Contrasting effects of convective flow on catheter ablation lesion size: cryo versus radiofrequency energy

A Bionic Testbed for Cardiac Ablation Tools

Bionic-engineered tissues have been proposed for testing the performance of cardiovascular medical devices and predicting clinical outcomes ex vivo. Progress has been made in the development of compliant electronics that are capable of monitoring treatment parameters and being coupled to engineered tissues; however, the scale of most engineered tissues is too small to accommodate the size of clinical-grade medical devices. Here, we show substantial progress toward bionic tissues for evaluating cardiac ablation tools by generating a centimeter-scale human cardiac disk and coupling it to a hydrogel-based soft-pressure sensor. The cardiac tissue with contiguous electromechanical function was made possible by our recently established method to 3D bioprint human pluripotent stem cells in an extracellular matrix-based bioink that allows for in situ cell expansion prior to cardiac differentiation. The pressure sensor described here utilized electrical impedance tomography to enable the real-time spatiotemporal mapping of pressure distribution. A cryoablation tip catheter was applied to the composite bionic tissues with varied pressure. We found a close correlation between the cell response to ablation and the applied pressure. Under some conditions, cardiomyocytes could survive in the ablated region with more rounded morphology compared to the unablated controls, and connectivity was disrupted. This is the first known functional characterization of living human cardiomyocytes following an ablation procedure that suggests several mechanisms by which arrhythmia might redevelop following an ablation. Thus, bionic-engineered testbeds of this type can be indicators of tissue health and function and provide unique insight into human cell responses to ablative interventions.

Distance between the descending aorta and the left inferior pulmonary vein as a determinant of biophysical parameters during paroxysmal atrial fibrillation cryoablation

INTRODUCTION

The distance from the descending aorta (DA) to the posterior wall of the left atrium (LA) is variable. We aimed to determine whether the proximity between the DA and the left inferior pulmonary vein (LIPV) ostium has an impact on biophysical parameters and cryoballoon (CB) ablation efficacy during LIPV freezing.

METHODS

Patients referred for CB-ablation of atrial fibrillation (AF) in two high-volume centers were included. Cryoablation data were collected prospectively for each patient. The anatomical relationships between the LIPV and the DA (distance LIPV ostium-DA, presence of an aortic imprint on the posterior aspect of the LIPV) were then retrospectively analysed on the LA computed tomography scans realized before AF ablation.

RESULTS

A total of 350 patients were included (70% men, 59.7 ± 11.5 years). The decrease in the Ostium-DA distance was significantly correlated to the increase in the time-to-isolation (TTI) (r = -.31; p = .036), with less negative temperature (r = -.11; p = .045). Similarly, the presence of an aortic imprint on the LIPV was associated with a longer TTI (p < .001). The analysis of redo procedures data shows a trend toward the presence of shorter ostium-DA distances (15.3 ± 3.29 vs. 18.1 ± 4.99, p = .15) and more frequent aortic imprints (63.6% vs. 47.5%, p = .34) in patients with LIPV reconnection as opposed to patients without reconnection in the LIPV.

CONCLUSION

Our findings indicated that the DA seems to have a "radiator" effect influencing LIPV cryoablation parameters during CB-ablation. Additional studies will be needed to elucidate whether this biophysical influence has a clinical impact in LIPVs reconnections.

Ultralow temperature cryoablation using near-critical nitrogen for cavotricuspid isthmus-ablation, first-in-human results

INTRODUCTION

Cryoablation has evolved as a safe alternative to radiofrequency ablation in the treatment of several supraventricular arrhythmias and has potential advantages, yet is limited by the properties of the cryogen used. We investigated a novel ultralow temperature cryoablation (ULTC) system using nitrogen near its liquid-vapor critical point as a freezing source, achieving temperatures as low as -196 degrees Celsius in a long linear catheter with a continuous energy release. Initial safety, procedural and efficacy outcomes of ULTC are described in patients undergoing cavotricuspid isthmus (CTI) ablation.

METHODS AND RESULTS

The Cryocure studies (NCT02355106, NCT02839304) are prospective, single-arm, multi-center, first-in-human clinical studies in 17 patients with atrial flutter (AFL) and 13 patients with atrial fibrillation (AF). A total of 30 patients, mean age 65 ± 8 years old and 67% male, were enrolled and underwent ablation of the CTI. Acute success, defined as the confirmation of stable bidirectional conduction block across the CTI, was achieved in all 30 patients. After 12 months of follow-up, 14 out of 17 AFL patients remained free from any AFL. One (3.3%) procedure-related but not device-related serious adverse event was reported, involving transient inferolateral ST-elevation associated with temporary AV conduction block.

CONCLUSION

In this first-in-human clinical study the safety and performance results demonstrate the capabilities of ultralow temperature near-critical nitrogen as an effective energy source for CTI ablation. Ongoing, larger, studies should confirm our findings and evaluate the capabilities to create linear and focal transmural lesions in other arrhythmias.

"A Song of Ice and Fire"-another verse from the world of ablation

The debate between the use of radiofrequency (RF) or cryoenergy for ablation near the atrioventricular (AV) conducting system or small coronaries has been fueled by the relative efficacies and risks of the two technologies, particularly in smaller hearts. The manuscript by Schneider et al adds another chapter to that ongoing debate.

Permanent and Transient Electrophysiological Effects During Cardiac Cryoablation Documented by Optical Activation Mapping and Thermal Imaging

OBJECTIVE

Cardiac catheter cryoablation is a safer alternative to radiofrequency ablation for arrhythmia treatment, but electrophysiological (EP) effects during and after freezing are not adequately characterized. The goal of this study was to determine transient and permanent temperature induced EP effects, during and after localized tissue freezing.

METHODS

Conduction in right (RV) and left ventricles (LV) was studied by optical activation mapping during and after cryoablation in paced, isolated Langendorff-perfused porcine hearts. Cryoablation was performed endocardially (n=4) or epicardially (n=4) by a cryoprobe cooled to -120 °C for 8 minutes. Epicardial surface temperature was imaged with an infrared camera. Viability staining was performed after ablation. Motion compensation and co-registration was performed between optical mapping data, temperature image data, and lesion images.

RESULTS

Cryoablation produced lesions 14.9 +/- 3.1 mm in diameter and 5.8 +/- 1.7 mm deep. A permanent lesion was formed in tissue cooled below -5 +/- 4 °C. Transient EP changes observed at temperatures between 17 and 37 °C during cryoablation surrounding the frozen tissue region directly correlated with local temperature, and include action potential (AP) duration prolongation, decrease in AP magnitude, and slowing in conduction velocity (Q10=2.0). Transient conduction block was observed when epicardial temperature reached <17 °C, but completely resolved upon tissue rewarming, within 5 minutes.

CONCLUSION

Transient EP changes were observed surrounding the permanent cryo lesion (<-5 °C), including conduction block (-5 to 17 °C), and reduced conduction velocity (>17 °C).

SIGNIFICANCE

The observed changes explain effects observed during clinical cryoablation, including transient increases in effective refractory period, transient conduction block, and transient slowing of conduction. The presented quantitative data on temperature dependence of EP effects may enable the prediction of the effects of clinical cryoablation devices.

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.

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.

Anatomic Challenges In Pediatric Catheter Ablation

Pediatric patients present unique anatomic challenges for catheter ablation. Small patient size requires special adaptation and understanding to perform safe procedures when clinically indicated. The anatomic variations of congenital heart disease also create problems that require pre-procedural preparation for each case in addition to a specialized understanding of a vast anatomic variation and surgical repairs. This understanding coupled with the knowledge of the pathophysiology of arrhythmia disorders and the biophysics of catheter ablation technology are required to perform successful and safe ablation procedures in this special population.

Contrast in intracardiac acoustic radiation force impulse images of radiofrequency ablation lesions

We have previously shown that intracardiac acoustic radiation force impulse (ARFI) imaging visualizes tissue stiffness changes caused by radiofrequency ablation (RFA). The objectives of this in vivo study were to (1) quantify measured ARFI-induced displacements in RFA lesion and unablated myocardium and (2) calculate the lesion contrast (C) and contrast-to-noise ratio (CNR) in two-dimensional ARFI and conventional intracardiac echo images. In eight canine subjects, an ARFI imaging-electroanatomical mapping system was used to map right atrial ablation lesion sites and guide the acquisition of ARFI images at these sites before and after ablation. Readers of the ARFI images identified lesion sites with high sensitivity (90.2%) and specificity (94.3%) and the average measured ARFI-induced displacements were higher at unablated sites (11.23 ± 1.71 µm) than at ablated sites (6.06 ± 0.94 µm). The average lesion C (0.29 ± 0.33) and CNR (1.83 ± 1.75) were significantly higher for ARFI images than for spatially registered conventional B-mode images (C = -0.03 ± 0.28, CNR = 0.74 ± 0.68).

Direct thermography-a new in vitro method to characterize temperature kinetics of ablation catheters

PURPOSE

For the treatment of increasingly complex cardiac arrhythmias, new catheter designs as well as alternative energy sources are constantly being developed. However, there is presently no in vitro method available for assessment of the temperature changes induced at various myocardial levels during energy delivery. Therefore, our study was aimed at developing an in vitro model to record and display the temperature kinetics during ablation in the entire muscle cross section.

METHODS AND RESULTS

A sapphire glass pane was inserted into one wall of the in vitro experimental set-up. Due to its thermodynamic properties, the temperature distribution in an adjacent cross section of the cardiac muscle can be measured exactly ( 1 °C) through this pane by means of a thermography camera. Computer-supported image processing enables the colour-coded and two-dimensional display of the temperature kinetics during the energy application at any location of the myocardial cross section (± 0.5 mm). This new measuring methodology was validated by direct temperature measurements utilizing several intramyocardial thermo elements.

CONCLUSION

This new method allows a temporal and spatial analysis of the temperature phenomena during ablation without the interference and spatial limitation of intramyocardial temperature probes. New ablation technologies can thus be evaluated, independent of the catheter configuration or source of energy used.

An in vitro assessment of acoustic radiation force impulse imaging for visualizing cardiac radiofrequency ablation lesions

INTRODUCTION

Lesion placement and transmurality are critical factors in the success of cardiac transcatheter radiofrequency ablation (RFA) treatments for supraventricular arrhythmias. This study investigated the capabilities of catheter transducer based acoustic radiation force impulse (ARFI) ultrasound imaging for quantifying ablation lesion dimensions.

METHODS AND RESULTS

RFA lesions were created in vitro in porcine ventricular myocardium and imaged with an intracardiac ultrasound catheter transducer capable of acquiring spatially registered B-mode and ARFI images. The myocardium was sliced along the imaging plane and photographed. The maximum ARFI-induced displacement images of the lesion were normalized and spatially registered with the photograph by matching the surfaces of the tissue in the B-mode and photographic images. The lesion dimensions determined by a manual segmentation of the photographed lesion based on the visible discoloration of the tissue were compared to automatic segmentations of the ARFI image using 2 different calculated thresholds. ARFI imaging accurately localized and sized the lesions within the myocardium. Differences in the maximum lateral and axial dimensions were statistically below 2 mm and 1 mm, respectively, for the 2 thresholding methods, with mean percent overlap of 68.7 +/- 5.21% and 66.3 +/- 8.4% for the 2 thresholds used.

CONCLUSION

ARFI imaging is capable of visualizing myocardial RFA lesion dimensions to within 2 mm in vitro. Visualizing lesions during transcatheter cardiac ablation procedures could improve the success of the treatment by imaging lesion line discontinuity and potentially reducing the required number of ablation lesions and procedure time.

Typical atrial flutter can effectively be treated using single one-minute cryoapplications: results from a repeat electrophysiological study

Purpose

Catheter-based cryoablation (cryo) has proven to be as effective as radiofrequency energy (RF) ablation for the treatment of arrhythmias. Nevertheless, the duration of cryoapplications has been reported as being significantly longer than RF applications.

Methods

Thirty-seven consecutive patients (28 men; mean age 59 ± 14 years) with typical atrial flutter (AFL) underwent cryo of the cavotricuspid isthmus (CTI). Applications of 1 min were delivered with a 10-French, 10-mm tipped catheter (CryoCor™). If bidirectional CTI block was not obtained after 12 1-min applications, applications of 3 min were selectively delivered to areas of conduction breakthrough. The endpoint of the procedure was creation of bidirectional CTI block and non-inducibility of AFL.

Results

A median of 7 (range 3 to 12) 1-min applications were given along the CTI with a mean temperature of −88.6 ± 2.3°C. Mean fluoroscopy and procedure time were 27 ± 14 min and 110 ± 28 min respectively. Five patients required additional 3-min applications; in one patient an overextended ablation catheter prevented the completion of the index-procedure. The acute success rate of the index-procedure was 97%. In 12/24 patients, two with AFL recurrence, resumption of CTI conduction was found 4 months post-ablation. In all patients bidirectional CTI block was re-obtained after a median of one 1-min application. No additional AFL recurrences occurred, after a mean follow-up of 37 ± 3 (range 30 to 44) months.

Conclusions

Cryo of AFL can successfully be performed using the same application duration as used for RF ablation. Both acute and long-term results are comparable to RF ablation. AFL recurrences occurred in only a minority of patients with resumption of CTI conduction.