Experimental study on the effectiveness and safety of radiofrequency catheter ablation with the cooled ablation system

Use of infrared thermography to delineate temperature gradients and critical isotherms during catheter ablation with normal and half normal saline: Implications for safety and efficacy

BACKGROUND

Radiofrequency (RF) ablation with half-normal saline (HNS) has shown promise as a bail-out strategy following failed ventricular tachycardia ablation using standard approaches.

OBJECTIVE

To use a novel infrared thermal imaging (ITI) model to evaluate biophysical and lesion characteristics during RF ablation using normal saline (NS) and HNS irrigation.

METHODS

Left ventricular strips of myocardium were excised from fresh porcine hearts. RF ablation was performed using an open-irrigated ablation catheter (Thermocool ST/SF) with NS (n = 75) and HNS (n = 75) irrigation using different power settings (40/50 W), RF durations (30/60 s), contact force of 10-15 g, and flow rate of 15 ml/min. RF lesions were recorded using an infrared thermal camera and border zone, lethal, 100° isotherms were matched with necrotic borders after 2% triphenyltetrazolium chloride staining. Lesion dimensions and isotherms (mm² ) were measured.

RESULTS

In total, 150 lesions were delivered. HNS lesions were deeper (6.4 ± 1.1 vs. 5.7 ±0.8 mm; p = .03), and larger in volume (633 ± 153 vs. 468 ± 107 mm³ ; p = .007) than NS lesions. Steam pops (SPs) occurred during 19/75 lesions (25%) in the NS group and 32/75 lesions (43%) in the HNS group (p = .34). Lethal (57.8 ± 6.5 vs. 36.0 ± 3.9 mm² ; p = .001) and 100°C isotherm areas (16.9 ± 6.9 vs. 3.8 ± 4.2 mm² ; p = .003) areas were larger and were reached earlier in the HNS group.

CONCLUSIONS

RFA using HNS created larger lesions than NS irrigation but led to more frequent SPs. The presence of earlier lethal isotherms and temperature rises above 100°C on ITI suggest a potentially narrower therapeutic-safety window with HNS.

2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias

Ventricular arrhythmias are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation. Rapid developments have taken place over the past decade in our understanding of these arrhythmias and in our ability to diagnose and treat them. The field of catheter ablation has progressed with the development of new methods and tools, and with the publication of large clinical trials. Therefore, global cardiac electrophysiology professional societies undertook to outline recommendations and best practices for these procedures in a document that will update and replace the 2009 EHRA/HRS Expert Consensus on Catheter Ablation of Ventricular Arrhythmias. An expert writing group, after reviewing and discussing the literature, including a systematic review and meta-analysis published in conjunction with this document, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Each recommendation is presented in knowledge byte format and is accompanied by supportive text and references. Further sections provide a practical synopsis of the various techniques and of the specific ventricular arrhythmia sites and substrates encountered in the electrophysiology lab. The purpose of this document is to help electrophysiologists around the world to appropriately select patients for catheter ablation, to perform procedures in a safe and efficacious manner, and to provide follow-up and adjunctive care in order to obtain the best possible outcomes for patients with ventricular arrhythmias.

2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias

Ventricular arrhythmias are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation. Rapid developments have taken place over the past decade in our understanding of these arrhythmias and in our ability to diagnose and treat them. The field of catheter ablation has progressed with the development of new methods and tools, and with the publication of large clinical trials. Therefore, global cardiac electrophysiology professional societies undertook to outline recommendations and best practices for these procedures in a document that will update and replace the 2009 EHRA/HRS Expert Consensus on Catheter Ablation of Ventricular Arrhythmias. An expert writing group, after reviewing and discussing the literature, including a systematic review and meta-analysis published in conjunction with this document, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Each recommendation is presented in knowledge byte format and is accompanied by supportive text and references. Further sections provide a practical synopsis of the various techniques and of the specific ventricular arrhythmia sites and substrates encountered in the electrophysiology lab. The purpose of this document is to help electrophysiologists around the world to appropriately select patients for catheter ablation, to perform procedures in a safe and efficacious manner, and to provide follow-up and adjunctive care in order to obtain the best possible outcomes for patients with ventricular arrhythmias.

2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias

Ventricular arrhythmias are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation. Rapid developments have taken place over the past decade in our understanding of these arrhythmias and in our ability to diagnose and treat them. The field of catheter ablation has progressed with the development of new methods and tools, and with the publication of large clinical trials. Therefore, global cardiac electrophysiology professional societies undertook to outline recommendations and best practices for these procedures in a document that will update and replace the 2009 EHRA/HRS Expert Consensus on Catheter Ablation of Ventricular Arrhythmias. An expert writing group, after reviewing and discussing the literature, including a systematic review and meta-analysis published in conjunction with this document, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Each recommendation is presented in knowledge byte format and is accompanied by supportive text and references. Further sections provide a practical synopsis of the various techniques and of the specific ventricular arrhythmia sites and substrates encountered in the electrophysiology lab. The purpose of this document is to help electrophysiologists around the world to appropriately select patients for catheter ablation, to perform procedures in a safe and efficacious manner, and to provide follow-up and adjunctive care in order to obtain the best possible outcomes for patients with ventricular arrhythmias.

A Steam Pop Detected by Intracardiac Echocardiography During Catheter Ablation of the Left Ventricular Papillary Muscle

A 60-year-old female with premature ventricular contractions (PVCs) originating from the bottom of the posteromedial papillary muscle of the left ventricle underwent radiofrequency catheter ablation (RFCA) using an irrigated-tip catheter. During ablation of the PVCs, a loud steam pop was observed. Intracardiac echocardiography (ICE) revealed a growing, hyperechogenic intramyocardial microbubble formation around the catheter tip. The formation disappeared slowly and completely, leaving an endocardial laceration without pericardial effusion. ICE imaging is valuable during a difficult RFCA procedure, because ICE reveals the exact anatomical position of the catheter and thus allows rapid evaluation of the occurrence of steam popping and any possible subsequent complication.

Bipolar radiofrequency ablation of aneurysm remnants after coil embolization can improve endovascular treatment of experimental bifurcation aneurysms

OBJECTIVE Endovascular treatment of aneurysms may result in incomplete initial occlusion and aneurysm recurrence at angiographic follow-up studies. This study aimed to assess the feasibility and efficacy of bipolar radiofrequency ablation (RFA) of aneurysm remnants after coil embolization. METHODS Bipolar RFA was accomplished using the coil mass as 1 electrode, while the second electrode was a stent placed across the aneurysmal neck. After preliminary experiments and protocol approval from the Animal Care committee, wide-necked bifurcation aneurysms were constructed in 24 animals. Aneurysms were allocated to 1 of 3 groups: partial intraoperative coil embolization, followed by RFA (n = 12; treated group) or without RFA (n = 6; control group 1); or attempted complete endovascular coil embolization 2-4 weeks later (n = 6; control group 2). Angiographic results were compared at baseline, immediately after RFA, and at 12 weeks, using an ordinal scale. Pathological results and neointima formation at the neck were compared using a semiquantitative grading scale. RESULTS Bipolar RFA was able to reliably target the aneurysm neck when the coil mass and stent were used as electrodes. RFA improved angiographic results immediately after partial coiling (p = 0.0024). Two RFA-related complications occurred, involving transient occlusion of 1 carotid artery and 1 hemorrhage from an adventitial arterial blister. At 12 weeks, angiographic results were improved with RFA (median score of 0), when compared with controls (median score of 2; p = 0.0013). Neointimal closure of the aneurysm neck was better with RFA compared with controls (p = 0.0003). CONCLUSIONS Bipolar RFA can improve results of embolization in experimental models by selectively ablating residual lesions after coil embolization.

Contact forces during hybrid atrial fibrillation ablation: an in vitro evaluation

PURPOSE

Data on epicardial contact force efficacy in dual epicardial-endocardial atrial fibrillation ablation procedures are lacking. We present an in vitro study on the importance of epicardial and endocardial contact forces during this procedure.

METHODS

The in vitro setup consists of two separate chambers, mimicking the endocardial and epicardial sides of the heart. A circuit, including a pump and a heat exchanger, circulates porcine blood through the endocardial chamber. A septum, with a cut out, allows the placement of a magnetically fixed tissue holder, securing porcine atrial tissue, in the middle of both chambers. Two trocars provide access to the epicardium and endocardium. Force transducers mounted on both catheter holders allow real-time contact force monitoring, while a railing system allows controlled contact force adjustment. We histologically assessed different combinations of epi-endocardial radiofrequency ablation contact forces using porcine atria, evaluating the ablation's diameters, area, and volume.

RESULTS

An epicardial ablation with forces of 100 or 300 g, followed by an endocardial ablation with a force of 20 g did not achieve transmurality. Increasing endocardial forces to 30 and 40 g combined with an epicardial force ranging from 100 to 300 and 500 g led to transmurality with significant increases in lesion's diameters, area, and volumes.

CONCLUSIONS

Increased endocardial contact forces led to larger ablation lesions regardless of standard epicardial pressure forces. In order to gain transmurality in a model of a combined epicardial-endocardial procedure, a minimal endocardial force of 30 g combined with an epicardial force of 100 g is necessary.

Cardiac ablation via electroporation

Thermal-based ablation for the treatment of arrhythmias is known to cause issues (e.g. heat loss due to blood perfusion, mechanical damage of the tissue from excessive heat, etc.) that hamper the success of the treatment. A novel technique termed "electroporation" is a process that leads to pore formation in cell membranes. These pores may cause cellular death without inducing negative thermal effects. We successfully developed a system, tools, and methodology to operate this new ablation technique. Preliminary in vivo acute animal studies (ovine) suggest distinct lesion morphology. High transmurality success rates also suggest the possibility of applying this new ablation modality to cardiac ablation. A long term study confirming lesion durability is necessary to warrant the successful adoption of this technique.

Radiofrequency endothelial ablation prevents recanalization after endovascular coil occlusion: in vitro and in vivo assessment

PURPOSE

Coil embolization of intracranial aneurysms may be followed by recurrences. Radiofrequency (RF) ablation of the endothelium may prevent recanalization after coil embolization.

MATERIALS AND METHODS

The authors performed in vitro experiments in chicken meat and egg white models to investigate the thermal distribution and geometry of lesions created with RF applied through standard coils alone or by using a prototype RF electrode inserted in a coil or a mass of coils. A mathematic model was designed to predict perianeurysmal isotherm lesions by using the bio-heat equation. In an in vivo coil arterial occlusion model (six dogs), the authors compared angiographic and pathologic results of coil embolization (n = 8) with those of coil embolization preceded by RF ablation (n = 7) by using a cardiac electrode at 1 month.

RESULTS

Current coils offer high impedance (400 Omega) at high current frequencies and are damaged by RF transmission. A dedicated electrode generated reproducible lesions, but contact with coils interferes with lesion reproducibility. When the coil mass was used, a uniform RF lesion that conformed to the coil mass shape was produced. The mathematic model predicted a uniform heat distribution within 1 mm from the coil mass periphery. Arterial coil embolization led to occlusion followed by recanalization (n = 8), whereas RF ablation (20-30 W for 60 seconds) prevented recanalization in all coil-occluded arteries (P < .001, chi(2) test). Pathologic findings helped confirm complete arterial occlusion with RF ablation. One animal developed brachial plexus injury with excessive levels of RF ablation.

CONCLUSIONS

RF ablation can prevent recanalization after coil occlusion-at least in the arterial model. Modifications of coils, dedicated neurovascular electrodes, and technique optimization remain necessary before considering a clinical application.

Osteoid osteoma: diagnosis and treatment

Treatment of small but painful osteoid osteomas was traditionally based on either prolonged medication or resection. In the era of rapidly evolving minimally invasive techniques, reluctance has been posed against surgical interventions mostly due to their relatively high rates of recurrence, complications, or persistent pain. Nonetheless, incomplete pain control and intolerance to anti-inflammatory drugs unfavorably affect prognosis. The objective of this article is to explore the nature and clinical presentation of osteoid osteomas, discuss their imaging and histological features, review available data regarding surgical and percutaneous methods for addressing these lesions and comment on their feasibility, safety, and efficacy.

NaviStar ThermoCool catheter for ventricular tachycardia

Despite the relatively short history of catheter ablation, it has clearly demonstrated high efficacy and safety in treating a wide spectrum of cardiac arrhythmias. An important contributor to this success has been the rapid incorporation of evolving technologies that have changed the practice of electrophysiology remarkably. The introduction of irrigated radiofrequency ablation has allowed electrophysiologists to tackle complex arrhythmias, such as atrial fibrillation and ventricular tachycardia, with a higher success rate. Similarly, the introduction of 3D mapping systems has enhanced our understanding of arrhythmia mechanisms and allowed for integration of electrophysiologic and anatomically guided ablation. In 2006, the US FDA approved the Navistar ThermoCool ablation catheter, which incorporates an irrigated tip design with electroanatomical guidance, for ventricular tachycardia ablation. The design of this catheter, its clinical profile, its potential advantages and possible complications associated with its use in ventricular tachycardia ablation are discussed herein.

RF Catheter Ablation: Lessons on Lesions

The present treatment of atrial fibrillation by radiofrequency catheter ablation requires long continuous lesions in the thin walled left atrium where side effects may lead to serious complications. Better understanding of the physical processes that take place during ablation may help to improve the quality, safety, and outcome of these procedures. These processes include the distribution of power between blood, tissue, and patient; the mechanisms of tissue heating and coagulum formation; the relation between tissue and electrode temperatures; and the effects of increased electrode size and internal and external electrode cooling. With normal electrode-tissue contact, only a fraction of all power is effectively delivered to the tissue. Due to the variability of blood flow cooling, applied power and electrode temperature rise are poor indicators of lesion formation. With a longer electrode, the efficiency of tissue heating is decreased and the greater variation in tissue contact caused by electrode orientation makes lesion formation even more unpredictable. The absence of impedance rise during ablation does not guarantee the absence of blood clot formation on the tissue contact site. Blood clots may unnoticeably be created on the lesion surface and are caused by thermal denaturization of blood proteins, independent of heparinization. Irrigated ablation with external flush may prevent blood clot formation. Irrigation minimally affects lesion size by cooling the tissue surface. Larger lesions may only be created by the application of higher power levels. Electrode cooling, however, impedes electrode temperature feed back and blinds the operator for excessive tissue heating. External cooling alone with preservation of temperature feed back is a promising concept that may lead to improved procedural safety and success.

Discrepancies Between Catheter Tip and Tissue Temperature in Cooled-Tip Ablation

Background— It is not known whether catheter tip temperatures with a cooled-tip ablation can be reliably extrapolated to estimate actual tissue temperatures. The relationship between catheter tip temperatures, tissue temperatures, power, and microbubble formation is not known.

Methods and Results— Nine dogs underwent 111 radiofrequency energy deliveries at the pulmonary vein ostia with a cooled-tip catheter. Catheter tip and tissue temperatures were markedly discrepant. Catheter tip temperature plateaus at 36°C to 39°C with increasing power, whereas tissue temperature increases to a mean of 75±3°C at 45 W (maximum temperature >100°C). Seventy-two energy deliveries were performed, titrating power to microbubble formation guided by intracardiac echocardiography. Type I and II microbubble formation occurred in 45 (63%) and 19 (26%) ablations, respectively. Type I microbubble emergence occurred at lower powers (21±8 versus 26±4 W; P =0.05), catheter tip temperatures (38±5°C versus 48±10°C; P =0.02), and tissue temperatures (65±19°C versus 81±9°C; P <0.001) than type II microbubble formation. Maximum impedance decreases during ablation before microbubble formation were less with type I microbubble (20±9 versus 37±11 Ω; P <0.001) compared with type II microbubbles. One quarter of type I microbubbles abruptly transitioned to type II microbubbles with significant changes in power or catheter tip temperature. No microbubbles were seen in 19 ablations (26%) despite powers up to 26±9 W and tissue temperatures up to 81±17°C.

Conclusions— Catheter tip and tissue temperatures are markedly discrepant during cooled-tip ablation. Type I and II microbubble formation occurs at overlapping power and catheter tip and tissue temperature ranges. Neither the absence of microbubbles nor the presence of type I microbubble formation ensures against excessive tissue heating. The appearance of microbubbles may indicate possible tissue overheating and signal a need to decrease energy.

Osteoid osteoma: factors for increased risk of unsuccessful thermal coagulation

PURPOSE

To retrospectively identify risk factors that may impede a favorable clinical outcome after thermocoagulation for osteoid osteoma.

MATERIALS AND METHODS

Informed consent (permission for the procedure and permission to use patient data for analysis) was obtained from all patients who met study criteria, and institutional review board did not require approval. Analysis included age, sex, size and location of osteoid osteoma, presence of calcified nidus, number of needle positions used for coagulation, coagulation time, accuracy of needle position, learning curve of radiologist, and previous treatment in 95 consecutive patients with osteoid osteoma treated with thermocoagulation. With chi(2) analysis, Fisher exact test, or unpaired Student t test and logistic regression analysis, 23 unsuccessfully treated patients were compared with 72 successfully (pain-free) treated patients.

RESULTS

Parameters associated with decreased risk for treatment failure were advanced age (mean age, 24 years in treatment success group vs 20 years in treatment failure group) and increased number of needle positions during thermocoagulation. Estimated odds ratios were, respectively, 0.93 (95% confidence interval: 0.88, 0.99) and 0.10 (95% confidence interval: 0.02, 0.41). Patients with a lesion of 10 mm or larger seemed at risk for treatment failure (odds ratio = 2.68), but the 95% confidence interval of 0.84 to 8.52 included the 1.00 value. Needle position was inaccurate in nine of 23 patients with treatment failure; only one needle position was used in eight of these nine patients. Lesion location, calcification, sex, coagulation time, radiologist's learning curve, and previous treatment were not risk factors.

CONCLUSION

Multiple needle positions reduce the risk of treatment failure in all patients and should especially, but not exclusively, be used in large (> or =10-mm) lesions or lesions that are difficult to engage to reduce the risk for unsuccessful treatment.

Circumferential pulmonary vein ablation for treatment of atrial fibrillation using an irrigated-tip catheter

In this study, a series of 52 consecutive patients with atrial fibrillation from 1 institution underwent circumferential pulmonary vein ablation using an irrigated-tip catheter. The technique was safe, and 81% of the patients maintained sinus rhythm at 6 months. However, 1/3 of them required additional antiarrhythmic drug therapy.

Optimizing RF Output for Cooled RF Ablation

Cooled RF ablation catheters increase lesion size and facilitate ablation compared to standard RF ablation catheters. Cooling the ablation electrode increases the disparity between tissue temperature and electrode temperature, making use of temperature for guiding power application during ablation of less certain value. Appropriate energy titration is important, however, to produce large lesions, while avoiding overheating of tissue with steam formation leading to "pops." In addition to power, the rate of irrigant flow can be controlled. Electrode-tissue contact and orientation and the cooling effect of blood flow around the electrode and within the tissue are not as easily adjusted and also influence tissue heating. In addition to electrode temperature, a decrease in impedance, bubble formation detected by intracardiac ultrasound, and evidence of tissue heating from an effect on recorded electrograms or the arrhythmia can be used to guide ablation energy. Guidelines for adjusting power delivery and avoiding "pops" and coagulum formation are suggested.

Clinical study of the efficacy of a cooled-tip catheter ablation system for common atrial flutter

BACKGROUND

Radiofrequency catheter ablation (RF-CA) of common atrial flutter (AFL) requires the creation of a transmural incision to create a bidirectional conduction block in the cavotricuspid isthmus (ITH).

METHODS AND RESULTS

RF-CA of the ITH using a cooled-tip system was carried out in 40 patients. In the 'conventional' mode (CONV) of the system, RF energy was applied for 2 min with the temperature set at 60 degrees C and power of up to 50 W, and in the failed cases the 'cooled-tip' mode (COOL) was utilized at 45 degrees C with up to 30 W (with a 15 ml/min saline flow rate). Of the 40 patients, 29 crossed over from the CONV to the COOL after a failed ablation of the AFL. As a result, in all 40 patients a complete linear incision could be created with either the COOL or the CONV, resulting in the successful abolition of the AFL. Complete bi-directional block was successfully created in all patients. No significant side effects occurred.

CONCLUSIONS

The COOL was found to be more effective and just as safe as the CONV for AFL ablation, thus facilitating the rapid and complete elimination of the AFL.