Sick Sinus Syndrome is characterized on ECG by which pattern?

• A. Atrial fibrillation with rapid ventricular response
• B. Atrioventricular block type II
• C. Sinus arrest with alternating paroxysms of atrial tachyarrhythmias and bradyarrhythmias
• D. Ventricular tachycardia

Answer: (C)

Sick sinus syndrome reflects malfunction of the sinus node, so the ECG pattern you’d expect is a tachy-brady situation: periods of bradycardia or sinus pauses interspersed with episodes of atrial tachyarrhythmias. The classic description is sinus arrest with alternating paroxysms of atrial tachyarrhythmias and bradyarrhythmias. In practice, this means you can see long pauses or slow heart rhythms, then sudden bursts of fast atrial activity that eventually give way to another slow rhythm as the sinus node recovers. This differs from atrial fibrillation with rapid response, which is a continuous atrial tachyarrhythmia rather than a sinus node–driven pattern, from AV block type II, which is a conduction problem below the SA node, and from ventricular tachycardia, which originates in the ventricles.