This 58-year-old man presented to the Emergency Department with a two year history of paroxysmal palpitations accompanied by dyspnea and weakness:

• Atrial flutter with variable AV conduction – ventricular rate 100/min
• Minimal criteria for left ventricular hypertrophy

Typical atrial flutter with counterclockwise rotation (negative sawtooth flutter waves in II, III and aVF, positive flutter waves in V1). Counterclockwise rotation occurs in 90% of cases of flutter.

Three hours later, the following ECG was obtained:

• Atrial flutter with variable AV conduction- ventricular rate 78/min

Comment: This ECG shows the pattern of atrial flutter with clockwise rotation (flutter waves positive in II, III and aVF, negative in V1). Clockwise rotation is relatively uncommon, as it occurs in about 10% of cases of flutter. Interestingly, both the patterns of counterclockwise and clockwise rotation occurred in ECGs of this patient recorded with a period of three hours. Ablation may be carried out successfully both in cases of counterclockwise and clockwise rotation, as the reentrant loop in both rhythms involve the cavotricuspid isthmus (CTI). This patient underwent successful ablation and became free of tachyarrhythmias.