Sick sinus syndrome

Sick sinus syndrome is dysfunction of the heart’s sinus node that disrupts normal impulse formation. It can cause bradycardia, pauses, or alternating slow and fast heart rhythms.

Sinus node: The heart’s natural pacemaker, a cluster of cells in the right atrium that initiates each normal heartbeat. Dysfunction of this pacemaker produces the defining rhythm abnormalities.
Electrocardiography: The recording of the heart’s electrical activity from electrodes placed on the body. It can reveal slow rhythms, pauses, and associated atrial arrhythmias.
Cardiac conduction system: The network of specialized heart tissue that generates and conducts electrical impulses coordinating each heartbeat. Sinus-node dysfunction is one disorder within this impulse-generating and conducting network.
Syncope: A brief loss of consciousness caused by transiently reduced blood flow to the brain. Long pauses or very slow rates can temporarily reduce cerebral blood flow.
Sinus bradycardia: A sinus rhythm with a heart rate below the usual adult resting range. Impaired sinus-node impulse formation can slow the heart rate.
Holter monitor: A portable electrocardiogram that continuously records heart rhythm, usually for one or two days. Continuous recording can connect intermittent symptoms to rhythm disturbances.
Cardiac action potential: A brief change in cardiac-cell membrane voltage that generates and propagates electrical activity. Altered pacemaker-cell electrical activity underlies abnormal impulse formation.
Presyncope: A sensation of impending fainting without complete loss of consciousness. Reduced cardiac output during slow rhythms can cause near-fainting.
Sinus pause: A temporary absence of electrical impulses from the sinus node. Extended pauses are a characteristic expression of sinus-node dysfunction.
Event monitor: A wearable device that records heart rhythm during symptoms or over an extended monitoring period. Longer monitoring helps capture infrequent pauses or episodes of abnormal rhythm.

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