Practical ways to reduce radiation dose for patients and staff during device implantations and electrophysiological procedures

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Characteristics and time course of acute and chronic myocardial lesion formation after electroporation ablation in the porcine model

Introduction: Electroporation ablation creates deep and wide myocardial lesions. No data are available on time course and characteristics of acute lesion formation. Methods: For the acute phase of myocardial lesion development, seven pigs were investigated. Single 200 J applications were delivered at four different epicardial right ventricular sites using a linear suction device, yielding a total of 28 lesions. Timing of applications was designed to yield lesions at seven time points: 0, 10, 20, 30, 40, 50, and 60 min, with four lesions per time point. After killing, lesion characteristics were histologically investigated. For the chronic phase of myocardial lesion development, tissue samples were used from previously conducted studies where tissue was obtained at 3 weeks and 3 months after electroporation ablation. Results: Acute myocardial lesions induce a necrosis pattern with contraction band necrosis and interstitial edema, immediately present after electroporation ablation. No further histological changes such as hemorrhage or influx of inflammatory cells occurred in the first hour. After 3 weeks, the lesions consisted of sharply demarcated loose connective tissue that further developed to more fibrotic scar tissue after 3 months without additional changes. Within the scar tissue, arteries and nerves were unaffected. Conclusion: Electroporation ablation immediately induces contraction band necrosis and edema without additional tissue changes in the first hour. After 3 weeks, a sharply demarked scar has been developed that remains stable during follow-up of 3 months. This is highly relevant for clinical application of electroporation ablation in terms of the electrophysiological endpoint and waiting period after ablation

Multielectrode Contact Measurement Can Improve Long-Term Outcome of Pulmonary Vein Isolation Using Circular Single-Pulse Electroporation Ablation

Background: Irreversible electroporation (IRE) ablation is generally performed with multielectrode catheters. Electrode-tissue contact is an important predictor for the success of pulmonary vein (PV) isolation; however, contact force is difficult to measure with multielectrode ablation catheters. In a preclinical study, we assessed the feasibility of a multielectrode impedance system (MEIS) as a predictor of long-term success of PV isolation. In addition, we present the first-in-human clinical experience with MEIS. Methods: In 10 pigs, one PV was ablated based on impedance (MEIS group), and the other PV was solely based on local electrogram information (EP group). IRE ablations were performed at 200 J. After 3 months, recurrence of conduction was assessed. Subsequently, in 30 patients undergoing PV isolation with IRE, MEIS was evaluated and MEIS contact values were compared to local electrograms. Results: In the porcine study, 43 IRE applications were delivered in 19 PVs. Acutely, no reconnections were observed in either group. After 3 months, 0 versus 3 (P=0.21) PVs showed conduction recurrence in the MEIS and EP groups, respectively. Results from the clinical study showed a significant linear relation was found between mean MEIS value and bipolar dV/dt (r2=0.49, P<0.001), with a slope of 20.6 mV/s per Ohm. Conclusions: Data from the animal study suggest that MEIS values predict effective IRE applications. For the long-term success of electrical PV isolation with circular IRE applications, no significant difference in efficacy was found between ablation based on the measurement of electrode interface impedance and ablation using the classical EP approach for determining electrode-tissue contact. Experiences of the first clinical use of MEIS were promising and serve as an important basis for future research

Effects of heating on impulse propagation in superfused canine myocardium

Objectives.The goal of the study was to quantify the response of myocardial impulse propagation to hyperthermia and identify the temperatures required for transient and permanent block in conduction.Background.Although it is generally accepted that the effects of radiofrequency ablation are thermally mediated, the precise response of myocardial impulse conduction to heating remains to be quantified.Methods.Twenty-three preparations of ventricular myocardium from 10 beagle dogs were superfused at 36.5 to 37.5°C and paced at a cycle length of 600 ms. Heating was performed for 30 s at 5-min intervals by an independent flow of heated superfusate. A 16-electrode grid was used to record extracellular electrograms directly before each heating episode (control value) and at 10, 20 and 30 s.Results.Between 38.5 and 45.4°C, conduction velocity was higher than that at the directly preceding control value (p < 0.05), reaching a maximum of 114% between 41.5 and 42.5°C. Above 45.4°C, a gradual decrease occurred, with transient block (absence of impulse conduction for ≤5 min) after heating to 49.5 to 51.5°C. This was followed by tachycardia in 69% of all cases immediately after cessation of heating. Permanent block occurred after a significantly higher temperature of 51.7 to 54.4°C had been reached. Pacing at sites allowing preferential conduction either parallel or perpendicular to fiber orientation caused no difference in reaction to heating. Repeated heating of some preparations to 47.0 to 50.5°C revealed no cumulative effects on conduction velocity.Conclusions.Transient and permanent block in impulse conduction occurred at 49.5 to 51.5°C and 51.7 to 54.4°C, respectively, in superfused canine myocardium, the former frequently being followed directly by tachycardia. Reaction of conduction velocity to hyperthermia was independent of myocardial fiber orientation and number of preceding heating episodes. Results may contribute to a better understanding of electrophysiologic phenomena observed during radiofrequency ablation procedures

Feasibility of Linear Irreversible Electroporation Ablation in the Coronary Sinus

Introduction: Previous studies demonstrated that the coronary sinus (CS) is an important target for ablation in persistent atrial fibrillation. However, radiofrequency ablation in the CS is associated with coronary vessel damage and tamponade. Animal data suggest irreversible electroporation (IRE) ablation can be a safe ablation modality in vicinity of coronary arteries. We investigated the feasibility of IRE in the CS in a porcine model. Methods: Ablation and pacing was performed in the CS in six pigs (weight 60–75 kg) using a modified 9-French steerable linear hexapolar Tip-Versatile Ablation Catheter. Pacing maneuvers were performed from distal to proximal segments of the CS to assess atrial capture thresholds before and after IRE application. IRE ablations were performed with 100 J IRE pulses. After 3-week survival animals were euthanized and histological sections from the CS were analyzed. Results: A total of 27 IRE applications in six animals were performed. Mean peak voltage was 1509 ± 36 V, with a mean peak current of 22.9 ± 1.0 A. No complications occurred during procedure and 3-week survival. At 30 min post ablation 100% isolation was achieved in all animals. At 3 weeks follow-up pacing thresholds were significant higher as compared to baseline. Histological analysis showed transmural ablation lesions in muscular sleeves surrounding the CS. Conclusion: IRE ablation of the musculature along the CS using a multi-electrode catheter is feasible in a porcine model

Novel method for electrode-tissue contact measurement with multi-electrode catheters

With multi-electrode catheters, measuring contact force (CF) on each electrode is technically challenging. Present electrical methods, like the electrical coupling index (ECI) may yield false positive values in pulmonary veins. We developed a novel method that measures electrode-interface resistance (IR) by applying a very local electrical field between neighbouring catheter electrodes while measuring voltage between each catheter electrode and a skin patch. The aim of this study was to evaluate the new IR method to measure electrode-tissue contact. In vitro, effects of remote high-impedance structures were studied. In addition, both ECI and IR were directly compared with true electrode-tissue CF. In five pigs, the influence of high-impedance pulmonary tissue on ECI and IR was investigated while navigating the free floating catheter into the caval veins. Inside the left atrium (LA), IR was directly compared with CF. Finally, multi-electrode IR measurements in the LA and inferior pulmonary vein (IPV) were compared. In vitro, IR is much less affected by remote high-impedance structures than ECI (3% vs. 32%). Both IR and ECI strongly relate to electrode-tissue CF (r2=0.84). In vivo, and in contrast to ECI, IR was not affected by nearby pulmonary tissue. Inside the LA, a strong relation between IR and CF was found. This finding was confirmed by simultaneous multi-electrode measurements in LA and IPV. Data of the present study suggest that electrode-tissue contact affects the IR while being highly insensitive to remote structures. This method facilitates electrode-tissue contact measurements with circular multi-electrode ablation catheters