Differentiating atrial tachycardias with centrifugal activation: Lessons from high-resolution mapping

Background: Centrifugal activation is not always the origin of a focal atrial tachycardia (AT) ("true-focal"), but passive activation from the other structures ("pseudo-focal").

Objective: We aimed to establish a method to differentiate true-focal from pseudo-focal.

Methods: In 49 centrifugal activations in 35 patients with AT, 12-lead electrocardiogram, activation map, atrial global activation histogram (GAH), and local electrograms were analyzed. GAH demonstrates the relation between the activation area and timing through the cycle length, displayed with a normalized value, ranging from 0 (smallest activation area) to 1.0 (largest activation area).

Results: Of 30 centrifugal activations observed in the septal region, 6/30 (20.0%) were true-focal. The remaining 24/60 (80.0%) were pseudo-focal, of which 23 (95.8%) were from the opposite chamber. P-wave/flutter-wave duration < 200 ms discriminated true-focal from pseudo-focal (sensitivity 100%; specificity 54.5%; positive predictive value 33.3%; negative predictive value 100%). Multiple breakthrough ruled out the possibility of a true-focal AT. Other differentiating factors were an activation area within the initial 20 ms of <5 mm² and a typical QS pattern electrogram at the origin. Of 19 centrifugal activations observed outside the septal regions, 7 were true-focal and 12 were pseudo-focal exited from an epicardial structure: 10 of 12 (83.3%) were located around the left atrial appendage and ridge. Flutter wave, GAH score ≤ 0.05, and GAH score < 0.1 for >110 ms of cycle length differentiated true-focal from pseudo-focal with a sensitivity/negative predictive value of 100%. GAH score < 0.1 for >40% of the cycle length simply discriminated true-focal from pseudo-focal with 100% accuracy.

Conclusion: Centrifugal activation is not necessarily due to a focal AT but passive activation. The activation map with GAH in addition to the 12-lead electrocardiogram and local electrograms enables an accurate differentiation.