Background: Typical atrial flutter is the most common atrial macroreentrant tachycardia. It is usually associated with characteristic electrocardiographic findings, which are comprised of negative flutter waves with a sawtooth pattern in the inferior leads and positive P-waves in V1 (type I). However, in the absence of these characteristics (type II) typical atrial flutter revealed by Electrophysiology study (EPS) has been described.

Purpose: We investigated if typical atrial flutter (typAFL) is common in patients with type II Electrocardiogram (ECG).
Methods: We screened 634 consecutive ECGs from patients who presented with suspected regular atrial tachycardia. Only patients meeting the following criteria were included:

• type II (atypical) ECG

• atrial cycle-length ≤ 350 ms

• no prior left-atrial ablation

• tachycardia-mechanism (cavostricuspid-isthmus-dependent vs. non cavotricuspid-isthmus-dependent) determined by conventional mapping or 3D-electroanatomical mapping)

The most common reasons for exclusion were spontaneous conversion into sinus rhythm before determining the tachycardia mechanism by EPS (115 patients), prior left atrial ablation (105 patients) and typical ECG (250 patients). Other exclusion criteria were atrial cycle-length ≥ 350 ms and electrical cardioversion or atrioventricular node ablation without identifying tachycardia mechanism.

Results: We included 96 patients with type II ECG. Mean age was 70.4±12.8 years, 62 (65%) were male. All patients underwent EPS to differentiate between typical atrial flutter, and atypical atrial flutter, focal atrial tachycardia or microreentrant tachycardia.

Unexpectedly, the majority of patients (n=63, 66%) had CTI-dependent typAFL.

Patients diagnosed with typAFL underwent ablation of the cavotricuspid isthmus. Patients diagnosed with atypical atrial flutter or focal atrial tachycardia underwent further EPS including 3D-Mapping and ablation or electrical cardioversion.