Hereditary sick sinus syndrome

Hereditary sick sinus syndrome (also known as familial sick sinus syndrome or hereditary sinus node dysfunction) is a rare genetic cardiac rhythm disorder characterized by dysfunction of the sinoatrial (SA) node, the heart's natural pacemaker. Unlike the more common acquired form of sick sinus syndrome seen in elderly patients, the hereditary form is caused by inherited mutations in genes critical for normal SA node function, most notably SCN5A (encoding the cardiac sodium channel Nav1.5) and HCN4 (encoding the hyperpolarization-activated cyclic nucleotide-gated channel 4). These genetic defects impair the ability of the sinus node to generate or conduct electrical impulses properly. The condition primarily affects the cardiovascular system and manifests with inappropriate sinus bradycardia (abnormally slow heart rate), sinus arrest or sinus pauses, sinoatrial exit block, and chronotropic incompetence (inability of the heart rate to increase appropriately with physical activity). Patients may experience syncope (fainting), presyncope, dizziness, fatigue, exercise intolerance, and palpitations. In some cases, the condition can present with a tachy-brady syndrome, where episodes of atrial tachyarrhythmias alternate with periods of bradycardia. Severe cases may present in infancy or childhood, while milder forms may not become apparent until adulthood. Treatment of hereditary sick sinus syndrome is primarily symptomatic. Permanent pacemaker implantation is the mainstay of therapy for patients with symptomatic bradycardia, syncope, or hemodynamic compromise. Antiarrhythmic medications may be used to manage associated tachyarrhythmias, though these often require concurrent pacemaker support to prevent worsening of bradycardia. Genetic counseling is recommended for affected families. Long-term follow-up with a cardiologist or cardiac electrophysiologist is essential, as the condition may be progressive and associated with an increased risk of atrial fibrillation and thromboembolic events.

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