A 76-year-old woman had a 2 years history of episodes of atrial fibrillation with rapid ventricular response. She was on Digoxin and Atenolol. The following ECG is recorded in the emergency department, where she is brought by ambulance after she fainted at home: 

• Marked sinus bradycardia with sinus pause
• Escape junctional complexes
• One sinus complex shows aberrant conduction with right bundle branch block pattern (Ashman phenomenon)

This is a typical case of Sick Sinus node Syndrome (SSS). The patient had episodes of atrial fibrillation with rapid ventricular response, and two years later developed episodes of marked sinus bradycardia and sinus arrest (sinus pauses greater than 5 seconds). One month before the present admission she fainted and suffered from a fractured hip. During this admission an AV sequential pacemaker was implanted. Note the long-short pause with aberrant conduction (Ashman phenomenon).