Predictors of nonpulmonary vein triggers for atrial fibrillation: A clinical risk score

BACKGROUND

Targeting nonpulmonary vein triggers (NPVTs) after pulmonary vein isolation may reduce atrial fibrillation (AF) recurrence. Isoproterenol infusion and cardioversion of spontaneous or induced AF can provoke NPVTs but typically require vasopressor support and increased procedural time.

OBJECTIVE

The purpose of this study was to identify risk factors for the presence of NPVTs and create a risk score to identify higher-risk subgroups.

METHODS

Using the AF ablation registry at the Hospital of the University of Pennsylvania, we included consecutive patients who underwent AF ablation between January 2021 and December 2022. We excluded patients who did not receive NPVT provocation testing after failing to demonstrate spontaneous NPVTs. NPVTs were defined as nonpulmonary vein ectopic beats triggering AF or focal atrial tachycardia. We used risk factors associated with NPVTs with P <.1 in multivariable logistic regression model to create a risk score in a randomly split derivation set (80%) and tested its predictive accuracy in the validation set (20%).

RESULTS

In 1530 AF ablations included, NPVTs were observed in 235 (15.4%). In the derivation set, female sex (odds ratio [OR] 1.40; 95% confidence interval [CI] 0.96-2.03; P = .080), sinus node dysfunction (OR 1.67; 95% CI 0.98-2.87; P = .060), previous AF ablation (OR 2.50; 95% CI 1.70-3.65; P <.001), and left atrial scar (OR 2.90; 95% CI 1.94-4.36; P <.001) were risk factors associated with NPVTs. The risk score created from these risk factors (PRE2SSS2 score; [PRE]vious ablation: 2 points, female [S]ex: 1 point, [S]inus node dysfunction: 1 point, left atrial [S]car: 2 points) had good predictive accuracy in the validation cohort (area under the receiver operating characteristic curve 0.728; 95% CI 0.648-0.807).

CONCLUSION

A risk score incorporating predictors for NPVTs may allow provocation of triggers to be performed in patients with greatest expected yield.

Identifying Origin of Nonpulmonary Vein Triggers Using 2 Stationary Linear Decapolar Catheters: A Novel Algorithm

BACKGROUND

Targeting nonpulmonary vein triggers (NPVTs) of atrial fibrillation (AF) after pulmonary vein isolation can be challenging. NPVTs are often single ectopic beats with a surface P-wave obscured by a QRS or T-wave.

OBJECTIVES

The goal of this study was to construct an algorithm to regionalize the site of origin of NPVTs using only intracardiac bipolar electrograms from 2 linear decapolar catheters positioned in the posterolateral right atrium (along the crista terminalis with the distal bipole pair in the superior vena cava) and in the proximal coronary sinus (CS).

METHODS

After pulmonary vein isolation in 42 patients with AF, pacing from 15 typical anatomic NPVT sites was conducted. For each pacing site, the electrogram activation sequence was analyzed from the CS catheter (simultaneous/chevron/inverse chevron/distal-proximal/proximal-distal) and activation time (ie, CSCTAT) between the earliest electrograms from the 2 decapolar catheters was measured referencing the earliest CS electrogram; a negative CSCTAT value indicates the crista terminalis catheter electrogram was earlier, and a positive CSCTAT value indicates the CS catheter electrogram was earlier. A regionalization algorithm with high predictive value was defined and tested in a validation cohort with AF NPVTs localized with electroanatomic mapping.

RESULTS

In the study patient cohort (71% male; 43% with persistent AF, 52% with left atrial dilation), the algorithm grouped with high precision (positive predictive value 81%-99%, specificity 94%-100%, and sensitivity 30%-94%) the 15 distinct pacing sites into 9 clinically useful regions. Algorithm testing in a 98 patient validation cohort showed predictive accuracy of 91%.

CONCLUSIONS

An algorithm defined by the activation sequence and timing of electrograms from 2 linear multipolar catheters provided accurate regionalization of AF NPVTs to guide focused detailed mapping.

Impact of Median Sternotomy on Safety and Efficacy of the Subcutaneous Implantable Cardioverter Defibrillator

BACKGROUND

Subcutaneous implantable cardioverter defibrillators (S-ICDs) are an attractive alternative to transvenous ICDs among those not requiring pacing. However, the risks of damage to the S-ICD electrode during sternotomy and adverse interactions with sternal wires remain unclear. We sought to determine the rates of damage to the S-ICD lead during sternotomy, inappropriate shocks from electrical noise due to interaction with sternal wires, and failure to terminate spontaneous or induced ventricular arrhythmias.

METHODS

Retrospective, multicenter study of patients undergoing sternotomy before or after S-ICD implantation. Clinical, procedural, and device-related data were collected by each center and analyzed by the coordinating center. These data were compared with a historical control cohort of nonsternotomy patients.

RESULTS

Of 196 identified patients (52±16 years, 47 women), 166 underwent S-ICD implantation after sternotomy and 30 sternotomy after S-ICD. There was no damage to any lead among those who underwent sternotomy after S-ICD. Defibrillation threshold testing was performed in 63% at implant, with 91% first shock success. During a median follow-up of 29 months (range, 1-188), S-ICD first shocks successfully terminated spontaneous ventricular arrhythmias in 31 of 32 patients (97%). Inappropriate shocks occurred in 22 patients, most commonly related to T wave oversensing (n=14). Compared with the nonsternotomy controls, there were no differences in rates of first shock success for induced or spontaneous arrhythmias or rate of inappropriate shocks.

CONCLUSIONS

Sternotomy before or after S-ICD does not confer additional risk relative to a historical control group without sternotomy.

Effects of Pulsed Electric Fields on the Coronary Arteries in Swine

BACKGROUND

Previous animal studies have shown no significant vascular injury from pulsed electrical field (PEF) ablation. We sought to assess the effect of PEF on swine coronary arteries.

METHODS

We performed intracoronary and epicardial (near the coronary artery) PEF ablations in swine pretreated with dual antiplatelet and antiarrhythmic therapy. Intracoronary PEF was delivered using MapiT catheters (Biotronik, Berlin), whereas epicardial PEF was delivered using EPT catheters (Boston Scientific, MA). PEF pulse duration was microseconds (Nanoknife 3.0, Angio Dynamics, NY) or nanoseconds (CellFX, Pulse Biosciences, CA).

RESULTS

We performed 39 intracoronary ablations in 10 swine and 20 epicardial-pericoronary ablations in 4 separate swine. Intracoronary PEF was delivered at higher energy compared with epicardial PEF (46 [interquartile range, IQR 20-85] J versus 10 [IQR 10-11] J, P < 0.01). Reversible coronary spasm occurred in 49% intracoronary ablations and 45% epicardial ablations (P=0.80). At the end study, fixed coronary stenosis was demonstrated in 44% intracoronary ablations (80% for microsecond PEF and 18% for nanosecond PEF) and 0% epicardial ablations. Visible hemorrhagic and/or fibrotic myocardial lesions were observed at necropsy with similar frequency between intracoronary and epicardial PEF (45% versus 50%, P=0.70). Nanosecond PEF (49 ablations in 11 swine), when compared with microsecond PEF (10 intracoronary ablations in 3 swine), resulted in lower energy delivery (21 [IQR 10-46] J versus 129 [IQR 24-143] J, P=0.03) and less incidence of fixed coronary stenosis (18% versus 80%, P=0.04).

CONCLUSIONS

In the swine model, intracoronary PEF resulted both in significant coronary spasm and fixed coronary stenosis. Epicardial PEF, delivered at lower energy, resulted in reversible spasm but no fixed coronary stenosis.

Cardiac ablation with pulsed electric fields: principles and biophysics

Pulsed electric fields (PEFs) have emerged as an ideal cardiac ablation modality. At present numerous clinical trials in humans are exploring PEF as an ablation strategy for both atrial and ventricular arrhythmias, with early data showing significant promise. As this is a relatively new technology there is limited understanding of its principles and biophysics. Importantly, PEF biophysics and principles are starkly different to current energy modalities (radiofrequency and cryoballoon). Given the relatively novel nature of PEFs, this review aims to provide an understanding of the principles and biophysics of PEF ablation. The goal is to enhance academic research and ultimately enable optimization of ablation parameters to maximize procedure success and minimize risk.

Outcomes of Direct Oral Anticoagulants Co-Prescribed with Common Interacting Medications

Direct oral anticoagulants (DOACs) can potentially interact with multiple prescription medications. We examined the prevalence of co-prescription of DOACs with interacting medications and its impact on outcomes in patients with atrial fibrillation (AF). Patients with AF treated with a DOAC from 2010 to 2017 at the Mayo Clinic and co-prescribed medications that are inhibitors or inducers of the P-glycoprotein and/or Cytochrome P450 3A4 pathways were identified. The outcomes of stroke, transient ischemic attack, or systemic embolism, major bleeding, and minor bleeds were compared between patients with and without an enzyme inducer. Cox proportional hazards model was used to assess the association between interacting medications and outcomes. Of 8,576 patients with AF (mean age 70 ± 12 years, 35% female) prescribed a DOAC (38.6% apixaban, 35.8% rivaroxaban, 25.6% dabigatran), 2,610 (30.4%) were on at least 1 interacting agent: the majority were on an enzyme inhibitor (n = 2,592). Prescribed medications included non-dihydropyridine calcium channel blocker (n = 1,412; 16.5%), antiarrhythmic medication (n = 790; 9.2%), antidepressant (n = 659; 7.7%), antibiotic/antifungal (n = 77; 0.90%), antiepileptics (n = 17; 0.2%) and immunosuppressant medications (n = 19; 0.2%). Patients on an interacting medication were more likely to receive a lower dose of DOAC than indicated by the manufacturer's labeling (15.0% vs 11.4%, p <0.0001). In multivariable analysis, co-prescription of an enzyme inhibitor was not associated with risk of any bleeding (hazard ratio 0.87 [0.71 to 1.05], p = 0.15) or stroke, transient ischemic attack, or systemic embolism (hazard ratio 0.82 [0.51 to 1.31], p = 0.39). In conclusion, DOACs are co-prescribed with medications with potential interactions in 30.4% of patients with AF. Co-prescription of DOACs and these drugs are not associated with increased risk of adverse embolic or bleeding outcomes in our cohort.

Incremental benefit of a novel signal recording system during mapping and ablation

AIMS

Current electrophysiology signal recording and mapping systems have limited dynamic range (DR) and bandwidth, which causes loss of valuable information during acquisition of cardiac signals. We evaluated a novel advanced signal processing platform with the objective to obtain and assess additional information of clinical importance.

METHODS AND RESULTS

Over 10 canines, we compared intracardiac recordings within all cardiac chambers, in various rhythms, in pacing and during radiofrequency (RF) ablation across two platforms; a conventional system and the PURE EP™ [(PEP); Bio Sig Technologies, Inc., Los Angeles, CA, USA]. Recording cardiac signals with varying amplitudes were consistently and reproducibly observed, without loss of detail or introduction of artefact. Further the amplitude of current of injury (COI) on the unipolar signals correlated with the instantaneous contact force (CF) recorded on the sensing catheter in all the animals (r2 = 0.94 in ventricle). The maximum change in the unipolar COI correlated with the change in local electrogram amplitude during non-irrigated RF ablation (r2 = 0.61 in atrium). Reduction in artefact attributable to pacing (20 sites) and noise during ablation (48 sites) was present on the PEP system. Within the PEP system, simultaneous display of identical signals, filtered differently, aided the visualization of discrete conduction tissue signals.

CONCLUSION

Compared to current system, the PEP system provided incremental information including identifying conduction tissue signals, estimates of CF and a surrogate for lesion formation. This novel signal processing platform with increased DR and minimal front-end filtering may be useful in clinical practice.

Sustained Improvement in Diastolic Reserve Following Percutaneous Pericardiotomy in a Porcine Model of Heart Failure With Preserved Ejection Fraction

BACKGROUND

Heart failure with preserved ejection fraction is increasing in prevalence, but few effective treatments are available. Elevated left ventricular (LV) diastolic filling pressures represent a key therapeutic target. Pericardial restraint contributes to elevated LV end-diastolic pressure, and acute studies have shown that pericardiotomy attenuates the rise in LV end-diastolic pressure with volume loading. However, whether these acute effects are sustained chronically remains unknown.

METHODS

Minimally invasive pericardiotomy was performed percutaneously using a novel device in a porcine model of heart failure with preserved ejection fraction. Hemodynamics were assessed at baseline and following volume loading with pericardium intact, acutely following pericardiotomy, and then again chronically after 4 weeks. Cardiac structure was assessed by magnetic resonance imaging.

RESULTS

The increase in LV end-diastolic pressure with volume loading was mitigated by 41% (95% CI, 27%-45%, P<0.0001; ΔLV end-diastolic pressure reduced from +9±3 mm Hg to +5±3 mm Hg, P=0.0003, 95% CI, -2.2 to -5.5). The effect was sustained at 4 weeks (+5±2 mm Hg, P=0.28 versus acute). There was no statistically significant effect of pericardiotomy on ventricular remodeling compared with age-matched controls. None of the animals developed hemodynamic or pathological indicators of pericardial constriction or frank systolic dysfunction.

CONCLUSIONS

The acute hemodynamic benefits of pericardiotomy are sustained for at least 4 weeks in a swine model of heart failure with preserved ejection fraction, without excessive chamber remodeling, pericarditis, or clinically significant systolic dysfunction. These data support trials evaluating minimally invasive pericardiotomy as a novel treatment for heart failure with preserved ejection fraction in humans.

A cool modality to restore sinus rhythm

Background

Slowing electrical conduction by cooling the myocardium can be used for defibrillation. We previously demonstrated the efficacy of a small cold device placed in oblique sinus (OS) in terminating atrial fibrillation (AF). However, the parameters needed to achieve effective atrial defibrillation are unknown.

Purpose

Assess effect of the size of cooled myocardium on frequency of AF termination in acute canine animal models.

Methods

Sternotomy was performed under general anesthesia in 10 acute canine experiments. AF was induced using rapid atrial pacing and intra-myocardial epinephrine and acetylcholine injections. Once AF sustained for at least 30s, either a cool (7–9°C) or placebo (body temperature) device was placed in the OS. Four device sizes were tested; ½X½, ¾X¾, and 1X1 inch devices and two ¾X¾ inch devices placed side by side simultaneously. Time to AF termination was recorded. Chi-squared or Fisher's exact test were used to compare the frequency of arrhythmia termination with cooling versus placebo.

Results

A total of 166 applications were performed (89 cool vs 77 placebo) in 10 animal experiments. Overall, AF terminated in 82% of the cooling applications vs. 67.5% of placebo (P=0.03, Figure 1). For the ½X½ inch device 88% of cold applications restored sinus rhythm vs. 63.6% for placebo (P=0.05). The frequency of sinus restoration for cold ¾X¾, 1X1 and two ¾X¾ side by side devices was 86.7%, 83.3% and 70% respectively. Time to sinus restoration when achieved was within three minutes was also not significantly changed.

Conclusion

Placing a cool device in the oblique sinus can terminate AF and efficacy is not affected by the size of device.

Funding Acknowledgement

Type of funding source: Private grant(s) and/or Sponsorship. Main funding source(s): MediCool Technologies

Combined local impedance and contact force for radiofrequency ablation assessment

BACKGROUND

The combination of contact force (CF) and local impedance (LI) may improve tissue characterization and lesion prediction during radiofrequency (RF) ablation.

OBJECTIVE

The purpose of this study was to evaluate the utility of LI combined with CF in assessing RF ablation efficacy.

METHODS

An LI catheter with CF sensing was evaluated in swine (n = 11) and in vitro (n = 14). The relationship between LI and CF in different tissue types was evaluated in vivo. Discrete lesions were created in vitro and in vivo at a range of forces, powers, and durations. Finally, an intercaval line was created in 3 groups at 30 W: 30s, Δ20Ω, and Δ30Ω. In the Δ20Ω and Δ30Ω groups, the user ablated until a 20 or 30 Ω LI drop. In the 30s group, the user was blinded to LI.

RESULTS

In vivo, distinction in LI was found between the blood pool and the myocardium (blood pool: 122 ± 7.02 Ω; perpendicular contact: 220 ± 29 Ω; parallel contact: 207 ± 31 Ω). LI drop correlated with lesion depth both in vitro (R = 0.84) and in vivo (R = 0.79), informing sufficient lesion creation (LI drop >20 Ω) and warning of excessive heating (LI drop >65 Ω). When creating an intercaval line, the total RF time was significantly reduced when using LI guidance (6.4 ± 2 minutes in Δ20Ω and 8.1 ± 1 minutes in Δ30Ω) compared with a standard 30-second workflow (18 ± 7 minutes). Acute conduction block was achieved in all Δ30Ω and 30s lines.

CONCLUSION

The addition of LI to CF provides feedback on both electrical and mechanical loads. This provides information on tissue type and catheter-tissue coupling; provides feedback on whether volumetric tissue heating is inadequate, sufficient, or excessive; and reduces ablation time.

Fundamentals of Cardiac Mapping

To characterize cardiac activity and arrhythmias, electrophysiologists can record the electrical activity of the heart in relation to its anatomy through a process called cardiac mapping (electroanatomic mapping, EAM). A solid understanding of the basic cardiac biopotentials, called electrograms, is imperative to construct and interpret the cardiac EAM correctly. There are several mapping approaches available to the electrophysiologist, each optimized for specific arrhythmia mechanisms. This article provides an overview of the fundamentals of EAM.

Feasibility of selective cardiac ventricular electroporation

Introduction

The application of brief high voltage electrical pulses to tissue can lead to an irreversible or reversible electroporation effect in a cell-specific manner. In the management of ventricular arrhythmias, the ability to target different tissue types, specifically cardiac conduction tissue (His-Purkinje System) vs. cardiac myocardium would be advantageous. We hypothesize that pulsed electric fields (PEFs) can be applied safely to the beating heart through a catheter-based approach, and we tested whether the superficial Purkinje cells can be targeted with PEFs without injury to underlying myocardial tissue.

Methods

In an acute (n = 5) and chronic canine model (n = 6), detailed electroanatomical mapping of the left ventricle identified electrical signals from myocardial and overlying Purkinje tissue. Electroporation was effected via percutaneous catheter-based Intracardiac bipolar current delivery in the anesthetized animal. Repeat Intracardiac electrical mapping of the heart was performed at acute and chronic time points; followed by histological analysis to assess effects.

Results

PEF demonstrated an acute dose-dependent functional effect on Purkinje, with titration of pulse duration and/or voltage associated with successful acute Purkinje damage. Electrical conduction in the insulated bundle of His (n = 2) and anterior fascicle bundle (n = 2), was not affected. At 30 days repeat cardiac mapping demonstrated resilient, normal electrical conduction throughout the targeted area with no significant change in myocardial amplitude (pre 5.9 ± 1.8 mV, 30 days 5.4 ± 1.2 mV, p = 0.92). Histopathological analysis confirmed acute Purkinje fiber targeting, with chronic studies showing normal Purkinje fibers, with minimal subendocardial myocardial fibrosis.

Conclusion

PEF provides a novel, safe method for non-thermal acute modulation of the Purkinje fibers without significant injury to the underlying myocardium. Future optimization of this energy delivery is required to optimize conditions so that selective electroporation can be utilized in humans the treatment of cardiac disease.

P2862Complementary use of contact force and local catheter impedance during RF ablation reduces ablation time in an in vivo swine model

Acknowledgement/Funding

This study was funded by Boston Scientific.

Anatomic Considerations Relevant to Atrial and Ventricular Arrhythmias

Knowledge of relevant cardiac anatomy is crucial in understanding the pathophysiology and treatment of arrhythmias, and helps avoid potential complications in mapping and ablation. This article explores the anatomy, relevant to electrophysiologists, relating to atrial flutter and atrial fibrillation, ventricular tachycardia relating to the outflow tracts as well as endocardial structure, and also epicardial considerations for mapping and ablation.

Development of a novel ablation hood to prevent systemic embolization of microbubbles and particulate emboli

BACKGROUND

Atrial fibrillation ablation results in microbubbles and particulate emboli formation. We aimed to develop and test the early feasibility of a novel ablation hood to contain microbubbles and particulate emboli with the ultimate goal of preventing systemic embolization.

METHODS

In seven canines, we developed, iterated, and tested a novel retractable hood that can cover the catheter-tissue ablation site. The number and volume (nL) of microbubbles formed during ablation with and without the hood was measured using an extracorporeal circulation loop. Wilcoxon's signed-rank test was used to compare the number of bubbles detected with and without the hood.

RESULTS

The hood reduced systemic embolization of microbubbles in 21/28 (75%) of ablations. Both atrial and ventricular ablations showed a statistically significant reduction in bubble number (476 ± 811 without hood vs 173 ± 226 with hood, p = 0.02; 2669 ± 1623 without hood vs 1417 ± 970 with hood, p = 0.04, respectively) and bubble volume (3.3 ± 7.6 nL without hood vs 0.2 ± 0.56 nL with hood, p = 0.006; 6.1 ± 5.2 nL without hood vs 1.9 ± 1.4 nL with hood, p = 0.05, respectively).

CONCLUSIONS

Use of a novel hood to cover the ablation catheter at the site of catheter-tissue contact has the potential to provide a means to reduce systematic embolization of microbubbles. Further work is required to examine particulate emboli, but these data show the early feasibility of this design concept.

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.

Anatomy and Physiologic Roles of the Left Atrial Appendage: Implications for Endocardial and Epicardial Device Closure

The left atrial appendage has been implicated as a major nidus for thrombus formation, particularly in atrial fibrillation. This discovery has prompted substantial interest in the development of left atrial appendage exclusion devices aimed at decreasing systemic thromboembolism risk. Its deceptively simple appearance belies the remarkable complexity that characterizes its anatomy and physiology. We highlight the key anatomic features and variations of the left atrial appendage as well as its relationships with surrounding structures. We also summarize crucial anatomic factors that should be taken into account by the interventional cardiologist when planning for or performing left atrial appendage exclusion procedures.

Comparing the incidence of ventricular arrhythmias during epicardial ablation in swine versus canine models

BACKGROUND

Choosing the appropriate animal model for development of novel technologies requires an understanding of anatomy and physiology of these different models. There are little data about the characteristics of different animal models for the study of technologies used for epicardial ablation. We aimed to compare the incidence of ventricular arrhythmias during epicardial radiofrequency ablation between swine and canine models using novel epicardial ablation catheters.

METHODS

We conducted a retrospective study using data obtained from epicardial ablation experiments performed on swine (Sus Scrofa) and canine (Canis familiaris) models. We compared the incidence of ventricular arrhythmias during ablation between swine and canine using multivariate regression analysis. Six swine and six canine animals underwent successful epicardial radiofrequency ablation. A total of 103 ablation applications were recorded.

RESULTS

Ventricular arrhythmias requiring cardioversion occurred in 13.11% of radiofrequency ablation applications in swine and 9.75% in canine (relative risk: 117.6%, 95% confidence interval [CI]: 83.97-164.69, animal-based odds ratio [OR]: .55, 95% CI: .23-61.33; P = .184). When adjusting for application position, duration of ablation and power, the odds of developing potentially lethal ventricular arrhythmia in swine increased significantly compared to canine (OR: 3.60, 95% CI: 1.35-9.55; P = .010).

CONCLUSIONS

The swine myocardium is more susceptible to developing ventricular arrhythmias compared to canine model during epicardial ablation. This issue should be carefully considered in future studies.

His Bundle (Conduction System) Pacing: A Contemporary Appraisal

The His bundle (conduction system) is an attractive target for physiologic pacing because it uses the native conduction system. Although the potential benefits of conduction system pacing were recognized in the 1970s, in the past 2 decades, it has grown in interest as a potentially preferred method of ventricular stimulation in appropriate patients. This review provides an appraisal of conduction system pacing, with focus on anatomy, physiology, tools, and techniques as well as an appraisal of current published data and thoughts on future directions.

Putting down the phone: the obsolescence of transtelephonic monitoring for pacemaker follow-up

PURPOSE

The evolution of heart rhythm monitoring technology over the past few decades has seen a decline in the use and need of transtelephonic monitoring (TTM). We sought to establish a predicted date for the sun setting of TTM at our institution, as well as establish the current demographics of the patients still using this technology.

METHODS

We retrospectively reviewed all patients with permanent pacemakers receiving routine device follow-up at our institution (Mayo Clinic-Rochester) between 2015 and 2018. From this cohort, we reviewed and analyzed patients using TTM for device follow-up and utilized projected battery longevity to determine cessation date. Pacemaker implantation date, underlying arrhythmia, and most recent device interrogation reports were also collected.

RESULTS

As of March 2018, a total of 3543 patients with permanent pacemakers were being followed at our institution and 289 (8.2%) are using TTM for monitoring device function (147 male, mean age 79.9 ± 12.0 years). Of those currently using TTM, by January of 2020, only 122 (42.2%) are predicted to be using this technology for device follow-up, 40 (13.8%) by January 2022, with zero patients by November of 2024.

CONCLUSIONS

The use of TTM will continue to significantly diminish over the next few years. Based on battery longevity estimates, we predict that by the end of 2024 TTM will no longer be used for device follow-up at our institution.

Noninvasive assessment of dofetilide plasma concentration using a deep learning (neural network) analysis of the surface electrocardiogram: A proof of concept study

Background

Dofetilide is an effective antiarrhythmic medication for rhythm control in atrial fibrillation, but carries a significant risk of pro-arrhythmia and requires meticulous dosing and monitoring. The cornerstone of this monitoring, measurement of the QT/QTc interval, is an imperfect surrogate for plasma concentration, efficacy, and risk of pro-arrhythmic potential.

Objective

The aim of our study was to test the application of a deep learning approach (using a convolutional neural network) to assess morphological changes on the surface ECG (beyond the QT interval) in relation to dofetilide plasma concentrations.

Methods

We obtained publically available serial ECGs and plasma drug concentrations from 42 healthy subjects who received dofetilide or placebo in a placebo‐controlled cross‐over randomized controlled clinical trial. Three replicate 10-s ECGs were extracted at predefined time-points with simultaneous measurement of dofetilide plasma concentration We developed a deep learning algorithm to predict dofetilide plasma concentration in 30 subjects and then tested the model in the remaining 12 subjects. We compared the deep leaning approach to a linear model based only on QTc.

Results

Fourty two healthy subjects (21 females, 21 males) were studied with a mean age of 26.9 ± 5.5 years. A linear model of the QTc correlated reasonably well with dofetilide drug levels (r = 0.64). The best correlation to dofetilide level was achieved with the deep learning model (r = 0.85).

Conclusion

This proof of concept study suggests that artificial intelligence (deep learning/neural network) applied to the surface ECG is superior to analysis of the QT interval alone in predicting plasma dofetilide concentration.

Elimination of Purkinje Fibers by Electroporation Reduces Ventricular Fibrillation Vulnerability

Background The Purkinje network appears to play a pivotal role in the triggering as well as maintenance of ventricular fibrillation. Irreversible electroporation ( IRE ) using direct current has shown promise as a nonthermal ablation modality in the heart, but its ability to target and ablate the Purkinje tissue is undefined. Our aim was to investigate the potential for selective ablation of Purkinje/fascicular fibers using IRE . Methods and Results In an ex vivo Langendorff model of canine heart (n=8), direct current was delivered in a unipolar manner at various dosages from 750 to 2500 V, in 10 pulses with a 90-μs duration at a frequency of 1 Hz. The window of ventricular fibrillation vulnerability was assessed before and after delivery of electroporation energy using a shock on T-wave method. IRE consistently eradicated all Purkinje potentials at voltages between 750 and 2500 V (minimum field strength of 250-833 V/cm). The ventricular electrogram amplitude was only minimally reduced by ablation: 0.6±2.3 mV ( P=0.03). In 4 hearts after IRE delivery, ventricular fibrillation could not be reinduced. At baseline, the lower limit of vulnerability to ventricular fibrillation was 1.8±0.4 J, and the upper limit of vulnerability was 19.5±3.0 J. The window of vulnerability was 17.8±2.9 J. Delivery of electroporation energy significantly reduced the window of vulnerability to 5.7±2.9 J ( P=0.0003), with a postablation lower limit of vulnerability=7.3±2.63 J, and the upper limit of vulnerability=18.8±5.2 J. Conclusions Our study highlights that Purkinje tissue can be ablated with IRE without any evidence of underlying myocardial damage.

Intrapulmonary Vein Ablation Without Stenosis: A Novel Balloon-Based Direct Current Electroporation Approach

Background

Current thermal ablation methods for atrial fibrillation, including radiofrequency and cryoablation, have a suboptimal success rate. To avoid pulmonary vein (PV) stenosis, ablation is performed outside of the PV, despite the importance of triggers inside the vein. We previously reported on the acute effects of a novel direct current electroporation approach with a balloon catheter to create lesions inside the PVs in addition to the antrum. In this study, we aimed to determine whether the effects created by this nonthermal ablation method were associated with irreversible lesions and whether PV stenosis or other adverse effects occurred after a survival period.

Methods and Results

Initial and survival studies were performed in 5 canines. At the initial study, the balloon catheter was inflated to contact the antrum and interior of the PV. Direct current energy was delivered between 2 electrodes on the catheter in ECG‐gated 100 μs pulses. A total of 10 PVs were treated demonstrating significant acute local electrogram diminution (mean amplitude decrease of 61.2±19.8%). After the survival period (mean 27 days), computed tomography imaging showed no PV stenosis. On histologic evaluation, transmural, although not circumferential, lesions were seen in each treated vein. No PV stenosis or esophageal injury was present.

Conclusions

Irreversible, transmural lesions can be created inside the PV without evidence of stenosis after a 27‐day survival period using this balloon‐based direct current ablation approach. These early data show promise for an ablation approach that could directly treat PV triggers in addition to traditional PV antrum ablation.

Atrial Fibrillation: Beyond Rate Control

Atrial fibrillation is the most common cardiac dysrhythmia encountered in the primary care setting. Although a rate control strategy is pursued by physicians for the initial treatment of atrial fibrillation, the efficacy of a rhythm control approach is often undervalued despite offering effective treatment options. There are many pharmacological therapies available to patients, with drug choice often dictated by safety concerns (toxicities and proarrhythmic adverse effects) as well as patient characteristics and comorbidities. This article presents a simplified approach to understanding the rhythm control strategy, including the advantages and disadvantages of various antiarrhythmic drugs and common drug-drug interactions encountered in the primary care setting.

Impact of sedation vs. general anaesthesia on percutaneous epicardial access safety and procedural outcomes

Aims

Patient movement while under moderate/deep sedation may complicate percutaneous epicardial access (EpiAcc), mapping and ablation. We sought to compare procedural outcomes in patients undergoing EpiAcc under sedation vs. general anaesthesia (GA) for ablation.

Methods and results

Patients undergoing EpiAcc between January 2004 and July 2014 were included. Safety, procedural, and clinical outcomes were compared between patients undergoing EpiAcc under sedation or GA for ventricular tachycardia or premature ventricular complex ablation. Between January 2004 and July 2014, 170 patients underwent EpiAcc (mean age, 53.2 ± 15.8 years; average ejection fraction, 44.3 ± 15.3%). The majority (122 [72%] patients) were male. GA was used in 69 (40.6%). There was no difference in route of access (more often anterior, 53.0%) or the rate of successful access (96% overall) between groups. Similarly, the site of ablation (endocardial vs. epicardial vs. combined endocardial/epicardial) was similar between groups. Complications were equally seen between groups-the most frequent event/complication was pericardial effusion, occurring in 10.6% of patients. Finally, procedural and clinical success rates between GA and sedation groups were comparable (93 vs. 91% and 44 vs. 51%, respectively, P > 0.05).

Conclusions

Choice of anaesthesia for EpiAcc does not appear to significantly affect safety and procedural or clinical outcomes. For patients in whom anaesthesia may pose increased risk, it is reasonable to obtain epicardial access under sedation.

Abstract 60: Inducible Arrythmogenicity of Direct Current Electroporation Ablation: Insight from a Series of Acute Canine Studies

Background: The use of direct current electroporation has the potential for significant utility because of its non-thermal approach to tissue destruction. However, the fear of inducibility of cardiac arrhythmias (particular ventricular fibrillation) when using electroporation remains of concern due to membrane poration and ion flux during periods of vulnerability occurring in ventricular repolarization.

Objectives: Critically examine the incidence of arrhythmias in a series of acute canine studies to retrospectively determine cause and safe electoporative dosing margins.

Methods: We performed electroporation ablation in 6 acute canine studies. These were experimental studies performed at sites critical in arrhytmogenesis. Sites included the pulmonary veins, left atrial appendage, superior vena cavae, right atrium and ventricle. Electroporation was delivered using an ECG gating algorithm so that QRS complexes are tagged and direct current energy is not delivered during the vulnerable portion of the T wave.

Results: In 6 acute canine experiments, we delivered a total of 62 electroporation applications for ablation purposes. The average electroporation dosage delivered involved an average of 1427 Volts (range 750-3000 V), Pulse length of 100 ms, and number of pulses of 20.2 (range 10-100). AF was induced in 27.4% of electroporiatve applications. Atrial flutter/tachycardia occurred in 8.1%. VF occurred in only one application at a location of the left superior pulmonary vein.

Conclusion: These data suggest that induction of VF is relatively uncommon with ECG gating and highlight its importance when using this modality. However, the induction of AF occurs with higher frequency. The actual mechanism as to why this occurs requires further systematic study.

Abstract 55: Use of a Novel Electrogram Filter to Visualise the Conduction Tissue Signals in the Ventricle in Sinus Rhythm and Arrhythmia: Canine Studies

Background: Conduction tissue in the ventricles is closely intertwined with myocardium. Owing to high velocity of conduction, there is near simultaneous activation , making it difficult to discern. Restricted sampling rates and limited dynamic range make real time signal processing challenging for these signals in routine recording systems.

Objectives: We aimed to use novel signal processing techniques in a new system to isolate the conduction tissue signals from the rest of the myocardial activation.

Methods: We used the PURE-EP™ (BioSig Technologies, MN) signal processing system to record endocardial and epicardial signals from 6 anesthetized canines in an acute study setting. A novel filter based on proprietary algorithms to isolate the high frequency signal was applied at sites where the electrogram signals were thought to have a conduction tissue component to them. . In addition, ventricular fibrillation (VF) was induced at the end of the experiment and signals were then recorded from the endocardium and the conduction system.

Results: This filter was successfully able to isolate conduction tissue signals in the myocardium from those of the ventricular muscle. It did over sense atrial signals at the basal left ventricular septum owing to the high frequency components of the atrial signal at this location. When applied to epicardial signals, it did not pick up any conduction tissue signals. In VF, we could discern signals originating from the conduction system endocardially. (Figure 1)

Conclusions: This filter can isolate conduction tissue signals from those of the myocardium and may prove to be a useful adjunct in mapping arrhythmias originating near the conduction system.

Outflow tract ventricular arrhythmias : Electrocardiographic features in relation to mapping and ablation

Ventricular arrhythmia arising from the outflow tracts can manifest itself as frequent premature ventricular complexes (PVCs), salvos of ventricular tachycardia (VT), and/or sustained VT. It is amenable to management with medication and catheter ablation without need for an intracardiac defibrillator. The electrocardiogram (ECG) is a crucial tool in the management of these patients as it is can help localize the site of origin, thereby helping guide the electrophysiologist. An appreciation of the unique anatomy of the outflow tracts as well as their relationships with the surrounding structures is essential in interpreting the ECG. In this review, we examine the ECG features of the various outflow tract arrhythmia morphologies with a focus on anatomy and provide an approach to the ablation of these abnormal rhythms.

Automated T-wave analysis can differentiate acquired QT prolongation from congenital long QT syndrome

BACKGROUND

Prolongation of the QT on the surface electrocardiogram can be due to either genetic or acquired causes. Distinguishing congenital long QT syndrome (LQTS) from acquired QT prolongation has important prognostic and management implications. We aimed to investigate if quantitative T-wave analysis could provide a tool for the physician to differentiate between congenital and acquired QT prolongation.

METHODS

Patients were identified through an institution-wide computer-based QT screening system which alerts the physician if the QTc ≥ 500 ms. ECGs were retrospectively analyzed with an automated T-wave analysis program. Congenital LQTS was compared in a 1:3 ratio to those with an identified acquired etiology for QT prolongation (electrolyte abnormality and/or prescription of known QT prolongation medications). Linear discriminant analysis was performed using 10-fold cross-validation to statistically test the selected features.

RESULTS

The 12-lead ECG of 38 patients with congenital LQTS and 114 patients with drug-induced and/or electrolyte-mediated QT prolongation were analyzed. In lead V₅ , patients with acquired QT prolongation had a shallower T wave right slope (-2,322 vs. -3,593 mV/s), greater T-peak-Tend interval (109 vs. 92 ms), and smaller T wave center of gravity on the x axis (290 ms vs. 310 ms; p < .001). These features could distinguish congenital from acquired causes in 77% of cases (sensitivity 90%, specificity 58%).

CONCLUSION

T-wave morphological analysis on lead V₅ of the surface ECG could successfully differentiate congenital from acquired causes of QT prolongation.

Initial Experience with the BioSig PURE EP™ Signal Recording System: An Animal Laboratory Experience

Current signal recording and processing systems have come a long way since their initial inception and use. There is, however, still ample scope for improvement, not only in the troubleshooting of their limitations, but also in the expansion of the boundaries in the recording of intracardiac signals. Here, we recount our experience with the use of the PURE EP™ signal recording system (BioSig Technologies, Inc., Minneapolis, MN, USA) in the animal laboratory.

Utility of T-wave amplitude as a non-invasive risk marker of sudden cardiac death in hypertrophic cardiomyopathy

Objective

Sudden cardiac arrest (SCA) is the most devastating outcome in hypertrophic cardiomyopathy (HCM). We evaluated repolarisation features on the surface electrocardiogram (ECG) to identify the potential risk factors for SCA.

Methods

Data was collected from 52 patients with HCM who underwent implantable cardioverter defibrillator (ICD) implantation. Leads V2 and V5 from the ECG closest to the time of ICD implant were utilised for measuring the Tpeak-Tend interval (Tpe), QTc, Tpe/QTc, T-wave duration and T-wave amplitude. The presence of the five traditional SCA-associated risk factors was assessed, as well as the HCM risk-SCD score.

Results

16 (30%) patients experienced aborted cardiac arrest over 8.5±4.1 years, with 9 receiving an ICD shock and 7 receiving ATP. On univariate analysis, T-wave amplitude was associated with appropriate ICD therapy (HR per 0.1 mV 0.79, 95% CI 0.56 to 0.96, p=0.02). Aborted SCA was not associated with a greater mean QTc duration, Tpeak-Tend interval, T-wave duration, or Tpe/QT ratio. Multivariate analysis (adjusting for cardinal HCM SCA-risk factors) showed T-wave amplitude in Lead V2 was an independent predictor of risk (adjusted HR per 0.1 mV 0.74, 95% CI 0.57 to 0.97, p=0.03). Addition of T-wave amplitude in Lead V2 to the traditional risk factors resulted in significant improvement in risk stratification (C-statistic from 0.65 to 0.75) but did not improve the performance of the HCM SCD-risk score.

Conclusions

T-wave amplitude is a novel marker of SCA in this high risk HCM population and may provide incremental predictive value to established risk factors. Further work is needed to define the role of repolarisation abnormalities in predicting SCA in HCM.

Outcomes of Combined Endocardial-Epicardial Ablation Compared With Endocardial Ablation Alone in Patients Who Undergo Epicardial Access

Percutaneous epicardial access (EpiAcc) is used in an attempt to improve outcomes of ablation. We aim to report our experience in EpiAcc for management of symptomatic ventricular premature complexes (VPC) and ventricular tachycardia (VT). All patients from January 2004 to July 2014 who underwent EpiAcc as part of a VPC or VT ablation procedure were included. Outcomes between those with endocardial-only (Gp1) and endocardial/epicardial (Gp2) ablation and those for VPC and VT ablation were compared. EpiAcc for VPC or VT ablation was attempted in 173 patients; 10 patients were excluded because of failure of access (n = 7) or no ablation performed (n = 3). Of the remaining 163, 131 patients (80.4%) had undergone previous endocardial ablation. Mean age was 53.7 ± 15.7 years; 115 (71%) were men. VT ablation was the indication in 105 patients (64%). The underlying substrate was predominately nonischemic cardiomyopathy (49.1%). Epicardial ablation was performed in 115 (70.6%). Procedural and clinical success was obtained in 92.0% and 69.9% of patients, respectively, with no difference between Gp1 and Gp2. Those who underwent VPC ablation had superior clinical outcomes at 1-year follow-up. EpiAcc is feasible in almost all patients with no previous cardiac surgery and permits acute procedural success in >90% of patients, most of whom had failed previous ablation. However, epicardial ablation was not delivered in 1/3 of patients. Epicardial mapping may be helpful as in the absence of an appropriate epicardial site for ablation, and focus can be shifted to more detailed endocardial mapping and ablation.

Identification of Concealed and Manifest Long QT Syndrome Using a Novel T Wave Analysis Program

Background—

Congenital long QT syndrome (LQTS) is characterized by QT prolongation. However, the QT interval itself is insufficient for diagnosis, unless the corrected QT interval is repeatedly ≥500 ms without an acquired explanation. Further, the majority of LQTS patients have a corrected QT interval below this threshold, and a significant minority has normal resting corrected QT interval values. Here, we aimed to develop and validate a novel, quantitative T wave morphological analysis program to differentiate LQTS patients from healthy controls.

Methods and Results—

We analyzed a genotyped cohort of 420 patients (22±16 years, 43% male) with either LQT1 (61%) or LQT2 (39%). ECG analysis was conducted using a novel, proprietary T wave analysis program that quantitates subtle changes in T wave morphology. The top 3 discriminating features in each ECG lead were determined and the lead with the best discrimination selected. Classification was performed using a linear discriminant classifier and validated on an untouched cohort. The top 3 features were Tpeak–Tend interval, T wave left slope, and T wave center of gravity x axis (last 25% of the T wave). Lead V6 had the best discrimination. It could distinguish 86.8% of LQTS patients from healthy controls. Moreover, it distinguished 83.33% of patients with concealed LQTS from controls, despite having essentially identical resting corrected QT interval values.

Conclusions—

T wave quantitative analysis on the 12-lead surface ECG provides an effective, novel tool to distinguish patients with either LQT1/LQT2 from healthy matched controls. It can provide guidance while mutation-specific genetic testing is in motion for family members.