Electrophysiologically guided PVI involves recording PV potentials from a circular mapping catheter (e.g., Lasso) situated at the ostium of the targeted vein and therefore generally requires two transeptal punctures unless a double or retained guide wire approach is used. To help avoid entrapment of the catheter in the mitral valve apparatus, the circular mapping catheter should be torqued clockwise (posteriorly) when exiting the transeptal sheath and positioned in the PV away from the more anterior mitral valve. The circular mapping catheter records fused electrograms consisting of a blunt LA (far-field) and high-frequency PV (near-field) potential. During left PV ablation, these electrograms overlap during sinus rhythm because of synchronous activation and best separated by distal CS pacing (Fig. 15-5). Two approaches to PVI include segmental ostial and wide area circumferential ablation (WACA)—the latter having a higher success rate.²²,²³,²⁴,²⁵,²⁶,²⁷ Segmental ostial ablation successively targets the earliest breakthrough site of PV potentials around the circular mapping catheter until PV muscle conduction is eliminated or dissociated from the LA (Fig. 15-6).²² WACA targets the antrum of the PVs (≥5 mm outside the PV ostium), debulking the atrium and causing PVI with contiguous focal lesions around the PVs individually, ipsilaterally, or entirely en bloc (Fig. 15-7).²³ Voltage abatement (≤0.05 mV) within encircled areas validate line continuity. Clues that the ablation catheter





is in the PV where RF delivery should be avoided include 1) fluoroscopic demonstration of the catheter tip beyond the cardiac silhouette, 2) ICE imaging of catheter tip beyond the PV ostium, 3) loss of electrical signals, and 4) increase in catheter impedance (>140-150 ohms). The endpoint of PVI is entrance block (elimination or dissociation of PV potentials from the LA) and exit block (PV stimulation causes PV sleeve capture without conduction to the atrium) (Figs. 15-8, 15-9, 15-10, 15-11 and 15-12).

Rather than point-by-point focal RF ablation, cryoablation is an alternative PVI technique using a balloon catheter to occlude the PV and liquid nitrogen to freeze its antrum.³⁵,³⁶,³⁷ A circular mapping catheter inserted through the lumen of the cryoballoon allows monitoring of PV potentials while providing distal support, and therefore, only a single transeptal puncture is required. The transeptal puncture site should be low and anterior on the fossa ovalis allowing for a large turning radius of the cryocatheter to reach the posterior and superior PVs (particularly, the more difficult right inferior pulmonary vein [RIPV]). Keeping the cryoballoon coaxial to the vein with maintenance of forward pressure, advancing the sheath to the back hemisphere of the balloon for proximal support, and using the circular mapping catheter as a distal luminal supporting wire (“rail”) in different vein branches (inferior for inferior veins/superior for superior veins) facilitate balloon occlusion of the targeted vein. Because the balloon heads superiorly toward the PV antrum, inferior leaks during initial attempts at vein occlusion are common (worst site of balloon-to-PV contact) and can be sealed by a 1) “pull down” technique (pulling the entire assembly down to prevent the balloon from “riding” upward) or 2) curving the cryosheath and pushing the assembly inferiorly downward toward the antrum (“hockey stick” sign—especially for RIPV). A large common or oval ostium can make complete occlusion difficult. Signs of PV occlusion are 1) difficult contrast injection with retention in the vein (“hang up”), 2) absence of leaks on color Doppler sweep, and 3) pulmonary venous pressure waveforms (transition from LA [venous A and V wave] to pulmonary


artery pressure [only higher pressure V wave]). Because of the different viscosities between contrast and saline, it is important to adequately flush any dye out of the lumen of the cryoballoon in order to accurately record pulmonary venous pressures (Figs. 15-16, 15-17, 15-18, 15-19 and 15-20).³⁸ Optimal cryoablation endpoints include 1) nadir temperatures (<−50°C), 2) time to isolation (TTI) <60 sec, 3) freezing time (−30°C by 30 sec, −40°C by 60 sec) (rapid freezing with shorter freezing times correlates with effective cryoablation), and 4) rewarming time (interval thaw time to 0°C by ≥10 sec) (longer rewarming times indicate more therapeutic ice crystallization with tissue-ice bonding at 0°C).³⁹,⁴⁰,⁴¹,⁴² In contrast to the abrupt loss of PV potentials that signify entrance block during RF ablation, cryoablation causes LA-PV delay prior to disappearance of PV potentials (Fig. 15-21).⁴³ (A distally positioned circular mapping catheter can be pulled back to the nose of the cryoballoon within 10 sec of the cryofreeze to record PV potential before the central lumen freezes.) Pacing from the circular mapping catheter can also show PV-LA delay prior to exit block. The dosing and duration of cryofreeze applications depends on how successful the cryoablation endpoints were achieved (e.g., 180 sec [TTI <90 sec] or 150 sec [TTI <30 sec]). After the freeze, the cryoballoon should not be manipulated until the temperature reaches 35°C during the thaw in order to avoid tissue tearing from cryoadherence.