Safety and efficacy of epicardial cryoablation in a canine model

Epicardial Ventricular Tachycardia Ablation: Patient Selection, Access, and Ablation Techniques and Strategies to Manage Complications

Epicardial ventricular tachycardia ablation is an important treatment modality for refractory ventricular tachycardia. This comprehensive review guides clinicians through optimized strategies for improved procedural outcomes and patient safety during epicardial ventricular tachycardia ablation. Patient selection criteria, including cardiomyopathy type, electrocardiogram findings, and prior ablation history, are discussed. Detailed techniques for safe pericardial access are provided. Potential complications and strategies for prevention and management are explored. The review also addresses challenges and pitfalls of epicardial mapping and ablation.

Improvement in Lesion Formation with Radiofrequency Energy and Utilization of Alternate Energy Sources (Cryoablation and Pulsed Field Ablation) for Ventricular Arrhythmia Ablation

Current ablation systems rely on thermal energy to produce ablation lesions (heating: RF, laser and ultrasound, and cooling: cryo-thermia). While thermal ablation has been proven to be effective, there are several limitations: 1) relatively long procedural times; 2) high recurrence rate of ventricular arrhythmias; and 3) excessive heating potentially leading to serious complications, including steam pop (perforation), coronary arterial injury and thrombo-embolism. Pulsed field ablation (PFA)/irreversible electroporation (IRE) offers a unique non-thermal ablation strategy which has the potential to overcome these limitations. Recent pre-clinical studies suggest that PFA/IRE might be effective and safe for the treatment of cardiac arrhythmias.

Effect of Epicardial Pulsed Field Ablation Directly on Coronary Arteries

BACKGROUND

The unique tissue selectivity of pulsed field ablation (PFA) allows for minimizing collateral damage to the nerves/esophagus. However, the safety profile of epicardial PFA on coronary arteries (CAs) has not been well defined.

OBJECTIVES

This study sought to evaluate the effect of epicardial PFA directly on CAs in a swine model.

METHODS

In 4 swine, an 8-F linear quadripolar PFA catheter (FARAPULSE Inc) was introduced into the pericardial space via a subxiphoid puncture. After coronary angiography (Angio), QRS synchronized, biphasic, bipolar PFA was delivered directly on the left anterior descending artery, left circumflex artery, or normal myocardium (control) (2.0 kV × 4 applications per site). Angio was repeated immediately after ablation and repeated every 5 minutes to quantify the degree of CA narrowing. After 4- or 8-week survival, repeat Angio was performed followed by gross and histologic lesion analyses.

RESULTS

A total of 15 lesions were delivered (8 left anterior descending arteries, 3 left circumflexes, and 4 controls). Target site Angio revealed median of 47% (IQR: 38%-69%) acute luminal narrowing immediately after PFA, which gradually resolved over 30 minutes. Epicardial PFA lesions extended into the myocardium with a median depth of 4.1 mm (IQR: 3.6-5.6 mm) passing across the CAs and adipose tissue. However, 87.5% of the CAs demonstrated minimal to mild CA stenosis associated with neointimal hyperplasia and tunica media fibrosis.

CONCLUSIONS

In a swine model, epicardial PFA directly on CAs allowed the creation of myocardial lesions but led to a CA response characterized by acute moderate spasm and chronic mild stenosis via neointimal hyperplasia.

Feasibility and safety of trans-biliary cryoablation: Preclinical evaluation of a novel flexible cryoprobe

Cryoablation, as a well-characterized technology, has multifarious clinical applications in solid malignancy. However, trans-biliary cryoablation for malignant biliary obstruction has not been reported yet. Thus, this study aimed to determine the efficacy and safety of trans-biliary cryoablation with a novel CO₂ gas-based flexible cryoprobe in standardized preclinical settings. For fresh porcine liver ex vivo, the freezing efficacy of cryoablation was evaluated by using fresh porcine liver. The real-time CO2 flow rate, freezing temperature and freezing range were examined and the frozen appearance was visualized. In vivo study, acute and chronical effects were investigated by using the models of canine bile duct. Histopathology and laboratory examination were performed. The lowest temperature that the electrode could deliver to the tissue was -60.7 °C. At 60s after freezing, the tissue temperature dropped to -22.6 °C and -4.3 °C at 0.1 and 0.2 cm from the electrode center, respectively. The frozen size was greater in liver tissue ex vivo than that in bile duct tissue in vivo. No biliary hemorrhage, perforation, stricture, obstruction, and adjacent organ injury were observed. With histopathologic examination, acute intercellular vacuoles were observed in the lamina propria adjacent to the lumen. Chronic changes, including uneven coagulative necrosis, fibro-proliferation, inflammatory infiltration and connective tissue thickening were observed in the lamina propria of the all biliary samples. The results demonstrated CO₂ gas-based trans-biliary cryoablation is safe and efficacious. These findings may provide a potential new modality for primary malignant biliary obstruction and malignant obstruction within a biliary stent and contribute to cryoablation of clinical practice.

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.

Epicardial Ablation Biophysics and Novel Radiofrequency Energy Delivery Techniques

Important physiologic and anatomic differences exist between the epicardium and endocardium, particularly of the ventricles, and these differences affect ablation biophysics. Absence of passive convective effects conferred by circulating blood as well as the presence of epicardial fat and vessels and absence of intracavitary ridges and structures affect ablation lesion size when performing epicardial catheter-based ablation, whether using radiofrequency or cryothermal energy. Understanding differential effects in each environment is important in informing strategies to increase ablation lesion depth. When using actively cooled radiofrequency ablation, local impedance can be altered to selectively augment energy delivery.

Patient Selection for Epicardial Ablation-Part II: The Epicardial Approach and Current Challenges Associated with Epicardial Ablation

Since their inception, percutaneous epicardial approaches have become increasingly common in clinical practice with the advent of new technology and the growth of catheter ablation for both ventricular and supraventricular arrhythmias. In addition to identifying the arrhythmogenic foci, there remain challenges to successful epicardial ablation such as the choice of energy source, optimizing irrigation during ablation, and anatomic barriers such as epicardial fat and coronary vessels. The performance of continued translational studies to understand how each of these factors contribute to lesion formation will be essential to guide future advances in the field of epicardial ablation.

Irrigated Microwave Catheter Ablation Can Create Deep Ventricular Lesions Through Epicardial Fat With Relative Sparing of Adjacent Coronary Arteries

BACKGROUND

Radiofrequency ablation depth can be inadequate to reach intramural or epicardial substrate, and energy delivery in the pericardium is limited by penetration through epicardial fat and coronary anatomy. We hypothesized that open irrigated microwave catheter ablation can create deep myocardial lesions endocardially and epicardially though fat while acutely sparing nearby the coronary arteries.

METHODS

In-house designed and constructed irrigated microwave catheters were tested in in vitro phantom models and in 15 sheep. Endocardial ablations were performed at 140 to 180 W for 4 minutes; epicardial ablations via subxiphoid access were performed at 90 to 100 W for 4 minutes at sites near coronary arteries.

RESULTS

Epicardial ablations at 90 to 100 W produced mean lesion depth of 10±4 mm, width 18±10 mm, and length 29±8 mm through median epicardial fat thickness of 1.2 mm. Endocardial ablations at 180 W reached depths of 10.7±3.3 mm, width of 16.6±5 mm, and length of 20±5 mm. Acute coronary occlusion or spasm was not observed at a median separation distance of 2.7 mm (IQR, 1.2-3.4 mm). Saline electrodes recorded unipolar and bipolar electrograms; microwave ablation caused reductions in voltage and changes in electrogram morphology with loss of pace-capture. In vitro models demonstrated the heat sink effect of coronary flow, as well as preferential microwave coupling to myocardium and blood as opposed to lung and epicardial fat phantoms.

CONCLUSIONS

Irrigated microwave catheter ablation may be an effective ablation modality for deep ventricular lesion creation with capacity for fat penetration and sparing of nearby coronary arteries because of cooling endoluminal flow. Clinical translation could improve the treatment of ventricular tachycardia arising from mid myocardial or epicardial substrates.

Development of a Shock-Wave Catheter Ablation System for Ventricular Tachyarrhythmias: Validation Study in Pigs In Vivo

Background

Although radiofrequency catheter ablation is the current state‐of‐the‐art treatment for ventricular tachyarrhythmias, it has limited success for several reasons, including insufficient lesion depth, prolonged inflammation with subsequent recurrence, and thromboembolisms due to myoendocardial thermal injury. Because shock waves can be applied to deep lesions without heat, we have been developing a shock‐wave catheter ablation (SWCA) system to overcome these fundamental limitations of radiofrequency catheter ablation. In this study, we evaluated the efficacy and safety of our SWCA system for clinical application to treat ventricular tachyarrhythmia.

Methods and Results

In 33 pigs, we examined SWCA in vivo for the following 4 protocols. First, in an epicardial substrate model (n=8), endocardial SWCA significantly decreased the sensing threshold (pre‐ versus postablation: 11.4±3.8 versus 6.8±3.6 mV; P<0.05) and increased the pacing threshold (pre‐ versus postablation: 1.6±0.8 versus 2.0±1.1 V; P<0.05), whereas endocardial radiofrequency catheter ablation failed to do so. Second, in a myocardial infarction model (n=3), epicardial SWCA of the border zone of the infarcted lesion was as effective as ablation of the normal myocardium. Third, in a coronary artery application model (n=10), direct application of shock waves to the epicardial coronary arteries caused no adverse effects in either the acute or chronic phase. Fourth, with an epicardial approach (n=8), we found that 90 shots per site provided an ideal therapeutic condition to create deep lesions with less superficial damage.

Conclusions

These results indicate that our new SWCA system is effective and safe for treatment of ventricular tachyarrhythmias with deep arrhythmogenic substrates.

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.

Epicardial Ablation of Ventricular Tachycardia: a Review

For over 3 decades, it has been known that reentry circuits for ventricular tachycardia (VT) are not limited to the subendocardial myocardium. Rather, intramural or subepicardial substrates may also give rise to VT, particularly in those with non-ischemic cardiomyopathy. Percutaneous epicardial mapping and ablation has been successfully introduced for the treatment of such subepicardial VT. Herein, we review the indications for epicardial ablation and the identification of epicardial VT by electrocardiographic and imaging modalities. We also discuss the optimal technique for epicardial access and the implications of epicardial fat which has the potential to mimic scar, decreasing the specificity of electrogram morphology and impeding energy delivery to the tissue. Finally, we also report on possible complications of the procedure and strategies to mitigate adverse events.

Epicardial ablation of tachyarrhythmia in children: Experience at two academic centers

BACKGROUND

Experience with percutaneous epicardial ablation of tachyarrhythmia in pediatrics is limited. This case series addresses the feasibility, safety, and complications of the procedure in children.

METHODS

A total of nine patients underwent 10 epicardial ablation procedures from 2002 to 2013 at two academic centers. Activation mapping was performed in all cases, and electroanatomic map was utilized in nine of the 10 procedures. Patients had undergone one to three failed endocardial catheter ablations in addition to medical management, and all had symptoms, a high-risk accessory pathway (AP), aborted cardiac arrest with Wolff-Parkinson-White syndrome (WPW), or ventricular dysfunction. A standard epicardial approach was used for access in all cases, using a 7- or 8- Fr sheath. Epicardial ablation modality was radiofrequency (RF) in seven, cryoablation (CRYO) in one, and CRYO plus RF in one.

RESULTS

Median age was 14 (range 8-19) years.

INDICATIONS

drug refractory ectopic atrial tachycardia (one), ventricular tachycardia (VT) (five), high-risk AP (two), and aborted cardiac arrest from WPW - (one). Epicardial ablation was not performed in one case despite access due to an inability to maneuver the catheter around a former pericardial scar. VT foci included the right ventricular outflow tract septum, high posterior left ventricle (LV), LV outflow tract, postero-basal LV, and scar from previous rhabdomyoma surgery. WPW foci were in the area of the posterior septum and coronary sinus in all three cases. Overall procedural success was 70% (7/10), with epicardial ablation success in five and endocardial ablation success after epicardial mapping in two. The VT focus was close to the left anterior descending coronary artery in one of the unsuccessful cases in which both RF and CRYO were used. There was one recurrence after a successful epicardial VT ablation, which was managed with a second successful epicardial procedure. There were no other recurrences at more than 1 year of follow-up. Complications were minimal, with one case of inadvertent pleural access requiring no specific therapy. No pericarditis or effusion was seen in any of the patients who underwent epicardial ablation.

CONCLUSION

Epicardial ablation in pediatric patients can be performed with low complications and acceptable success. It can be considered for a spectrum of tachycardia mechanisms after failed endocardial ablation attempts and suspected epicardial foci. Success and recurrence may be related to foci in proximity to the epicardial coronaries, pericardial scar, or a distant location from the closest epicardial location. Repeat procedures may be necessary.

Epicardial Catheter Ablation of Ventricular Tachycardia

Over the last two decades, epicardial catheter ablation has evolved into a practical approach for treatment of ventricular tachycardia (VT). There are certain considerations when performing this procedure. First, presence of epicardial fat can diminish peak-to-peak electrogram amplitude and also impede radiofrequency energy delivery. Hence, epicardial VT ablation should be performed with cooled-tip radiofrequency using reduced irrigation flow within a relatively 'dry' pericardial milieu. Furthermore, catheter orientation is key when performing epicardial ablation. Lastly, hemo-pericardium remains the most common major adverse event of epicardial ablation and its presenting timeline may be used to identify the precise nature of this complication.

Serial examinations of right coronary artery directly injured by radiofrequency catheter ablation with optical coherence tomography and intravascular ultrasound

A 42-year-old man was referred for ablation. The origin of VT was localized close to the right coronary ostium. During ablation, the catheter tip inadvertently fell into a RCA ostium. The patient developed chest discomfort and ST-segment elevation in the inferior leads was observed. Coronary angiography confirmed severe narrowing of the ostial RCA. Stenting was deferred after satisfactory dilatation by a balloon. The patient discharged with eventless clinical course afterward. Follow-up coronary angiographic, FD-OCT, IVUS, and iMap examinations were performed at 3, 6, and 15 months after index procedure. The lesion showed progressive positive remodeling associated with intimal proliferation, medial thickening, and lumen narrowing up to 6 months. The patient underwent stenting at 15 months after the index procedure. The lesion required high-pressure post dilatation to obtain optimal stent expansion.

Risk of Coronary Artery Injury With Radiofrequency Ablation and Cryoablation of Epicardial Posteroseptal Accessory Pathways Within the Coronary Venous System

Background—

Ablation of epicardial posteroseptal accessory pathways requires ablation within the coronary venous system. We assessed the risk of coronary artery (CA) injury with radiofrequency ablation (RFA) within the coronary venous system as a function of the distance between the CA and ablation site. We also examined the efficacy and safety of cryoablation close to a CA.

Methods and Results—

Two-hundred forty patients underwent ablation for epicardial posteroseptal accessory pathways. Coronary angiography was performed before ablation in the last 169 patients and was repeated after ablation if performed in the coronary venous system within 5 mm of a significant CA. The distance between the ideal ablation site and closest CA was <2 mm in 100 (59%), 3 to 5 mm in 28 (16%), and >5 mm in 41 of 169 (25%) patients. CA injury was observed in 11 of 22 (50%) and 1 of 15 (7%) patients when RFA was performed within 2 and 3 to 5 mm of a CA, respectively. Cryoablation was performed in 26 patients with a significant CA located within 5 mm. Cryoablation alone eliminated epicardial posteroseptal accessory pathway conduction in 17 of 26 (65%) patients and in 8 patients with additional RFA without CA narrowing in any patient. During a follow-up period of 3 to 6 months, single procedure success rates were 90% and 77% for RFA and cryoablation at the ideal site, respectively.

Conclusions—

The risk of CA injury with RFA is correlated inversely with the distance from the ablation site. Cryoablation is a safe and reasonably effective alternative when a significant CA is located close to the ideal ablation site.

Acute and Chronic Effects of Epicardial Radiofrequency Applications Delivered on Epicardial Coronary Arteries

Background—

Epicardial coronary injury is by far the most feared complication of epicardial ablation. Little information is available regarding the chronic effects of delivering radiofrequency in the vicinity of large coronary vessels, and the long-term impact of this approach for mapping and ablation on epicardial vessel integrity is poorly understood. Therefore, the aim of this study was to characterize the acute and chronic histopathologic changes produced by in vivo epicardial pulses of radiofrequency ablation on coronary artery of porcine hearts.

Methods and Results—

Seven pigs underwent a left thoracotomy. The catheter was sutured adjacent to the left anterior descending artery and left circumflex artery, and 20 pulses of radiofrequency energy were applied. Radiofrequency lesions located no more than 1 mm of the vessel were used for this analysis. Three animals were euthanized 20 days (acute phase) after the procedure and 4 animals after 70 days (chronic phase). The following parameters were obtained in each vessel analyzed: (1) internal and external perimeter; (2) vessel wall thickness; (3) tunica media thickness, and (4) tunica intima thickness. The presence of adipose tissue around the coronary arteries, the distance between the artery and the epicardium, and the anatomic relationship of the artery with the coronary vein was also documented for each section. Sixteen of 20 (80%) sections analyzed, showed intimal thickening with a mean of 0.18±0.14 mm compared with 0.13±0.16 mm in the acute phase ( P =0.331). The mean tunica media thickness was 0.25±0.10 mm in the chronic phase animals compared with 0.18±0.03 mm in the acute phase animals ( P =0.021). A clear protective effect of pericardial fat and coronary veins was also present. A positive correlation between depth of radiofrequency lesion and the degree of vessel injury expressed as intimal and media thickening ( P =0.001) was present. A negative correlation was identified ( r =−0.83; P =0.002) between intimal thickening and distance between epicardium and coronary artery.

Conclusions—

In this porcine model of in vivo epicardial radiofrequency ablation in proximity to coronary arteries leads to acute and chronic histopathologic changes characterized by tunica intima and media thickening, with replacement of smooth muscle cells with extracellular matrix, but no significant stenosis was observed up to 70 days after the ablation. The absence of acute coronary occlusion or injury does not preclude subsequent significant arterial damage, which frequently occurs when epicardial radiofrequency applications are delivered in close vicinity to the vessels.

Safety and efficacy of high-intensity focused ultrasound atop coronary arteries during epicardial catheter ablation

BACKGROUND

Coronary arterial injury continues to be a limitation of epicardial catheter ablation using currently available energy sources. Application of high intensity focused ultrasound (HIFU) energy may avoid such injury due to its theoretical ability to focus energy beyond the ablation element and create lesions at depth.

OBJECTIVE

This study evaluated the safety of HIFU applications delivered directly over the left anterior descending (LAD) artery in an open-chest swine model.

METHODS

Ten swine underwent median sternotomy. A prototype HIFU probe was placed atop the LAD. Forty-three therapies along the LAD (60-seconds/6 watt) were analyzed. Three, 3, and 4 swine were studied at 2, 4, and 8 weeks and subsequently sacrificed. Lesions were scored (0-4) depending on the percent circumferential involvement of arteries.

RESULTS

Lesion area increased minimally from 54.5 ± 18.0 mm(2) at 2 weeks to 56.9 ± 20.6 mm(2) at 8 weeks, and depth increased moderately from 13.2 ± 2.5 mm to 15.5 ± 3.4 mm. At 2, 4, and 8 weeks, the mean injury score of the LAD was 0.8 ± 0.3, 1.5 ± 0.9, and 2.0 ± 0.7. No/minimal arterial injury was seen in 64% of all sections. However, a progressive increase in injury resulted in 89% of all sections showing any injury at 8 weeks. One animal developed occlusion of the distal LAD.

CONCLUSIONS

HIFU has the potential to create deep ventricular lesions with relative sparing of the LAD. The incremental arterial damage noted over time warrants further evaluation to support the viability of focusing ultrasound energy beyond vulnerable critical structures to ablate deeper targets.

Epicardial Ablation of Ischemic Ventricular Tachycardia

Endocardial catheter ablation for ventricular arrhythmias in patients with ischemic cardiomyopathy decreases ventricular tachycardia (VT) episodes, and painful implantable defibrillator shocks and can be lifesaving in the context of VT storm. Unfortunately, up to approximately one-third of postinfarction VTs are not accessible for ablation from the endocardium. Percutaneous access to the epicardial space has allowed ablation of a portion of these circuits, although anatomic barriers, such as the phrenic nerve, coronary arteries, and intramural circuits, still limit success in some cases. Adhesions, most often due to prior cardiac surgery, frequently necessitate a surgical approach to the pericardial space.

Experimental cryosurgery investigations in vivo

Cryosurgery is the use of freezing temperatures to elicit an ablative response in a targeted tissue. This review provides a global overview of experimentation in vivo which has been the basis of advancement of this widely applied therapeutic option. The cellular and tissue-related events that underlie the mechanisms of destruction, including direct cell injury (cryolysis), vascular stasis, apoptosis and necrosis, are described and are related to the optimal methods of technique of freezing to achieve efficacious therapy. In vivo experiments with major organs, including wound healing, the putative immunological response following thawing, and the use of cryoadjunctive strategies to enhance cancer cell sensitivity to freezing, are described.

Ablation of ventricular tachycardia

Ablation is an important management tool for the treatment of ventricular arrhythmias. Even at experienced centers ventricular tachycardia ablation carries a minor but significant risk for potential complications, including vascular and thromboembolic complications, air embolism, volume overload and the precipitation of congestive heart failure, cardiac tamponade from catheter perforation or from steam pop with RF energy delivery, valve or subvalvular support structure disruption, conduction system disruption with development of heart block, coronary artery injury when ablating in the coronary cusps region or trying to gain access to the LV chamber, precipitation of cardiogenic shock from ablation of viable myocardium in patients with marginal reserve and failure to resuscitate or precipitation of cardiogenic shock from repeated VT induction, and with epicardial ablation the potential complications of epicardial access, coronary arteries and phrenic nerve damage. Recognition of these risks is paramount for their avoidance with careful pre-procedure planning and intraprocedural technique being essential to minimize the potential for complications.

Angiographic analysis of the anatomic relation of coronary arteries to mitral and tricuspid annulus and implications for radiofrequency ablation

Coronary artery (CA) narrowings and/or occlusions after radiofrequency ablation (RFA) have been reported. The aim of this study was to describe the in vivo topographic anatomy of CAs and their anatomic relation to the mitral and tricuspid annulus using selective coronary angiography. Fifty consecutive patients undergoing RFA for narrow QRS complex tachycardia were included in the study. Multipolar electrode catheters were inserted into the right atrial appendage, His bundle region, distal coronary sinus (CS), and right ventricle. A mapping catheter was placed across the subeustachian isthmus (SEI). Selective coronary angiography was performed. The maximum and minimum distances between the distal CAs and the mapping catheter located along the mitral and tricuspid annulus were measured during systole and diastole and in right and left anterior oblique projections. The large (> or =1.5 mm) distal right CA was < or =5 mm from the mapping catheter in the SEI in 4 patients (8%). The large posterolateral branch of the right CA was < or =2 mm from the CS Os-middle cardiac vein in 10 patients (20%). The large left circumflex CA was < or =2 mm from the floor or ceiling of the CS in 7 patients (14%) and < or =2 mm from the CS catheter at the lateral and anterolateral mitral annulus in 12 patients (24%). RFA was canceled in 2 patients because of the close proximity (< or =2 mm) of the distal CA to the ablation site. In conclusion, large CAs are frequently located in close proximity to the common ablation sites. Coronary angiography should be considered in children and adults who may develop any signs or symptoms suggestive of acute CA occlusion until larger controlled series are available.

Catheter Ablation of Right Ventricular Outflow Tract Tachycardia: Value of Defining Coronary Anatomy

INTRODUCTION

Thermal damage to coronary arteries during catheter ablation has been previously reported. Coronary artery damage during LV outflow tract ventricular tachycardia is well recognized. However, the relationship of the coronary arteries to the RV outflow tract during catheter ablation has not been delineated. The purpose of this study was to define the relationship between the RV outflow tract and the coronary arteries utilizing arteriography, echocardiography, CT angiography, and gross anatomic pathology.

METHODS

The relationship of the coronaries to the RV outflow tract was analyzed in three patients groups: Group 1: patients (n = 10) undergoing RV outflow tract ventricular tachycardia; Group 2: patients (n = 50) undergoing CT coronary angiography; Group 3: patients (n = 4) undergoing echocardiography during open heart surgery and intracardiac echocardiography (ICE) during catheter ablation of atrial fibrillation (n = 5).

RESULTS

Group 1: The left main coronary artery was found to be 3.8 +/- 1.2 mm from the right ventricular outflow tract in patients undergoing ablation. Group 2: The minimum distance between the left main, left anterior descending, and right coronary artery to the RV outflow tract endocardial wall were 4.1 +/- 1.9 mm, 2.0 +/- 0.6 mm, and 4.3 +/- 1.9 mm (average +/- SD) respectively. Group 3: During open heart surgery using echocardiography, the minimum distance between the left main and the right coronary artery to the RV outflow tract were 3.4 +/- 0.35 mm and 2.0 +/- 0.1 mm, respectively. The distance between the let main coronary artery and the RVOT by ICE was 3.8 +/- 0.45 mm.

CONCLUSIONS

The major coronary arteries lie in close proximity of the RVOT, and their anatomic course should be taken into consideration during ablation of ventricular tachycardias arising from the RV outflow tract.

Idiopathic Epicardial Left Ventricular Tachycardia Originating Remote From the Sinus of Valsalva

Background— Despite the success of catheter ablation for treatment of idiopathic ventricular tachycardia (VT), occasional patients have been reported in whom VT could not be ablated from the right or left ventricular endocardium or from the aortic sinus of Valsalva (ASOV).

Methods and Results— In 12 of 138 patients (9%) with idiopathic VT referred for ablation, an epicardial left ventricular site of origin was identified >10 mm from the ASOV. Coronary venous mapping demonstrated epicardial preceding endocardial activation by >10 ms (41±7 versus 15±11 ms before QRS onset; P <0.001). VT induction was facilitated by catecholamines and terminated by adenosine. Ablation through the coronary veins or via percutaneous transpericardial catheterization was successful in 9 patients; 2 required direct surgical ablation as a result of anatomic constraints. No ECG pattern was specific for epicardial VT. However, slowed initial precordial QRS activation, as quantified by a novel metric, the maximum deflection index, was more useful. A delayed precordial maximum deflection index ≥0.55 identified epicardial VT remote from the ASOV with a sensitivity of 100% and a specificity of 98.7% relative to all other sites of origin ( P <0.001).

Conclusions— Although clinically underrecognized, idiopathic VT may originate from the perivascular sites on the left ventricular epicardium. The mechanism is consistent with triggered activity. It is amenable to ablation by transvenous or transpericardial approaches, although technical challenges remain. Recognition of a prolonged precordial maximum deflection index and early use of transvenous epicardial mapping are critical to avoid protracted and unsuccessful ablation elsewhere in the ventricles.