A 66-year-old man presents to the emergency department with palpitations and dyspnea:

• Atrial flutter with 2:1 AV conduction
• Ventricular rate 146/min

Clues that suggest atrial flutter with 2:1 AV conduction:

• A regular narrow-QRS tachycardia with a ventricular rate close to 150/min
• Broad negative waves in the inferior leads  
• Pseudo-r’ waves in V1 that are equidistant from the P waves preceding the QRS

The patient is admitted to hospital for investigation and treatment. He receives digoxin and his symptoms improve. The following ECG is recorded the next day:

• Atrial flutter with variable AV conduction
• Ventricular rate 109/min
• ST and T wave abnormality, consider ischemia or digitalis effect