Typical atrial flutter is a macro-reentrant tachycardia. It differs from an atrial tachycardia (which emanates from a discrete focus) by its continuous electrical activity around a relatively large anatomic structure, such as the right tricuspid valve. It is principally a right atrial disease, but can occasionally occur in the left atrium or around surgical scars. Classic atrial flutter most frequently moves counterclockwise around the right atrial structures, but occasionally may move clockwise. This chapter shows a 12-lead ECG in a patient with typical atrial flutter. Note the sawtooth flutter waves seen in the inferior leads (II, III, and aVF).
To diagnose atrial flutter and its mechanism, it is useful to position a multipolar electrode catheter from the femoral vein and cross the isthmus into the coronary sinus. The catheter traverses the isthmus and records continuous atrial conduction, as observed in the figure at an atrial cycle length of 259 milliseconds (ms). One can pace directly on the isthmus in a critical zone of the tachycardia and entrain (get into the circuit of) the tachycardia. Typically, a large (10-mm) ablation tip catheter is placed across the tricuspid valve in order to record a large ventricular electrogram with a small atrial electrogram. Alternatively, smaller (3.5-mm) irrigated tip catheters such as the ThermoCool® Bidirectional Catheter (Biosense Webster, Inc.) also may facilitate lesion creation by cooling the myocardium during the resistive heating, which occurs with radiofrequency catheter ablation. Additionally, in the left anterior oblique fluoroscopic projection at approximately 45 degrees, the tricuspid valve is open and resembles a clock facing right at the operator. The ablation is performed from that viewpoint, and the catheter tip serves as the small hand of the clock for location purposes. The operator typically performs a cavotricuspid isthmus ablation with the catheter at 6 o’clock, as viewed in the left anterior oblique projection. The author typically delivers 40 seconds of radiofrequency energy at 100 watts and a temperature of 60 degrees centigrade. Other operators may have subtle variations of the precise power, temperature, and duration of the particular radiofrequency energy applications.