Electroanatomic mapping was performed in all cases with CARTO 3 system (Biosense Webster Inc) in sinus rhythmfor voltage map, in the setting of 0.05 to 0.5 mV to assess PVI and PWI. Activation window for atrial flutters was set at 50% -50% of the cycle length. Roof was the line drawn between the upper ends and floor was the line drawn between the lower ends of the right and left superior PVs. The area contained within roof, floor and PV antra were designated as the PW. The attenuated area < 0.05 mV after ablation divided by the total area of the PW was considered the percent of PWI.

For patients in group CRYO, ablation involved two applicationsto create lesions using cryoballoon (ArcticFront Advance™, 28 mm second generation, Medtronic, Inc., Minneapolis, MN) for 180 sec and 120 sec at all the PVs, after ensuring adequate occlusion by pressure monitoring and PV Doppler signals on the intra-cardiac echocardiogram.Then anchoring the Achieve mapping catheter (Abbott Inc.) in the PVs,sequential retraction and posterior rotation of the balloon was employed to create overlapping and contiguous stamp lesions spanning the LA roof and floor to complete PWI.[Figure 1]We incorporated the use of CartoSound™ (Biosense Webster Inc, Diamond Bar, CA) to integrate catheter position and orientation in real time into the electro-anatomical map during PW applications to draw “CartosOund Rings” (COR Imaging). [Figure 1D] Esophageal temperature monitoring [Figure 1A] and phrenic nerve pacing for right sided lesions were employed during ablation and applications were stopped for loss of phrenic capture or esophageal temperature drop < 29°C. Lesions on the roof and floor were created with single applications of 180sec and were stopped early if esophageal temperature dropped. Remapping with Pentarray multipolar catheter (Biosense Webster Inc) following ablation was used to confirm complete and well-demarcated PVI, roof, and floor lines to demonstrate dense PWI with no electrograms >0.05mV; if necessary additional ablation with thermo-cool radiofrequency catheter was applied to close gaps. If atrial flutter was inducible, additional RF ablation was applied to eliminate the atrial flutter circuit. Posterior wall was considered isolated if there was complete electrogram attenuation to < 0.05 mV.

Figure 1. A - Fluoroscopic view of Cryoballoon retracted from left upper pulmonary vein position at the roof; White arrowhead indicates esophageal temperature probe. B -Visualization of cryoballoon with intracardiac echo; C-CartosOund contours (COR imaging); D- Contours drawn on the cryo balloon yellow and blue lines represent non ablating and ablating segments respectively.

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Patients in group HABL underwent surgical ablation: bilateral video assisted thoracoscopic surgery (VATS) with bipolar PVI (Atricure Inc), LA roof/floor lines, RA bicaval line, ablation of ganglionic plexi/the ligament of Marshall, and LA appendage clipping. After recovery from surgery, the patients returned for electrophysiology study/ablation for confirmation of PVI, PWI and additional ablations if required to achieve this as well as ablation of clinical or inducible atrial flutter.

Group CRAconsisted of patients who had received conventional endocardial ablation including CPVA for antral PVI with the addition of empiric linear lines in the LA roof and MVI with thermo-coolRF catheter. Confirmation of bidirectional block was documented for linear lesions. Inducible flutterswere targeted for further ablation.

Patients were seen post ablation at 1 week, 3 month, 6 month and 1 year and were monitored by ECG, Holter or event monitor or through existing implantable cardiac device. All patients discontinued antiarrhythmic therapy 8-12 weeks after the procedure; continuation of anticoagulation was based on their CHADS 2 VASC score.

Primary outcomes were first recurrent AF> 30 seconds, Atrial flutter (AFL)> 30 seconds or any atrial arrhythmia (AF or AFL) at one year, after the three month blinding period. We also analyzedantiarrhythmic drug utilization, referral for repeat ablation, peri-procedural complications, length of stay and control of AF at one year follow up. Procedural time was as recorded in the Apollo LX (version 6.2.0) records and includes time from femoral venous access to the patient exiting the electrophysiology laboratory. If patients remained in sinus rhythm after the initial recurrence assisted by cardioversion or antiarrhythmic drug, they were considered to have controlled AF.

STATA 13.1 was used for all statistical analyses. Continuous variables are expressed as mean + SD or SE; categorical variables are presented as percentages, comparisons were performed with t-test and χ2 test respectively. Differences between three groups were assessed using ANOVA for continuous variables, and Kruskal -Wallis for nominal variables. Adjustment of comorbidities for the clinical outcomes were performed with models as: (1) demographics- age and sex; (2) consisted of cardiovascular risk factors- hypertension, diabetes, coronary artery disease/peripheral vascular disease , transient ischemic attack / stroke, heart failure; (3) included body mass index (BMI), chronic obstructive pulmonary diseaseand obstructive sleep apnea; (4)LA dimension and left ventricular ejection fraction. Kaplan Meier survival analysis was used to compare freedom from AF, or AFLamong the groups; p-value < 0.05 was considered significant.

([Table 1]) There were61 patients ([Table 1])with persistent AF who fit the inclusion criteria; mean duration of AF was 1.3 ± 0.4 yrs. Majority was anticoagulated,without significant differences among the three groups, however more patients in group HABL had long standing persistent AF.

([Table 2]) All patients had CPVA to accomplish PVI, more than half the patients utilized magnetic robotic navigation in HABL and CRA. There was more MVI in HABL and CRAvs CRYO (p= 0.001); there was no difference in cavo-tricuspid isthmus (CTI ablation). More patientsin HABL converted to SR during ablation compared to other groups; there was no difference in conversion to AFL. Majority of the patients had inducible AFL, without differences among the groups. Electrophysiology procedure time was longest at 321± 98 min in CRA, (p=0.02) without a significant difference in fluoroscopy time or Dose Area Product among the groups.

In CRYO, the total number of cryo applications to achieve PVI and PWI was 23.5± 5 for total 3675±776 seconds. Esophageal temperature nadir was -31± -2.6°C. Additional RF ablation was necessary to close small gaps for PWI in 46% of patients with mean RF time 136 ±42 sec (SE). Common locations for PWI gaps were in the mid floor and mid roof. No additional RF ablation was necessary to complete PVI. Additional ablations in LA for inducible AFL were required in 70%. COR imaging had a reduction in the procedure time (257 ± 52 vs 270 ± 59 min, ns), and fluoroscopy time (20 ± 5 vs 26 ± 10, p=0.08), and a reduced need for PW touch up with radiofrequency ablation catheter (33% vs 67%, ns) compared to those without COR imaging.

InHABL, EP/ablationwas performed 75 ± 26 (SE) days after VATS maze, when 59% of the PWarea had low voltage at baseline representing the extent of PWI due to surgery. Thegaps noted in roof and mid floor were closed (radiofrequency time 2754 ± 1572 sec) to accomplish > 90% area of low voltage in the PW [Figure 2b] and [Figure 2C]; due to gaps in PV, ablation for PVI was required in 43%.Four patients presented for the second stage in AF, three patients in AFL, which terminated on ablation. Although not statistically significant, there were more inducible AFL (mean 1.8 ± 0.8) in this group localized to CTI, MVI, and roof requiring additional LA ablation in all the patients.

All CRA patients had CPVA and roof line; 87% had MVI line with 95% achieving bidirectional block. Induced AFL was treated by activation mapping and ablation in 65% of the patients with a total of 5355 ± 1666 sec ablation time in this group.

Figure 2. A shows left atrial posterior wall voltage mapping with dense homogeneous isolation of the pulmonary veins and posterior wall. B shows voltage mapping (0.05-0.5mV) following surgical ablation (pre-endocardial). The bilateral pulmonary veins are isolated and posterior wall is partially isolated with gaps in floor line. C is a different hybrid ablation patient also pre-endocardial ablation; as compared to middle panel posterior wall is densely isolated. All voltage maps 0.05-0.5mV.

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Recurrent AFoccurred in 24.6%, recurrent AFL in 21.3%, any atrial arrhythmia in 31% and repeat ablation in 16.3% of the entire cohort. Age, sex, hypertension, diabetes, cardiovascular disease, prior stroke, heart failure, chronic pulmonary obstructive disease, sleep apnea, smoking and alcohol use did not predict recurrent arrhythmia. Patients with recurrent AF had lower BMI 27.8 ±3 (vs 31.4 ±6.3, p=0.05) and27% had coronary artery bypass surgery (vs 4%, p=0.01)compared to those without recurrence. Recurrent AFL was not predicted by any of these demographics or comorbidities.

([Table 3]) Since CRYO and HABL had PWI, they were together (group P) and compared to CRA. Group P had less recurrent AF (10.5% vs 47.8%, p=0.008), any atrial arrhythmia (23.7 vs 52.2%, p=0.02), but no difference in AFL [Figure 3B],[Figure 3D]; there was less repeat ablation (5.3% vs 30.4%, p=0.007) and more control of AF (95% vs 73%, p=0.02), compared to CRA. There was no difference in time to recurrence in both these groups.

Figure 3. Kaplan Meier survival estimates of freedom from recurrent AF (A and B) and Atrial flutter (C and D). A and C: comparison of three groups- cryo ablation (red line), hybrid ablation (blue line), and conventional radiofrequency ablation (green line). B and D: Comparison of posterior wall isolation (red line) vs conventional radiofrequency ablation (blue line)

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AF recurrence remained less for group P (< two times less likely) compared to CRA, after adjusting for models one (p=0.01), two (p=0.03) and three (p=0.003), model four (p=0.01) and duration of AF (p=0.002). Please see methods section for details regarding the models. After adjustment of individual comorbidities of hypertension (p=0.005), diabetes (p=0.005), coronary artery disease/ peripheral vascular disease (p=0.005), heart failure (p=0.004) and TIA/ stroke (p=0.001), the recurrent AF remained lower by multivariate logistic regression analysis.

[Table 3] For a follow-up of 366± 62 days AF recurrence was highest in CRA compared to CRYO and HABL (p=0.005), [Figure 3A] without a difference in recurrent AFL among the groups.[Figure 3C]Occurrence of any atrial arrhythmia was highest in CRA mainly due torecurrent AF; there was no difference in cardioversion among the groups. While repeat ablation was not required in HABL (who already had the second ablation as a planned procedure), there were more repeat ablationsand antiarrhythmic drug use use in CRA compared to other groups.

Length of stay was longest in HABL(145 ± 53 hours) as it included both stages vs CRYO (42 ± 58 hours, p<0.0001) or CRA (38 ± 25 hours, p<0.0001). At the end of follow up control of AF was achieved in 95.8, 93% and 72.7% (p=0.001) of the patients in CRYO, HABL and CRA respectively.

Conversion to sinus rhythm or AFL, inducibility of AFL, achievement of MVI block, CTI ablation and prior ablation did not predict recurrence of AF or AFL. Robotic magnetic navigationused predominantly in HABL and CRA had higher risk for recurrent AF 40% vs 14.3% in manual ablation cases (p=0.02). Patients with PWI were 1.9 times less likely to have recurrent of AF (p=0.002) after adjustment for robotic magnetic navigation catheter utilization.

In CRYO, small hematoma and transient phrenic nerve palsy resolving by hospital dischargeoccurred each in one patient. In group HABL, therewas drug reaction in onepatient, abdominal ileus in one patient, pleural effusion in two patients, and pneumonia in three patients one of whom died within one year post procedure due to non cardiac problems. In CRA, two patients had prolonged hospitalization (> 23 hours) for heart failure exacerbation one of who also had pneumonia. Other complications such as atrial-esophageal fistula, CVA, pericardial effusion/ tamponade, or peri-procedural mortality did not occur in this cohort.