Radiofrequency catheter ablation in recurrent ventricular tachycardia

Irreversible electroporation for catheter-based cardiac ablation: a systematic review of the preclinical experience

INTRODUCTION

Irreversible electroporation (IRE) utilizing high voltage pulses is an emerging strategy for catheter-based cardiac ablation with considerable growth in the preclinical arena.

METHODS

A systematic search for articles was performed from three sources (PubMed, EMBASE, and Google Scholar). The primary outcome was the efficacy of tissue ablation with characteristics of lesion formation evaluated by histologic analysis. The secondary outcome was focused on safety and damage to collateral structures.

RESULTS

Sixteen studies met inclusion criteria. IRE was most commonly applied to the ventricular myocardium (n = 7/16, 44%) by a LifePak 9 Defibrillator (n = 9/16, 56%), NanoKnife Generator (n = 2/16, 13%), or other custom generators (n = 5/16, 31%). There was significant heterogeneity regarding electroporation protocols. On histological analysis, IRE was successful in creating ablation lesions with variable transmurality depending on the electric pulse parameters and catheter used.

CONCLUSION

Preclinical studies suggest that cardiac tissue ablation using IRE shows promise in delivering efficacious, safe lesions.

Spatiotemporal electrophysiological changes in a murine ablation model

AIMS

High recurrence rates after complex radiofrequency ablation procedures, such as for atrial fibrillation, remain a major clinical problem. Local electrophysiological changes that occur following cardiac ablation therapy are incompletely described in the literature. The purpose of this study was to determine whether alterations in conduction velocity, action potential duration (APD), and effective refractory period resolve dynamically following cardiac ablation.

METHODS AND RESULTS

Lesions were delivered to the right ventricle of mice using a subxiphoid approach. The sham-operated control group (SHAM) received the same procedure without energy delivery. Hearts were isolated at 0, 1, 7, 30, and 60 days following the procedure and electrophysiological parameters were obtained using high-resolution optical mapping with a voltage-sensitive dye. Conduction velocity was significantly decreased at the lesion border in the 0, 7, and 30 day groups compared to SHAM. APD(70) at the lesion border was significantly increased at all time points compared to SHAM. Effective refractory period was significantly increased at the lesion border at 0, 1, 7, and 30 days but not at 60 days post-ablation. This study demonstrated that post-ablation electrophysiological changes take place immediately following energy delivery and resolve within 60 days.

CONCLUSIONS

Cardiac ablation causes significant electrophysiological changes both within the lesion and beyond the border zone. Late recovery of electrical conduction in individual lesions is consistent with clinical data demonstrating that arrhythmia recurrence is associated with failure to maintain bi-directional conduction block.

Effect of inter-electrode distance on bipolar intramural radiofrequency ablation

OBJECTIVES

We aimed at evaluating bipolar radiofrequency ablation by correlating inter-electrode distance (ILD) with lesion dimensions and continuity.

BACKGROUND

Previous reports indicated that bipolar radiofrequency (RF) current applied to two adjacent sites in vitro, synergistically increased lesion sizes greater than that observed for unipolar RF current delivery using the same electrodes.

METHODS

Ablations were performed intramurally to ensure that each electrode surface (radius = 0.4 mm, area = 3.52 mm(2)) provided consistent contact with the myocardium. Ninety-six ablations were performed in four greyhounds using bipolar ablation needles with ILDs of 1, 2, 3, and 4 mm. An epicardial approach was used to ensure accurate positioning of the needles within the myocardium. Lesions were created using temperature-controlled RF delivery for a duration of 60 seconds to achieve 90 degrees C at the electrode proximal to the needle base. Lesion dimensions were determined histologically.

RESULTS

Increasing the ILD, decreased lesion width (P = 0.003) but increased lesion depth (P = 0.001). Lesions remained continuous with ILDs of 1-3 mm but became discontinuous at 4 mm. Energy requirements during ablation increased with increasing ILDs.

CONCLUSION

Using the above parameters (electrode radius, RF power delivery, time) during bipolar ablation, lesion continuity was critically dependent on the ILD. The maximum ILD threshold to create contiguous overlapping lesions was 3 mm. Lesions of greater width were created using shorter ILDs. Clinically, greater control over lesion dimensions can be obtained by manipulating the ILD distance.

Repetitive ventricular responses induced by radiofrequency ablation for idiopathic ventricular tachycardia originating from the outflow tract of the right ventricle

In 23 consecutive patients, radiofrequency (RF) ablation was used as treatment for idiopathic ventricular tachycardia (VT) originating from the outflow tract of the right ventricle. In this study, we focused on the repetitive ventricular response (> 5 consecutive QRS beats during RF application). The incidence and clinical implications of the repetitive ventricular response were examined through the results of endocardial mapping and RF ablation. VT origin was mapped as the earliest activation site during VT, and it was determined within 0.5 x 0.5 cm (narrow site) in 13 patients and wider than 0.5 x 0.5 cm (wide origin) in the other 10 patients. The repetitive ventricular response was induced during application of RF current in 14 of 23 patients (61%), and it was more frequently observed in VT from a wide origin (100%) than in the VT from a narrow site (31%). The QRS morphology of the repetitive ventricular response was identical to that of clinical VT. As RF application was continued and/or repeated, the RR interval of the repetitive ventricular response was gradually prolonged, the number of consecutive QRS complexes was decreased, and clinical VT was finally eliminated. The overall success rate of RF ablation was 96% (22/23 patients), and no complications were observed. In conclusion, a repetitive ventricular response was frequently observed in idiopathic right VT. The changing pattern of repetitive ventricular response, slowly and/or disappearing was consistent with successful RF ablation.

Morphological variation of nonreentrant idiopathic ventricular tachycardia originating from the right ventricular outflow tract and effect of radiofrequency lesion

RF catheter ablation was performed in 16 patients with nonreentrant idiopathic VT originating from the RVOT. All documented VT was monomorphic, but subtle morphological variation in the VT-QRS complex was observed in 10 (63%) of 16 patients. Through endocardial mapping, VT origin was determined within a narrow site (< 0.5 x 0.5 cm) in 4 of the 10 patients with the morphological variation. In the other 6 of 10 patients, the origin extended to an area of > 0.5 x 0.5 cm. In VT with morphological variation, the local electrogram at the site of VT origin also showed variation in morphology and activation sequence. For VT of narrow origin, RF application to the site eliminated the VT. However, in VT from a wide arrhythmogenic area, RF current had to be delivered to 3-7 distinct sites to cover the possible origin, and specific QRS configuration of VT and/or PVC was ablated at each of the earliest activation site. All but one VT were successfully ablated by RF current. Subtle morphological variation was frequent in this type of VT, and about half were associated with a wide arrhythmogenic area. Precise mapping and analysis of the efficacy of each RF application might be helpful to better understand the relationship between subtle changes of VT-QRS morphology and their origins.

The efficacy of radiofrequency catheter ablation for the treatment of ventricular tachycardia associated with cardiomyopathy

We performed radiofrequency catheter ablation (RF ablation) for ventricular tachycardia (VT) in 2 patients with dilated cardiomyopathy (DCM) and 1 patient with arrhythmogenic right ventricular dysplasia (ARVD). Patient 1 had incessant VT associated with DCM. RF ablation was performed where diastolic potentials were recorded and concealed entrainment was demonstrated. VT was terminated by RF ablation. Patient 2 had drug-resistant VT associated with ARVD. RF ablation was performed where perfect pace-mapping was obtained during sinus rhythm, diastolic potentials were recorded and concealed entrainment was demonstrated. VT was terminated by RF ablation. Patient 3 had 2 morphologically distinct VTs associated with DCM. The target for RF ablation was 1 of the 2, which was a drug-resistant type. Perfect pace mapping was obtained where delayed potentials were recorded. As the current strength of pacing was reduced, the QRS complex configuration switched to the other type. This site was thought to be the common slow conduction zone for the re-entry circuit of the 2 types and RF ablation was performed at this site. In these 3 cases, VT did not recur after ablation. RF ablation is effective for the treatment of VT associated with cardiomyopathy.

Transcatheter subendocardial infusion. A novel technique for mapping and ablation of ventricular myocardium

BACKGROUND

Catheter ablation with radiofrequency energy is feasible in a limited subset of patients with ventricular tachycardia. The purpose of this study was to evaluate a technique for mapping and ablation of ventricular myocardium with the use of transcatheter subendocardial infusion.

METHODS AND RESULTS

A needle-tipped deflectable electrode catheter was used to deliver reagents to endocardial target sites. This was equipped with two central lumens to allow sequential administration of mapping and ablation injectants with minimal admixture. The mapping injectant consisted of a mixture of lidocaine, iohexal, and glycerin; the ablation injectant contained ethanol, iohexal, and glycerin. Infusion of the mapping injectant (1 cm3 over 3 or 5 seconds, n = 14) produced a stain on fluoroscopy and increased local capture threshold by 61%. No lesions resulted from mapping infusions. Infusion of the ethanol-containing injectant (n = 48) produced discrete lesions, with a mean volume ranging from 0.6 to 1.5 cm3. There was a direct relationship between infusion volume, infusion duration, and resultant lesion volume. Fibrosis in a region of healed myocardial infarction did not impair diffusion of the injectant or affect lesion dimensions. Microscopic analysis of chronic lesions showed a sharply demarcated border zone between fibrotic and normal myocardium.

CONCLUSIONS

Transcatheter subendocardial infusion can be used to reversibly impair local excitability and mark an injection site fluoroscopically. Subendocardial injection of ethanol can predictably ablate a large volume of ventricular myocardium. Additional study of this system in an arrhythmia model will help to define its potential for mapping and ablation of hypotensive ventricular tachycardia.

Therapeutic options for malignant ventricular tachyarrhythmias: is the implantable cardioverter-defibrillator a primary alternative or merely complementary?

In considering alternatives to the implantable cardioverter-defibrillator (ICD) in patients with malignant ventricular arrhythmias, both pharmacologic and nonpharmacologic therapies are available. Unfortunately, both pharmacologic methods (even when therapy is individualized and optimized) and nonpharmacologic methods (including coronary revascularization and radiofrequency or surgical ablation) yield long-term results that are unacceptable for many patients. Thus, the ICD should be strongly considered as complementary therapy, even when alternative methods are selected. More importantly, early implantation of an ICD often may be justified as the first therapeutic alternative, rather than as complementary therapy, in patients with life-threatening ventricular arrhythmias.

Catheter ablation of ventricular tachycardia with radiofrequency currents, with special reference to the termination and minor morphologic change of reinduced ventricular tachycardia

During catheter ablation with radiofrequency (RF) currents, the incidence of the termination of reentrant ventricular tachycardia (VT) during application of RF energy and the morphologic change of the reinduced VT were analyzed. Twenty-five patients (20 men and 5 women, aged 44 +/- 17 years) were studied. After induction of monomorphic sustained VT, the ablation site was determined by endocardial activation mapping, identification of isolated mid-diastolic potential, and pacing during tachycardia. Thirty-six monomorphic VTs were induced in 25 patients and terminated with programmed stimulation. The cycle length was 323 +/- 55 ms and all VTs were entrained with rapid ventricular pacing. The target site was the earliest site of activation of VT in 26 VTs in 16 patients, and the area of slow conduction in 10 VTs in 9 patients. VT was terminated soon after the application of RF currents in 33 VTs in 22 patients at 6.0 +/- 3.1 seconds, and VT was induced immediately after the cessation of RF currents in 11 patients. Of these, 4 patients with idiopathic left ventricular VT had an alternation in the QRS configuration before catheter ablation and required repeat ablation of the other VT morphology. In the other 7 patients, such morphology was not observed before ablation, but was observed in VT induced when the original VT was terminated. Repeated attempts of catheter ablation 2 to 9 times at the remapped site was, however, successful in 7 of 8 VTs.(ABSTRACT TRUNCATED AT 250 WORDS)

Catheter ablation of ventricular tachycardia in 136 patients with coronary artery disease: results and long-term follow-up

OBJECTIVES

This study attempted to determine the feasibility and long-term efficacy of catheter ablation by means of either radiofrequency or direct current energy in a selected group of patients with coronary artery disease.

BACKGROUND

Catheter ablation of ventricular tachycardia has proved to be highly effective in patients with idiopathic and bundle branch reentrant ventricular tachycardia. In patients with coronary artery disease and recurrent sustained ventricular tachycardia resistant to medical antiarrhythmic management, the value of catheter ablation has not yet been established.

METHODS

One hundred thirty-six patients with coronary artery disease and one configuration of monomorphic sustained ventricular tachycardia underwent radiofrequency (72 patients) or direct current catheter ablation (64 patients). The mapping procedure to localize an adequate site for ablation included pace mapping during sinus rhythm, endocardial activation mapping, identification of isolated mid-diastolic potentials and pacing interventions during ventricular tachycardia.

RESULTS

Primary success was achieved in 102 (75%) of 136 patients (74% of 72 undergoing radiofrequency and 77% of 64 with direct current ablation). Complications were noted in 12% of patients. During a mean (+/- SD) follow-up period of 24 +/- 13 months (range 3 to 68), ventricular tachycardia recurred in 16% of patients.

CONCLUSIONS

Catheter ablation of ventricular tachycardia in coronary artery disease is feasible in patients with one configuration of monomorphic sustained ventricular tachycardia. There is no significant difference with respect to the type of energy applied. The follow-up data show that in a selected group of patients with coronary artery disease, catheter ablation offers a therapy alternative.

Encircling endocardial cryoablation for ventricular tachycardia after myocardial infarction: experience with 33 patients

Encircling endocardial cryoablation, consisting of circumferential cryoablation of the infarct scar, can be curative in selected patients with ventricular tachycardia (VT). We describe our experience with and long-term outcome in 33 patients undergoing this procedure. The interval between myocardial infarction and the onset of tachycardia varied from 2 weeks to 22 years (mean 38 +/- 63 months and median 3 months). All patients had a left ventricular aneurysm (anterior in 20, posterior in 12, and lateral in 1) and significant coronary artery disease. Fourteen patients had clinical evidence of heart failure preoperatively. Twenty-eight patients had sustained monomorphic VT (incessant in 3); 3 had polymorphic or nonsustained tachycardia; 2 had primary ventricular fibrillation; and 1 had associated Wolff-Parkinson-White syndrome. Surgery was undertaken after failed drug therapy and consideration of left ventricular anatomy and function. At surgery, 32 patients had encircling endocardial cryoablation, and 1 patient had partial right ventricular free-wall disconnection (right ventricular infarct). Thirteen patients underwent concomitant coronary artery bypass grafting. An implantable cardioverter defibrillator (ICD) was implanted in 2 patients and prophylactic ICD patches in 1. One patient died postoperatively; 3 had recurrent VT perioperatively; 1 was treated with amiodarone; and 2 had ICD implantation. During long-term follow-up (mean 5 years), all patients who were free of tachycardia at discharge remained alive and free of arrhythmias or syncope. The patient receiving amiodarone sustained a cardiac arrest subsequently and received an ICD implant. One patient with an ICD continued to receive appropriate shocks frequently and died 2 years after surgery. Nine patients had congestive heart failure postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)

Management of patients after catheter ablation of ventricular tachycardia

The management of patients after catheter ablation of ventricular tachycardia is not well defined. In this article we summarize recently published results and report our own experience. Factors influencing the clinical outcome of these patients and methods to identify patients with an increased risk of recurrence of ventricular tachycardia are discussed. Furthermore, a review is given on current concomitant therapeutic tools including antiarrhythmic drugs and the implantation of an automatic cardioverter defibrillator.

Treatment of ventricular tachycardia by transcatheter radiofrequency ablation in patients with ischemic heart disease

BACKGROUND

Recurrent sustained ventricular tachycardia (VT) is not responsive to antiarrhythmic drugs in the majority of patients, who therefore need therapy with nonpharmacological methods. We evaluated prospectively the feasibility, safety, and efficacy of transcatheter radiofrequency (RF) ablation of VT in 21 selected patients with ischemic heart disease and VT.

METHODS AND RESULTS

Twenty-one patients with ischemic heart disease and recurrent, drug-refractory VT documented by 12-lead ECG were selected who had sufficient hemodynamic tolerance of VT to undergo transcatheter mapping. Documented clinical VT was reproduced by programmed cardiac stimulation (PCS), and the site of origin was localized by a combination of techniques, including pace mapping, activation-sequence mapping, recordings of middiastolic potentials, and application of resetting and entrainment principles. RF current at 55 V was applied (3.8 +/- 3.1 applications per patient) for as long as 30 seconds at a time to target sites. Twenty-four distinct clinical VTs (mean cycle length, 445 +/- 52 milliseconds) were mapped and ablated in 21 patients. In 17 of 21 patients (81%), the procedure was acutely successful, and the target clinical VT could no longer be induced by PCS after the procedure, whereas in 4 patients, clinical VT remained inducible. By contrast, VTs with shorter cycle length and different QRS morphology than the ablated VT could still be induced by PCS in 12 of 21 patients. One patient died in intractable congestive heart failure 10 days after the procedure, and the remaining 20 are alive at the end of the follow-up period. The majority of the patients continued to be treated with at least one additional mode of antiarrhythmic therapy; 12 patients were still taking antiarrhythmic drugs, and 9 patients received an implantable cardioverter/defibrillator. During a mean follow-up period of 13.2 +/- 5.0 months, 9 of 20 patients (45%) had recurrent VT. In 4 patients, the recurrent VT was different than the previously ablated one. Clinical VT recurred in all 4 patients in whom RF ablation had been acutely unsuccessful. Four patients with recurrent VT underwent repeat RF ablation procedures that were acutely successful and had no further recurrence.

CONCLUSION

Transcatheter RF ablation is feasible but has only moderately high efficacy in a small, selected group of patients with ischemic heart disease and drug-refractory, highly frequent, hemodynamically tolerated, sustained VT. In the majority of the patients, this treatment technique is palliative rather than definitive, and many of the patients continue to require other methods of antiarrhythmic therapy.

Cardiovascular applications of laser technology

Laser technology has been evaluated for the treatment of coronary artery disease, ventricular and supraventricular arrythmias, hypertrophic cardiomyopathy, and congenital heart disease. Developments in laser angioplasty, laser thrombolysis, transmyocardial laser revascularization, photochemotherapy, laser treatment of arrhythmias and/or laser diagnostics are directed at improving upon conventional non-laser approaches, and providing new therapeutic and diagnostic options. This review will summarize the current status of the multiple applications of laser technology for cardiovascular diagnosis and therapy.

Radiofrequency catheter ablation of the slow reentrant pathway of sustained ventricular tachycardia

The article reports the cases of two patients with severe coronary artery disease and associated recurrent sustained ventricular tachycardia successfully treated with radiofrequency catheter ablation. In the first patient, two different types of ventricular tachycardia (one incessant) were eliminated. In all procedures, an area of slow conduction critical for tachycardia maintenance was localized by endocardial mapping techniques. Radiofrequency energy delivered to this area could permanently modify the anatomical substrate of the arrhythmia. After single follow-ups of 19, 14, and 13 months regarding the arrhythmic entities, the patients are well and free from spontaneous recurrences.

Radiofrequency catheter ablation of ventricular tachycardia following implantation of an automatic cardioverter defibrillator

OBJECTIVES

The present study reports on the complementary role of two nonpharmacological options of antiarrhythmic therapy.

BACKGROUND

Catheter ablation, antitachycardia surgery, and the implantable cardioverter defibrillator (ICD) have become important tools in the management of ventricular tachyarrhythmias. However, the emergence of ventricular tachyarrhythmias after implantation of an ICD is possible because the arrhythmogenic substrate is not affected.

PATIENTS AND METHODS

Six of 180 patients developed frequent episodes of monomorphic ventricular tachycardia (n = 2) or incessant ventricular tachycardia (n = 4) following implantation of an ICD and underwent radiofrequency (RF) catheter ablation. Catheter ablation was performed using a RF generator HAT 200. Energy was delivered between a 4-mm tip electrode of the ablation catheter and a patch electrode.

RESULTS

Catheter ablation was done 6.8 +/- 5 months following ICD implantation; 6 +/- 2.2 RF impulses were delivered at the site of origin of ventricular tachycardia characterized by early endocardial activation during ventricular tachycardia, identical pace mapping and long latency between stimulus, and QRS-complex in five patients. New bundle branch reentry was the underlying mechanism of ventricular tachycardia in one patient. RF catheter ablation resulted in termination of incessant ventricular tachycardia. Immediately postablation, the documented ventricular tachycardia was rendered noninducible in all patients. No ICD malfunctions have been observed. One patient died due to heart failure 24 hours after successful ablation of the incessant ventricular tachycardia. During a follow-up of 5-19 months, episodes of ventricular tachycardia recurred in four patients. All episodes could be controlled by the ICD without frequent cardioversions.

CONCLUSION

RF catheter ablation is a complementary therapeutic option in case of frequent or incessant ventricular tachycardia after ICD implantation.

Catheter ablation with radiofrequency current of ventricular tachycardia originating from the right ventricle

Catheter ablation of ventricular tachycardia (VT) with radiofrequency current would be safer than the conventional ablation with direct current shocks. Seven patients who had eight morphologically distinct symptomatic monomorphic VTs underwent catheter ablation with radiofrequency current. The mean age +/- SD was 52 +/- 16 years, and the mean cycle length of the clinical VT was 298 +/- 36 milliseconds. Sustained VT was induced by programmed stimulation with or without isoproterenol in four patients and developed during the infusion of isoproterenol alone in two patients. Of these, four VTs were entrained with rapid pacing. The ablation was attempted at the site of earliest activation through the distal electrode and the external patch electrode on the back during VT in seven episodes in six patients. In the other patient it was applied during sinus rhythm. Energy was 40 to 50 W in the first case and 30 to 40 W in the others, and was given for 30 seconds. All VTs were terminated within 6 seconds, 3.6 +/- 0.8 seconds after the application of the radiofrequency current. Additional current was given to one to four predetermined sites by mapping. The mean number of applications was 4.0 +/- 1.3 sites. Except in the first patient, VT was eliminated successfully and VT was not induced by programmed stimulation, by the administration of isoproterenol, or by treadmill exercise testing. VT did not recur during the follow-up period of 6.8 +/- 1.1 months.

Successful radiofrequency current catheter ablation of sustained ventricular tachycardia

We performed radiofrequency current catheter ablation in two patients with nonischemic sustained ventricular tachycardia (VT). In one patient, two morphologically distinct VTs were induced by electrical stimulation. One showed right bundle branch block pattern and the other left bundle branch block pattern. The earliest site of activation during each VT was determined at the septum of the right ventricle. However, these two sites were close to the His-bundle electrogram recording area. In the other patient, a VT with a left bundle branch block pattern occurred spontaneously after the administration of isoproterenol. The earliest site of activation during VT was determined at the outflow tract of the right ventricle. During tachycardia, radiofrequency current ablation (40 W x 30 sec) was delivered to the earliest site of activation. A few seconds after fulguration, each VT was terminated and additional radiofrequency currents were given near these sites. After the ablation, VT could not be induced by the electrical stimulations, nor did it recur. No side effects were observed and the atrioventricular conduction remained intact. We feel that nonischemic VTs could possibly be treated by using radiofrequency current catheter ablation.