Assaf Govari

High-Power and Short-Duration Ablation for Pulmonary Vein Isolation: Biophysical Characterization

OBJECTIVESnThis study sought to examine the biophysical properties of high-power and short-duration (HP-SD) radiofrequency ablation for pulmonary vein isolation.nnnBACKGROUNDnPulmonary vein isolation is the cornerstone of atrial fibrillation ablation. However, pulmonary vein reconnection is frequent and is often the result of catheter instability, tissue edema, and a reversible nontransmural injury. We postulated that HP-SD ablation increases lesion-to-lesion uniformity and transmurality.nnnMETHODSnThis study included 20 swine and a novel open-irrigated ablation catheter with a thermocouple system able to record temperature at the catheter-tissue interface (QDOT Micro Catheter). Step 1 compared 3 HP-SD ablation settings:xa090 W/4 s, 90 W/6 s, and 70 W/8 s in a thigh muscle preparation. Ablation at 90 W/4 s was identified as the best compromise between lesion size and safety parameters, with no steam-pop or char. In step 2, a total of 174 single ablation applications were performed in the beating heart and resulted in 3 (1.7%) steam-pops, all occurring at catheter-tissue interface temperaturexa0≥85°C. Additional 233 applications at 90 W/4 s and temperature limit of 65°C were applied without steam-pop. Step 3 compared the presence of gaps and lesion transmurality in atrial lines and pulmonary vein isolation between HP-SD (90 W/4 s, Txa0≤65°C) and standard (25 W/20 s) ablation.nnnRESULTSnHP-SD ablation resulted in 100% contiguous lines with all transmural lesions, whereas standard ablation had linear gaps in 25% and partial thickness lesions in 29%. Ablation with HP-SD produced wider lesions (6.02 ± 0.2 mm vs. 4.43 ± 1.0 mm; pxa0= 0.003) at similar depth (3.58 ± 0.3 mm vs. 3.53 ± 0.6 mm; pxa0= 0.81) and improved lesion-to-lesion uniformity with comparable safety end points.nnnCONCLUSIONSnIn a preclinical model, HP-SD ablation (90 W/4 s, Txa0≤65°C) produced an improved lesion-to-lesionxa0uniformity, linear contiguity, and transmurality at a similar safety profile of conventional ablation.

Improved cardiac magnetic resonance thermometry and dosimetry for monitoring lesion formation during catheter ablation

A new real‐time MR‐thermometry pipeline was developed to measure multiple temperature images per heartbeat with 1.6×1.6×3u2009mm3 spatial resolution. The method was evaluated on 10 healthy volunteers and during radiofrequency ablation (RFA) in sheep.

High-Resolution Mapping of Ventricular Scar: Evaluation of a Novel Integrated Multielectrode Mapping and Ablation Catheter

OBJECTIVESnThis study sought to evaluate an investigational catheter that incorporates 3 microelectrodes embedded along the circumference of a standard 3.5-mm open-irrigated catheter.nnnBACKGROUNDnMapping resolution is influenced by both electrode size and interelectrode spacing. Multielectrode mapping catheters enhance mapping resolution within scar compared with standard ablation catheters; however, this requires the use of 2 separate catheters for mapping and ablation.nnnMETHODSnSix swine with healed infarction and 2 healthy controls underwent mapping of the left ventricle using a THERMOCOOL SMARTTOUCH SF catheter with 3 additional microelectrodes (0.167 mm2) along its circumference (Qdot, Biosense Webster, Diamond Bar, California). Mapping resolution in healthy and scarred tissue was compared between the standard electrodes and microelectrodes using electrogram characteristics, cardiac magnetic resonance, and histology.nnnRESULTSnIn healthy myocardium, bipolar voltage amplitude was similar between the standard electrodes and microelectrodes, with a fifth percentile of 1.19 and 1.30 mV, respectively. In healed infarction, the area of low bipolar voltage (defined asxa0<1.5 mV) was smaller with microelectrodes (16.8 cm2 vs. 25.3 cm2; pxa0= 0.033). Specifically, the microelectrodes detected zones of increased bipolar voltage amplitude, with normal electrogram characteristics occurring at the end of or after the QRS, consistent with channels of preserved subendocardium. Identification of surviving subendocardium by the microelectrodes was consistent with cardiac magnetic resonance and histology. The microelectrodes also improved distinction between near-field and far-field electrograms, with more precise identification of scar border zones.nnnCONCLUSIONSnThis novel catheter combines high-resolution mapping and radiofrequency ablation with an open-irrigated, tissue contact-sensing technology. It improves scar mapping resolution while limiting the need forxa0andxa0cost associated with the use of a separate mapping catheter.

Prediction of radiofrequency ablation lesion formation using a novel temperature sensing technology incorporated in a force sensing catheter.

BACKGROUNDnReal-time radiofrequency (RF) ablation lesion assessment is a major unmet need in cardiac electrophysiology.nnnOBJECTIVEnThe purpose of this study was to assess whether improved temperature measurement using a novel thermocoupling (TC) technology combined with information derived from impedance change, contact force (CF) sensing, and catheter orientation allows accurate real-time prediction of ablation lesion formation.nnnMETHODSnRF ablation lesions were delivered in the ventricles of 15 swine using a novel externally irrigated-tip catheter containing 6 miniature TC sensors in addition to force sensing technology. Ablation duration, power, irrigation rate, impedance drop, CF, and temperature from each sensor were recorded. The catheter orientation factor was calculated using measurements from the different TC sensors. Information derived from all the sources was included in a mathematical model developed to predict lesion depth and validated against histologic measurements.nnnRESULTSnA total of 143 ablation lesions were delivered to the left ventricle (n = 74) and right ventricle (n = 69). Mean CF applied during the ablations was 14.34 ± 3.55g, and mean impedance drop achieved during the ablations was 17.5 ± 6.41 Ω. Mean difference between predicted and measured ablation lesion depth was 0.72 ± 0.56 mm. In the majority of lesions (91.6%), the difference between estimated and measured depth was ≤1.5 mm.nnnCONCLUSIONnAccurate real-time prediction of RF lesion depth is feasible using a novel ablation catheter-based system in conjunction with a mathematical prediction model, combining elaborate temperature measurements with information derived from catheter orientation, CF sensing, impedance change, and additional ablation parameters.

Magnetic resonance imaging-compatible circular mapping catheter: an in vivo feasibility and safety study

AimsnInterventional cardiac catheter mapping is routinely guided by X-ray fluoroscopy, although radiation exposure remains a significant concern. Feasibility of catheter ablation for common flutter has recently been demonstrated under magnetic resonance imaging (MRI) guidance. The benefit of catheter ablation under MRI could be significant for complex arrhythmias such as atrial fibrillation (AF), but MRI-compatible multi-electrode catheters such as Lasso have not yet been developed. This study aimed at demonstrating the feasibility and safety of using a multi-electrode catheter [magnetic resonance (MR)-compatible Lasso] during MRI for cardiac mapping. We also aimed at measuring the level of interference between MR and electrophysiological (EP) systems.nnnMethods and resultsnExperiments were performed in vivo in sheep (N = 5) using a multi-electrode, circular, steerable, MR-compatible diagnostic catheter.xa0The most common MRI sequences (1.5T) relevant for cardiac examination were run with the catheter positioned in the right atrium. High-quality electrograms were recorded while imaging with a maximal signal-to-noise ratio (peak-to-peak signal amplitude/peak-to-peak noise amplitude) ranging from 5.8 to 165. Importantly, MRI image quality was unchanged. Artefacts induced by MRI sequences during mapping were demonstrated to be compatible with clinical use. Phantom data demonstrated that this 10-pole circular catheter can be used safely with a maximum of 4°C increase in temperature.nnnConclusionsnThis new MR-compatible 10-pole catheter appears to be safe and effective. Combining MR and multipolar EP in a single session offers the possibility to correlate substrate information (scar, fibrosis) and EP mapping as well as online monitoring of lesion formation and electrical endpoint.

Safety and efficacy of delivering high-power short-duration radiofrequency ablation lesions utilizing a novel temperature sensing technology

AimsnDelivery of high-power short-duration radiofrequency (RF) ablation lesions is not commonly used, in part because conventional thermocouple (TC) technology underestimates tissue temperature, increasing the risk of steam pop, and thrombus formation. We aimed to test whether utilization of an ablation catheter equipped with a highly accurate novel TC technology could facilitate safe and effective delivery of high-power RF lesions.nnnMethods and resultsnAdult male Yorkshire swine were used for the study. High-power short-duration ablations (10-s total; 90u2009W for 4u2009s followed by 50u2009W for 6u2009s) were delivered using an irrigated force sensing catheter, equipped with six miniature TC sensors embedded in the tip electrode shell. Power modulation was automatically performed when the temperature reached 65°C. Ablation parameters were recorded and histopathological analysis was performed to assess lesion formation. One hundred and fourteen RF applications, delivered using the study ablation protocol in the ventricles of eight swine [53 in the right ventricle (RV), 61 in the left ventricle (LV)], were analysed. Average power delivered was 55.4u2009±u20095.3u2009W and none of the ablations resulted in a steam pop. Fourteen out of the 114 (12.3%) lesions were transmural. The mean lesion depth was 3.9u2009±u20091.1u2009mm for the 100 non-transmural lesions. Similar ablation parameters resulted in bigger impedance drop (11.6u2009Ω vs. 9.1u2009Ω, Pu2009=u20090.009) and deeper lesions in the LV compared with the RV (4.3u2009±u20091.2u2009mm vs. 3.3u2009±u20090.8u2009mm, Pu2009<u20090.001).nnnConclusionnDelivery of high-power short-duration RF energy applications, facilitated by a novel ablation catheter system equipped with advanced TC technology, is feasible, safe, and results in the formation of effective ablation lesions.