Sinus Node Disease
The term sinus node disease, sometimes referred to as sick sinus syndrome, is applied to a wide range of sinus node conduction abnormalities, including:
- Inappropriate sinus bradycardia — a slow heart rate that does not increase with exertion and which is not caused by drugs.
- Sinoatrial exit block — missed (or ‘dropped’) beats, where the underlying rhythm is retained. Each heartbeat is initiated within the sinus node, but fails to conduct to the atria.
- Tachy-brady syndrome — sudden changes between rapid and slow heart rates controlled by the sinus node.
- Sinus arrest and asystole — pauses in excess of three seconds.
Sinus node disease increases in incidence with age and is a strong indication for artificial pacemaker implantation.
The following example shows a delay between beats of over four seconds. The RR interval is highlighted.