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Sinus node dysfunction, previously known as sick sinus syndrome, is characterized by abnormal initiation and propagation of electrical impulses from the sinoatrial node (SAN). The resulting abnormalities include bradycardia (less than 50 beats per minute [bpm]), sinus pause (more than three seconds), sinus arrest, and sinoatrial exit blocks, which are sometimes associated with supraventricular tachyarrhythmias in bradycardia-tachycardia syndrome1–4 (Table 15–11). Bradycardia-tachycardia syndrome occurs in approximately 50% of patients with sinus node dysfunction and increases the risk of stroke and death.5,12 Symptoms manifest as end-organ hypoperfusion, including palpitations, decreased physical activity tolerance, easy fatigability, dizziness, and syncope.2,5,6,13 To diagnose sinus node dysfunction, a combination of symptoms and documented electrical abnormalities must be present.5,7
SORT: KEY RECOMMENDATIONS FOR PRACTICE
| Clinical recommendation | Evidence rating | Comments |
|---|---|---|
| A diagnosis of sinus node dysfunction requires direct correlation of observed bradyarrhythmia with symptoms of end-organ hypoperfusion.2,5 | C | Expert opinion and consensus guideline |
| Permanent pacemaker placement with atrial-based pacing is the first-line therapy for symptomatic treatment of sinus node dysfunction.2,5,37,38 | B | Expert opinion, consensus guidelines, and randomized controlled trial with three-year follow-up analysis |
| In patients who decline permanent pacemaker placement, a trial of phosphodiesterase inhibitors may be effective for controlling symptoms associated with sinus node dysfunction.2,35 | C | Consensus guideline and retrospective case-control study |
A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to
Bradyarrhythmia Electrocardiography Findings in Sinus Node Dysfunction
| Finding | Description |
|---|---|
| Bradycardia | Sinus bradycardia: sinus rhythm with HR < 50 bpm |
| Bradycardia-tachycardia syndrome | Present in 50% of patients at time of sinus node dysfunction diagnosis; atrial tachyarrhythmias alternating with bradycardia |
| Sinus node arrest | Complete loss of automaticity of the sinus node; prolonged asystole with or without escape rhythm (junctional or idioventricular) |
| Sinoatrial exit block | First-degree: conduction delay between the sinoatrial node and atrial tissue; bradycardia as above |