supraventricular tachyarrhythmias, in which case it is referred to as tachycardia-bradycardia syndrome. The most common SSS arrhythmias are sinus bradycardia and non-respiratory sinus arrhythmia. SSS typically occurs in the elderly. Depending on the extent of bradycardia or tachycardia, the condition may be asymptomatic or present with symptoms such as palpitations or dyspnea. More serious manifestations, such as lightheadedness and syncope, are indications for pacemaker placement.

• Degeneration and fibrosis of the sinoatrial node and surrounding myocardium (most common cause)
• Medications (e.g., β-blockers, digoxin, non-dihydropyridine calcium channel blockers such as verapamil and diltiazem)

References:^[1]

Symptoms vary or may be entirely absent depending on the extent of bradycardia or tachycardia.

• Symptoms of bradycardia
  • Dizziness
  • Syncope, presyncope
  • Lack of increasing heart rate during physical activity
  • Adams-Stokes attacks
• Tachycardia-bradycardia syndrome presents with additional symptoms:
  • Palpitations
  • Dyspnea
  • Angina pectoris

References:^[1][2][3][4]

Symptoms or ECG findings may be inconclusive if considered on their own. Therefore, it is very important to establish a correlation between the underlying rhythm and symptom manifestation.

• ECG:
  • Non-respiratory sinus arrhythmia, bradycardia, sinus arrest, sinoatrial pauses, or SA block
  • In cases of tachycardia-bradycardia syndrome: atrial tachycardia, atrial flutter, or atrial fibrillation
  • Holter monitor: detects bradycardic episodes and sinus pauses
• Exercise stress testing; : shows an inadequate increasing heart rate during physical activity (also called chronotropic incompetence)
• Atropine challenge test: shows an inadequate increasing heart rate after administration of atropine.
• Electrophysiology studies: may show prolonged sinus node recovery time.

References:^[1][2][3]

Management depends on the symptoms of each patient, most notably on the length of sinus pauses.

• All patients: address reversible causes (e.g., side effects of medication)
• Asymptomatic patients: no pacemaker placement needed
• Symptomatic patients
  • Initial therapy for hemodynamically unstable patients
    1. First-line: atropine
    2. Temporary cardiac pacing
  • Long-term therapy
    • Isolated symptoms of bradycardia; : pacemaker placement
    • Tachycardia-bradycardia syndrome requires treatment of both tachycardia and bradycardia.
      • In the case of atrial fibrillation or flutter: The need for anticoagulation should be evaluated (see CHA₂DS₂-VASc score).
      • Pacemaker placement
      • Medical therapy: e.g., ß1-selective (cardioselective) beta blockers (e.g., metoprolol, bisoprolol)

References:^[3]