Bi-morphic atrial flutter

A case of atrial flutter whose classic "saw-tooth" morphology, resistant to full doses of digoxin and quinidine, was changed to an unusual form by low energy direct current shock is presented. The atrial and ventricular rates remained identical in spite of the different F wave pattern before and after attempted cardioversions. 0.5 mg digoxin was given after cardioversion failed and the patient reverted to normal sinus rhythm. This case strengthens the theory of rapidly discharging atrial focus as a mechanism of atrial flutter and the case for a change in intra-atrial conductions as cause for change in atrial electrograms.