Revisit of Typical Counterclockwise Atrial Flutter Wave in the ECG: Electroanatomic Studies on the Determinants of the Morphology

BACKGROUND: Cavotricuspid isthmus-dependent counterclockwise atrial flutter (typical AFL) is characterized by negative saw-tooth morphology flutter wave (F-wave) in the inferior leads, which is classified as type 1 with purely negative F-wave without positive terminal deflection (PTD), type 2 with small PTD, and type 3 with broad PTD. The determinants of these morphological differences remain to be elucidated. METHODS AND RESULTS: Of 72 patients (58 males, 65 ± 13 years) with typical AFL, 19 were classified as type 1 and 53 as types 2 and 3. We created an electroanatomic map of the right atrium (RA) during AFL and determined which RA site activation corresponded to which F-wave component by analyzing the activation map. It was revealed that F-wave component from the nadir to terminal deflection point coincided with the cranio-caudal activation of the RA free wall (RAFW) in all types. The bipolar voltage map showed that type 1 had the greater extent of low voltage (<0.5 mV) area (LVA) in RAFW (39 ± 24%) than types 2 and 3 (4 ± 3%) (P < 0.0001), explaining the absence of PTD in type 1. In types 2 and 3, F-wave amplitude determining the PTD magnitude was highly correlated with the longitudinal distance between two points on RAFW corresponding to the nadir and peak of F-wave (r = 0.73, P < 0.0001). CONCLUSIONS: Terminal positivity and amplitude of F-wave in typical AFL are primarily related to the RAFW activity: negatively by the extent of LVA and positively by the longitudinal vector of activation.