Normal cardiac automaticity is essential for proper functioning of the heart as a rhythmic pump that moves the blood through the circulatory system. The sinus node normally displays the highest rate of automaticity and as such is the primary pacemaker in the normal heart. It initiates the heartbeat and adapts its rate to optimize cardiac performance according to metabolic demands. Sinus node dysfunction (SND), also called sick sinus syndrome, constitutes a spectrum of rhythm disturbances including sinus bradycardia, sinus pause, sino-atrial exit block, and tachy-brady syndrome.
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