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Introduction: The association between ambient circulating environments (CEs) and ablation lesions has been largely underexplored. Methods: Viable bovine myocardium was placed in a saline bath in an ex vivo endocardial model. Radiofrequency (RF) ablation was performed using three different ablation catheters: 3.5 mm open irrigated (OI), 4, and 8 mm. Variable flow rates of surrounding bath fluids were applied to simulate standard flow, high flow, and no flow. For in vivo epicardial ablation, 24 rats underwent a single OI ablation and performed with circulating saline (30 ml/min; n = 12), versus those immersed in saline without circulation (n = 12). Results: High flow reduced ablation lesion volumes for all three catheters. In no‐flow endocardial CE, both 4 mm and OI catheters produced smaller lesions compared with standard flow. However, the 8 mm catheter produced the largest lesions in a no‐flow CE. Ablation performed in an in vivo model with CE resulted in smaller lesions compared with ablation performed in a no‐flow environment. No statistically significant differences in steam pops were found among the groups. Conclusion: A higher endocardial CE flow can decrease RF effectiveness. Cardiac tissue subjected to no endocardial CE flow may also limit RF for 4 mm catheters, but not for OI catheters; these findings may have implications for RF ablation safety and efficacy, especially in the epicardial space without circulating fluid or in the endocardium under varying flow conditions. [ABSTRACT FROM AUTHOR]

Introduction: Esophageal injury is a well‐known complication associated with catheter ablation. Though novel methods to mitigate esophageal injury have been developed, few studies have evaluated temperature gradients with catheter ablation across the posterior wall of the left atrium, interstitium, and esophagus. Methods: To investigate temperature gradients across the tissue, we developed a porcine heart–esophageal model to perform ex vivo catheter ablation on the posterior wall of the left atrium (LA), with juxtaposed interstitial tissue and esophagus. Circulating saline (5 L/min) was used to mimic blood flow along the LA and alteration of ionic content to modulate impedance. Thermistors along the region of interest were used to analyze temperature gradients. Varying time and power, radiofrequency (RF) ablation lesions were applied with an externally irrigated ablation catheter. Ablation strategies were divided into standard approaches (SAs, 10–15 g, 25–35 W, 30 s) or high‐power short duration (HPSD, 10–15 g, 40–50 W, 10 s). Temperature gradients, time to the maximum measured temperature, and the relationship between measured temperature as a function of distance from the site of ablation was analyzed. Results: In total, five experiments were conducted each utilizing new porcine posterior LA wall‐esophageal specimens for RF ablation (n = 60 lesions each for SA and HPSD). For both SA and HPSD, maximum temperature rise from baseline was markedly higher at the anterior wall (AW) of the esophagus compared to the esophageal lumen (SA: 4.29°C vs. 0.41°C, p <.0001 and HPSD: 3.13°C vs. 0.28°C, p <.0001). Across ablation strategies, the average temperature rise at the AW of the esophagus was significantly higher with SA relative to HPSD ablation (4.29°C vs. 3.13°C, p =.01). From the start of ablation, the average time to reach a maximum temperature as measured at the AW of the esophagus with SA was 36.49 ± 12.12 s, compared to 16.57 ± 4.54 s with HPSD ablation, p <.0001. Fit to a linear scale, a 0.37°C drop in temperature was seen for every 1 cm increase in distance from the site of ablation and thermistor location at the AW of the esophagus. Conclusion: Both SA and HPSD ablation strategies resulted in markedly higher temperatures measured at the AW of the esophagus compared to the esophageal lumen, raising concern about the value of clinical intraluminal temperature monitoring. The temperature rise at the AW was lower with HPSD. A significant time delay was seen to reach the maximum measured temperature and a modest increase in distance between the site of ablation and thermistor location impacted the accuracy of monitored temperatures. [ABSTRACT FROM AUTHOR]

Introduction: Ablation of papillary muscles (PMs) for refractory ventricular arrhythmias can often be challenging. The catheter approach and orientation during ablation may affect optimal radiofrequency (RF) delivery. Yet, no previous study investigated the association between catheter orientation and PM lesion size. We evaluated ablation lesion characteristics with various catheter orientations relative to the PM tissue during open irrigated ablation, using a standardized, experimental setting. Methods: Viable bovine PM was positioned on a load cell in a circulating saline bath. RF ablation was performed over PM tissue at 50 W, with the open irrigated catheter positioned either perpendicular or parallel to the PM surface. Applied force was 10 g. Ablation lesions were sectioned and underwent quantitative morphometric analysis. Results: A catheter position oriented directly perpendicular to the PM tissue resulted in the largest ablation lesion volumes and depths compared with ablation with the catheter parallel to PM tissue (75.26 ± 8.40 mm3 vs. 34.04 ± 2.91 mm3, p <.001) and (3.33 ± 0.18 mm vs. 2.24 ± 0.10 mm, p <.001), respectively. There were no significant differences in initial impedance, peak voltage, peak current, or overall decrease in impedance among groups. Parallel catheter orientation resulted in higher peak temperature (41.33 ± 0.28°C vs. 40.28 ± 0.24°C, p =.003), yet, there were no steam pops in either group. Conclusion: For PM ablation, catheter orientation perpendicular to the PM tissue achieves more effective and larger ablation lesions, with greater lesion depth. This may have implications for the chosen ventricular access approach, the type of catheter used, consideration for remote navigation, and steerable sheaths. [ABSTRACT FROM AUTHOR]

Background: Epicardial adipose (EA) tissue may limit effective radiofrequency ablation (RFA). Objectives: We sought to evaluate the lesion formation of different ablation strategies on ventricular myocardium with overlying EA. Methods: Bovine myocardium with EA was placed in a circulating saline bath in an ex vivo model. Open‐irrigated (OI) RFA was performed, parallel to the myocardium, over fat at 50 W for variable RF durations, variable contact force, catheter configurations (unipolar RF vs bipolar RF), and catheter irrigants (normal saline vs half‐normal saline). Ablation was also performed with a needle‐tipped ablation catheter (NTAC), perpendicular to the myocardium. Results: Increasingly thick EA attenuated lesion size regardless of ablation strategy. RF applied with longer durations and increasing CF produced larger lesion volumes and deeper lesions with ablation over EA more than 3 mm but was unable to produce measurable lesions when EA less than 3 mm. Similarly, ablation with half normal saline irrigant created slightly deeper lesions than bipolar RF and unipolar RF with normal saline as EA thickness increased, but was unable to produce measurable lesions when EA more than 3 mm. Of all ablation strategies, only NTAC produced effective lesion volumes when ablating over thick (>3 mm) EA. Conclusions: While EA attenuates lesion depth and size, relatively larger, and deeper lesions can be achieved with longer RFA duration, higher CF, half normal saline irrigant, and, to a greater extent, by utilizing bipolar RF or NTAC, but only over thin adipose (<3 mm). Of those catheters/strategies tested, only NTAC was able to effectively deliver RF over thick (>3 mm) EA with this model. [ABSTRACT FROM AUTHOR]

Innovations in radiofrequency (RF) ablation and nonablative techniques have led to significant advances in addressing complex arrhythmogenic substrates for a variety of cardiac arrhythmias. Anatomical challenges, deep substrate, and mid‐myocardial locations may pose difficulties and decrease success rates using routine methods. In this review, we provide an update on novel RF technology and techniques including (a) high‐power, low‐duration ablation, (b) ablation facilitated by low‐ionic irrigant, and (c) bipolar ablation. In addition, we review emerging technologies including electroporation, needle catheter ablation, and ablation with the lattice catheter. [ABSTRACT FROM AUTHOR]

Introduction: Both bipolar and simultaneous radiofrequency ablation (bRFA, simRFA) have been used to treat thick midmyocardial substrate as well as during circular, multipolar ablation between shorter distances. Objectives: We sought to evaluate the biophysical parameters of simRFA, sequential unipolar RFA (seqRFA), and bRFA. Methods: Bovine myocardium was placed in a circulating saline bath. To simulate thick substrate conditions, two open irrigated ablation catheters were oriented across from each other, with myocardium in between. Thermocouples were placed in the center, ±2 mm, of the myocardium. Unipolar ablations were performed sequentially or simultaneously at 50 W for 60 seconds and compared to bRFA using the same settings. In addition, to simulate multipolar ablation, two open irrigated ablation catheters were oriented on the same side and perpendicular to myocardium at 1, 2, and 4 mm spacing. SimRFA were performed at 15 and 25 W for 60 seconds and compared to bRFA. Results: For thicker tissue, simRFA produced similar lesion volume and depth compared to bRFA but with a lesion geometry similar to seqRFA. Unlike seqRFA and simRFA, bRFA had a necrotic core spanning the myocardium. Core depths, volumes, and temperatures were significantly greater for bRFA lesions compared to simRFA or seqRFA (Figure, P < .001). Similar results were consistent for bRFA and simRFA at shorter spacings. Conclusions: BRFA has greater core lesion temperatures, corresponding to a denser and larger necrotic core, than either simRFA or seqRFA. This may have implications for considering the optimal strategy for deep midmyocardial substrates or during multipolar ablation. [ABSTRACT FROM AUTHOR]

A 62‐year‐old man was referred to our institution for high‐density, symptomatic premature ventricular contractions (PVCs) with resultant decrease in left ventricular (LV) function having failed prior ablation attempts. Successful, durable ablation of the patient's mid‐myocardial PVC arising from the LV summit region was achieved through the proximal great cardiac vein with ablation depth augmented by use of half‐normal saline irrigant. Though standard ablation of ventricular arrhythmias using normal saline irrigation from the coronary venous system has been well‐reported, this may be of limited value in addressing mid‐myocardial sites of origin. This novel case describes the safe use of cooled radiofrequency ablation with use of half‐normal saline irrigant from the distal coronary sinus as an option to address complex sites of PVC origin such as the LV summit. [ABSTRACT FROM AUTHOR]