Spherical Monopolar Irrigated RF Catheter — Ovine Ventricular Lesion Study (2019)

Authors, Journal, Affiliations, Type, DOI

• Authors: Takeshi Kitamura, Mélèze Hocini, Felix Bourier, Ruairidh Martin, Masateru Takigawa, Antonio Frontera, Nathaniel Thompson, Ghassen Cheniti, Konstantinos Vlachos, Claire A. Martin, Anna Lam, Josselin Duchateau, Thomas Pambrun, Arnaud Denis, Frédéric Sacher, Nicolas Derval, Hubert Cochet, Michel Haïssaguerre, Pierre Jaïs
• Journal: Journal of Cardiovascular Electrophysiology 2019;30:1644–1651
• Affiliations: IHU LIRYC, CHU de Bordeaux, University of Bordeaux, Bordeaux-Pessac, France
• Type: Preclinical animal study, 11 sheep, acute gross pathology
• DOI: 10.1111/jce.14089

Overview

The first ventricular lesion comparison for the Sphere-9 expandable spherical irrigated RF electrode — a 9-mm nitinol lattice that presents an effective surface area of about 275 mm² against 28 mm² for a conventional 3.5-mm tip, allowing roughly 170 W to be delivered at low current density. In 11 sheep, 20 lesions created with the sphere were compared with 25 created by a conventional irrigated catheter in healthy left ventricular endocardium: lesion volume was three times larger (1,707 vs 563 mm³) and depth roughly double (10.3 vs 5.5 mm), with no steam pops in the sphere group and one in the conventional group. The authors argue that 10-mm lesions would allow transmural ablation across almost any region of a preserved-thickness left ventricle, potentially reducing or removing the need for epicardial access — a claim that framed the subsequent clinical programme but has never been tested against epicardial ablation.

Keywords

Ablation; novel ablation catheter; spherical monopolar irrigated ablation catheter; ventricular tachycardia

Key Takeaways

Device and rationale

• 8-Fr deflectable catheter with a 9-mm expandable spherical monopolar irrigated RF tip; nine uniformly distributed mini surface electrodes plus a central reference electrode for local bipolar electrograms, and temperature measured at each of the nine surface electrodes so that delivery can be controlled by surface temperature. Open irrigation through a central nozzle at 30 mL/min.
• The stated problem is that RF failures in VT ablation reflect insufficient lesion depth, particularly in non-ischaemic cardiomyopathy where wall thickness is preserved and substrate sits mid-wall or epicardially.
• The proposed mechanism is geometric: resistive heating is proportional to the square of current density, and current density is current divided by effective surface area. Because blood and saline conduct current away from the metal, the effective area of the sphere is ~275 mm² versus ~28 mm² for a conventional irrigated tip — so much more current can be delivered before surface heating becomes limiting, producing a larger resistive-heating footprint and deeper conductive heating.

Lesion comparison

• Delivery settings: current limit 2.7 A, temperature limit 60 °C, irrigation 30 mL/min, 60–120 s; conventional comparator 30–35 W, 30 mL/min, 60 s.
• Local bipolar electrograms recorded from the catheter surface disappeared in 17 of 20 (85%) spherical-catheter lesions during delivery — the basis for using the same catheter as a lesion-assessment tool.
• Lesions were ~3× larger in volume and roughly twice as deep as with the conventional catheter; no steam pops occurred with the sphere versus one (without consequence) with the conventional catheter, and no charring or clotting was seen in any of the 11 animals.

Interpretation

• A 10-mm lesion depth "would allow transmural lesions in patients with preserved wall thickness in virtually any area of the LV", which the authors suggest could make epicardial ablation "anecdotal" and enable ablation of epicardial substrate beneath coronary arteries — currently a major limitation of epicardial RF.
• The sphere is also intended as a mapping catheter, allowing ablation at the site of signal acquisition without catheter exchange, which the authors argue improves localisation accuracy, shortens procedures and reduces air or thrombotic embolism from exchanges.
• Compared with needle ablation and bipolar RF, the authors argue the sphere avoids a second catheter, epicardial access and needle safety concerns, and is likely more forgiving of lesion contiguity than bipolar techniques.
• The catheter can reach substrate "as deep as 10 mm vs 5 mm for the conventional catheters used in clinical practice".

Limitations of the document

• Healthy ovine tissue only, assessed acutely. No scar, fatty or thinned myocardium, and no chronic healing — the substrate that actually determines clinical success.
• Unequal application duration. The spherical catheter was applied for longer (91.7 vs 63.2 s), which the authors acknowledge as the major limitation; part of the depth difference may be duration rather than electrode geometry.
• Small sample and one lesion type per animal group (20 vs 25 lesions across 6 vs 5 sheep), with no randomisation of lesion site.
• Animal model. Ovine ventricular wall thickness, blood flow and tissue conductivity differ from human scar.
• Sphere-9 developer in the authorship conflicts. Jaïs reports consulting fees from Affera; several authors report industry lecture fees and honoraria. The device's commercial owner (later Medtronic) funded it indirectly through national research grants rather than directly.
• Internal data inconsistency. The abstract reports the conventional catheter's lesion length as 8.2 ± 2.3 mm, but both Table 2 and the results text give 5.5 ± 2.4 mm for "length" — the same value as lesion depth, which suggests a transcription error. The 8.2 mm abstract value is used in this wiki; volume is reported as 537 ± 398 mm³ in the abstract and 563 ± 398 mm³ in Table 2.
• Acute lesion volume for the sphere was estimated from a single cross-sectional slice and surface area because the three-dimensional distribution was unverified, whereas conventional volumes used an established half-ellipsoid formula — so the headline 3× volume difference rests on non-equivalent volume calculations.

Key Concepts Mentioned

• concepts/VT-Ablation — the procedural problem of insufficient lesion depth
• concepts/Ventricular-PFA — the pulsed-field mode of the same platform
• concepts/Epicardial-VT-Ablation — the approach this technology was proposed to reduce
• concepts/VT-Ablation-Nonischemic-Cardiomyopathy — preserved wall thickness and intramural substrate
• concepts/Late-Gadolinium-Enhancement — imaging intramural substrate

Key Entities Mentioned

• Sphere-9 and Affera localisation system (Affera, Inc.)
• Thermocool irrigated catheter and CARTO system (Biosense Webster)
• IHU LIRYC, Bordeaux

Wiki Pages Updated

• Created: wiki/sources/lattice-tip-rf-lesion-jce-2019.md
• Created: wiki/entities/Sphere-9.md
• Updated: wiki/concepts/VT-Ablation.md, wiki/concepts/Ventricular-PFA.md, wiki/concepts/Epicardial-VT-Ablation.md
• Updated: wiki/sourceindex.md, wiki/wikiindex.md, log.md