A 59 year-old man with intermittent chest pain and positive enzymes was brought to the cardiac catheterization laboratory for coronary angiography.  Prior to the procedure, the following ECG was recorded:

• Atrial Flutter with 2:1 Conduction
• Possible anterior myocardial infarction (poor R-wave progression)

Comment: This ECG was incorrectly interpreted as sinus rhythm as the p-waves can be difficult to see but are clearly negative in the inferior leads.  Closer inspection shows that there are two p-waves for every QRS complex (noted by “P” below) and the baseline of the ECG in the inferior leads has an undulating appearance typical for atrial flutter.