Etiologies are either intrinsic (degenerative, ischemic, inflammatory, infiltrative [e.g., amyloid], or rare mutations in sodium channel or pacemaker current genes) or extrinsic (e.g., drugs [beta blockers, Ca++ channel blockers, digoxin], autonomic dysfunction, hypothyroidism).

Symptoms are due to bradycardia (fatigue, weakness, lightheadedness, syncope) and/or episodes of associated tachycardia (e.g., rapid palpitations, angina) in pts with sick sinus syndrome (SSS).

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