sick sinus syndrome

Sick sinus syndrome results from intrinsic SA node dysfunction, often due to idiopathic fibrosis of the SA node and surrounding atrial tissue in elderly patients. Other causes include ischemia (right coronary artery disease, since RCA typically supplies the SA node), infiltrative diseases (amyloidosis, sarcoidosis, hemochromatosis), surgical trauma, myocarditis, and drug effects (beta-blockers, calcium channel blockers, digoxin, antiarrhythmics).

Clinical manifestations are variable and include sinus bradycardia, sinus pauses or arrest, sinoatrial exit block, and tachy-brady syndrome (alternating bradyarrhythmias with paroxysmal atrial fibrillation/flutter or atrial tachycardia). Patients may be asymptomatic or present with fatigue, dizziness, presyncope, syncope (due to pauses), and palpitations (during tachycardic phases). Tachy-brady syndrome increases thromboembolic risk due to the atrial fibrillation component, necessitating anticoagulation consideration.

Diagnosis is primarily based on correlating symptoms with ECG findings during an arrhythmic episode. Since episodes can be paroxysmal, ambulatory monitoring (Holter monitor, event recorder, or implantable loop recorder) is often required to capture the abnormal rhythm. Electrophysiological study (sinus node recovery time) can be used in equivocal cases.

Management: Asymptomatic patients may only need observation. Symptomatic bradycardia or significant pauses typically require permanent pacemaker implantation, as pharmacologic therapy for bradycardia (e.g., atropine) is often ineffective long-term. If tachy-brady syndrome is present, rate-controlling or antiarrhythmic medications for the tachycardic component may worsen bradycardia, making pacemaker placement essential before initiating such therapy. Anticoagulation should be considered if atrial fibrillation is present given stroke risk.