Factors influencing lesion formation during radiofrequency catheter ablation

In radiofrequency (RF) ablation, the heating of cardiac tissue is mainly resistive. RF current heats cardiac tissue and in turn the catheter electrode is being heated. Consequently, the catheter tip temperature is always lower--or ideally equal--than the superficial tissue temperature. The lesion size is influenced by many parameters such as delivered RF power, electrode length, electrode orientation, blood flow and tissue contact. This review describes the influence of these different parameters on lesion formation and provides recommendations for different catheter types on selectable parameters such as target temperatures, power limits and RF durations.     

Mechanical compliance of the endocardium

Radio-frequency (RF) ablation is an accepted treatment for cardiac arrhythmias related to abnormal focal cardiac substrate. The penetration depth of the electrode into the endocardium affects lesion size, a critical determinant of success of RF ablation. We measured the relation between the mechanical compliance and the penetration depth of RF ablation catheter electrode at frequently ablated areas of the endocardium and examined the influence of time after death on mechanical properties of the tissue. We measured force versus time for eight insertion depths of the catheter electrode into full-thickness endocardial samples derived from the mitral valve annulus, the left ventricular free wall and the tricuspid valve annulus. We varied the time after death at 15, 40 min, 3, 8, and 18 h and repeated our measurements. At 15 min after death, the first 0.5 mm penetration depth caused the fastest relaxation at 55 s. Force decay decreased dramatically at 15 min after death as the penetration depth increased from 0.5 to 4 mm. We used the force data sampled at 60 s after insertion to approximate the elasticity. We observed the relations between the force versus the insertion depth. The force increased by a factor of 5 for the mitral valve annulus and 8 for the left free wall from 15 min to 18 h. We derived coefficients of a second-order polynomial equation relating the force data to insertion depth with R²>0.99.     

Ablation of Myocardial Tissue With Nanosecond Pulsed Electric Fields

Background

Ablation of cardiac tissue is an essential tool for the treatment of arrhythmias, particularly of atrial fibrillation, atrial flutter, and ventricular tachycardia. Current ablation technologies suffer from substantial recurrence rates, thermal side effects, and long procedure times. We demonstrate that ablation with nanosecond pulsed electric fields (nsPEFs) can potentially overcome these limitations.

Methods

We used optical mapping to monitor electrical activity in Langendorff-perfused New Zealand rabbit hearts (n = 12). We repeatedly inserted two shock electrodes, spaced 2–4 mm apart, into the ventricles (through the entire wall) and applied nanosecond pulsed electric fields (nsPEF) (5–20 kV/cm, 350 ns duration, at varying pulse numbers and frequencies) to create linear lesions of 12–18 mm length. Hearts were stained either with tetrazolium chloride (TTC) or propidium iodide (PI) to determine the extent of ablation. Some stained lesions were sectioned to obtain the three-dimensional geometry of the ablated volume.

Results

In all animals (12/12), we were able to create nonconducting lesions with less than 2 seconds of nsPEF application per site and minimal heating (< 0.2°C) of the tissue. The geometry of the ablated volume was smoother and more uniform throughout the wall than typical for RF ablation. The width of the lesions could be controlled up to 6 mm via the electrode spacing and the shock parameters.

Conclusions

Ablation with nsPEFs is a promising alternative to radiofrequency (RF) ablation of AF. It may dramatically reduce procedure times and produce more consistent lesion thickness than RF ablation.     

Development and validation of a model for radiofrequency ablation]

Since 1986, cardiac arrhythmias have been successfully treated by destroying the underlying arrhythmogenic substrate with radiofrequency energy (radiofrequency ablation). The aim of this study was to develop a model for radiofrequency ablation enabling evaluation of the temperature distribution within cardiac tissue and the influence of electrode tissue contact. The model describes a 7F electrode, 4 mm in length and positioned perpendicular to the tissue. Heat convection within the tissue and heat lost via the blood was taken into account. Simulation of constant tissue exposure to 4 W resulted in a temperature increase of 35 degrees C after 10 sec. The temperature increase in the depths was less steep, but constant, and exceeded the electrode temperature at depths of 1 mm after 40 sec, 2 mm after 100 sec, and 3 mm after 200 sec. Electrode tissue contact proved to have a great influence on tissue temperature. Poor contact resulted in a temperature rise of only 0.68 degree C with a maximum of 50 W, whereas with ideal contact, 4 W sufficed to achieve a chosen setpoint of 70 degrees C. The model was validated in an in vitro setup using ventricular tissue from the pig. A strong correlation was found between simulated heating efficiency during temperature-controlled ablations under different contact conditions, and the respective measured values in the in vitro setup with a correlation coefficient of 0.97.     

Computational Modeling of Open-Irrigated Electrodes for Radiofrequency Cardiac Ablation Including Blood Motion-Saline Flow Interaction

Radiofrequency catheter ablation (RFCA) is a routine treatment for cardiac arrhythmias. During RFCA, the electrode-tissue interface temperature should be kept below 80°C to avoid thrombus formation. Open-irrigated electrodes facilitate power delivery while keeping low temperatures around the catheter. No computational model of an open-irrigated electrode in endocardial RFCA accounting for both the saline irrigation flow and the blood motion in the cardiac chamber has been proposed yet. We present the first computational model including both effects at once. The model has been validated against existing experimental results. Computational results showed that the surface lesion width and blood temperature are affected by both the electrode design and the irrigation flow rate. Smaller surface lesion widths and blood temperatures are obtained with higher irrigation flow rate, while the lesion depth is not affected by changing the irrigation flow rate. Larger lesions are obtained with increasing power and the electrode-tissue contact. Also, larger lesions are obtained when electrode is placed horizontally. Overall, the computational findings are in close agreement with previous experimental results providing an excellent tool for future catheter research.     

Real‐time optical spectroscopic monitoring of nonirrigated lesion progression within atrial and ventricular tissues

Despite considerable advances in guidance of radiofrequency ablation (RFA) therapy for the treatment of cardiac arrhythmias, success rates have been hampered by a lack of tools for precise intraoperative evaluation of lesion extent. Near‐infrared spectroscopic (NIRS) techniques are sensitive to tissue structural and biomolecular properties, characteristics that are directly altered by radiofrequency (RF) treatment. In this work, a combined NIRS‐RFA catheter is developed for real‐time monitoring of tissue reflectance during RF energy delivery. An algorithm is proposed for processing NIR spectra to approximate nonirrigated lesion depth in both atrial and ventricular tissues. The probe optical geometry was designed to bias measurement influence toward absorption enabling enhanced sensitivity to changes in tissue composition. A set of parameters termed “lesion optical indices” are defined encapsulating spectral differences between ablated and unablated tissue. Utilizing these features, a model for real‐time tissue spectra classification and lesion size estimation is presented. Experimental validation conducted within freshly excised porcine cardiac specimens showed strong concordance between algorithm estimates and post‐hoc tissue assessment.      

External irrigation of a non-irrigated ablation catheter for effective AV node ablation during conduction system pacing

Ablation using non-irrigated catheter can lead to rapid rise in temperature of electrode tissue interface from tissue desiccation, steam and coagulum formation and this may limit power delivery and lesion size. We present a novel technique of external irrigation through the long sheath while using a non-irrigated ablation catheter during AV Node ablation and conduction system pacing. By bringing the long sheath closer to the tip of non-irrigated catheter and injecting cold normal saline allows cooling of electrode tissue interface leading to increase in power delivery resulting in a deeper lesion.     

A clinical approach to arrhythmias revisited in 2018

Understanding arrhythmias and their treatment is not always easy. The current straightforward approach with catheter ablation and device therapy is an amazing achievement, but does not make management of underlying or other cardiac disease and pharmacological therapy unnecessary. The goal of this paper is to describe how much of the knowledge of the 1980s and early 1990s can and should still be applied in the modern treatment of patients with arrhythmias. After an introduction, this review will focus on paroxysmal atrial fibrillation and a prototype of ‘idiopathic’ ventricular arrhythmias, two diseases with a striking similarity, and will discuss the arrhythmogenesis. The ECG continues to play an important role in diagnostics. Both diseases are associated with a structurally normal heart; the autonomic nervous system plays an important role in triggering arrhythmias at both the atrial and ventricular level.     

Phrenic nerve injury after catheter ablation of atrial fibrillation

Phrenic Nerve Injury (PNI) has been well studied by cardiac surgeons. More recently it has been recognized as a potential complication of catheter ablation with a prevalence of 0.11 to 0.48 % after atrial fibrillation (AF) ablation. This review will focus on PNI after AF ablation. Anatomical studies have shown a close relationship between the right phrenic nerve and it's proximity to the superior vena cava (SVC), and the antero-inferior part of the right superior pulmonary vein (RSPV). In addition, the proximity of the left phrenic nerve to the left atrial appendage has been well established. Independent of the type of ablation catheter (4 mm, 8 mm, irrigated tip, balloon) or energy source used (radiofrequency (RF), ultrasound, cryothermia, and laser); the risk of PNI exists during ablation at the critical areas listed above. Although up to thirty-one percent of patients with PNI after AF ablation remain asymptomatic, dyspnea remain the cardinal symptom and is present in all symptomatic patients. Despite the theoretical risk for significant adverse effect on functional status and quality of life, short-term outcomes from published studies appear favorable with 81% of patients with PNI having a complete recovery after 7 +/- 7 months. CONCLUSION: Existing studies have described PNI as an uncommon but avoidable complication in patients undergoing pulmonary vein isolation for AF. Prior to ablation at the SVC, antero-inferior RSPV ostium or the left atrial appendage, pacing should be performed before energy delivery. If phrenic nerve capture is documented, energy delivery should be avoided at this site. Electrophysiologist's vigilance as well as pacing prior to ablation at high risk sites in close proximity to the phrenic nerve are the currently available tools to avoid the complication of PNI.     

Tissue temperature feedback control of power: the key to successful ablation

Multiple ablation technologies are used to treat atrial fibrillation during cardiac operations. All such ablation technologies use locally induced temperature extremes (>50°C or <-20°C) to kill tissue and create a lesion pattern in the atria which blocks activation pathways that initiate and sustain atrial fibrillation. The technologies used to heat tissue have included radiofrequency (RF), microwave, high-intensity focused ultrasound, and infrared laser. RF accounts for more than 95% of the heating-based ablation technology used by cardiac surgeons. Energy delivery with RF is easier to control than with some other technologies, the heating produced by the energy source is well understood, and manufacturing costs are not excessive. Whichever heating technology is used, control of energy delivery is required to ensure both safe and effective heating of the targeted tissue. All targeted tissue needs to be heated above 50°C to achieve cell death. However, the targeted tissue should not be heated above 100°C, as this can cause perforation due to a steam pop. In addition, adjacent noncardiac tissues must not be damaged during the ablation procedure. The best method to achieve this control uses direct measurement of tissue temperature, because the tissue temperature defines both the safe and effective limits for the ablative process.     

Catheter ablation of recurrent polymorphic tachycardia: Use of sodium channel blockade to organize the tachycardia: A case report

A 55 year old male presented with recurrent implantable cardioverter defibrillator (ICD) shocks due to polymorphic ventricular tachycardia (PMVT). He had undergone prior catheter ablation for VT three years ago. During the prior attempt he underwent voltage guided substrate ablation. With programmed ventricular extrastimulation (PVES), PMVT was repeatedly induced requiring DC shock. Intravenous procainamide was administered and PVES was repeated which induced sustained monomorphic ventricular tachycardia (MMVT). This VT had pseudo delta waves with maximum deflection index of 0.68, suggestive of epicardial origin. Activation mapping was performed epicardially. Presystolic potentials were recorded in mid anterolateral wall of left ventricular epicardial region. Radiofrequency (RF) ablation at this site terminated the VT. Post ablation there was no inducible tachycardia and patient is free of arrhythmias during 2 years of follow-up.     

Idiopathic epicardial ventricular arrhythmias: diagnosis and ablation technique from the aortic sinus of Valsalva

Idiopathic outflow tract arrhythmias (ventricular tachycardias or symptomatic premature ventricular contractions; OT-VT/PVCs) can originate from the left ventricular (LV) epicardium (Epi-VT/PVCs), and radiofrequency (RF) energy applications from the aortic sinus of Valsalva can eliminate Epi-VT/PVCs in selected patients. Among the various ECG findings, the R-wave duration index and R/S amplitude index in leads V1 or V2 are useful for identifying Epi-VT/PVCs, and the Q-wave ratio of leads aVL to aVR and S-wave amplitude in lead V1 are useful for differentiating between an Epi-VT/PVC originating from the LV epicardium remote from the left sinus of Valsalva (LSV) and that from the LSV. Tissue tracking imaging is a promising modality for identifying the origin of OT-VT/PVCs and for differentiating between an Epi-VT/PVC originating from the LV epicardium remote from the LSV and that from the LSV. If the origin of the Epi-VT/PVC is identified within the LSV, coronary and aortic angiography should be performed to assess the anatomic relationships between the Epi-VT/PVC origin and coronary arteries and aortic valve before the RF energy delivery. To avoid potential complications, RF ablation should be performed at the LSV using a maximum power of 35 watts and maximum temperature of 55 degrees C. Epicardial mapping through the coronary venous system and the presence of potentials recorded from the ablation site within the LSV and their changes before and after the RF energy applications may be useful for diagnosing Epi-VT/PVCs or predicting a successful catheter ablation from the LSV.     

Advanced fully integrated radiofrequency/optical-coherence-tomography irrigated catheter for atrial fibrillation ablation

The inability of current catheter ablation procedures to accurately monitor lesion formation limits their safety and efficacy. An advanced fully integrated radiofrequency (RF)/optical coherence tomography (OCT) ablation catheter is developed, which enables real-time monitoring during ablation. An OCT fiber array is especially designed, developed and integrated into an off-the-shelf irrigated RF ablation catheter. In-vitro experimental studies performed on poultry and ovine hearts demonstrate the ability of the integrated RF/OCT system to provide information on the quality and orientation of catheter/wall contact. Experimental results show that adipose tissue can be accurately identified from normal myocardial tissue with 94% accuracy and lesion formation is monitored with an overall accuracy of 93%. The ability to predict pop events is also demonstrated, with an accuracy of 86%.     

Determination of lesion size by ultrasound during radiofrequency catheter ablation.

The catheter tip temperature that is used to control the radiofrequency generator output poorly correlates to lesion size. We, therefore, evaluated lesions created in vitro using a B-mode ultrasound imaging device as a potential means to assess lesion generation during RF applications non-invasively. Porcine ventricular tissue was immersed in saline solution at 37 degrees C. The catheter was fixed in a holder and positioned in a parallel orientation to the tissue with an array transducer (7.5 MHz) app. 3 cm above the tissue. Lesions were produced either in a temperature controlled mode with a 4-mm tip catheter with different target temperatures (50, 60, 70 and 80 degrees C, 80 W maximum output) or in a power controlled mode (25, 50 and 75 W, 20 ml/min irrigation flow) using an irrigated tip catheter. Different contact forces (0.5 N, 1.0 N) were tested, and RF was delivered for 60 s. A total of 138 lesions was produced. Out of these, 128 could be identified on the ultrasound image. The lesion depth and volume was on average 4.1 +/- 1.6 mm and 52 +/- 53 mm3 as determined by ultrasound and 3.9 +/- 1.7 mm and 52 +/- 55 mm3 as measured thereafter, respectively. A linear correlation between the lesion size determined by ultrasound and that measured thereafter was demonstrated with a correlation coefficient of r = 0.87 for lesion depth and r = 0.93 for lesion volume. We conclude that lesions can be assessed by B-mode ultrasound imaging.     

Wolff-Parkinson-White syndrome with an unroofed coronary sinus without persistent left superior vena cava treated with catheter cryoablation

Coronary sinus anomalies are rare congenital defects which are usually coexistent with a persistent left superior vena cava and may be associated with cardiac arrhythmias. We report an unroofed coronary sinus without persistent left superior vena cava diagnosed during a catheter ablation procedure for Wolff-Parkinson-White syndrome. Diagnostic and therapeutic options and outcomes are discussed. This condition is of relevance to electrophysiologists performing catheter-based procedures, as well as cardiologists implanting coronary sinus pacing leads, who may encounter this anomaly in their practice.     

Focal modification of electrical conduction in the heart by viral gene transfer

Modern treatment of cardiac arrhythmias is limited to pharmacotherapy, radiofrequency ablation, or implantable devices. Antiarrhythmic medications suppress arrhythmias, but their systemic effects are often poorly tolerated and their proarrhythmic tendencies increase mortality. Radiofrequency ablation can cure only a limited number of arrhythmias. Implantable devices can be curative for bradyarrhythmias and lifesaving for tachyarrhythmias, but require a lifetime commitment to repeated procedures, are a significant expense, and may lead to severe complications. One possibility is the use of gene therapy as an antiarrhythmic strategy. As an initial attempt to explore this option, we focused on genetic modification of the atrioventricular node. First, we developed an intracoronary perfusion model for gene delivery, building on our previous work in isolated cardiac myocytes and hearts perfused ex vivo. Using this method, we infected porcine hearts with Adbetagal (recombinant adenovirus expressing Escherichia coli beta-galactosidase) or with AdGi (adenovirus encoding the Galphai2 subunit). We hypothesized that excess Galphai2 would mimic the effects of beta-adreneric antagonists, in effect creating a localized beta-blockade. Galphai2 overexpression suppressed baseline atrioventricular conduction and slowed the heart rate during atrial fibrillation without producing complete heart block. In contrast, expression of the reporter gene beta-galactosidase had no electrophysiological effects. Our results demonstrate the feasibility of using myocardial gene transfer strategies to treat common arrhythmias.     

A linear ablating system in the left and right atrium: feasibility, catheter performance and clinical results

IntroductionWe describe the use of a ablating system to compartmentalise and regionally isolate the atria in paroxysmal and persistent atrial fibrillation (AF).Methods40 patients were studied, 25 paroxysmal AF and 14 persistent AF. One patient enrolled was later found to be in left atrial flutter and was excluded. The Cardima Revelation® TX catheter system with Intellitemp® Radiofrequency (RF) energy control device and a Medtronic Atakar® RF generator were used to place wide area circumferential ablations to achieve conduction block into the left and right sided pulmonary veins. Roof lines and mitral isthmus lines were also performed. In patients with persistent AF and in repeat procedures, right atrial compartmentalisation was performed with an anterior superior vena cava (SVC) to inferior vena cava (IVC) line and a septal SVC to IVC line.ResultsAt 6 months, 18 of the 39 patients were asymptomatic, 10 had improved symptoms and 22 were in sinus rhythm. In the paroxysmal group, 11 were asymptomatic, 7 had improved symptoms and 16 (64%) were in sinus rhythm. In the persistent group, 7 were asymptomatic, 3 had improved symptoms and 6 (43%) were in sinus rhythm. The total group AF burden was 37.8 ± 5.4 hrs pre-procedure and 23.1 ± 5.1 hrs at 6 months post procedure. Mean temperature, impedance and power recorded at each pole demonstrated effective power delivery at all poles. No catheter charring was observed, complication rates were comparable to standard AF ablation technique.ConclusionLinear ablation in the left and right atria to mimic Cox’s Maze is feasible and safe using this ablating system.     

Usefulness of remote magnetic navigation for ablation of ventricular arrhythmias originating from outflow regions

Monomorphic ventricular tachycardia (VT) and symptomatic monomorphic PVCs originating from the region of the right and left outflow tracts are increasingly treated by radiofrequency (RF) catheter ablation. Technical difficulties in catheter manipulation to access these outflow tract areas, very accurate mapping and reliable catheter stability are key issues for a successful treatment in this vulnerable region. VT ablation from the aortic sinus cusp (ASC) in particular carries a significant risk of perforation, of creating left coronary artery injury and of damage to the aorta and the aortic valve. This case series describes RF ablation of VT originating in the outflow region using the remote magnetic navigation system (MNS). Potential advantages of the MNS are catheter flexibility, steering accuracy and reproducibility to navigate to a desired location with a low probability of perforating the myocardium. This report supports the idea of using advanced MNS technology during RF ablation in regions which are difficult to reach and thin walled, such as parts of the outflow tract and the ASC. (Neth Heart J 2009;17:245–9.)     

Termination of Ventricular Tachycardia with Antitachycardia Pacing after Ineffective Shock Therapy in an ICD Recipient with Hypertrophic Cardiomyopathy

Implantable Cardioverter Defibrillator (ICD) implantation is the only established therapy for primary or secondary prevention of sudden cardiac death in patients with Hypertrophic Cardiomyopathy (HCM). Ineffectiveness of shock therapy for the termination of potentially fatal ventricular arrhythmias in ICD recipients is rare in the presence of appropriate arrhythmia detection by the device. We report the case of a 48-year-old woman with HCM and a single chamber ICD, who received five inefficient high-energy (35 Joules) shocks for the termination of an appropriately detected episode of Ventricular Tachycardia (VT). The episode was safely terminated with a subsequent application of Antitachycardia Pacing (ATP) by the device. At the following ICD control, an acceptable defibrillation threshold was detected.     

Importance of physical parameters for the effectiveness of radiofrequency catheter ablation]

Radiofrequency catheter ablation has been shown to be an effective form of treatment of accessory pathways in patients with WPW-syndrome and other supraventricular tachycardias. However, the biophysical parameters so far used in vivo neither correlated with the size of the myocardial lesion nor did they provide any information about contact of the electrode with the myocardial wall. In this study, 104 radiofrequency energy applications were performed on excised pig myocardium in circulating heparinized pig blood, and in blood alone, and root mean square (rms) voltage, current and phase angle were measured using a specially developed device. The calculated effective power and output power differed by only 2-7% measured at the point of maximum current during coagulation. A progressive drop in current following a rise in impedance led to a phase shift of more than 80 degrees with a decrease in effective power to 17% of the output power. Hence, apparent output power was mainly ineffective power. The time-dependent variations of phase angle, impedance and current were found to be useful for distinguishing between the coagulated media. These results show that physical parameters measured during radio-frequency catheter ablation may help to monitor electrode position in the clinical situation and reduce the number of ineffective energy applications.