Cryotherapy of cardiac arrhythmia: From basic science to the bedside

Impact of radiofrequency versus cryoballoon ablation on left atrial calcification after atrial fibrillation ablation: A propensity score-matched comparison

INTRODUCTION

Left atrial calcification (LAC) following atrial fibrillation (AF) ablation is associated with major adverse cardiovascular events, with prior reports focusing on radiofrequency catheter ablation (RFCA) rather than cryoballoon ablation (CBA). The aim of this study was to investigate the frequency of LAC and stiff LA physiology (SLAP) in patients undergoing CBA as the initial therapy for AF, compared with those undergoing RFCA, using a propensity score-matched (PSM) population.

METHODS

We conducted a retrospective cohort study involving 2680 consecutive patients who underwent AF ablation with RFCA or CBA. Patients with rheumatic valve disease or mitral valve replacement, those undergoing dialysis, and those without postoperative computed tomography (CT) imaging were excluded. CT images acquired ≥1 year after the initial procedure were used to evaluate the LAC.

RESULTS

In total, 473 eligible patients were identified. PSM created 125 pairs. After a median follow-up of 4.7 years, 9 (4 %) of 250 patients presented with LAC. Those who underwent CBA had a significantly lower incidence of LAC and SLAP compared to those who underwent RFCA (LAC: 1 % vs. 6 %, P = 0.03; SLAP: 1 % vs. 9 %, P = 0.005). Right ventricular systolic pressure significantly increased in the RFCA group (pre-ablation: 23 ± 8 vs. post-ablation: 26 ± 8, P = 0.01), but remained unchanged in the CBA group (pre-ablation: 23 ± 7 vs. post-ablation: 23 ± 8, P = 0.88).

CONCLUSIONS

The use of CBA as the initial ablation seems to have clinical benefits in preventing LAC and SLAP compared to RFCA.

Invasive strategies for rhythm control of atrial fibrillation: a narrative review

Atrial fibrillation (AF) is the most common sustained tachyarrhythmia and its increasing prevalence has resulted in a growing healthcare burden. A recent landmark randomized trial, the EAST-AFNET 4 (Early Treatment of Atrial Fibrillation for Stroke Prevention Trial), highlighted the importance of early rhythm control in AF, which was previously underemphasized. Rhythm control therapy includes antiarrhythmic drugs, direct-current cardioversion, and catheter ablation. Currently, catheter ablation is indicated for patients with AF who are either refractory or intolerant to antiarrhythmic drugs or who exhibit decreased left ventricular systolic function. Catheter ablation can be categorized according to the energy source used, including radiofrequency ablation (RFA), cryoablation, laser ablation, and the recently emerging pulsed field ablation (PFA). Catheter ablation techniques can also be divided into the point-by-point ablation method, which ablates the pulmonary vein (PV) antrum one point at a time, and the single-shot technique, which uses a spherical catheter to ablate the PV antrum in a single application. PFA is known to be applicable to both point-by-point and single-shot techniques and is expected to be promising owing to its tissue specificity, resulting in less collateral damage than catheter ablation involving thermal energy, such as RFA and cryoablation. In this review, we aimed to outline catheter ablation for rhythm control in AF by reviewing previous studies.

Computer Simulation of Catheter Cryoablation for Pulmonary Vein Isolation

Cryoablation is a well-established medical procedure for surgically treating atrial fibrillation. Cryothermal catheter therapy induces cellular necrosis by freezing the insides of pulmonary veins, with the goal of disrupting abnormal electrical heart signals. Nevertheless, tissue damage induced by cold temperatures may also lead to other complications after cardiac surgery. In this sense, the simulation of catheter ablation can provide safer environments for training and the performance of cryotherapy interventions. Therefore, in this paper, we propose a novel approach to help better understand how temperature rates can affect this procedure by using computer tools to develop a simulation framework to predict lesion size and determine optimal temperature conditions for reducing the risk of major complications. The results showed that a temperature profile of around -40 °C caused less penetration, reduced necrotic damage, and smaller lesion size in the tissue. Instead, cryotherapy close to -60 °C achieved a greater depth of temperature flow inside the tissue and a larger cross-section area of the lesion. With further development and validation, the framework could represent a cost-effective strategy for providing personalized modeling, better planning of cryocatheter-based treatment, and preventing surgical complications.

Safety and efficacy of the second-generation cryoballoon for left atrial appendage electrical isolation in canines

AIMS

Left atrial appendage electrical isolation (LAAEI) has demonstrated a significant enhancement in the success rate of atrial fibrillation (AF) ablation. Nevertheless, concerns persist about the safety of LAAEI, particularly regarding alterations in left atrial appendage (LAA) flow velocity and the potential risks of thrombus. This study aimed to assess the efficacy and safety of LAAEI, investigating changes in LAA flow velocity in canines.

METHODS AND RESULTS

The study comprised a total of 10 canines. The LAAEI procedure used by a 23 mm cryoballoon of the second generation was conducted at least 180 s. Intracardiac ultrasonography (ICE) was employed to quantify the velocity flow of the LAA both prior to and following LAAEI. Following a 3-month period, subsequent evaluations were performed to assess the LAA velocity flow and the potential reconnection. Histopathological examination was conducted. Left atrial appendage electrical isolation was effectively accomplished in all canines, resulting in a 100% acute success rate (10/10). The flow velocity in the LAA showed a notable reduction during LAAEI as compared with the values before the ablation procedure (53.12 ± 5.89 vs. 42.01 ± 9.22 cm/s, P = 0.007). After the follow-up, reconnection was observed in four canines, leading to a success rate of LAAEI of 60% (6/10). The flow velocity in the LAA was consistently lower (53.12 ± 5.89 vs. 44.33 ± 10.49 cm/s, P = 0.006), and no blood clot development was observed. The histopathological study indicated that there was consistent and complete injury to the LAA, affecting all layers of its wall. The injured tissue was subsequently replaced by fibrous tissue.

CONCLUSION

The feasibility of using cryoballoon ablation for LAAEI was confirmed in canines, leading to a significant reduction of LAA flow velocity after ablation. Some restoration of LAA flow velocity after ablation may be linked to the passive movement of the LAA and potential reconnecting. However, this conclusion is limited to animal study; more clinical data are needed to further illustrate the safety and accessibility of LAAEI in humans.

Symptomatic periesophageal vagal nerve injury by different energy sources during atrial fibrillation ablation

Background

Symptomatic gastric hypomotility (SGH) is a rare but major complication of atrial fibrillation (AF) ablation, but data on this are scarce.

Objective

We compared the clinical course of SGH occurring with different energy sources.

Methods

This multicenter study retrospectively collected the characteristics and clinical outcomes of patients with SGH after AF ablation.

Results

The data of 93 patients (67.0 ± 11.2 years, 68 men, 52 paroxysmal AF) with SGH after AF ablation were collected from 23 cardiovascular centers. Left atrial (LA) ablation sets included pulmonary vein isolation (PVI) alone, a PVI plus a roof-line, and an LA posterior wall isolation in 42 (45.2%), 11 (11.8%), and 40 (43.0%) patients, respectively. LA ablation was performed by radiofrequency ablation, cryoballoon ablation, or both in 38 (40.8%), 38 (40.8%), and 17 (18.3%) patients, respectively. SGH diagnoses were confirmed at 2 (1-4) days post-procedure, and 28 (30.1%) patients required re-hospitalizations. Fasting was required in 81 (92.0%) patients for 4 (2.5-5) days; the total hospitalization duration was 11 [7-19.8] days. After conservative treatment, symptoms disappeared in 22.3% of patients at 1 month, 48.9% at 2 months, 57.6% at 3 months, 84.6% at 6 months, and 89.7% at 12 months, however, one patient required surgery after radiofrequency ablation. Symptoms persisted for >1-year post-procedure in 7 patients. The outcomes were similar regardless of the energy source and LA lesion set.

Conclusions

The clinical course of SGH was similar regardless of the energy source. The diagnosis was often delayed, and most recovered within 6 months, yet could persist for over 1 year in 10%.

Liquid Nitrogen Cryoballoon Ablation System for Paroxysmal Atrial Fibrillation: A Multicenter, Prospective, Single-Arm Clinical Trial

BACKGROUND

Cryoballoon ablation (CBA) has emerged as an effective treatment for atrial fibrillation (AF).

OBJECTIVES

This study sought to assess the performance of a novel liquid nitrogen-driven CBA system and evaluate its safety and efficacy in the treatment of drug-resistant paroxysmal atrial fibrillation (PAF).

METHODS

This was a prospective multicenter single-arm clinical trial with 10 participating tertiary hospitals enrolling 176 patients with PAF. All participants received liquid nitrogen-driven CBA developed by the Cryofocus Medtech Company. Scheduled follow-up was performed before discharge and 3 months, 6 months, and 12 months after CBA. The primary endpoints were defined as 1) treatment success (freedom from antiarrhythmic drugs and atrial tachycardia at 12 months after CBA); and 2) immediate success rate of pulmonary vein isolation. The safety endpoint was the incidence of device- and procedure-related adverse events (AEs) and all-cause mortality.

RESULTS

A total of 172 participants were included, with an average age of 59.22 ± 9.25 years and 99 (57.56%) of them men. Immediate success rate was 97.67% (95% CI: 94.15%-99.36%) and 12-month treatment success rate was 82.56% (95% CI: 76.89%-88.23%), including a late recurrence rate of 13.61%. Incidences of device- and procedure-related AEs were 2.27% and 25.00%, respectively. Phrenic nerve palsy (PNP) occurred in 6 patients, of which 5 recovered during follow-up. Although the incidence of total severe AEs was 17.05%, including an all-cause mortality of 0.57%, only 1 case of permanent PNP was related to the CBA procedure.

CONCLUSIONS

This premarketing prospective multicenter single-arm clinical trial demonstrated that the liquid nitrogen cryoablation system is safe and effective in the treatment of PAF.

Left atrial appendage occlusion combined with cryoballoon or radiofrequency ablation: One-year follow-up comparison

Background

A one-stop procedure involving catheter ablation and left atrial appendage occlusion (LAAO) is an option for high-risk atrial fibrillation patients. Few studies have reported the efficacy and safety of cryoballoon ablation (CBA) combined with LAAO, and no studies have compared the combination of LAAO with CBA or radiofrequency ablation (RFA).

Methods

A total of 112 patients were enrolled in the present study; 45 patients received CBA combined with LAAO (group 1), and 67 patients received RFA combined with LAAO (group 2). Patient follow-up was performed for 1 year to detect peri-device leaks (PDLs) and safety outcomes (defined as a composite of peri-procedural and follow-up adverse events).

Results

The number of PDLs at the median 59 days follow-up was comparable between the two groups (33.3% in group 1 vs. 37.3% in group 2, p = 0.693). Safety outcomes were also comparable between the two groups (6.7% in group 1 vs. 7.5% in group 2, p = 1.000). Multivariable regression showed that PDLs risk and safety outcomes were all similar between the two groups. Subgroup analysis of PDLs indicated no significant differences. Follow-up safety outcomes were related to anticoagulant medication, and patients without PDLs were more likely to discontinue antithrombotic therapy. The total procedure and ablation times were all significantly shorter for group 1.

Conclusion

When compared with left atrial appendage occlusion combined with radiofrequency, left atrial appendage occlusion combined with cryoballoon ablation has the same risk of peri-device leaks and safety outcomes, but the procedure time was significantly reduced.

Evaluation of cryoballoon pulmonary vein isolation lesions during the acute and chronic phases using a high-resolution mapping system

BACKGROUND

An acute cryothermal ablation lesion contains both reversible and irreversible elements. However, differences in lesions created with cryoballoon pulmonary vein isolation (PVI) between the acute and chronic phases have not been fully elucidated.

METHODS

We retrospectively analyzed 23 consecutive patients with atrial fibrillation who underwent cryoballoon PVI during the initial procedure followed by a second ablation procedure. In all patients, cryoballoon PVI lesions were evaluated with high-resolution voltage mapping just after PVI (acute phase) and during the second session (chronic phase). We compared the area and width of the non-isolated left atrial posterior wall (NI-LAPW) with voltage ≥ 0.5 mV during both sessions.

RESULTS

PVI was successfully achieved in all patients. Cryoballoon PVI lesions were re-evaluated at 11 [2-17] months post-procedure. During the chronic phase, NI-LAPW width became significantly larger at the level of the roof (change, 5.8 ± 5.5 mm; p < 0.001) and at the level of the carina (change, 3.3 ± 7.0 mm; p < 0.05), and NI-LAPW area became significantly larger (change, 1.5 ± 1.9 cm²; p < 0.001) compared with the acute phase. Eight patients without any PV reconnections also had larger NI-LAPW areas (change, 1.3 ± 1.2 cm²; p < 0.05) during the chronic phase. Conduction resumption confined to the right carina was observed in 1 (4.3%) patient who presented with circumferential PVI that included the carina during the first session.

CONCLUSION

Acute cryoballoon PVI lesions significantly regressed during the chronic phase. PV reconnections and the isolation area should be carefully re-evaluated during the second procedure.

Peri-Balloon Leak Flow Velocity Assessed by Intra-Cardiac Echography Predicts Pulmonary Vein Electrical Gap - Intra-Cardiac Echography-Guided Contrast-Free Cryoballoon Ablation

BACKGROUND

The use of iodine contrast agents is one possible limitation in cryoballoon ablation (CBA) for atrial fibrillation (AF). This study investigated intracardiac echography (ICE)-guided contrast-free CBA.

METHODS AND RESULTS

The study was divided into 2 phases. First, 25 paroxysmal AF patients (Group 1) underwent CBA, and peri-balloon leak flow velocity (PLFV) was assessed using ICE and electrical pulmonary vein (PV) lesion gaps were assessed by high-density electroanatomical mapping. Then, 24 patients (Group 2) underwent ICE-guided CBA and were compared with 25 patients who underwent conventional CBA (historical controls). In Group 1, there was a significant correlation between PLFV and electrical PV gap diameter (r=-0.715, P<0.001). PLFV was higher without than with an electrical gap (mean [±SD] 127.0±28.6 vs. 66.6±21.0 cm/s; P<0.001) and the cut-off value of PLFV to predict electrical isolation was 105.7 cm/s (sensitivity 0.700, specificity 0.929). In Group 2, ICE-guided CBA was successfully performed with acute electrical isolation of all PVs and without the need for "rescue" contrast injection. Atrial tachyarrhythmia recurrence at 6 months did not differ between ICE-guided and conventional CBA (3/24 [12.5%] vs. 5/25 [20.0%], respectively; P=0.973, log-rank test).

CONCLUSIONS

PLFV predicted the presence of an electrical PV gap after CBA. ICE-guided CBA was feasible and safe, and could potentially be performed completely contrast-free without a decrease in ablation efficacy.

Characteristics of anatomical difficulty for cryoballoon ablation: insights from CT

Background

The limited availability of balloon sizes for cryoballoon leads to anatomical limitations for pulmonary vein (PV) isolation. We conducted a comprehensive systematic analysis on procedural success rate, atrial fibrillation (AF) recurrence rate and complications of cryoballoon ablation in association with the anatomy of the left atrium and PV based on preprocedural CT to gain insights into proper treatments of patients with AF using cryoballoon.

Method

A systematic search of literature databases, including PubMed, Web of Science and Cochrane Library, from the inception of each database through February 2021 was conducted. Search keywords included ‘atrial fibrillation’, ‘cryoballoon ablation’ and ‘anatomy’.

Results

Overall, 243 articles were identified. After screening, 16 articles comprising 1396 patients were included (3, 5 and 8 for acute success, AF recurrence and complications, respectively). Regarding acute success and AF recurrences, thinner width of the left lateral ridge, higher PV ovality, PV ostium-bifurcation distance, shorter distance from the non-coronary cusp to inferior PVs, shallower angle of right PVs against the atrial septum and larger right superior PV (RSPV) were associated with poor outcomes. Regarding complications, shorter distance between the RSPV ostium and the right phrenic nerve, larger RSPV-left atrium angle, larger RSPV area and smaller right carina width were associated with incidences of phrenic nerve injury.

Conclusion

This study elucidated several key anatomical features of PVs possibly affecting acute success, AF recurrence and complications in patients with AF using cryoballoon ablation. CT analysis has helped to describe benefits and anatomical limitations for cryoballoon ablation.

Key characteristics for effective acute pulmonary vein isolation when using a novel cryoballoon technology: insights from the CHARISMA registry

PURPOSE

A new cryoballoon (CB) technology (POLARx™; Boston Scientific) for pulmonary vein (PV) isolation in patients with atrial fibrillation (AF) has recently been introduced. The aim of this study was to evaluate procedural and biophysical parameters resulting in acute PV isolation when using this new CB.

METHODS

We assessed the first 69 consecutive patients indicated for AF ablation who underwent PV isolation by means of a novel CB system. Procedural metrics were prospectively recorded.

RESULTS

A total of 274 PVs were targeted in 69 patients. PV isolation was achieved in all patients by means of cryoablation alone. The median time to isolation (TTI) was 44 [31-68] s (median temperature at TTI =  - 49 [- 53 to - 41] °C). The median duration of CB ablation was 180 [180 to 240] s. The median nadir temperature was - 56.0 [- 61 to - 52] °C, and the median thaw time to 0 °C was 18 [15-21] s. The median grade of PV occlusion was 4 [3 to 4]. On the basis of ROC analysis, we defined the following cut-off values for acute PV isolation: - 56 °C for nadir temperature (sensitivity = 73.3%, specificity = 64.6%, AUC = 0.716; positive predictive value = 88.1%), 30 s for TTT (60.2%, 53.3%, 0.578; 79.7%), thaw time > 17 s (65.3%, 70.0%, 0.709; 86.9%), and grade of PV occlusion = 4 (79.4%, 66.7%, 0.738; 88.5%). No major procedure-related adverse events were observed at 30-day post-procedure.

CONCLUSIONS

The new POLARx™ CB appears to be effective and safe. A nadir temperature of - 56 °C, a thaw time to 0 °C ≥ 17 s, and complete PV occlusion were the best predictors of acute PV isolation.

CLINICAL TRIAL REGISTRATION

Catheter Ablation of Arrhythmias with a High-Density Mapping System in Real-World Practice (CHARISMA). URL: http://clinicaltrials.gov/Identifier : NCT03793998. Registration date: January 4, 2019.

Cellulose Nanocrystals Facilitate Needle-like Ice Crystal Growth and Modulate Molecular Targeted Ice Crystal Nucleation

Ice nucleators are of crucial and important implications in various fields including chemistry, climate, agriculture, and cryobiology. However, the complicated extract and biocompatibility of ice nucleators remain unresolved, and the mechanism of ice nucleation remains largely unknown. Herein, we show that natural nanocrystalline cellulose materials possess special properties to enhance ice nucleation and facilitate needle-like ice crystal growth. We reveal the molecular level mechanism that the efficient exposure of cellulose hydroxyl groups on (-110) surface leads to faster nucleation of water. We further design chitosan-decorated cellulose nanocrystals to accomplish molecular cryoablation in CD 44 high-expression cells; the cell viability shows more than ∼10 times decrease compared to cryoablation alone and does not show evident systematic toxicity. Collectively, our findings also offer improved knowledge in molecular level ice nucleation, which may benefit multiple research communities and disciplines.

Acute Safety and Efficacy of Fluoroless Cryoballoon Ablation for Atrial Fibrillation

Pulmonary vein isolation (PVI) is widely used for the ablation of atrial fibrillation, with prior reports suggesting good efficacy. Due to the widespread use of three-dimensional electroanatomic mapping systems and advances in intracardiac echocardiography, fluoroless ablation has been made possible. Fluoroless ablation with a cryoballoon (CB), however, has not been widely performed because of the need to prove occlusion of the vein with contrast dye and fluoroscopy. The objective of this study is to show that CB ablation can be performed safely and effectively without fluoroscopy. A dual-center, case–control study was performed of patients undergoing CB PVI with a fluoroless approach and a control group with traditional fluoroscopic techniques. The absence of color-flow Doppler signals around the periphery of the CB on intracardiac echocardiography and an increase in mean pressure by 5 mmHg, loss of the A-wave, and an increase in the V-wave as measured with continuous-wave pressure monitoring were adopted as indicators of vein occlusion in the absence of fluoroscopy. Temperature at 30 seconds, minimum temperature, time to isolation, procedure length, and complications were evaluated. During the study period of November 15, 2018 to November 15, 2019, a total of 100 patients underwent CB PVI at the participating centers. A total of 50 patients were enrolled in the fluoroless arm [35 men (70%), mean age: 64.9 ± 12 years, mean left atrium size: 44.2 ± 16 mL/m², left ventricular ejection fraction: 61% ± 5%], while 50 patients were enrolled in the control arm with similar characteristics. Four hundred forty-one 441 PVs were evaluated in the study cohort compared to 339 PVs in the control arm. When comparing fluoroless and traditional techniques, the mean temperature at 30 seconds was −31.7°C ± 6°C versus −32.8°C ± 5°C (p = 0.037), the minimum temperature was −47.4°C ± 6°C versus −47.7°C ± 9°C (p = 0.677), the time to isolation was 56.8 ± 28 seconds versus 74.8 ± 45 seconds (p = 0.212), and the procedure time was 102.2 ± 27.3 seconds versus 104.5 ± 16.9 seconds (p = 0.6436). Ultimately, this proof-of-concept study revealed that fluoroless ablation can be performed with success and efficiency outcomes similar to those of a traditional ablation approach. This suggests that the ablation of atrial fibrillation with CB can be performed safely and effectively without the use of fluoroscopy by experienced operators.

Visualization of intensive atrial inflammation and fibrosis after cryoballoon ablation: PET/MRI and LGE-MRI analysis

BACKGROUND

Atrial inflammation plays an important role in initiating atrial fibrosis, which could perpetuate atrial fibrillation (AF). However, the method of visualization of atrial inflammation has not been established. We sought to investigate whether the intensive atrial inflammation caused by cryoballoon ablation (CBA) could be detected by positron emission tomography/ magnetic resonance imaging (PET/MRI) and whether the atrial inflammation could be associated with consequent fibrosis.

METHODS

A total of 10 paroxysmal atrial fibrillation patients after CBA were enrolled. To detect and quantify intensive atrial inflammation, PET/MRI was performed to assess regional 18F-fluorodeoxyglucose (18F-FDG) uptake one day after the CBA, and the standardized uptake values (SUV) max were compared between the pulmonary vein (PV) antrum where CBA could be applied and the healthy left atrial (LA) wall where CBA could not be applied. Furthermore, the atrial inflammation one day after the procedure and atrial fibrosis areas one month after the procedure were three-dimensionally quantified by PET/MRI and late-gadolinium enhancement magnetic resonance imaging (LGE-MRI), respectively.

RESULTS

The mean SUV max at the PV antrum was significantly higher than that on the healthy LA wall (2.12 ± 0.35 vs 1.73 ± 0.30, P = .00021). The volume of the atrial inflammation strongly correlated with that of the atrial fibrosis (r = .94 [.76-.99], P = .00006).

CONCLUSIONS

The atrial inflammation after CBA could be detected by PET/MRI. CBA-induced atrial inflammation was strongly associated with consequent lesion maturation.

Cool enough? Lessons learned from cryoballoon-guided catheter ablation for atrial fibrillation in young adults

INTRODUCTION

Cryoballoon (CB)-guided ablation of atrial fibrillation (AF) is established in symptomatic AF patients. This study sought to determine the safety and efficacy of CB pulmonary vein isolation (PVI) in young adults.

METHODS AND RESULTS

A total of 93 consecutive patients aged <45 years referred to our center for AF ablation were included in this observational study. All patients received CB-guided PVI according to a standardized institutional protocol. Follow-up was performed in our outpatient clinic using 72-h Holter monitoring and periodic telephone interview. Recurrence was defined as any AF/atrial tachycardia (AT) episode >30 s following a 3-month blanking period. A propensity matched control group consisting of patients older than 45 years were used for further evaluation. Mean age was 35 ± 7 years, 22% suffered from persistent AF, 85% were male. Mean follow-up was 2.6 ± 2 years. At the end of the observational period, 83% of patients were free of any AF/AT episodes. There was an excellent overall 12-month success rate of 92%. In comparison to a matched group the overall recurrence rate was noticeably lower in the young group (15% vs. 27%). Increasing age was associated with a hazard ratio of 1.16 for recurrence. In a multivariate analysis model, left atrial diameter remained as significant predictor of AF/AT recurrence. The complication rate was low, no permanent phrenic nerve palsy was observed.

CONCLUSION

CB-guided PVI in young adults is safe and effective with favorable long-term results. It may be considered as first-line therapy in this relatively healthy population.

Acute left atrial ridge lesion after cryoballoon ablation: How does this affect left atrial appendage closure combined procedure?

BACKGROUND

Acute left atrial ridge (LAR) lesions have been observed following atrial fibrillation (AF) ablation. However, LAR lesions had not yet been quantitatively evaluated and their influence on procedure combining cryoballoon (CB) ablation with left atrial appendage closure (LAAC) remained to be explored.

METHODS

The profile of LAR lesions was measured by transesophageal echocardiography (TEE) in 117 consecutive nonvalvular AF patients, who underwent the combined procedure of CB ablation and LAAC. We thoroughly investigated how LAR lesions correlated with baseline variables and clinical outcomes.

RESULTS

A total of 95 out of 96 available TEE images presented prominent acute LAR lesions. In terms of dimensions, there was a greater change in width (Δwidth = 3.6 ± 2.3 mm) than the thickness (Δthickness = 2.6 ± 3.5 mm), and the outer ostium was narrowed (Δouter ostium diameter = -3.4 ± 4.0 mm), while the inner ostium remained unchanged. A higher nadir temperature when freezing the left superior pulmonary vein (LSPV) led to an LAR lesion with a two times greater width (adjusted odds ratio = 1.16; 95% confidence interval, 1.02-1.31). In the evaluation of LAAC outcomes, four patients implanted with Watchman devices had minimal residual flow at the inferior border, while two implanted with LAmbre devices developed residual flow at the LAR side. Clinical outcomes were similar between groups divided by lesion size.

CONCLUSION

Acute LAR lesions frequently occurred following the CB ablation combined procedure, and lesion width positively correlates with LSPV nadir temperature. The presence of these lesions affects the measurement of pacifier devices but has little impact on that of occluder devices.

Liquid Metal Hybrid Platform-Mediated Ice-Fire Dual Noninvasive Conformable Melanoma Therapy

Cryoablation and photothermal therapy are anticancer therapeutic strategies that destroy tumors by external energy intervention of achieving extremely low temperature and very high temperature in a short time. Compared to traditional surgical resection, radiotherapy, and chemotherapy, they have the advantages of being minimally invasive and having less side effects. However, single cryoablation or photothermal therapy itself has limited therapeutic accuracy, which greatly restricts its clinical application. There is still a common phenomenon that the energy transport at the tumor target site cannot be accurately controlled in space and time dimensions, resulting in limited thermal effect and difficulty to form a conformable treatment area, which will result in low targeted killing efficiency, and tumor cells will become residual and undergo metastasis and recurrence. Herein, a multimodal therapy of cryoablation combined with photothermal therapy was proposed. To further enhance the therapeutic performance, a liquid metal hybrid platform, which is composed of a high-thermal-conductivity liquid metal paste and high-photothermal-conversion-efficiency liquid metal nanoparticles, is mediated for cryoablation and photothermal therapy. Cold and heat synergistic effects are realized through this multimodal therapy. Due to the liquid metal hybrid platform, enhanced antitumor efficacy is achieved in vitro and in vivo. More importantly, the liquid metal hybrid platform-mediated dual therapy is totally noninvasive and does not show obvious systemic toxicity. Collectively, this study has first realized ice (cryoablation)-fire (photothermal therapy) dual noninvasive therapy by one liquid metal platform and demonstrated superior antitumor effect for melanoma treatment. This work explores a new promising multimodal cancer therapy strategy based on the liquid metal platform, which has great potential application in cancer treatment in the future.

Biophysical properties, efficacy, and lesion characteristics of a new linear cryoablation catheter in a canine model

BACKGROUND

The cryoballoon (CB) catheter is an established tool for pulmonary vein isolation (PVI), but its use is limited for that purpose.

OBJECTIVE

The purpose of this study was to investigate the biophysical properties of a newly developed linear cryoablation catheter for creation of linear ablation lesions in an in vivo model.

METHODS

Twenty-nine dogs (14 acutely ablated, 15 chronically followed) underwent cryoablation using the linear cryoablation catheter. Regions of interest included the cavotricuspid isthmus (CTI), mitral isthmus (MI), left atrial (LA) roof, and LA posterior wall in an acute study. Cryoablations for CTI and MI were performed in 14 atrial fibrillation animals after PVI and followed over 1 month in the chronic study. Tissue temperature during cryoablation was monitored using implanted thermocouples in the regions of interest. Gross and microscopic pathologic characteristics of the lesions were assessed.

RESULTS

In acute animals, lesion length (transmurality) was CTI 34 ± 4 mm (89% ± 11%); MI 29 ± 4 mm (90% ± 13%); LA roof 19 ± 3 mm (90% ± 8%); and LA posterior wall 19 ± 2 mm (81% ± 13%), with 1 or 2 freezes. Chronic bidirectional block was achieved in 13 of 14 CTI (93%) and 10 of 14 MI (71%) ablations after 1-month follow-up and was consistent with lesion continuity and transmurality upon pathology. The lowest tissue temperature correlated well with the closest distance to the linear cryocatheter (r = 0.688; P <.001).

CONCLUSION

This linear cryocatheter created continuous and transmural linear lesions with "single-shot" cryoenergy application and has the potential for clinical use in the setting of various arrhythmias.

Cryoballoon ablation dosing: From the bench to the bedside and back

To date, multiple modes of research have been leveraged to study the optimal cryoballoon ablation parameters to safely, effectively, and efficiently isolate the pulmonary veins for the treatment of atrial fibrillation. Basic scientific investigation, preclinical studies, clinical observations, trials, and, more recently, computational modeling have helped to generate and test new hypotheses for the advancement of cryoballoon treatment in patients with atrial fibrillation. In this review, we examine the data and evidence that have contributed to the development of patient-tailored dosing strategies that are currently used for pulmonary vein isolation by using the Arctic Front series of cryoballoon ablation catheters.

Cryoballoon Ablation for Patients With Paroxysmal Atrial Fibrillation

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia in clinical practice and induces cardiac dysfunction and stroke. The development of AF requires a trigger and also an electroanatomic substrate capable of both initiating and perpetuating AF. In the past decade, ectopic beats originating from the pulmonary veins (PV) have been identified as a source of paroxysmal AF. Thus, strategies that target the PV, including the PV antrum, are the cornerstone of most AF ablation procedures. Recently, alternative technologies to radiofrequency catheter ablation for paroxysmal AF such as balloon ablation modalities have been developed. The purpose of this review is to discuss cryoballoon ablation for paroxysmal AF.

Cryoablation-activated enhanced nanodoxorubicin release for the therapy of chemoresistant mammary cancer stem-like cells

Anticancer nanodoxorubicin with targeting ability, thermal responsive and pH sensitive characteristic is fabricated. Nanodrug could realize controllable and enhanced drug release when cryoablation is applied at the target tumor site.

Recent advances in cryoballoon ablation for atrial fibrillation

Introduction: Pulmonary vein isolation (PVI), by catheter ablation, represents the current treatment for drug-resistant atrial fibrillation (AF). Nowadays cryoballoon (CB) is a recognized ablation method in patients with atrial fibrillation, mainly due to its ease of use, leading to reproducible and fast procedures. This novel single shot technology literally revolutionized the approach to AF ablation. Areas covered: The historical development of the cryoballoon, ablation techniques and new approaches beyond the ordinary PVI and complications are summarized here. Expert opinion: Although cryoballoon ablation has greatly standardized the approach to PVI a few critical points still need to be clarified scientifically in order to further uniform this procedure in cath labs worldwide. Duration and dosage of the cryoapplication is undoubtedly a topic of great interest.

Determination of single cryoablation outcome within 30 to 60 seconds of freezing based on ice impedance

Background

A direct indicator of effective pulmonary vein isolation (PVI) based on early ice formation is presently lacking.

Objective

The initial impedance rise within 30 to 60 seconds (sec) of single cryoablation relating to ice on the distal surface of the cryoballoon could; predict effective PVI with early termination, the need for prolonging the cryoablation, or failure to achieve effective ablation.

Methods

Impedance measurements were taken between two ring electrodes, at the anterior balloon surface and at the shaft behind the balloon. Ice covering the anterior ring leads to impedance rise. Single cryoablation (eight animals, 37 veins) was applied for 90 to 180 sec. Cryoapplication was terminated if the impedance reached ≥500 Ω. Impedance levels at ≤60 sec of cryoablation were divided into three groups based on the characteristics of the impedance rise. PVI was confirmed acutely and at 45 ± 9 days recovery by electrophysiology mapping and histopathology.

Results

At 60 sec of freezing, an impedance rise of 34.1 ± 15.2 Ω (13‐50 Ω) and slope of the impedance rise (measured during 15‐30 sec of cryoapplication) less than 1 Ω/sec resulted in failed PVI. An impedance rise of 104.4 ± 31.5 Ω (76‐159 Ω) and slope of 2 Ω/sec resulted in 100% PVIs. An impedance rise of 130.9 ± 137.8 Ω (40‐590 Ω) and slope of 10 Ω/sec resulted in 100% PVIs with early termination at 90 sec.

Conclusion

The efficacy of single cryoablation can be defined within 30 to 60 sec based on ice impedance. Three unique impedance profiles described in this investigation are associated with the uniformity and thickness of the ice buildup on the anterior surface of the balloon. One cryoablation with an adequate impedance rise is needed for successful outcomes.

Long-term impact of a bonus freeze on clinical outcome: Analysis of effective and non-effective bonus freezes in cryoballoon ablation

Purpose

Data on bonus freeze characteristics and their impact on complication rates and long-term clinical outcome are limited.

Methods

Pulmonary vein isolation (PVI) using a 28 mm 2^nd-generation cryoballoon (CB) was performed in 169 patients (pts). The isolation temperatures, time to isolation and minimal temperatures of the cryoapplications were documented.

Results

The study included 92 pts who received one bonus freeze after PVI in group I and 77 pts who did not receive a bonus freeze in group II. After a mean follow-up time of 19.0±8.6 months in group I and 16.4±7.5 months in group II, 67 of 92 pts (72.8%) and 49 of 75 pts available to follow up (65.3%; p = 0.221) were free of atrial tachyarrhythmia, respectively. Phrenic nerve palsy occurred in 5.4% of the pts in group I (5/92 pts) and 1.3% of the pts in group II (1/77 pts; p = 0.22). Both the mean nadir temperatures of the bonus freezes and mean nadir temperatures of the isolation freezes differed significantly between the recurrent and non-recurrent pts in group I. The predilection sites of the reconduction for both groups were the inferior aspect of the inferior pulmonary veins.

Conclusion

The impact of a bonus freeze on long-term clinical outcome was not significant for two reasons: 1) The necessity of a bonus freeze was low because the long-term clinical success rate without a bonus freeze was high; and 2) the majority of bonus freezes, especially at the predilection sites, such as the inferior PV, appeared to be ineffective.

Early Tissue Reaction After Second-Generation Cryoballoon Ablation Evaluated with Intracardiac Echocardiography

Radiofrequency energy applications immediately produce tissue edema. This study aimed to investigate the acute tissue reaction immediately after second-generation cryoballoon applications using 3-dimensional intracardiac echocardiography (ICE) imaging technology.This study consisted of 10 patients with paroxysmal atrial fibrillation who underwent pulmonary vein isolation (PVI) using second-generation cryoballoons. Ablation was performed with a single 3-minute freeze strategy and exclusively 28-mm balloons. The left atrial and right pulmonary vein (PV) antra geometries were created with 3-dimensional ICE technology before and immediately after the PVI.Out of 20 right PVs, 19 were isolated exclusively with cryoballoons, and one right inferior PV (RIPV) required touch-up ablation. All 10 right superior PVs (RSPVs) were isolated by single cryoballoon applications, and RIPVs were isolated by a mean of 1.2 ± 0.4 applications. The total application time was 171 ± 19 and 203 ± 71 seconds, and nadir balloon temperature was -56.0 ± 4.9 and -53.8 ± 5.4°C for the RSPVs and RIPVs, respectively. In all patients, diffuse wall thickening of the antra and ostium of the right PVs was observed as compared to baseline. The wall thickening was 0-0.25 mm in 3 patients, and 0.25-0.5 mm in the remaining 7. During the median follow-up of 13 [10.2-17.2] months, 8 (80%) patients were free from arrhythmia recurrences. Nine (90%) patients underwent repeat cardiac computed tomography at a median of 6.0 [4.5-12.0] months after the initial procedure, and no PV stenosis was observed in all.Tissue edema and wall thickening appeared in the human left atrium immediately after second-generation cryoballoon ablation.

Parameters associated with acute morphometric lesion dimensions created by cryocatheters

PURPOSE

Despite the wide use of cryoenergy, there is a paucity of data regarding the impact of certain ablation parameters on lesion size. Specifically, this study sought to evaluate the impact of catheter type, ablation time, heat load, and tip orientation on lesion dimensions using a porcine thigh model with focal cryoablation catheters.

METHODS

In 6 pigs, 251 lesions were created on thigh muscle with parameter permutations to compare the acute impact of catheter type (electrode tip sizes 4, 6, and 8 mm), ablation time (2, 2 × 2, 3, 4, and 2 × 4 min), heat load (1 and 2 L/min), and tip orientation (perpendicular or parallel) on lesion dimensions (length, depth, and cross-sectional area) immediately post-ablation. As a sub-study to evaluate the importance of tissue contact during the cryoablation procedure, a 1-min freeze was performed without tissue contact until an ice ball formed, followed by an additional 2-3 min freeze.

RESULTS

The linear regression model revealed that catheter type (p < 0.0001) and the interaction between catheter orientation and catheter type (p = 0.027) were significantly associated with lesion cross-sectional area. Lesion length and depth, but not cross-sectional area, are significantly impacted by the catheter type (p < 0.0001; p = 0.003) and orientation (p < 0.0001; p < 0.0001), respectively. Compared to parallel catheter placement, lesions created with the perpendicular orientation were deeper using 4-mm (p = 0.136), 6-mm (p = 0.005), and 8-mm tip catheter (p = 0.004). Lesion creation with an ice ball significantly reduced lesion depth compared to lesions made without an ice ball (p < 0.05). In contrast, ablation time (p = 0.097) and heat load (p = 0.467) were not significantly associated with lesion size. Additionally, there was no statistical significant difference in lesion size between 2 × 2 and 4 min ablation times.

CONCLUSIONS

The present study demonstrated that lesion size was significantly impacted by catheter type and catheter tip orientation and that maintaining tissue contact prior to applying cryoenergy is essential.

Enhanced cancer therapy with cold-controlled drug release and photothermal warming enabled by one nanoplatform

Stimuli-responsive nanoparticles hold great promise for drug delivery to improve the safety and efficacy of cancer therapy. One of the most investigated stimuli-responsive strategies is to induce drug release by heating with laser, ultrasound, or electromagnetic field. More recently, cryosurgery (also called cryotherapy and cryoablation), destruction of diseased tissues by first cooling/freezing and then warming back, has been used to treat various diseases including cancer in the clinic. Here we developed a cold-responsive nanoparticle for controlled drug release as a result of the irreversible disassembly of the nanoparticle when cooled to below ∼10 °C. Furthermore, this nanoparticle can be used to generate localized heating under near infrared (NIR) laser irradiation, which can facilitate the warming process after cooling/freezing during cryosurgery. Indeed, the combination of this cold-responsive nanoparticle with ice cooling and NIR laser irradiation can greatly augment cancer destruction both in vitro and in vivo with no evident systemic toxicity.

Overcoming Ovarian Cancer Drug Resistance with a Cold Responsive Nanomaterial

Drug resistance due to overexpression of membrane transporters in cancer cells and the existence of cancer stem cells (CSCs) is a major hurdle to effective and safe cancer chemotherapy. Nanoparticles have been explored to overcome cancer drug resistance. However, drug slowly released from nanoparticles can still be efficiently pumped out of drug-resistant cells. Here, a hybrid nanoparticle of phospholipid and polymers is developed to achieve cold-triggered burst release of encapsulated drug. With ice cooling to below ∼12 °C for both burst drug release and reduced membrane transporter activity, binding of the drug with its target in drug-resistant cells is evident, while it is minimal in the cells kept at 37 °C. Moreover, targeted drug delivery with the cold-responsive nanoparticles in combination with ice cooling not only can effectively kill drug-resistant ovarian cancer cells and their CSCs in vitro but also destroy both subcutaneous and orthotopic ovarian tumors in vivo with no evident systemic toxicity.

A new cryoenergy for ventricular tachycardia ablation: a proof-of-concept study

Introduction

Lack of transmural lesion formation during radiofrequency (RF) ablation for ventricular tachycardia (VT) is an important determinant of arrhythmia recurrence. The aim of this proof-of-concept study was to evaluate safety and efficacy of a new and more powerful cryoablation system for ventricular ablation.

Methods and results

Five healthy female sheep (59 ± 6 kg) underwent a surgical sternotomy for epicardial and endocardial access [endocardial access via right atrial appendage and left ventricular (LV) apex]. A cryoablation system with liquid nitrogen (IceCure) was used to create 3 min freezes at the right ventricle (RV). Left ventricular cryoablation was performed with either a 6 min or 2 × 4 min freezes. To assess safety, ablation was also performed on the mid left anterior descending artery and the proximal coronary sinus. A total of 45 lesions were created (RV epicardial, n = 12; LV epicardial, n = 18; RV endocardial, n = 7; LV endocardial, n = 8; LAD, n = 4; and CS, n = 4). The mean lesion volume was 5055 ± 92 mm3 (length: 32 ± 4.6 mm, width: 16.0 ± 6.4 mm, and depth: 11.2 ± 4.4 mm). Lesions were transmural in 28/45 (62%) and >10 mm in depth in 35/45 (78%). Of the endocardial lesions, 12/15 were transmural (80%). There was no benefit of the bonus freeze in LV lesions (6 vs. 2 × 4 min: 6790 ± 44 vs. 5595 ± 63 mm3; P = 0.44). All ablated vascular structures appeared macroscopically normal without acute stenosis. One animal died due to incessant Ventricular fibrillation (VF).

Conclusion

Our results indicate that a more powerful cryoablation system is able to create large, transmural ventricular lesions from both the endocardium and the epicardium. The technology may hold potential for both surgical and catheter-based VT ablation in humans.

Chromosome 4q25 variants and recurrence after second-generation cryoballoon ablation in patients with paroxysmal atrial fibrillation

BACKGROUND

Chromosome 4q25 single-nucleotide polymorphisms (SNPs) are associated with atrial fibrillation (AF) recurrence after radiofrequency catheter ablation, however the underlying mechanism is unknown. Pulmonary vein (PV) reconnections are common post-radiofrequency ablation. We explored the pre-procedural parameters, including AF susceptibility SNPs, predicting the response to PV isolation (PVI) using second-generation cryoballoons.

METHODS

One hundred fifty-seven paroxysmal AF patients undergoing PVI using second-generation cryoballoons and genetic testing were enrolled. The top 6 AF-associated Japanese ancestry SNPs were evaluated. Fourteen-day consecutive monitoring was performed to detect AF recurrences.

RESULTS

Early recurrence of AF (ERAF) was detected in 74(47.1%) patients, and the AF-free survival at 12-months after single procedures was 72.1%. Cox's proportional models determined that higher pro-BNP values (hazard ratio [HR]=1.001; 95% confidence interval [CI]=1.000-1.001; p=0.003) and the rs1906617 risk allele (HR=2.440; 95% CI=1.062-5.605; p=0.035) were independently associated with ERAFs, and the rs1906617 risk allele (HR=4.339; 95% CI=1.044-18.028; p=0.043) was the sole factor significantly associated with AF recurrence. Second procedures were performed in 41 patients a median of 6.0[5.0-9.5] months later, and 42/162(25.9%) PVs were reconnected. Reconnections were similarly observed in rs1906617 risk allele carriers and wild-type patients. Risk allele carriers at rs1906617 were more likely to have non-PV foci, but did not reach statistical significance (10/35 vs. 0/6, p=0.132).

CONCLUSIONS

AF risk alleles on chromosome 4q25 modulated the risk of AF recurrence after PVI using second-generation cryoballoons in patients with paroxysmal AF. Our study results suggested that non-PV foci might be the more likely mechanism of a high AF recurrence in chromosome 4q25 variant carriers.

Cryoballoon ablation of atrial fibrillation: a practical and effective approach

Medical management of atrial fibrillation (AF), the most common arrhythmia in the general population, has had modest efficacy in controlling symptoms and restoring and maintaining sinus rhythm. Since the seminal observation in 1998 that pulmonary veins host the triggers of AF in the majority of cases, electrical isolation of all pulmonary veins constitutes the cornerstone of ablation in patients with symptomatic AF. However, due to the elaborate and tedious technique of the conventional point-by-point method with radiofrequency ablation guided by electroanatomical mapping, newer, more versatile single-shot techniques, such as cryoballoon ablation, have been sought and developed over recent years and are progressively prevailing. Cryoballoon ablation appears to be the most promising practical and effective approach, and we review it here by presenting all available relevant data from the literature as well as from our own experience in an attempt to apprise colleagues of the significant progress made over the last several years in this important field of electrophysiology.