Successful Pulmonary Vein Isolation in 90 Seconds: Cryo Titration Based on Ice Impedance

Background: A direct indicator for effective pulmonary vein isolation (PVI) based on ice formation is presently lacking.
Objective: We hypothesized that the amplitude of impedance(Imp) rise at 60seconds(sec) of cryo application could 1)predict effective PVI with termination at 90sec, 2)the need for prolonging cryo application to 90-180sec, or 3)failure to achieve effective ablation and the need to re-position the balloon.
Methods: Since ice is a poor electrical conductor, continuous impedance measurements were taken from a ring electrode positioned just adjacent to the anterior balloon surface and a reference ring placed on the shaft behind the balloon. Ice covering the anterior ring leads to impedance rise that corresponds to the anterior balloon ice formation. In 5 animals, 25 veins, including middle veins were targeted. PVI was achieved by a single Cryo application of 90-180 sec. The application time was terminated when the impedance achieved 500Ω but not less than 90 sec. PVI was confirmed acutely and at 4 weeks recovery by EP mapping and histopathology.
Results: An Imp rise of 17±4.8Ω(n=3,<20Ω) at 60sec and maximum(max) of 44±28Ω at 180sec was associated with failed PVI. An imp rise of 93.7±36Ω(N=11,33-149Ω) at 60sec resulted in 100% PVI when Cryo was applied for 176.1±9.2sec(152-180sec; max Imp of 303±143Ω at time of Cryo termination). In contrast, an Imp rise of 619±468Ω(N=11,119-1395Ω) at 60sec, reaching 500Ω at 64±19sec(29-90sec). These cryo applications resulted in 100% PVI when Cryo was applied for only 90sec (max Imp reached 3255±2075Ω at 90sec). Conclusion: The cryo lesion outcome can be defined within 60 sec of Cryo application based on Imp. Low imp rise (<20Ω) at 60sec of Cryo application is an indication for balloon re-positioning. Ninety sec effective lesion is defined by achieving >119Ω at 60sec and ≥500Ω at 90sec. Cryo effective PVI can be reliably achieved single application of 90sec.