The aim of this study was to compare the results of pulmonary vein isolation using conventional irrigated radiofrequency (RF) approach versus the cryoballoon (CB) ablation. From January 2008 to December 2011, a total of 426 patients with drug-resistant symptomatic paroxysmal atrial fibrillation underwent pulmonary vein isolation as the index procedure by conventional manual RF or CB ablation at our center. A final population of 396 patients was considered for analysis and divided into 2 groups: conventional RF ablation (n = 260) and CB ablation (n = 136). At a mean follow-up of 23 ± 13 months (median 27, range 4 to 68), the success rate for RF ablation group was 57.3% (149 patients) and was 63.2% (86 patients) for cryoablation group (p = 0.25). Procedural times were significantly shorter in the cryoablation group (192 ± 49 vs 112 ± 58 minutes, p <0.000001) but not fluoroscopy times (36 ± 14 vs 31 ± 17 minutes, p = 0.45). No clinical predictors were found to predict atrial fibrillation recurrences. Complication rates were similar in both groups except for phrenic nerve palsy that was uniquely observed in the CB group (8.1%, p <0.00001). All phrenic nerve palsies resolved during follow-up. In conclusion, on a medium-term follow-up, conventional point-by-point RF ablation and CB ablation showed similar success rates. Procedural times were significantly shorter in the CB approach. The most frequent complication during CB procedures was phrenic nerve palsy, which occurred in 8.1% of patients and resolved in all during the follow-up period.
Pulmonary vein (PV) isolation is nowadays the cornerstone of percutaneous transcatheter ablation for drug-resistant paroxysmal atrial fibrillation (AF). Traditionally, these procedures are performed with a “point-by-point” ablation technique by means of radiofrequency (RF) energy; however, in the last years, the use of novel alternative technologies such as cryoballoon (CB) ablation is growing rapidly. Despite continuous improvements in catheter technology, RF ablation by means of a focal-tip catheter is still a challenging procedure and is highly dependent on operators’ skills. In contrast, CB technology might offer more reproducible and standardizable procedures by significantly simplifying the ablation itself. To the best of our knowledge, published data on comparison of medium- and long-term results between CB and conventional manual RF ablation are limited. In the present study, we sought to compare the outcomes of both approaches on a medium-term follow-up in a series of consecutive patients who underwent PV isolation at our center for drug-resistant paroxysmal AF.
Methods
From January 2008 to December 2011, all consecutive patients who underwent PV isolation as the index procedure by RF ablation or CB ablation at our department for documented symptomatic paroxysmal AF were taken into consideration for our retrospective analysis. In all procedures, the acute end point was the achievement of electrical PV isolation in all veins. Paroxysmal AF was defined as self-terminating AF episodes lasting <7 days as per guidelines. Exclusion criteria were repeat procedures for recurrent AF after the index procedure, first-line ablation treatment, acute complications disrupting procedure continuation, and persistent AF. Before the procedure, all patients underwent a 2-dimensional transthoracic echocardiography to assess left ventricular ejection fraction and to rule out any structural and/or valvular disease. A cardiac computed tomography and a transesophageal echocardiography were performed the day before ablation to analyze left atrial (LA) and PV anatomy and to rule out intracardiac thrombus formation.
RF ablation was performed as follows. After having accessed the left atrium with a double transseptal puncture, a 70 UI/kg heparin intravenous bolus was given. A selective PV angiogram was performed to assess all PV ostium positions. A circumferential mapping catheter (Lasso; Biosense Webster Inc., Diamond Bar, California) was positioned into the proximal portion of the PV ostium to get baseline electrical information. Then an electroanatomic map of the left atrium was performed with a nonfluoroscopic navigation system (CARTO; Biosense Webster Inc.). RF ablation was performed with an open irrigated cool tip 3.5-mm catheter (NaviStar ThermoCool; Biosense Webster Inc.) in a power-controlled mode with a power limit of 35 W and at a maximum temperature of 48°C. Each application lasted a maximum of 60 seconds. Power was reduced to 25 W during ablation of LA posterior wall to prevent esophageal injury. The ablation strategy consisted in creating contiguous focal lesions at a distance of >5 mm from the ostia of the PVs resulting in circumferential lines around ipsilateral PVs. During the whole procedure, activated clotting time was maintained at >300 seconds by supplementing heparin infusion.
CB ablation was performed as follows. A single transseptal puncture was achieved under fluoroscopic guidance, using the right femoral venous approach. After gaining the LA access, a 70 UI/kg heparin intravenous bolus was given. A 0.32Fr Emerald exchange wire (Cordis, Johnson and Johnson, Diamond Bar, California) was advanced in the left superior PV and a steerable 15Fr over-the-wire sheath (FlexCath; Cryocath, Montreal, Quebec, Canada) was positioned in the left atrium. A circular mapping catheter (Lasso; Biosense Webster Inc.) was then advanced in each PV ostium to obtain baseline electrical information. After withdrawing the mapping catheter, a first-generation 28-mm double-walled CB (Arctic Front; Cryocath) was advanced over the wire to the left atrium, inflated, and positioned in the PV ostium of each vein. Vessel occlusion was evaluated according to a semiquantitative grading ranging from grade 0 (very poor occlusion) to grade 4 (perfect occlusion) in 2 different fluoroscopic projections; after dye injection, optimal vessel occlusion was deemed as total contrast retention with no backflow in the atrium. For each vein, cryoablation consisted of a minimum of 2 applications lasting 5 minutes each. Whenever possible, we tried to engage 2 different branches of the same vein and to orient the balloon differently, to cover a wider ostial surface. However, if successful occlusion could be obtained in only 1 branch, both applications were delivered by leaving the guidewire in the same branch. Usually, the left PVs were treated first followed by the right-sided veins. To avoid phrenic nerve palsy, a quadripolar catheter was inserted in the superior vena cava, and diaphragmatic stimulation was achieved by pacing the ipsilateral phrenic nerve with a 1,000-ms cycle and a 12-mA output. The reason for pacing at such a slow rate was to prevent catheter displacement due to diaphragmatic contraction during the early phases of application. After ablation in all PVs, the circular mapping catheter (Lasso; Biosense Webster Inc.) was then positioned in each ostium to verify isolation. In case of persistence of PV potentials, extra CB applications were performed until complete PV isolation. During the whole procedure, activated clotting time was maintained at >300 seconds by supplementing heparin infusion, as required.
A 2-dimensional transthoracic echocardiogram was repeated the day after the procedure to rule out the presence of pericardial effusion. Therapy with low-molecular-weight heparin was started the same day after ablation. Oral anticoagulation was started the day after the procedure. Patients were discharged on both oral anticoagulation and low-molecular-weight heparin. When a target international normalized ratio of 2 to 3 was reached, low-molecular-weight heparin was stopped and oral anticoagulation was continued for at least 3 months. Antiarrhythmic therapy was administered for 2 months after the procedure and stopped if the patient was free of AF relapse.
Clinical follow-up consisted of physical examinations, electrocardiography, and 24-hour Holter recording performed at 1, 3, 6, and 12 months after ablation and every 6 months after the first year. A blanking period of 3 months was considered for the study. All documented episodes of atrial tachyarrhythmias lasting ≥30 seconds were considered as recurrence.
All continuous variables are expressed as mean ± SD and, if appropriate, were compared using the Student t test. Categorical variables are expressed as numbers and percentages and, if appropriate, were compared with the chi-square analysis. Kaplan-Meier event-free survival analysis was conducted to assess the cumulative freedom from recurrence. Predictive analysis of recurrence over the follow-up time was assessed through the Cox regression method. The multivariate model was applied, adjusting for gender, age >65 years, LA diameters, AF duration before procedure, body mass index, E/E′, antiarrhythmic drugs, arterial hypertension, and coronary artery disease. A p value of <0.05 was deemed statistically significant. Statistical analyses were conducted using SPSS software (SPSS v22.0, SPSS Inc., Chicago, Illinois).
Results
In a larger series of patients, 426 consecutive patients who underwent PV isolation for paroxysmal AF as the index procedure were taken into consideration. Of these patients, 10 were excluded for impossibility to retrieve information about their follow-up, 18 because of first-line treatment, and 2 because of the occurrence of an acute complication impeding procedure termination. A total of 396 patients (279 men, 58 ± 13.3 years) were finally considered in our analysis. All patients were affected by highly symptomatic drug-resistant paroxysmal AF. In the RF ablation group, 17.3% of patients (n = 45) had undergone cavotricuspid isthmus ablation for typical atrial flutter before AF ablation. Furthermore, 0.8% (n = 2) underwent accessory pathway ablation for atrioventricular re-entrant tachycardia before PV isolation. In the CB group, 8.1% of patients (n = 11) had undergone ablation for cavotricuspid isthmus ablation and 1.5% of patients (n = 2) had undergone accessory pathway ablation (p = 0.01 and p = 0.51, respectively). Paroxysmal AF was documented in all patients in the follow-up after these procedures. No statistical differences between the 2 groups were found in terms of baseline population characteristics ( Table 1 ). No significant difference in follow-up duration was found (RF ablation: 24.0 ± 13.4 months with a median of 27, CB ablation: 22.1 ± 14 months with a median of 24, p = 0.10).
| Variable | RF Ablation (n = 260) | CB Ablation (n = 136) | p Value |
|---|---|---|---|
| Men | 181 (69.6) | 98 (72.1) | 0.61 |
| Age, yrs (median, range) | 58.3 ± 8.7 (60, 30–77) | 57 ± 13.3 (56, 15–78) | 0.08 |
| AF duration (mo) | 25.4 ± 37.1 (10) | 25.1 ± 24 (10.5) | 0.30 |
| Body mass index (kg/m 2 ) | 27.4 ± 4.8 (26.2) | 26.2 ± 3.8 (25.5) | 0.08 |
| Follow-up (mo) | 24.0 ± 13.4 (27) | 22.1 ± 14 (24) | 0.10 |
| LA diameter (mm) | 42.8 ± 6.7 (42.6) | 41.6 ± 6.8 (42) | 0.26 |
| Left ventricular ejection fraction ≥50% | 248 (95.4) | 131 (96.3) | 0.66 |
| Left ventricular ejection fraction <40% | 6 (2.3) | 2 (1.5) | 0.57 |
| Arterial hypertension | 90 (34.9) | 35 (25.7) | 0.07 |
| Diabetes | 18 (6.9) | 4 (2.9) | 0.10 |
| Dyslipidemia | 64 (24.4) | 45 (33.1) | 0.07 |
| Previous stroke/TIA | 20 (7.6) | 6 (4.4) | 0.21 |
| CHA 2 DS 2 -VASc score | 1.44 ± 1.28 | 1.16 ± 1.28 | 0.13 |
| Coronary artery disease | 25 (9.6) | 7 (5.1) | 0.12 |
| Cardiomyopathy | 13 (5) | 6 (4.4) | 0.79 |
| Valve disease | 4 (1.5) | 2 (1.5) | 0.96 |
| Previous cavotricuspid isthmus ablation | 45 (17.3) | 11 (8.1) | 0.01 |
| Previous accessory pathway ablation | 2 (0.8) | 2 (1.5) | 0.51 |
Procedural time was significantly shorter in the CB group (192 ± 49 vs 112 ± 58 minutes, p <0.000001); fluoroscopy time was similar in both groups (36 ± 14 vs 31 ± 17 minutes, p = 0.45). In all patients, PVs were completely isolated at the end of the procedure. In 5 patients (right inferior PVs in 4 and left inferior PVs in 1) who underwent CB ablation, a focal touch-up with either a focal-tip cryocatheter (Freezor Max; CryoCath Technologies Inc., Montreal, Quebec, Canada) or an irrigated-tip RF catheter (NaviStar ThermoCool; Biosense Webster Inc.) was delivered. In the CB ablation group, the mean number of freeze-thaw cycles was 2.2 ± 0.7 in the left superior PV, 2.2 ± 0.8 in the left inferior PV, 2.0 ± 0.5 in the right superior PV, and 2.6 ± 0.4 in the right inferior PV. In the RF group, mean energy application time was 43 ± 6 min/patient.
All procedural complications are listed in Table 2 . Procedural complications were similar in both groups with the exception of phrenic nerve palsy, which only occurred in the cryoablation group (0% vs 8.1%, p <0.00001). In 81.8% of patients (9 of 11), phrenic nerve palsy resolved completely before discharge, but in 18.2% (2 of 11), this complication persisted after discharge. In these 2 patients, a complete recovery was observed after 7 and 15 months, respectively.
| Variable | RF Ablation (n = 260) | CB Ablation (n = 136) | p Value |
|---|---|---|---|
| Death | 0 | 0 | |
| Stroke/transient ischemic attack | 0 | 0 | |
| Tamponade | 4 (1.5) | 1 (0.7) | 0.50 |
| Pericardial effusion (not hemodynamically significant) | 26 (10) | 10 (7.3) | 0.38 |
| PV stenosis | 0 | 0 | |
| Atrial-esophageal fistula | 0 | 0 | |
| Femoral artery pseudoaneurysm | 2 (0.8) | 0 | 0.30 |
| Groin hematoma | 0 | 2 (1.5) | 0.05 |
| Sinus arrest/third-degree atrioventricular block | 2 (0.8) | 0 | 0.30 |
| Transient ST elevation | 2 (0.8) | 2 (1.5) | 0.51 |
| Phrenic nerve palsy | 0 | 11 (8.1) | <0.00001 |
| Contrast reactions | 1 (0.4) | 0 | 0.47 |
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