Feasibility and safety of zero-fluoro, “apron-less” approach to repeat pulmonary vein isolation procedures using radiofrequency energy after initial cryoballoon ablation
Pulmonary vein isolation (PVI) has become a first-line treatment of atrial fibrillation (AF), especially in patients with paroxysmal forms of the disease or with heart failure. The procedure can be performed using either radiofrequency (RF) or cryoballoon (CB) catheters, or, as of recently, pulse field electroporation (PFE). Ablation of AF is by far the most commonly performed cardiac ablation procedure worldwide , . Historically, ablation procedures have been performed in a catheter laboratory using fluoroscopy. AF ablation frequently results in significantly higher radiations doses than other ablation procedures, and radiation exposure is also known to vary significantly depending on the local clinical practice. Ionizing radiation is associated with detrimental stochastic effects (elevated risk of fatal and non-fatal cancers), and deterministic effects (immediate dose-dependent cellular damage), including when used in cardiac ablation procedures , . Furthermore, doses applied during CB ablation, and lately PFE, are consistently higher when compared to RF-based ablation procedures . Therefore, minimizing the radiation exposure during the ablation procedures is important for both patients and operators . Recently, various strategies have been developed to completely abandon the use of fluoroscopy during the PVI procedures. Most commonly, so called “zero-fluoro” (ZF) strategies have been used with RF catheters, with the help of 3D mapping technology , . Even CB ablation can be performed using the intracardiac echo (ICE), entirely without the fluoroscopy, but this is not widely adopted at present . Initial AF ablation procedures have reported more than 20% symptomatic recurrences that warrant repeat procedures . However, repeat procedures carry more risk and are generally associated with higher complications rates . There are already abundance of data comparing the zero-fluoro approach to conventional ablation for de novo AF ablation procedures . Generally, zero-fluoro strategy results in significant reduction in radiation exposure and procedure time, without compromising the acute and long-term success rates and without increasing the complication rates. However, less is known about using the zero-fluoro strategy for the repeat procedures, especially after the initial CB ablation. Moreover, it has been suggested that zero-fluoro repeat procedures may carry greater risk of complications, in particular, the cardiac tamponade . The objective of our study was to demonstrate the feasibility and safety of zero-fluoro, apron-less, repeat procedures after initial CB ablation and to report the midterm outcomes regarding the AF recurrence. 

Study population Data were retrospectively collected for consecutive AF patients who have undergone zero-fluoro repeat ablations with RF catheters between July 2020 and June 2023 at the University Hospital Centre of Zagreb, Croatia. All patients received a second or fourth generation, 28 mm cryoballoon ablation for the initial procedure. The indication for the repeat procedure was symptomatic recurrence of AF at least 3 months after the initial procedure. Data were acquired from the hospital electronic database and from communication with patients. All procedures were performed by experienced operators. Exclusion criteria were: de novo pulmonary vein isolation procedure, index procedure performed by RF energy, intracardiac thrombi, uncontrolled heart failure (NYHA III-IV, recent acute heart failure), significant structural or valvular heart disease, or left atrial (LA) diameter > 55 mm. Patients without complete follow-up were excluded from the study. All patients provided written informed consent for the ablation and the study was approved by the local ethics committee. The research was conducted in accordance with the principles of the Declaration of Helsinki. Preprocedural preparation A transthoracic echocardiogram was performed prior to repeat ablation (within 3 months), to assess the left ventricular ejection fraction and to rule out any significant structural heart and/or valvular disease. A transesophageal echocardiogram to exclude left atrial appendage thrombi was performed before the procedure only in patients who presented with persistent AF. For patients with persistent AF, our strategy was to perform early direct current (DC) cardioversion in the outpatient setting and to schedule the patients for ablation at subsequent hospitalization. We used the uninterrupted anticoagulation strategy in all patients in accordance to recent recommendations . In patients taking direct oral anticoagulant agents (DOAC), anticoagulation was stopped 12 h before the procedure (the last dose of dabigatran, rivaroxaban, apixaban or endoxaban was given in the evening of the day before the procedure). An uninterrupted vitamin K antagonist (VKA) strategy was used, and the ablation was performed when the (international normalized ratio) INR was between 2 and 3, measured on the day of the procedure. Ablation protocol All patients underwent cryoballoon pulmonary vein isolation as an initial procedure, and no other lesion sets were performed. Briefly, cryoablation was performed in a standard fashion using a 28-mm second or fourth-generation CB (Arctic Front Advance (Pro), Medtronic). A 20 mm octapolar intraluminal circular catheter (ICC) (Achieve, Medtronic) was advanced to each PV ostium to collect baseline electrical activity. Using the “over-the-wire” technique, CB was positioned at PV antrum/ostium. Optimal vessel occlusion was considered achieved when selective contrast injection showed total contrast retention with no anterograde flow to the atrium. A single 3-minute freeze was applied to each PV. In the case of late isolation (> 60 s) or unsuccessful isolation, the balloon was repositioned and a second freeze was applied. If real time recordings were not present, a second freeze cycle of 180 s was delivered provided that the temperature of -40 °C was not reached within 60 s of the first freeze. Whenever PV potentials were not visible during the freeze, to confirm the PV isolation, the ICC was retracted to a more proximal position in the ostium where electrical information had been recorded prior to ablation. The procedural endpoint was defined as persistent PVI verified by circular mapping catheter recordings. Details of our CB ablation strategy are provided elsewhere . Repeat procedures were performed under conscious sedation combining fentanyl and midazolam. In patients who presented for the ablation with persistent AF, direct current conversion was performed at the beginning of the procedure. Two right sided femoral venous access points were obtained. A 23 cm, 11 F venous sheath was placed for the intracardiac echography (ICE) catheter (Accuson Acunav phase array catheter, Siemens AG). The ICE was used to examine the left atrial appendage, to guide the transeptal puncture (TSP) and ablation, and to monitor for potential complications. Second puncture was used for the left sided access which was achieved exclusively under ICE guidance using a transseptal sheath and transseptal needle (SL1 and BRK1, St. Jude Medical). Using over-the-wire technique SL1 sheath was exchanged for 8.5 steerable sheath (Vizigo, Biosense-Webster). Following steps are required for a safe and successful zero-fluoro transseptal puncture (TSP): (a) Initial Visualization : Using intracardiac echocardiography, a long wire has to be visualized in the superior vena cava (SVC), ensuring that the wire is not positioned in the right ventricle or right atrial appendage. (b) Advancing the Sheath : The SL1 sheath must be advanced over the wire into the SVC under ICE guidance. Typically, the tip of the ICE probe has to be positioned in high RA/SVC junction to obtain optimal images. (c) Pull down maneuver : After exchanging the wire for a BRK1 needle, transseptal system (TSS) has to be pulled down under ICE monitoring. It is typically possible to follow the entire trajectory of the TSS from the SVC to the fossa ovalis. (d) Needle Advancement : Once proper visualization of TSS tenting the fossa ovalis is achieved, the needle is advanced. Successful TSP is confirmed by visualizing saline flush in the left atrium. (e) Final Wire Placement : The needle is exchanged again for a long wire, which is placed in the left pulmonary veins under ICE guidance. d) Steerable Sheath Exchange : Finally, exchange the steerable sheath over the wire while maintaining careful ICE monitoring. Continuous visualization of the long guide wire is crucial to ensure all steps are completed safely (Fig. ). An intravenous bolus dose of unfractionated heparin (UFH) 100–150 IU/kg was administered immediately after the transseptal puncture. Activated clotting time (ACT) was measured every 10–15 min and supplemental UFH boluses were given to achieve the target ACT of > 300s. A high density anatomic and voltage map of the left atrium was created with CARTO 3 system (Biosense-Webster) using dedicated multipolar mapping catheter (Pentaray, Biosense-Webster). Pulmonary vein (PV) reconnections were assessed (lack of entry block) alongside with potential low-voltage zones (0.2–0.5 mV) demarking diseased LA tissue. Following the creation of a high-density map, the multipolar mapping catheter was replaced for a 3.5 mm open irrigated radiofrequency ablation catheter (Navistar Thermocool SmartTouch SF NAV, Biosense-Webster). Before the ablation, absence of exit block was confirmed for the reconnected PVs by pacing with the ablation catheter. The ablation strategy consisted of the encirclement of reconnected parts of PVs by creating contiguous lesions at a distance of more than 5 mm from the ostia to achieve wide antral re-isolation. If no reconnections were present and the previous CB lesions were ostial, a more antral lesions were created. In patients with persistent AF and significant posterior wall scarring, a box lesion set was performed. After a successful zero-fluoro TSP, a multipolar mapping catheter is advanced until the splines become visible on ICE images. Safe movement of the mapping catheter in the left atrium (LA) and cannulation of the pulmonary veins are achieved under constant ICE monitoring, in combination with an electroanatomic mapping system (EAM) that creates the relevant anatomy. The combination of these two methods eliminates the need for fluoroscopy. After creating the map, and again under ICE guidance, the mapping catheter is exchanged for the ablation catheter. A crucial step is ensuring the proper position of the steerable sheath in the LA, which is achieved using both ICE and the 3D mapping system. Finally, safe manipulation of the ablation catheter is accomplished with the EAM in conjunction with ICE guidance. Proper tissue contact before ablation is ensured through precise measurement of contact (in grams) by the contact-sensing catheter. In cases of uncertainty regarding the exact position of the ablation catheter on EAM, ICE can be helpful. Radiofrequency ablations were performed in a power-controlled mode with a maximum power of 50 W for the anterior wall and 40 W for the posterior wall, using a maximum temperature of 43 °C. Ablation index with the CARTO VISITAG™ Module was utilized with targets set at 400 for the posterior wall and 550 for the anterior wall. CF was carefully maintained within the range of 5 to 15 g throughout the ablation process. Following the completion of ablation, the ablation catheter was again exchanged for multipolar mapping catheter for the verification of electrical isolation of the PVs or the posterior wall. Both entry and exit block were confirmed at the end of the procedure (Fig. ). If a patient had typical flutter documented, a cavo-tricuspid isthmus (CTI) ablation was also performed with the goal of achieving a bidirectional CTI block. Furthermore, if a patient developed atypical flutter during the procedure, high density activation mapping and associated ablation was performed. A decapolar catheter (DecaNav, Biosense- Webseter) was used and placed in coronary sinus (CS) only if patient required atrial flutter ablation. We did not perform adenosine testing to verify PV isolation after the ablation. The figure of eight suture for groin access closure was used with no heparin reversal . During the procedure, ICE is used to continuously monitor for any significant complications, such as cardiac perforation and tamponade. Since our procedures were performed under mild conscious sedation, any potential thromboembolic events, such as stroke or transient ischemic attack, are readily visible. Therefore, we did not perform any head computed tomography (CT) or magnetic resonance imaging (MRI) scans after the procedure. Postprocedural care The first dose of oral anticoagulant (OAC), either DOAC or VKA, was given 4–6 h after the procedure. All patients remained in the decubitus position until the following morning. Before discharge, all patients underwent bedside transthoracic echo to exclude pericardial complications. All patients were discharged 1 day after the procedure. Post-ablation anti-arrhythmic medications were managed at the discretion of the leading physician. Anticoagulation therapy was maintained for at least 8 weeks, or longer, depending on the CHA2DS2-VASc score. Follow-up After hospital discharge, patients were scheduled for a follow-up visit at 3, 6, and 12 months, with annual visits during the long-term follow-up. If patients reported palpitations, additional visits were scheduled. Twenty-four-hour Holter recordings were obtained at each follow-up visit. Furthermore, telephone calls to patients were made during the follow-up. All documented AF episodes of > 30s after the index procedure were considered to be a recurrence. A blanking period of 3 months was applied. Other modalities of ECG monitoring, such as smart watches, trans-telephonic monitoring, or ECG patches were not available for this study. Endpoints The primary endpoints were defined as feasibility - possibility of completing the procedure without fluoroscopy and safety - procedure related major complications of zero-fluoro procedures after the initial CB ablation. Secondary endpoints included (i) procedural parameters like procedure duration and ablation time, etc., (ii) number of PV reconnections after initial CB ablation and (iii) midterm outcomes – freedom from atrial arrythmia after 1 year follow up. Statistical analysis Categorical variables are expressed as numbers and proportions. Continuous variables followed normal distribution and were therefore expressed as mean ± standard deviation. Statistical analyses were conducted using the SPSS software (SPSS v22, Chicago, IL, USA). 

Data were retrospectively collected for consecutive AF patients who have undergone zero-fluoro repeat ablations with RF catheters between July 2020 and June 2023 at the University Hospital Centre of Zagreb, Croatia. All patients received a second or fourth generation, 28 mm cryoballoon ablation for the initial procedure. The indication for the repeat procedure was symptomatic recurrence of AF at least 3 months after the initial procedure. Data were acquired from the hospital electronic database and from communication with patients. All procedures were performed by experienced operators. Exclusion criteria were: de novo pulmonary vein isolation procedure, index procedure performed by RF energy, intracardiac thrombi, uncontrolled heart failure (NYHA III-IV, recent acute heart failure), significant structural or valvular heart disease, or left atrial (LA) diameter > 55 mm. Patients without complete follow-up were excluded from the study. All patients provided written informed consent for the ablation and the study was approved by the local ethics committee. The research was conducted in accordance with the principles of the Declaration of Helsinki. 

A transthoracic echocardiogram was performed prior to repeat ablation (within 3 months), to assess the left ventricular ejection fraction and to rule out any significant structural heart and/or valvular disease. A transesophageal echocardiogram to exclude left atrial appendage thrombi was performed before the procedure only in patients who presented with persistent AF. For patients with persistent AF, our strategy was to perform early direct current (DC) cardioversion in the outpatient setting and to schedule the patients for ablation at subsequent hospitalization. We used the uninterrupted anticoagulation strategy in all patients in accordance to recent recommendations . In patients taking direct oral anticoagulant agents (DOAC), anticoagulation was stopped 12 h before the procedure (the last dose of dabigatran, rivaroxaban, apixaban or endoxaban was given in the evening of the day before the procedure). An uninterrupted vitamin K antagonist (VKA) strategy was used, and the ablation was performed when the (international normalized ratio) INR was between 2 and 3, measured on the day of the procedure. 

All patients underwent cryoballoon pulmonary vein isolation as an initial procedure, and no other lesion sets were performed. Briefly, cryoablation was performed in a standard fashion using a 28-mm second or fourth-generation CB (Arctic Front Advance (Pro), Medtronic). A 20 mm octapolar intraluminal circular catheter (ICC) (Achieve, Medtronic) was advanced to each PV ostium to collect baseline electrical activity. Using the “over-the-wire” technique, CB was positioned at PV antrum/ostium. Optimal vessel occlusion was considered achieved when selective contrast injection showed total contrast retention with no anterograde flow to the atrium. A single 3-minute freeze was applied to each PV. In the case of late isolation (> 60 s) or unsuccessful isolation, the balloon was repositioned and a second freeze was applied. If real time recordings were not present, a second freeze cycle of 180 s was delivered provided that the temperature of -40 °C was not reached within 60 s of the first freeze. Whenever PV potentials were not visible during the freeze, to confirm the PV isolation, the ICC was retracted to a more proximal position in the ostium where electrical information had been recorded prior to ablation. The procedural endpoint was defined as persistent PVI verified by circular mapping catheter recordings. Details of our CB ablation strategy are provided elsewhere . Repeat procedures were performed under conscious sedation combining fentanyl and midazolam. In patients who presented for the ablation with persistent AF, direct current conversion was performed at the beginning of the procedure. Two right sided femoral venous access points were obtained. A 23 cm, 11 F venous sheath was placed for the intracardiac echography (ICE) catheter (Accuson Acunav phase array catheter, Siemens AG). The ICE was used to examine the left atrial appendage, to guide the transeptal puncture (TSP) and ablation, and to monitor for potential complications. Second puncture was used for the left sided access which was achieved exclusively under ICE guidance using a transseptal sheath and transseptal needle (SL1 and BRK1, St. Jude Medical). Using over-the-wire technique SL1 sheath was exchanged for 8.5 steerable sheath (Vizigo, Biosense-Webster). Following steps are required for a safe and successful zero-fluoro transseptal puncture (TSP): (a) Initial Visualization : Using intracardiac echocardiography, a long wire has to be visualized in the superior vena cava (SVC), ensuring that the wire is not positioned in the right ventricle or right atrial appendage. (b) Advancing the Sheath : The SL1 sheath must be advanced over the wire into the SVC under ICE guidance. Typically, the tip of the ICE probe has to be positioned in high RA/SVC junction to obtain optimal images. (c) Pull down maneuver : After exchanging the wire for a BRK1 needle, transseptal system (TSS) has to be pulled down under ICE monitoring. It is typically possible to follow the entire trajectory of the TSS from the SVC to the fossa ovalis. (d) Needle Advancement : Once proper visualization of TSS tenting the fossa ovalis is achieved, the needle is advanced. Successful TSP is confirmed by visualizing saline flush in the left atrium. (e) Final Wire Placement : The needle is exchanged again for a long wire, which is placed in the left pulmonary veins under ICE guidance. d) Steerable Sheath Exchange : Finally, exchange the steerable sheath over the wire while maintaining careful ICE monitoring. Continuous visualization of the long guide wire is crucial to ensure all steps are completed safely (Fig. ). An intravenous bolus dose of unfractionated heparin (UFH) 100–150 IU/kg was administered immediately after the transseptal puncture. Activated clotting time (ACT) was measured every 10–15 min and supplemental UFH boluses were given to achieve the target ACT of > 300s. A high density anatomic and voltage map of the left atrium was created with CARTO 3 system (Biosense-Webster) using dedicated multipolar mapping catheter (Pentaray, Biosense-Webster). Pulmonary vein (PV) reconnections were assessed (lack of entry block) alongside with potential low-voltage zones (0.2–0.5 mV) demarking diseased LA tissue. Following the creation of a high-density map, the multipolar mapping catheter was replaced for a 3.5 mm open irrigated radiofrequency ablation catheter (Navistar Thermocool SmartTouch SF NAV, Biosense-Webster). Before the ablation, absence of exit block was confirmed for the reconnected PVs by pacing with the ablation catheter. The ablation strategy consisted of the encirclement of reconnected parts of PVs by creating contiguous lesions at a distance of more than 5 mm from the ostia to achieve wide antral re-isolation. If no reconnections were present and the previous CB lesions were ostial, a more antral lesions were created. In patients with persistent AF and significant posterior wall scarring, a box lesion set was performed. After a successful zero-fluoro TSP, a multipolar mapping catheter is advanced until the splines become visible on ICE images. Safe movement of the mapping catheter in the left atrium (LA) and cannulation of the pulmonary veins are achieved under constant ICE monitoring, in combination with an electroanatomic mapping system (EAM) that creates the relevant anatomy. The combination of these two methods eliminates the need for fluoroscopy. After creating the map, and again under ICE guidance, the mapping catheter is exchanged for the ablation catheter. A crucial step is ensuring the proper position of the steerable sheath in the LA, which is achieved using both ICE and the 3D mapping system. Finally, safe manipulation of the ablation catheter is accomplished with the EAM in conjunction with ICE guidance. Proper tissue contact before ablation is ensured through precise measurement of contact (in grams) by the contact-sensing catheter. In cases of uncertainty regarding the exact position of the ablation catheter on EAM, ICE can be helpful. Radiofrequency ablations were performed in a power-controlled mode with a maximum power of 50 W for the anterior wall and 40 W for the posterior wall, using a maximum temperature of 43 °C. Ablation index with the CARTO VISITAG™ Module was utilized with targets set at 400 for the posterior wall and 550 for the anterior wall. CF was carefully maintained within the range of 5 to 15 g throughout the ablation process. Following the completion of ablation, the ablation catheter was again exchanged for multipolar mapping catheter for the verification of electrical isolation of the PVs or the posterior wall. Both entry and exit block were confirmed at the end of the procedure (Fig. ). If a patient had typical flutter documented, a cavo-tricuspid isthmus (CTI) ablation was also performed with the goal of achieving a bidirectional CTI block. Furthermore, if a patient developed atypical flutter during the procedure, high density activation mapping and associated ablation was performed. A decapolar catheter (DecaNav, Biosense- Webseter) was used and placed in coronary sinus (CS) only if patient required atrial flutter ablation. We did not perform adenosine testing to verify PV isolation after the ablation. The figure of eight suture for groin access closure was used with no heparin reversal . During the procedure, ICE is used to continuously monitor for any significant complications, such as cardiac perforation and tamponade. Since our procedures were performed under mild conscious sedation, any potential thromboembolic events, such as stroke or transient ischemic attack, are readily visible. Therefore, we did not perform any head computed tomography (CT) or magnetic resonance imaging (MRI) scans after the procedure. 

The first dose of oral anticoagulant (OAC), either DOAC or VKA, was given 4–6 h after the procedure. All patients remained in the decubitus position until the following morning. Before discharge, all patients underwent bedside transthoracic echo to exclude pericardial complications. All patients were discharged 1 day after the procedure. Post-ablation anti-arrhythmic medications were managed at the discretion of the leading physician. Anticoagulation therapy was maintained for at least 8 weeks, or longer, depending on the CHA2DS2-VASc score. 

After hospital discharge, patients were scheduled for a follow-up visit at 3, 6, and 12 months, with annual visits during the long-term follow-up. If patients reported palpitations, additional visits were scheduled. Twenty-four-hour Holter recordings were obtained at each follow-up visit. Furthermore, telephone calls to patients were made during the follow-up. All documented AF episodes of > 30s after the index procedure were considered to be a recurrence. A blanking period of 3 months was applied. Other modalities of ECG monitoring, such as smart watches, trans-telephonic monitoring, or ECG patches were not available for this study. 

The primary endpoints were defined as feasibility - possibility of completing the procedure without fluoroscopy and safety - procedure related major complications of zero-fluoro procedures after the initial CB ablation. Secondary endpoints included (i) procedural parameters like procedure duration and ablation time, etc., (ii) number of PV reconnections after initial CB ablation and (iii) midterm outcomes – freedom from atrial arrythmia after 1 year follow up. 

Categorical variables are expressed as numbers and proportions. Continuous variables followed normal distribution and were therefore expressed as mean ± standard deviation. Statistical analyses were conducted using the SPSS software (SPSS v22, Chicago, IL, USA). 

Study population A total of 50 patients were included in our retrospective analysis. Overall, 76% were male and the mean age was 57.9 ± 10.2 years. Twenty-five patients (50%) had paroxysmal AF and the rest suffered from persistent forms of AF. Mean CHA 2 DS 2 VAS C score was 1.7 ± 1.3 and mean LA diameter was 44 ± 6 mm. Mean BMI was 28 ± 5. The mean time from the index procedure to repeat procedure was 915 ± 602 days. With respect to anticoagulation, the majority of patients were on DOAC (94%). The detailed baseline clinical characteristics of the study population are provided in Table . Procedural characteristics Zero-fluoro strategy was feasible in all patients. No patients required conversion to fluoroscopy. Therefore, all procedures were finished without leaded aprons. In 2 patients (4%) RF energy delivered through BRK1 needle was needed to cross the septum (Fig. ). The mean procedure time was 93.9 ± 27.1 min. The mean ablation time was 825 ± 468 s. The mean of 0.98 ± 0.91 veins were reconnected per patient and 36% of patients did not have any PV reconnections (Table ). The left superior and left inferior pulmonary veins were the most commonly reconnected, at rates of 29.6% and 22.2%, respectively. The right-sided veins had fewer reconnections, with the right superior pulmonary vein reconnecting in 20% of cases and the right inferior pulmonary vein in 18% of cases. The left common pulmonary vein was reconnected in 33.5% of cases. In all patients with pulmonary vein (PV) reconnections, successful PV re-isolation was performed, confirmed by entry and exit block. In two patients (4%), successful cavotricuspid isthmus (CTI) ablation was performed, confirmed by differential pacing. In three patients (6%) who developed atypical left-sided flutter, related ablation lines were created, resulting in conversion to sinus rhythm. Additionally, in nine patients (18%) with left posterior wall scarring, successful “box” isolations were performed, confirmed by entrance and exit block. Midterm outcomes and complications In the entire cohort, at a mean follow-up of 12.5 ± 3.4 months after the procedure, there were 16 patients (32%) with recurrences of atrial arrhythmia. One-year success rate in patients with paroxysmal AF after redo procedure was 76%. Patients with persistent forms of AF had somewhat lower success rates, 60% of patients remained free of AF. Eleven patients (22%) remained on antiarrhythmic drugs after the blanking period. Two minor complications (4%) occurred during the study period and there were no major complications. One patient developed symptoms of pericarditis that quickly resolved on non-steroidal anti-inflammatory drugs and one patient developed pericardial effusion that did not require active treatment. There were no tamponades, atrio-esophageal (AE) fistulae, thromboembolic events, symptomatic pulmonary vein stenoses or death related to procedure. (Table ). 

A total of 50 patients were included in our retrospective analysis. Overall, 76% were male and the mean age was 57.9 ± 10.2 years. Twenty-five patients (50%) had paroxysmal AF and the rest suffered from persistent forms of AF. Mean CHA 2 DS 2 VAS C score was 1.7 ± 1.3 and mean LA diameter was 44 ± 6 mm. Mean BMI was 28 ± 5. The mean time from the index procedure to repeat procedure was 915 ± 602 days. With respect to anticoagulation, the majority of patients were on DOAC (94%). The detailed baseline clinical characteristics of the study population are provided in Table . 

Zero-fluoro strategy was feasible in all patients. No patients required conversion to fluoroscopy. Therefore, all procedures were finished without leaded aprons. In 2 patients (4%) RF energy delivered through BRK1 needle was needed to cross the septum (Fig. ). The mean procedure time was 93.9 ± 27.1 min. The mean ablation time was 825 ± 468 s. The mean of 0.98 ± 0.91 veins were reconnected per patient and 36% of patients did not have any PV reconnections (Table ). The left superior and left inferior pulmonary veins were the most commonly reconnected, at rates of 29.6% and 22.2%, respectively. The right-sided veins had fewer reconnections, with the right superior pulmonary vein reconnecting in 20% of cases and the right inferior pulmonary vein in 18% of cases. The left common pulmonary vein was reconnected in 33.5% of cases. In all patients with pulmonary vein (PV) reconnections, successful PV re-isolation was performed, confirmed by entry and exit block. In two patients (4%), successful cavotricuspid isthmus (CTI) ablation was performed, confirmed by differential pacing. In three patients (6%) who developed atypical left-sided flutter, related ablation lines were created, resulting in conversion to sinus rhythm. Additionally, in nine patients (18%) with left posterior wall scarring, successful “box” isolations were performed, confirmed by entrance and exit block. 

In the entire cohort, at a mean follow-up of 12.5 ± 3.4 months after the procedure, there were 16 patients (32%) with recurrences of atrial arrhythmia. One-year success rate in patients with paroxysmal AF after redo procedure was 76%. Patients with persistent forms of AF had somewhat lower success rates, 60% of patients remained free of AF. Eleven patients (22%) remained on antiarrhythmic drugs after the blanking period. Two minor complications (4%) occurred during the study period and there were no major complications. One patient developed symptoms of pericarditis that quickly resolved on non-steroidal anti-inflammatory drugs and one patient developed pericardial effusion that did not require active treatment. There were no tamponades, atrio-esophageal (AE) fistulae, thromboembolic events, symptomatic pulmonary vein stenoses or death related to procedure. (Table ). 

The main findings of the study are: (a) Zero-fluoro, apron-less repeat procedures after index CB ablation are feasible and are not necessarily associated with increased complications rates, (b) more than one third of patients did not have any PV reconnections after the initial CB ablation procedure, and PV reconnection rates are less than 1 PV per patient d) midterm recurrence rates of AF are deemed acceptable following zero-fluoro repeat procedures. Medical personnel present during procedures requiring fluoroscopy are among those with the highest level of occupational radiation exposure . To mitigate the risk of radiation, the use of leaded aprons is mandatory during these procedures. Interventional cardiologists, including interventional electrophysiologists (EP) have a 10% higher risk of radiation-related illness and over 50% higher risk of orthopaedic injury compared to other cardiologists . Some estimates show that a typical AF ablation procedure raises the risk of fatal cancer by 0.008% . Therefore, the so-called ALARA (as low as reasonably possible) principle must be followed in all interventional procedures . Prevention of X-ray associated, potentially fatal stochastic effects that can occur even with the lowest radiation doses is as important, as prevention of debilitating orthopaedic injuries that are quite common among the EP physicians and other staff . Zero-fluoro approach was initially used for basic EP procedures like supraventricular tachycardia ablation . However, recent advances in 3D mapping technology, especially the advent of magnet-based electroanatomic mapping systems and the wide use of intracardiac echocardiography have allowed the development zero-fluoro strategy for more complex ablations like pulmonary vein isolation. In our centre, zero-fluoro approach is characterized by the operator’s decision to completely avoid the X-ray radiation throughout the procedure, from the very beginning, which includes fluoro-less transseptal puncture. Therefore, for the intended zero-fluoro procedures, the operator and the rest of the team are not wearing any X-ray protection – thus the name “apron-less” approach. Beside the comfort, apron-less approach is devised to exclude serious orthopaedic risks associated with electrophysiology . If radiation is required during the procedure, aprons are necessary and zero-fluoro strategy is deemed unsuccessful. In recent meta-analysis, including 1593 patients, zero-fluoro strategy was achievable in more than 95% of cases of RF-based atrial fibrillation ablation procedures . Generally, fluoroscopy is needed at the beginning of AF ablation procedures for TSP and initial catheter positioning. Therefore, some operators remove lead aprons after the initial phase of the procedure to limit orthopaedic problems. Our centre is using simplified ablation approach with only two venous and one trans-septal puncture for repeat AF procedures. We are consistently using the ICE catheters that are essential for fluoro-less ablation. Some studies report conversion to fluoroscopy for ICE catheter navigation in tortuous distal venous anatomy . However, we are consistently using the long wires for vein access and longer, 23 cm sheaths specifically to avoid that problem. Also, we are usually not using coronary sinus catheter, but if needed (for atrial flutter ablation), decapolar catheter can also be easily placed in coronary sinus without fluoroscopy, using solely 3D mapping technology. Furthermore, a small number of patients (4%) in our cohort required RF energy to cross the fibrous septum, which was probably the consequence of previous ablation with large bore trans-septal sheath. Even without dedicated RF transeptal devices like VersaCross (Boston Scientific) or FlexCathCross (Medtronic), RF mediated TSP was feasible with ICE guidance, without X-ray . Zero-fluoro procedure for repeat AF ablation was first reported eight years ago, however larger dataset examining safety and feasibility are scarce . When performing the procedures without fluoroscopy, patient safety is certainly the main concern. Furthermore, repeat procedures are burdened with higher complication rates: in one report examining zero-fluoro AF ablations, a high incidence (7%) of tamponade was observed, only in repeat ablation group. Because TSP may be more challenging in repeat cases, if intra-atrial septum is resistant, conversion to the fluoroscopy is recommended by the authors . However, in our cohort, with the appropriate use of intracardiac echo imaging, even the RF-mediated TSP was possible without fluoroscopy. In the largest meta-analysis to date comparing zero-fluoro to conventional PVI procedures, safety of zero-fluoro strategy was not compromised - the major complication rates were 2.69% and 2.82%, respectively, and acute and long-term success rates were similar in two groups . Reported feasibility of fluoro-less RF ablation approach was 88.5–100%, even when patients required CTI, mitral isthmus and other linear LA ablations, which further corroborates our findings. While our cohort may be limited in size, transseptal puncture as well as the rest of the procedure (which includes mapping and ablation) were doable without conversion to fluoroscopy. This was achievable without any major complications, even when using uninterrupted anticoagulation strategy. Although complete zero-fluoro procedures were possible in our cohort, conversion to fluoroscopy may be necessary for safety in certain circumstances. For instance, patients with implanted pacemakers may have a higher risk of lead dislocation when using only a zero-fluoro strategy. Additionally, in cases of difficult transseptal puncture, such as a resistant septum or complicated wire positioning in the SVC, fluoroscopy might be required. Furthermore, if a patient has anatomical variations (like a persistent left vena cava) or other implanted cardiac devices, such as septal or left appendage occluders, fluoroscopy is advisable to ensure safety and accuracy during the procedure. Certainly, ICE may have limitations in spatial resolution, and after TSP, we kept the ICE probe in the right atrium without advancing it to the left atrium. This limits the visibility of certain anatomical structures, such as the right-sided pulmonary veins. However, in conjunction with an electroanatomical mapping system, mapping and ablation procedures can still be successfully performed even with the ICE probe positioned on the right side. This typically requires greater experience and advanced manipulation skills with the ICE probe. Like most of authors performing the fluoro-less AF ablation, we were using solely magnetic navigational system (Carto 3, Biosense-Webster) because of the greater system stability and less map distortion (map shifting). However, other impedance-based systems could also be used (e.g. Ensite Precision, Abbott), especially if patients are under general anaesthesia and movement is unlikely . In our cohort, after the initial CB ablation one third of patients were free from PV reconnections which is in line with previous studies; this highlights the benefit of single shot devices for the index pulmonary vein isolation procedures . In one large series of patients after CB ablation, the rate of late PV reconnection was low (1.18 PVs/patient) and 41% of patients did not have any PV reconnections, which is quite similar to our findings . Low rates of reconnections after CB ablation allow faster repeat procedures with lower RF ablation time needed for achieving the re-isolation. Historically, CB ablation was associated with significantly lower reconnection rates than RF-based ablation , but it seems that with the advent of PFE technology the PV reconnection rates could be brought to even lower levels. For example, in recent propensity score-matched comparison of different technologies, PV reconnection rate was only 19.1% after PFA, 27.5% after CB, and 34.8% after RF ( P = 0.01) . Mid-term outcomes in our patient cohort were acceptable: 68% of mixed AF population patients were free from AF after one year. That is in line with previous studies of repeat ablation with RF energy following index CB ablation, where up to 75% did not experience recurrence of atrial arrhythmias in one year . Nonetheless, AF is a chronic disease without a definitive cure, and more recurrences can be expected with longer follow-up, especially in patients with persistent forms of the disease . Therefore, a longer follow up would be more beneficial to precisely determine the value and success of the zero-fluoro approach. However, in the largest meta-analysis published to date, the reported follow-up ranged from 3 to a maximum of 15 months . For this reason, currently it is not possible to compare the long-term outcomes of the zero-fluoro versus conventional approaches in AF ablation. As zero-fluoro procedures become increasingly popular, we can expect that relevant data will become available soon. Currently, we have some favorable long-term data for supraventricular tachycardia ablation performed without fluoroscopy , . Intracardiac echo catheters, which are essential tool for zero-fluoro AF ablation procedures, are not widely available globally due to serious financial constraints. They are designated for single use only, and their high cost precludes widespread adoption. To overcome this issue, ICE catheter reprocessing might be utilized. Recent data show that ICE probe reprocessing is feasible and safe, and that significant economic and environmental savings could be achieved through this strategy . Therefore, ICE probe reprocessing could increase the number of ICE-guided cardiac procedures worldwide and further enhance the possibility of performing electrophysiology interventions without fluoroscopy. Furthermore, it may lead to a lower incidence of serious procedure-related complications. 

Our data suggests that zero-fluoro, apron-less approach for repeat PVI procedures after index cryoballoon ablation is feasible and safe. Developing zero-fluoro strategies in cardiac ablation is important to avoid radiation related risks, for both patients and staff. Furthermore, this strategy could significantly alleviate the risks of orthopaedic injury for the operators and staff. Index CB ablation resulted in low rates of PV reconnections (< 1 pulmonary vein/patient), and more than one third of patients had durable PVI after first ablation. Mid-term results of zero-fluoro, repeat procedures seem favourable. Limitations This was a retrospective, single centre study with all inherent limitations of this type of research. Our manuscript lacks a direct comparison of the zero-fluoro strategy for repeat ablation with the conventional approach, which is important for demonstrating the true value of this novel technique. Ideally, a randomized trial is needed to accurately determine the actual differences. The number of study participants was not high, and the procedures were performed by highly experienced operators, which questions the generalization of our results. We did not detect any major complications in our cohort which seems promising, but with the higher number of patients, surely, major complications will occur. Intracardiac echo catheters are not widely available globally because of the reimbursement issues. This represents an important limitation that may prevent wide adoption of our strategy. Furthermore, we conducted a conventional one-year clinical follow-up of the patients after the ablation, so some subclinical recurrences may have been missed. A longer follow-up would provide a more comprehensive view of the durability of the zero-fluoro approach. 

This was a retrospective, single centre study with all inherent limitations of this type of research. Our manuscript lacks a direct comparison of the zero-fluoro strategy for repeat ablation with the conventional approach, which is important for demonstrating the true value of this novel technique. Ideally, a randomized trial is needed to accurately determine the actual differences. The number of study participants was not high, and the procedures were performed by highly experienced operators, which questions the generalization of our results. We did not detect any major complications in our cohort which seems promising, but with the higher number of patients, surely, major complications will occur. Intracardiac echo catheters are not widely available globally because of the reimbursement issues. This represents an important limitation that may prevent wide adoption of our strategy. Furthermore, we conducted a conventional one-year clinical follow-up of the patients after the ablation, so some subclinical recurrences may have been missed. A longer follow-up would provide a more comprehensive view of the durability of the zero-fluoro approach. 

