Pulsed field ablation using focal contact force-sensing catheters for treatment of atrial fibrillation: acute and 90-day invasive remapping results.

AIMS: Pulsed field ablation (PFA) has emerged as a promising alternative to thermal ablation for treatment of atrial fibrillation (AF). We report performance and safety using the CENTAURI™ System (Galvanize Therapeutics) with three commercial, focal ablation catheters. METHODS AND RESULTS: ECLIPSE AF (NCT04523545) was a prospective, single-arm, multi-centre study evaluating safety and acute and chronic pulmonary vein isolation (PVI) durability using the CENTAURI System in conjunction with the TactiCath SE, StablePoint, and ThermoCool ST ablation catheters. Patients with paroxysmal or persistent AF were treated at two centres. Patients were analysed in five cohorts based upon ablation settings, catheter, and mapping system. Pulsed field ablation was performed in 82 patients (74% male, 42 paroxysmal AF). Pulmonary vein isolation was achieved in 100% of pulmonary veins (322/322) with first-pass isolation in 92.2% (297/322). There were four serious adverse events of interest (three vascular access complications and one lacunar stroke). Eighty patients (98%) underwent invasive remapping. Pulsed field ablation development Cohorts 1 and 2 showed a per-patient isolation rate of 38% and 26% and a per-PV isolation rate of 47% and 53%, respectively. Optimized PFA Cohorts 3-5 showed a per-patient isolation rate of 60%, 73%, and 81% and a per-PV isolation rate of 84%, 90%, and 92%, respectively. CONCLUSION: ECLIPSE AF demonstrated that optimized PFA using the CENTAURI System with three commercial, contact force-sensing, solid-tip focal ablation catheters resulted in transmural lesion formation and high proportion of durable PVI with a favourable safety profile, thus providing a viable treatment option for AF that integrates with contemporary focal ablation workflows.

Effects of Contact Force on Lesion Size During Pulsed Field Catheter Ablation: Histochemical Characterization of Ventricular Lesion Boundaries.

BACKGROUND: Effects of contact force (CF) on lesion formation during pulsed field ablation (PFA) have not been well validated. The purpose of this study was to determine the relationship between average CF and lesion size during PFA using a swine-beating heart model. METHODS: A 7F catheter with a 3.5-mm ablation electrode and CF sensor (TactiCath SE, Abbott) was connected to a PFA system (CENTAURI, Galvanize Therapeutics). In 5 closed-chest swine, biphasic PFA current was delivered between the ablation electrode and a skin patch at 40 separate sites in right ventricle (28 Amp) and 55 separate sites in left ventricle (35 Amp) with 4 different levels of CF: (1) low (CF range of 4-13 g; median, 9.5 g); (2) moderate (15-30 g; median, 21.5 g); (3) high (34-55 g; median, 40 g); and (4) no electrode contact, 2 mm away from the endocardium. Swine were sacrificed at 2 hours after ablation, and lesion size was measured using triphenyl tetrazolium chloride staining. In 1 additional swine, COX (cytochrome c oxidase) staining was performed to examine mitochondrial activity to delineate reversible and irreversible lesion boundaries. Histological examination was performed with hematoxylin and eosin and Masson trichrome staining. RESULTS: Ablation lesions were well demarcated with triphenyl tetrazolium chloride staining, showing (1) a dark central zone (contraction band necrosis and hemorrhage); (2) a pale zone (no mitochondrial activity and nuclear pyknosis, indicating apoptosis zone); and a hyperstained zone by triphenyl tetrazolium chloride and COX staining (unaffected normal myocardium with preserved mitochondrial activity, consistent with reversible zone). At constant PFA current intensity, lesion depth increased significantly with increasing CF. There were no detectable lesions resulting from ablation without electrode contact. CONCLUSIONS: Acute PFA ventricular lesions show irreversible and reversible lesion boundaries by triphenyl tetrazolium chloride staining. Electrode-tissue contact is required for effective lesion formation during PFA. At the same PFA dose, lesion depth increases significantly with increasing CF.

Wild-type and mutant HCN channels in a tandem biological-electronic cardiac pacemaker.

BACKGROUND: Biological pacemakers (BPM) implanted in canine left bundle branch function competitively with electronic pacemakers (EPM). We hypothesized that BPM engineered with the use of mE324A mutant murine HCN2 (mHCN2) genes would improve function over mHCN2 and that BPM/EPM tandems confer advantage over either approach alone. METHODS AND RESULTS: In cultured neonatal rat myocytes, activation midpoint was -46.9 mV in mE324A versus -66.1 mV in mHCN2 (P < 0.05). mE324A manifested a positive shift of voltage dependence of gating kinetics of activation and deactivation compared with mHCN2 (P < 0.05) in myocytes as well as Xenopus oocytes. In intact dogs in complete atrioventricular block, saline (control), mHCN2, or mE324A virus was injected into left bundle branch, and EPM were implanted (VVI 45 bpm). Twenty-four-hour ECGs were monitored for 14 days. With EPM discontinued, there was no difference in duration of overdrive suppression among groups. However, basal heart rates in controls were less than those in mHCN2, which did not differ from those in E324A (45 versus 57 versus 53 bpm; P < 0.05). When spontaneous rate fell below 45 bpm, EPM intervened at that rate, triggering 83% of beats in control, contrasting (P < 0.05) with 26% (mHCN2) and 36% (mE324A). On day 14, epinephrine (1 microg/kg per minute IV) induced a 50% heart rate increase in all mE324A, one third of mHCN2, and one fifth of control (P < 0.05 mE324A versus control or mHCN2). CONCLUSIONS: mE324A induces faster, more positive pacemaker current activation than mHCN2 and stable, catecholamine-sensitive rhythms in situ that compete with EPM comparably but more catecholamine responsively than mHCN2. BPM/EPM tandems function reliably, reduce the number of EPM beats, and confer sympathetic responsiveness to the tandem.

Differential regional gene expression from cardiac dyssynchrony induced by chronic right ventricular free wall pacing in the mouse.

Routine clinical right ventricular pacing generates left ventricular dyssynchrony manifested by early septal shortening followed by late lateral contraction, which, in turn, reciprocally stretches the septum. Dyssynchrony is disadvantageous to cardiac mechanoenergetics and worsens clinical prognosis, yet little is known about its molecular consequences. Here, we report the influence of cardiac dyssynchrony on regional cardiac gene expression in mice. Mice were implanted with a custom-designed miniature cardiac pacemaker and subjected to 1-wk overdrive right ventricular free wall pacing (720 beats/min, baseline heart rate 520-620 beats/min) to generate dyssynchrony (pacemaker: 3-V lithium battery, rate programmable, 1.5 g, bipolar lead). Electrical capture was confirmed by pulsed-wave Doppler and dyssynchrony by echocardiography. Gene expression from the left ventricular septal and lateral wall myocardium was assessed by microarray (dual-dye method, Agilent) using oligonucleotide probes and dye swap. Identical analysis was applied to four synchronously contracting controls. Of the 22,000 genes surveyed, only 18 genes displayed significant (P < 0.01) differential expression between septal/lateral walls >1.5 times that in synchronous controls. Gene changes were confirmed by quantitative PCR with excellent correlations. Most of the genes (n = 16) showed greater septal expression. Of particular interest were seven genes coding proteins involved with stretch responses, matrix remodeling, stem cell differentiation to myocyte lineage, and Purkinje fiber differentiation. One week of iatrogenic cardiac dyssynchrony triggered regional differential expression in relatively few select genes. Such analysis using a murine implantable pacemaker should facilitate molecular studies of cardiac dyssynchrony and help elucidate novel mechanisms by which stress/stretch stimuli due to dyssynchrony impact the normal and failing heart.

Chronic myocardial infarction is a substrate for bradycardia-induced spontaneous tachyarrhythmias and sudden death in conscious animals.

INTRODUCTION: Patients with bradycardia can have severe tachyarrhythmias but it is unclear whether bradycardia alone can induce arrhythmias or whether an additional substrate is necessary. While several animal models of ventricular tachycardia (VT) exist, no model has been reported to mimic the clinical condition of spontaneous VT and sudden cardiac death (SCD) in the presence of bradycardia and chronic myocardial infarction (MI) in large animals without manipulation of the autonomic nervous system. We tested the hypothesis that MI and bradycardia cause more spontaneous sustained VT than does bradycardia alone. METHODS AND RESULTS: Sheep (42-56 kg) underwent atrioventricular (AV) node catheter ablation alone (n = 5) or AV node ablation and 150 minutes of angioplasty balloon occlusion of the left anterior descending coronary artery (n = 9). An implantable cardioverter defibrillator delivered rescue shocks and demand pacing at 90 beats per minute for the first week and at 40 beats per minute thereafter. Electrograms were continuously radiotelemetered and recorded for 6 weeks. Acute post-MI VT disappeared by day 4. The sudden bradycardia on day 8 triggered numerous premature ventricular contractions (PVCs) and episodes of sustained VT lasting >30 seconds during the next 5 weeks. There were 43 episodes of sustained VT and no spontaneous ventricular fibrillation (VF) with bradycardia alone. However, in the presence of both MI and bradycardia there were 970 episodes of VT/VF (P < 0.05) and three deaths at days 13, 15, and 34. The average 24-hour count of PVCs was similar at day 7 between the two groups but by days 11 and 40, the PVC counts were 35 times and 4 times greater, respectively, in the presence of bradycardia and chronic MI compared to bradycardia alone. No significant difference in the incidence of PVCs was detected because of large individual variation between the two groups (P = 0.21). A high PVC count did not appear to predict SCD. CONCLUSION: The combination of MI and bradycardia secondary to AV node ablation in sheep produces a higher incidence of VT than bradycardia alone, suggesting that this preparation can serve as a model for the study of VT and sudden cardiac death.

Left ventricular resynchronization therapy in a canine model of left bundle branch block.

Positive responses to left (LV) and biventricular (BV) stimulation observed in heart failure patients with left bundle branch block (LBBB) suggest a possible mechanism of LV resynchronization. An anesthetized canine LBBB model was developed using radio frequency ablation. Before and after ablation, LV pressure derivative over time (dP/dt) and aortic pulse pressure (PP) were assessed during normal sinus rhythm with right ventricle (RV), LV, or BV stimulation combined with four atrioventricular delays in six dogs. In three more dogs, M-mode echocardiograms of septal and LV posterior wall motion were obtained before and after LBBB and during LV stimulation. LBBB caused QRS widening and hemodynamics deterioration. Before ablation, stimulation alone worsened LV dP/dt and PP. After ablation, LV and BV stimulation maximally increased LV dP/dt by 16% and PP by 7% (P < 0.001), whereas little improvement was observed during RV stimulation. M-mode echocardiogram showed that LBBB resulted in a paradoxical septal wall motion that was corrected by LV stimulation. In conclusion, LV and BV stimulation improved cardiac function in a canine LBBB model via resynchronization of LV excitation and contraction.