Mode and Characteristics of Arrhythmia Initiation in Idiopathic Ventricular Fibrillation: A THESIS Substudy.

BACKGROUND: There is limited information on the mode of arrhythmia initiation in idiopathic ventricular fibrillation (IVF). A non-pause-dependent mechanism has been suggested to be the rule. OBJECTIVES: The aim of this study was to assess the mode and characteristics of initiation of polymorphic ventricular tachycardia (PVT) in patients with short or long-coupled PVT/IVF included in THESIS (THerapy Efficacy in Short or long-coupled idiopathic ventricular fibrillation: an International Survey), a multicenter study involving 287 IVF patients treated with drugs or radiofrequency ablation. METHODS: We reviewed the initiation of 410 episodes of ≥1 PVT triplet in 180 patients (58.3% females; age 39.6 ± 13.6 years) with IVF. The incidence of pause-dependency arrhythmia initiation (prolongation by >20 ms of the preceding cycle length) was assessed. RESULTS: Most arrhythmias (n = 295; 72%) occurred during baseline supraventricular rhythm without ambient premature ventricular complexes (PVCs), whereas 106 (25.9%) occurred during baseline rhythm including PVCs. Nine (2.2%) arrhythmias occurred during atrial/ventricular pacing and were excluded from further analysis. Mode of PVT initiation was pause-dependent in 45 (15.6%) and 64 (60.4%) of instances in the first and second settings, respectively, for a total of 109 of 401 (27.2%). More than one type of pause-dependent and/or non-pause-dependent initiation (mean: 2.6) occurred in 94.4% of patients with ≥4 events. Coupling intervals of initiating PVCs were <350 ms, 350-500 ms, and >500 ms in 76.6%, 20.72%, and 2.7% of arrhythmia initiations, respectively. CONCLUSIONS: Pause-dependent initiation occurred in more than a quarter of arrhythmic episodes in IVF patients. PVCs having long (between 350 and 500 ms) and very long (>500 ms) coupling intervals were observed at the initiation of nearly a quarter of PVT episodes.

A Clinical Diagnostic Test for Calcium Release Deficiency Syndrome.

Importance: Sudden death and cardiac arrest frequently occur without explanation, even after a thorough clinical evaluation. Calcium release deficiency syndrome (CRDS), a life-threatening genetic arrhythmia syndrome, is undetectable with standard testing and leads to unexplained cardiac arrest. Objective: To explore the cardiac repolarization response on an electrocardiogram after brief tachycardia and a pause as a clinical diagnostic test for CRDS. Design, Setting, and Participants: An international, multicenter, case-control study including individual cases of CRDS, 3 patient control groups (individuals with suspected supraventricular tachycardia; survivors of unexplained cardiac arrest [UCA]; and individuals with genotype-positive catecholaminergic polymorphic ventricular tachycardia [CPVT]), and genetic mouse models (CRDS, wild type, and CPVT were used to define the cellular mechanism) conducted at 10 centers in 7 countries. Patient tracings were recorded between June 2005 and December 2023, and the analyses were performed from April 2023 to December 2023. Intervention: Brief tachycardia and a subsequent pause (either spontaneous or mediated through cardiac pacing). Main Outcomes and Measures: Change in QT interval and change in T-wave amplitude (defined as the difference between their absolute values on the postpause sinus beat and the last beat prior to tachycardia). Results: Among 10 case patients with CRDS, 45 control patients with suspected supraventricular tachycardia, 10 control patients who experienced UCA, and 3 control patients with genotype-positive CPVT, the median change in T-wave amplitude on the postpause sinus beat (after brief ventricular tachycardia at ≥150 beats/min) was higher in patients with CRDS (P < .001). The smallest change in T-wave amplitude was 0.250 mV for a CRDS case patient compared with the largest change in T-wave amplitude of 0.160 mV for a control patient, indicating 100% discrimination. Although the median change in QT interval was longer in CRDS cases (P = .002), an overlap between the cases and controls was present. The genetic mouse models recapitulated the findings observed in humans and suggested the repolarization response was secondary to a pathologically large systolic release of calcium from the sarcoplasmic reticulum. Conclusions and Relevance: There is a unique repolarization response on an electrocardiogram after provocation with brief tachycardia and a subsequent pause in CRDS cases and mouse models, which is absent from the controls. If these findings are confirmed in larger studies, this easy to perform maneuver may serve as an effective clinical diagnostic test for CRDS and become an important part of the evaluation of cardiac arrest.

Left atrial to coronary sinus shunting for treatment of heart failure with mildly reduced or preserved ejection fraction: The ALT FLOW Early Feasibility Study 1-year results.

AIMS: Patients with heart failure and mildly reduced or preserved ejection fraction have limited therapeutic options. The ALT-FLOW Early Feasibility Study evaluated safety, haemodynamics and outcomes for the APTURE transcatheter shunt system, a novel left atrium to coronary sinus shunt in these patients. METHODS AND RESULTS: Safety and shunt implantation success was evaluated for all 116 enrolled patients. An analysis population of implanted patients with a left ventricular ejection fraction (LVEF) >40% (n = 95) was chosen to assess efficacy via paired comparison between baseline and follow-up haemodynamic (3 and 6 months), and echocardiographic, clinical and functional outcomes (6 months and 1 year). Health status and quality of life outcomes were assessed using the Kansas City Cardiomyopathy Questionnaire overall summary score (KCCQ-OSS). The primary safety endpoint, major adverse cardiac, cerebral, and renal events, and reintervention through 30 days, occurred in 3/116 patients (2.6%). All implanted shunts were patent at 1 year. In patients with LVEF >40%, the mean (95% confidence interval) reduction in exercise pulmonary capillary wedge pressure (PCWP) at 20 W was -5.7 (-8.6, -2.9) mmHg at 6 months (p < 0.001). At baseline, 8% had New York Heart Association class I-II status and improved to 68% at 1 year (p < 0.001). KCCQ-OSS at baseline was 39 (35, 43) and improved at 6 months and 1 year by 25 (20-30) and 27 (22-32) points, respectively (both p < 0.0001). No adverse changes in haemodynamic and echocardiographic indices of right heart function were observed at 1 year. Overall, the reduction in PCWP at 20 W and improvement in KCCQ-OSS in multiple subgroups were consistent with those observed for the entire population. CONCLUSIONS: In patients with heart failure and LVEF >40%, the APTURE shunt demonstrated an acceptable safety profile with significant sustained improvements in haemodynamic and patient-centred outcomes, underscoring the need for further evaluation of the APTURE shunt in a randomized trial.

Impact of COVID-19 pandemic on the volume, cost, and outcomes of cardiac electrophysiology procedures in the United States.

BACKGROUND: During the COVID-19 pandemic, professional societies recommended deferral of elective procedures for optimal resource utilization. OBJECTIVE: We sought to assess changes in procedural trends and outcomes of electrophysiology (EP) procedures during the pandemic. METHODS: National Inpatient Sample databases were used to identify all EP procedures performed in the United States (2016-2020) by International Classification of Diseases, Tenth Revision codes. We evaluated trends in utilization, cost/revenue, and outcomes from EP procedures performed. RESULTS: An estimated 1.35 million EP procedures (82% devices and 18% catheter ablations) were performed (2016-2020) with significant yearly uptrend. During the pandemic, there was a substantial decline in EP procedure utilization from a 5-year peak of 298 cases/million population in the second quarter of 2019 to a nadir of 220 cases in the second quarter of 2020. In 2020, the pandemic was associated with the loss of 50,233 projected EP procedures (39,337 devices and 10,896 ablations) with subsequent revenue loss of $7.06 billion. This deficit was driven by revenue deficit from dual-chamber permanent pacemaker (PPM) utilization ($2.88 billion, 49.3% of lost cases), ablation procedures ($1.84 billion, 21.7% of lost cases), and implantable cardioverter-defibrillator implantation ($1.36 billion, 12.0% of lost cases). To the contrary, there was a 9.4% increase in the utilization of leadless PPM. EP device implantation during the pandemic was associated with higher adverse in-hospital events (9.4% vs 8.0%; P < .001). CONCLUSION: In the United States, the significant decline in EP procedures during the pandemic was primarily driven by the reduction in dual-chamber PPM utilization, followed by arrhythmia ablation and implantable cardioverter-defibrillator implantation. There was a substantial increase in leadless PPM utilization during the pandemic.

Bipolar ablation involving coronary venous system for refractory left ventricular summit arrhythmias.

Background: Catheter ablation of premature ventricular complexes (PVCs) and ventricular tachycardia (VT) from the left ventricular summit (LVS) may require advanced ablation techniques. Bipolar ablation from the coronary veins and adjacent endocardial structures can be effective for refractory LVS arrhythmias. Objective: The aim of this study was to investigate the outcomes of bipolar ablation performed between the coronary venous system and adjacent endocardial left ventricular outflow tract (LVOT) or right ventricular outflow tract (RVOT). Methods: This multicenter study included consecutive patients with LVS PVC/VT who underwent bipolar ablation between the anterior interventricular vein (AIV) or great cardiac vein (GCV) and the endocardial LVOT/RVOT after failed unipolar ablation. Ablation was started with powers of 10-20 W and uptitrated to achieve an impedance drop of at least 10%. Angiography was performed in all cases to confirm a safe distance (>5 mm) of the catheter from the major coronary arteries. Results: Between 2013 and 2023, bipolar radiofrequency ablation between the AIV/GCV and the adjacent LVOT/RVOT was attempted in 20 patients (4 female; age 57 ± 16 years). Unipolar ablation from sites of early activation (AIV/GCV, LVOT, aortic cusps, RVOT) failed to effectively suppress the PVC/VT in all subjects. Bipolar ablation was delivered with a maximum power of 30 ± 8 W and total duration of 238 ± 217 s and led to acute PVC/VT elimination in all patients. No procedural-related complications occurred. Over a follow-up period of 30 ± 24 months, the freedom from arrhythmia recurrence was 85% (1 recurrence in the VT group and 2 in the PVC group). PVC burden was reduced from 22% ± 10% to 4% ± 8% (P <.001). Conclusion: In cases of LVS PVC/VT refractory to unipolar ablation, bipolar ablation between the coronary venous system and adjacent endocardial LVOT/RVOT is safe and effective if careful titration of power and intraprocedural angiography are performed to ensure a safe distance from the coronary arteries.

Impact of concomitant surgical interventions on outcomes of septal myectomy in obstructive hypertrophic cardiomyopathy.

BACKGROUND: Septal myectomy (SM) is offered to symptomatic patients with obstructive hypertrophic cardiomyopathy (oHCM) despite medical therapy. Frequently, patients undergo concomitant planned or ad-hoc mitral valve replacement (MVR), aortic valve replacement (SAVR), or coronary artery bypass grafting (CABG). OBJECTIVES: We sought to assess characteristics and outcomes of patients with oHCM undergoing concomitant surgical interventions at the time of SM. METHODS: The National Readmission Databases were used to identify all SM admissions in the United States (2010-2019). Patients undergoing SM were stratified into: isolated SM (±MV repair), SM + CABG only, SM + MVR, SM + SAVR, and SM + MVR + SAVR. Primary outcomes were in-hospital mortality, in-hospital adverse events, and 30-day readmission. RESULTS: 12,063 encounters of patients who underwent SM were included (56.1% isolated SM, 9.0% SM + CABG only, 17.5% SM + MVR, 13.1% SM + SAVR, and 4.3% SM + MVR + SAVR). Patients who underwent isolated SM were younger (54.3 vs. 67.1 years-old, p < 0.01) and had lower overall comorbidity burden. In-hospital mortality was lowest in isolated SM, followed by CABG only, SM + SAVR, SM + MVR, and SM + SAVR+MVR groups (2.3% vs. 3.7% vs. 5.3% vs. 6.7% vs. 13.7%, p < 0.01), respectively. SM with combined surgical interventions was associated with higher adverse in-hospital events (24.3% vs. 11.1%, p < 0.01) and 30-day readmissions (16.9% vs. 10.4%, p < 0.01). MV repair performed concomitantly with SM was not associated with increased in-hospital mortality (3.9% vs. 3.4%, p = 0.72; aOR 0.99; 95% CI: 0.54-1.80, p = 0.97]) or adverse clinical events. CONCLUSIONS: In SM for oHCM, patients undergoing concomitant surgical interventions were characteristically distinct. Aside from MV repair, concomitant interventions were associated with worse in-hospital death, adverse in-hospital events, and 30-day readmission.

Efficacy and safety of dofetilide and sotalol in patients with hypertrophic cardiomyopathy.

BACKGROUND: Professional society practice guidelines conflict regarding their recommendations of dofetilide (DOF) and sotalol (STL) for treatment of arrhythmias in hypertrophic cardiomyopathy (HCM), and supporting data is sparse. We aim to assess safety and efficacy of DOF and STL on arrhythmias in HCM. METHODS: This was an observational study of HCM patients treated with DOF or STL for atrial fibrillation (AF) and ventricular arrhythmias (VA). Outcomes of drug discontinuation and arrhythmia recurrence were compared at 1 year and latest follow-up by Kaplan-Meier analysis. Predictors of drug failure were studied using uni- and multi-variable analyses. Drug-related adverse events were quantitated. RESULTS: Here we show that of our cohort of 72 patients (54 ± 14 years old, 75% male), 21 were prescribed DOF for AF, 52 STL for AF, and 18 STL for VA. At 1 year, discontinuation and recurrence rates were similar for DOF-AF (38% and 43%) and STL-AF (29% and 44%) groups. Efficacy data was similar at long-term follow-up of 1603 (IQR 994-4131) days, and for STL-VA. Drug inefficacy was the most common reason for discontinuation (28%) followed by side-effects (13%). Incidences of heart failure hospitalization (5%) and mortality (3%) were low. One STL-AF patient developed non-sustained torsades de pointes in the setting of severe pneumonia and acute kidney injury, but there were no other drug-related serious adverse events. CONCLUSIONS: DOF and STL demonstrate modest efficacy and satisfactory safety when used for AF and VA in HCM patients.

Hypertrophic cardiomyopathy (HCM) is a genetic condition that affects the heart muscle by making it abnormally thick. It often also causes abnormalities in the heartbeat, known as arrhythmias, which can cause symptoms such as dizziness and shortness of breath, or death. Historically it has been advised that some drugs that can affect the heartbeat should not be used in those with HCM, leaving people with HCM to be treated with other drugs that have undesirable side effects. We studied HCM patients who had been prescribed two of the drugs that were advised not to be used, called dofetilide and sotalol. The drugs were found to have been safe and effective over a 4-year period. These results suggest that clinical guidelines should be updated to support the use of these drugs for the treatment of arrhythmias in patients with HCM.

Comparative Outcomes of a Transthyretin Amyloid Cardiomyopathy Cohort Versus Patients With Heart Failure With Preserved Ejection Fraction Enrolled in the TOPCAT Trial.

Background Transthyretin cardiac amyloidosis (ATTR-CM), found in 6% to 15% of cohorts with heart failure with preserved ejection fraction, has long been considered a rare disease with poor prognosis. New treatments have made it one of the few directly treatable causes of heart failure. This study sought to determine whether patients with ATTR-CM, particularly those treated with tafamidis, have comparable survival to an unselected cohort with heart failure with preserved ejection fraction. Methods and Results We compared the clinical characteristics and outcomes between a single-center cohort of patients with ATTR-CM (n=114) and patients with heart failure with preserved ejection fraction enrolled in the TOPCAT (Treatment of Preserved Cardiac Function Heart Failure With an Aldosterone Antagonist) trial (n=1761, excluding Russia and Georgia). The primary outcome was a composite of all-cause death, heart failure hospitalization, myocardial infarction, and stroke. Subgroup analysis of patients with ATTR-CM treated with tafamidis was also performed. Patients with ATTR-CM had higher rates of the primary composite outcome compared with patients enrolled in the TOPCAT trial (hazard ratio [HR], 1.44 [95% CI, 1.09-1.91]; P=0.01), with similar rates of all-cause death (HR, 1.43 [95% CI, 0.99-2.06]; P=0.06) but higher rates of heart failure hospitalizations (HR, 1.62 [95% CI, 1.15-2.28]; P<0.01). Compared with patients enrolled in TOPCAT, patients with ATTR-CM treated with tafamidis had similar rates of the primary composite outcome (HR, 1.30 [95% CI, 0.86-1.96]; P=0.21) and all-cause death (HR, 1.10 [95% CI, 0.57-2.14]; P=0.78) but higher rates of heart failure hospitalizations (HR, 1.96 [95% CI, 1.27-3.02]; P<0.01). Conclusions Patients with ATTR-CM treated with tafamidis have similar rates of all-cause death compared with patients with heart failure with preserved ejection fraction, with higher rates of heart failure hospitalizations.

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.

Multi-modality imaging assessment of microbubbles and cerebral emboli in left ventricular pulsed field ablation.

BACKGROUND: Pulsed field ablation (PFA) may have a superior safety profile compared to other technologies, but it has the potential to cause gaseous microbubbles (MB), which may be associated with cerebral emboli. Limited relative safety data has been published regarding PFA in the left ventricle (LV). METHODS: Healthy and chronic myocardial infarction (MI) swine underwent PFA (monopolar, biphasic, 25 Amps) in the LV using an irrigated focal catheter under intra-cardiac echocardiography (ICE) guidance for MB monitoring. Two control swine received air MBs through the lumen of the ablation catheter. Swine underwent brain MRI before and after PFA (or control air MB injection). Gross pathology and histology of brains with abnormal MRI findings were performed. RESULTS: Four healthy and 5 chronic MI swine underwent 124 left ventricular PFA applications. No PFA-related MB formation was noted on ICE. Both control swine developed multiple acute emboli in the thalamus and caudate on DWI, ADC, and FLAIR brain MRI images in response to air MB injection. Of the 9 PFA swine, there were no abnormalities on ADC or FLAIR images. There was one hyperintense focus in the left putamen on the DWI trace image, but the absence of ADC or FLAIR affirmation suggested it was artifact. Gross pathology and histopathology of this region did not detect any abnormalities. CONCLUSIONS: Focal monopolar biphasic PFA of both healthy and chronically infarcted left ventricular myocardium does not generate any MB or cerebral emboli observable on ICE and brain MRI.

Hospital Procedural Volume and Clinical Outcomes Following Septal Reduction Therapy in Obstructive Hypertrophic Cardiomyopathy.

Background Prior national data showed a substantial in-hospital mortality in septal myectomy (SM) with an inverse volume-outcomes relationship. This study sought to assess the contemporary outcomes of septal reduction therapy and volume-outcome relationship in obstructive hypertrophic cardiomyopathy. Methods and Results All septal reduction therapy admissions between 2010 to 2019 in the United States were analyzed using the National Readmission Databases. Hospitals were stratified into tertiles of low-, medium-, and high-volume based on annualized procedural volume of alcohol septal ablation and SM. Of 19 007 patients with obstructive hypertrophic cardiomyopathy who underwent septal reduction therapy, 12 065 (63%) had SM. Two-thirds of hospitals performed ≤5 SM or alcohol septal ablation annually. In all SM encounters, 482 patients (4.0%) died in-hospital post-SM. In-hospital mortality was <1% in 1505 (88.4%) hospitals, 1% to 10% in 30 (1.8%) hospitals, and ≥10% in 167 (9.8%) hospitals. There were 63 (3.7%) hospitals (averaging 2.2 SM cases/year) with 100% in-hospital mortality. Post-SM (in low-, medium-, and high-volume centers, respectively), in-hospital mortality (5.7% versus 3.9% versus 2.4%, P=0.003; adjusted odds ratio [aOR], 2.86 [95% CI, 1.70-4.80], P=0.001), adverse in-hospital events (21.30% versus 18.0% versus 12.6%, P=0.001; aOR, 1.88 [95% CI, 1.45-2.43], P=0.001), and 30-day readmission (17.1% versus 12.9% versus 9.7%, P=0.001; adjusted hazard ratio, 1.53 [95% CI, 1.27-1.96], P=0.001) were significantly higher in low- versus high-volume hospitals. For alcohol septal ablation, the incidence of in-hospital death and all other outcomes did not differ by hospital volume. Conclusions In-hospital SM mortality was 4% with an inverse volume-mortality relationship. Mortality post-alcohol septal ablation was similar across all volume tertiles. Morbidity associated with SM was substantial across all volume tertiles.

Left Atrial to Coronary Sinus Shunting for Treatment of Symptomatic Heart Failure.

BACKGROUND: Heart failure (HF) is associated with both mortality and a significant decline in health status. Interatrial shunting is increasingly being investigated as a novel therapeutic option. OBJECTIVES: The ALT FLOW Early Feasibility Study was designed to evaluate the safety of the Edwards left atrial to coronary sinus APTURE Transcatheter Shunt System in patients with symptomatic HF. METHODS: A total of 18 centers enrolled patients with symptomatic HF with a pulmonary capillary wedge pressure >15 mm Hg at rest or 25 mm Hg during exercise. RESULTS: Between May 2018 and September 2022, 87 patients underwent attempted APTURE shunt implantation. Mean age was 71 years, and 53% were male. At baseline, mean left ventricular ejection fraction was 59% with 90% of the patients being in NYHA functional class III. Device success was achieved in 78 patients (90%), with no device occlusions or associated adverse events identified after implantation. The primary safety outcome occurred in only 2 patients (2.3%) at 30 days. At 6 months, health status improved: 67% of participants achieved NYHA functional class I to II status, with a 23-point improvement (P < 0.0001; 95% CI: 17-29 points) in the Kansas City Cardiomyopathy Questionnaire overall summary score. Also at 6 months, 20-W exercise pulmonary capillary wedge pressure was 7 mm Hg lower (P < 0.0001; 95% CI: -11 to -4 mm Hg) without change in right atrial pressure or other right heart function indices. CONCLUSIONS: In this single-arm experience, the APTURE Transcatheter Shunt System in patients with symptomatic HF was observed to be safe and resulted in reduction in pulmonary capillary wedge pressure and clinically meaningful improvements in HF symptoms and quality of life indices.

In vivo pulsed-field ablation in healthy vs. chronically infarcted ventricular myocardium: biophysical and histologic characterization.

AIMS: Data on ventricular pulsed-field ablation (PFA) are sparse in the setting of chronic myocardial infarction (MI). The objective of this study was to compare the biophysical and histopathologic characteristics of PFA in healthy and MI swine ventricular myocardium. METHODS AND RESULTS: Myocardial infarction swine (n = 8) underwent coronary balloon occlusion and survived for 30 days. We then performed endocardial unipolar, biphasic PFA of the MI border zone and a dense scar with electroanatomic mapping and using an irrigated contact force (CF)-sensing catheter with the CENTAURI System (Galaxy Medical). Lesion and biophysical characteristics were compared with three controls: MI swine undergoing thermal ablation, MI swine undergoing no ablation, and healthy swine undergoing similar PFA applications that included linear lesion sets. Tissues were systematically assessed by gross pathology utilizing 2,3,5-triphenyl-2H-tetrazolium chloride staining and histologically with haematoxylin and eosin and trichrome. Pulsed-field ablation in healthy myocardium generated well-demarcated ellipsoid lesions (7.2 ± 2.1 mm depth) with contraction band necrosis and myocytolysis. Pulsed-field ablation in MI demonstrated slightly smaller lesions (depth 5.3 ± 1.9 mm, P = 0.0002), and lesions infiltrated into the irregular scar border, resulting in contraction band necrosis and myocytolysis of surviving myocytes and extending to the epicardial border of the scar. Coagulative necrosis was present in 75% of thermal ablation controls but only in 16% of PFA lesions. Linear PFA resulted in contiguous linear lesions with no gaps in gross pathology. Neither CF nor local R-wave amplitude reduction correlated with lesion size. CONCLUSION: Pulsed-field ablation of a heterogeneous chronic MI scar effectively ablates surviving myocytes within and beyond the scar, demonstrating promise for the clinical ablation of scar-mediated ventricular arrhythmias.