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

Methods – We investigated predictors for type II ECG in patients with confirmed cavotricuspid isthmus-dependent atrial flutter. 

Results – We included 197 patients undergoing cavotricuspid isthmus-dependent atrial flutter ablation in our study. Upon hospital admission 146 patients (74%) had a type I ECG and 51 patients (26%) showed a type II ECG. The strongest predictor for a type II ECG in multivariate logistic regression analyses was atrial cycle length (OR 1.019 per ms increment; 95% CI 1.008 – 1.029; p=<0.001) and clockwise flutter (OR 7.853; 95% CI 2.710 – 22.758; p<0.001). Receiver-Operator-Characteristics (ROC) analyses identified a combination of atrial cycle length and clockwise flutter to predict a type II ECG in CTI-dependent atrial flutter with an area under the curve of 0.76.

Conclusion – Even in confirmed cavotricuspid isthmus-dependent atrial flutter there is a considerable prevalence of a type II ECG. Combination of atrial cycle length and clockwise flutter are the main determinants of a type II ECG in CTI-dependent flutter.