Efficacy of Pulsed Field vs Radiofrequency for the Reablation of Chronic Radiofrequency Ablation Substrate: Redo Pulsed Field Ablation.

BACKGROUND: The efficacy of pulsed field ablation (PFA) for redo procedures is unknown. OBJECTIVES: In this study, the authors aimed to evaluate the effectiveness of PFA when performing PFA over chronic RFA (redo environment). METHODS: This was a 3-step in vivo study. In step 1 (creation of redo environment), 6 swine underwent radiofrequency ablation (RFA) with a local impedance measuring catheter and a contact force-enabled catheter in 3 different sites: the right atrium (RA) (intercaval line with intentional gaps), the left atrium (LA) (pulmonary vein isolation [PVI] with intentional gaps and superficial posterior wall ablations), and the left ventricle (LV) (short RFA applications [chronic RFA]). In step 2 (re-ablation), following a survival period of ≈5 weeks, animals were retreated as follows: in the RA, a focal PFA catheter over the prior intercaval line; in the LA, PVI using a pentaspline PFA catheter; and in the LV, animals were randomized to focal PFA or RFA. In each arm, 2 types of lesions were performed: acute or acute over chronic. In step 3 (remapping and euthanization), following an additional 3 to 5 days, all animals were remapped and sacrificed. RESULTS: In the RA, re-ablation with PFA resulted in a complete intercaval block in all animals, expanding and homogenizing the disparate chronic RFA lesions from a width of 4 to 7 mm (chronic RFA) to a width of 16 to 28 mm (PFA over chronic RFA). In the LA, re-ablation with PFA resulted in complete PVI and transmural ablation of the PW. In the LV, the mean depth for acute RFA (post 2-5 days survival) was 7.6 ± 1.3 mm vs 3.9 ± 1.6 mm in the acute over chronic RFA lesions (P < 0.01). In contrast, the mean depth for acute PFA was 7.0 ± 1.6 mm, similar to when ablating with PFA over RFA (7.1 ± 1.3 mm; P = 0.94). CONCLUSIONS: PFA is highly efficient for ablation following prior RFA, which may be beneficial in patients presenting for redo procedures. In the ventricle, PFA resulted in lesions that are deeper than RFA when ablating over chronic superficial RFA lesions.

Effect of sodium glucose cotransporter 2 inhibitors on atrial tachy-arrhythmia burden in patients with cardiac implantable electronic devices.

INTRODUCTION: Use of sodium glucose cotransporter 2 inhibitors (SGLT2i) was associated with a reduction in atrial fibrillation hospitalizations. Therefore, we aim to evaluate the effects of SGLT2i on atrial tachy-arrhythmias (ATA) in patients with cardiac implantable electronic devices (CIEDs). METHODS: All 13 888 consecutive patients implanted with a CIED in two tertiary medical centers were enrolled. Treatment with SGLT2i was assessed as a time dependent variable. The primary endpoint was the total number of ATA. Secondary endpoints included total number of ventricular tachy-arrhythmias (VTA), ATA and VTA, and death. All events were independently adjudicated blinded to the treatment. Multivariable propensity score modeling was performed. RESULTS: During a total follow-up of 24 442 patient years there were 62 725 ATA and 10 324 VTA events. Use of SGLT2i (N = 696) was independently associated with a significant 22% reduction in the risk of ATA (hazard ratio [HR] = 0.78 [95% confidence interval {CI} = 0.70-0.87]; p < .001); 22% reduction in the risk of ATA/VTA (HR = 0.78 [95% CI = 0.71-0.85]; p < .001); and with a 35% reduction in the risk of all-cause mortality (HR = 0.65 [95% CI = 0.45-0.92]; p = .015), but was not significantly associated with VTA risk (HR = 0.92 [95% CI = 0.80-1.06]; p = .26). SGLT2i were associated with a lower ATA burden in heart failure (HF) patients but not among diabetes patients (HF: HR = 0.68, 95% CI = 0.58-0.80, p < .001 vs. Diabetes: HR = 0.95, 95% CI = 0.86-1.05, p = .29; p < .001 for interaction between SGLT2i indication and ATA burden). CONCLUSION: Our real world findings suggest that in CIED HF patients, those with SGLT2i had a pronounced reduction in ATA burden and all-cause mortality when compared with those not on SGLT2i.

Lattice-tip catheter for single-shot pulmonary vein isolation with pulsed field ablation.

BACKGROUND: A compressible lattice-tip catheter designed for focal ablation using radiofrequency or pulsed-field energies has been recently described. The objective of this study is to describe a new lattice catheter designed for single-shot pulmonary vein isolation (PVI). METHODS: This 8F catheter consists of a compressible lattice tip that is delivered over the wire and is expandable up to 34 mm (SpherePVI™, Affera Inc.). Pulsed field ablation (PFA) was applied from 6 elements using a biphasic waveform of microsecond scale (± 1.3-2.0 kV, 5 s per application). In 12 swine, the superior vena cava (SVC) and right superior pulmonary vein (RSPV) were targeted for isolation. Animals were survived for 12-24 h (n = 6) or 3 weeks (n = 6) for evaluation of short and long-term safety and efficacy parameters. PVI was evaluated immediately after ablation and at the terminal procedure. Ablation-related microbubbles were examined using intracardiac echocardiography and phrenic nerve function by pacing. The tissue was examined by histopathology. RESULTS: In all 12 animals, PFA resulted in successful acute isolation of the SVC and RSPV using 2.8 ± 1.1 and 3.2 ± 1.2 applications per vein, respectively. After a survival period of 23 ± 5.9 days, all targeted veins remained isolated, and the level of isolation persisted without significant regression or expansion. In one animal, SVC isolation at the level of the right atrial appendage resulted in sinus node arrest. PFA did not affect phrenic nerve function, and it was associated with a few isolated bubbles formation. CONCLUSIONS: In this pre-clinical study, a new expandable lattice catheter designed for single-shot PVI was able to achieve rapid and durable isolation.

Effect of Pulsed-Field and Radiofrequency Ablation on Heterogeneous Ventricular Scar in a Swine Model of Healed Myocardial Infarction.

BACKGROUND: Pulsed-field ablation (PFA) is a nonthermal energy with higher selectivity to myocardial tissue in comparison to radiofrequency ablation (RFA). We compared the effects of PFA and RFA on heterogeneous ventricular scar in a swine model of healed infarction. METHODS: In 9 swine, myocardial infarction was created by balloon occlusion of the left anterior descending artery. After a survival period of 8 to 10 weeks, ablation with PFA or RFA was performed at infarct border zones identified by abnormal electrograms. In the PFA group (4 swine), ablation was performed with a lattice catheter (Sphere-9, Affera, Inc). In the RFA group (5 swine), ablation was performed using a 3.5-mm tip catheter (Thermocool ST-SF; Biosense Webster). To further investigate the effect of RFA on temperature development in scar tissue, intramyocardial temperature was measured in healthy and infarcted myocardium using an ex vivo bath model. RESULTS: A total of 11 PFA and 15 RFA lesions were created at infarct border zones with heterogeneous scar. PFA produced uniform and well-demarcated lesions exhibiting irreversible injury characterized by cardiomyocyte death, contraction bands, and lymphocytic infiltration. This effect of PFA extended from the subendocardium through collagen and fat to the epicardial layers. In contrast, the effect of RFA is less uniform and largely limited to the subendocardium with minimal effect on viable myocardium deeper to separating layers of collagen and fat. PFA produced deeper and more transmural lesions (6.4 [interquartile range, 5.5-7.5) versus 5.4 [interquartile range, 4.8-5.9]), 72% versus 30%, respectively; P≤0.02 for each comparison). The limited effect of RFA on viable myocardium at deeper infarct layers was related to a lower intramyocardial maximal temperature compared with healthy myocardium (P=0.01). CONCLUSIONS: PFA may be advantageous for ablation in ventricular scar, producing lesions that unlike RFA are not limited to the subendocardium, but also eliminate viable myocardium separated from the catheter by collagen and fat.

Increasing Lesion Dimensions of Bipolar Ablation by Modulating the Surface Area of the Return Electrode.

OBJECTIVES: This study sought to examine the effect of the return electrode's surface area on bipolar RFA lesion size. BACKGROUND: Bipolar radiofrequency ablation (RFA) is typically performed between 2 3.5-mm tip catheters serving as active and return electrodes. We hypothesized that increasing the surface area of the return electrode would increase lesion dimensions by reducing the circuit impedance, thus increasing the current into a larger tissue volume enclosed between the electrodes. METHODS: In step 1, ex vivo bipolar RFA was performed between 3.5-mm and custom-made return electrodes with increasing surface areas (20, 80, 180 mm2). In step 2, ex vivo bipolar RFA was performed between 3.5-mm and 3.5-mm or 8-mm electrode catheters positioned perpendicular or parallel to the tissue. In step 3, in vivo bipolar RFA was performed between 3.5-mm and either 3.5-mm or 8-mm parallel electrode at the: 1) left ventricular summit; 2) interventricular septum; and 3) healed anterior infarction. RESULTS: In step 1, increasing the surface area of the return electrode resulted in lower circuit impedance (R = -0.65; P < 0.001), higher current (R = +0.80; P < 0.001), and larger lesion volume (R = +0.88; P < 0.001). In step 2, an 8-mm return electrode parallel to tissue produced larger and deeper lesions compared with a 3.5-mm return electrode (P = 0.014 and P = 0.02). Similarly, in step 3, compared with a 3.5-mm, bipolar RFA with an 8-mm return electrode produced larger (volume: 1,525 ± 871 mm3 vs 306 ± 310 mm3, respectively; P < 0.001) and more transmural lesions (88% vs 0%; P < 0.001). CONCLUSIONS: Bipolar RFA using an 8-mm return electrode positioned parallel to the tissue produces larger lesions in comparison with a 3.5-mm return electrode.

How to use bipolar and unipolar electrograms for selecting successful ablation sites of ventricular premature contractions.

BACKGROUND: Local activation time is often determined by the maximal negative of the extracellular unipolar potential (-dV/dTmax). While this is accurate in 2-dimensional uniform tissue, propagation through nonuniform or 3-dimensional structures have shown discordance between -dV/dTmax and local activation time. OBJECTIVE: The purpose of this study was to examine the relationship between bipolar and unipolar electrograms for selecting successful ablation sites of endocardial (superficial) vs intramural (deep) ventricular premature contractions (VPCs). METHODS: This cohort consisted of 66 patients with VPCs presenting for ablation in a bigeminy, trigeminy, or quadrigeminy pattern. VPCs were classified as endocardial if ablation at the earliest endocardial site resulted in immediate suppression (<10 seconds) or as intramural if ablation resulted in delayed suppression (≥10 seconds), required multiple applications, or was not achieved. Unipolar and bipolar electrograms were analyzed. RESULTS: In endocardial VPCs, the first rapid bipolar deflection corresponded with unipolar -dV/dTmax, occurring 20.5 ms (17.8-26.0 ms) and 16.0 ms (6.8-22.0 ms), respectively, before the QRS onset. In successfully ablated intramural VPCs, the first rapid bipolar deflection preceded the QRS onset by 14.0 ms (11.2-22.6 ms) and coincided with the first rapid unipolar deflection, although -dV/dTmax occurred 10.5 ms (0.0-20.8 ms) after the QRS onset and often coincided with far-field activity. In unsuccessfully ablated intramural VPCs, the first rapid bipolar deflection to QRS onset interval was shorter in comparison to successfully ablated intramural VPCs (1.5 ms vs 14.0 ms; P < .001) while the unipolar -dV/dTmax to QRS onset interval was similar (P = .095). CONCLUSION: Mapping of VPCs should be guided by the first rapid bipolar deflection that corresponds to a similarly early unipolar deflection but not with -dV/dTmax.

Direction-aware mapping algorithms have minimal impact on bipolar voltage maps created using high-resolution multielectrode catheters.

INTRODUCTION: Direction-aware mapping algorithms improve the accuracy of voltage mapping by measuring the maximal voltage amplitude recorded in the direction of wavefront propagation. While beneficial for stationary catheters, its utility for roving catheters collecting electrograms (EGMs) at multiple angles is unknown. OBJECTIVE: To compare the directional dependence of bipolar voltage amplitude between stationary and roving catheters. METHODS: In 10 swine, a transcaval ablation line with a gap was created. The gap was mapped using an array catheter (Optrell™; Biosense Webster). In Step 1, the array was kept stationary over the gap, and four voltage maps were created during activation of the gap from superior, inferior, septal, and lateral directions. In Step 2, four additional maps were created; however, the catheter was allowed to move with points acquired at multiple angles. In Step 3, the gap was remapped; however, bipoles were computed using a direction-aware mapping algorithm. RESULTS: In a stationary catheter position, bipolar voltage distribution was influenced by the direction of activation with maximal differences obtained between orthogonal directions 32% (13%-53%). However, roving the catheter produced similar bipolar voltage maps irrespective of the direction of activation 11% (5%-18%). A direction-aware mapping algorithm was beneficial for reducing the directional dependence of voltage maps created by stationary catheters but not by roving catheters. CONCLUSION: The directional dependency of bipolar voltage amplitude is greatest when the catheter is stationary. However, when the catheter is allowed to rove and collect EGMs at multiple angles as occurs clinically, the directional dependence of bipolar voltage is minimal.

Impact of High-Power Short-Duration Radiofrequency Ablation on Esophageal Temperature Dynamic.

BACKGROUND: High-power short-duration (HP-SD) radiofrequency ablation (RFA) has been proposed as a method for producing rapid and effective lesions for pulmonary vein isolation. The underlying hypothesis assumes an increased resistive heating phase and decreased conductive heating phase, potentially reducing the risk for esophageal thermal injury. The objective of this study was to compare the esophageal temperature dynamic profile between HP-SD and moderate-power moderate-duration (MP-MD) RFA ablation strategies. METHODS: In patients undergoing pulmonary vein isolation, RFA juxtaposed to the esophagus was delivered in an alternate sequence of HP-SD (50 W, 8-10 s) and MP-MD (25 W, 15-20 s) between adjacent applications (distance, ≤4 mm). Esophageal temperature was recorded using a multisensor probe (CIRCA S-CATH). Temperature data included magnitude of temperature rise, maximal temperature, time to maximal temperature, and time return to baseline. In swine, a similar experimental design compared the effect of HP-SD and MP-MD on patterns of esophageal injury. RESULTS: In 20 patients (68.9±5.8 years old; 60% persistent atrial fibrillation), 55 paired HP-SD and MP-MD applications were analyzed. The esophageal temperature dynamic profile was similar between HP-SD and MP-MD ablation strategies. Specifically, the magnitude of temperature rise (2.1 °C [1.4-3] versus 2.0 °C [1.5-3]; P=0.22), maximal temperature (38.4 °C [37.8-39.3] versus 38.5 °C [37.9-39.4]; P=0.17), time to maximal temperature (24.9±7.5 versus 26.3±6.8 s; P=0.1), and time of temperature to return to baseline (110±23.2 versus 111±25.1 s; P=0.86) were similar between HP-SD and MP-MD ablation strategies. In 6 swine, esophageal injury was qualitatively similar between HP-SD and MP-MD strategies. CONCLUSIONS: Esophageal temperature dynamics are similar between HP-SD and MP-MD RFA strategies and result in comparable esophageal tissue injury. Therefore, when using a HP-SD RFA strategy, the shorter application duration should not prompt shorter intervals between applications.

Pulsed-Field Ablation in Ventricular Myocardium Using a Focal Catheter: The Impact of Application Repetition on Lesion Dimensions.

[Figure: see text].

Propagation Vectors Facilitate Differentiation Between Conduction Block, Slow Conduction, and Wavefront Collision.

[Figure: see text].

Impact of High-Power Short-Duration Radiofrequency Ablation on Long-Term Lesion Durability for Atrial Fibrillation Ablation.

OBJECTIVES: The goal of this study was to compare lesion durability between high-power short-duration (HP-SD) and moderate-power moderate-duration (MP-MD) ablation strategies. BACKGROUND: HP-SD radiofrequency ablation (RFA) was developed to improve pulmonary vein isolation (PVI) by reducing the effect of catheter instability inherent to MP-MD ablation strategies. However, its long-term effect on lesion durability for the treatment of atrial fibrillation is unknown. METHODS: Patients with atrial fibrillation (n = 112) underwent PVI using HP-SD ablation (45 to 50 W, 8 to 15 s) with contact force-sensing open irrigated catheter. Cavotricuspid isthmus, mitral annular, and roof lines were permitted. A control group (n = 112) underwent ablation using MP-MD ablation (20 to 40 W, 20 to 30 s) with similar technology. Chronic PV reconnection was examined in patients who required a redo procedure (HP-SD ablation, n = 18; MP-MD ablation, n = 23). RESULTS: The rate of PVI at the completion of the initial encirclement was similar between the HP-SD and MP-MD ablation strategies (90.2% vs. 83.0%; p = 0.006). The HP-SD strategy required shorter RFA time (17.2 ± 3.4 min vs. 31.1 ± 5.6 min; p < 0.001). The incidence of chronic PV reconnection was lower with HP-SD ablation (16.6% vs. 52.2%; p = 0.03). Areas of chronic reconnection were associated with catheter motion ≥1 mm for ≥50% application duration. In a higher proportion of HP-SD applications, catheter motion was <1 mm during ≥50% duration (88.6% vs. 72.8%; p < 0.001), allowing energy delivery with greater stability. Both ablation strategies were effective for cavotricuspid isthmus; however, the HP-SD strategy was less effective for mitral annular lines, requiring ablation at lower power for longer duration to avoid steam pops. CONCLUSIONS: HP-SD ablation may improve PVI durability, and it shortens RFA time. However, ablation in thicker myocardium often requires lower power applied for longer duration, allowing deeper lesions without tissue overheating.