Sphere-9 (AFFERA Lattice-Tip Ablation System)
Details
Sphere-9 is the ablation catheter at the centre of the AFFERA electroanatomical mapping and ablation system, developed by Affera (Watertown, MA) and now owned by Medtronic. It is an 8-Fr bidirectional deflectable catheter whose distal electrode is an expandable nitinol lattice that opens into a 9-mm sphere. The lattice carries nine surface sensors that serve both as microelectrodes and as thermocouples, arranged in two rings of four plus one at the tip about 5 mm apart, with a central protected irrigation nozzle. Because blood and saline conduct current away from the metal, the lattice presents an effective ablating surface area of ≈275 mm² — roughly ten times that of a 3.5-mm irrigated tip — and a central electrode that by design never contacts tissue, which helps separate near-field from far-field electrograms. (sources/lattice-tip-rf-lesion-circep-2019, rating: medium)
The system is dual-energy: a unified generator and control architecture switches between high-current temperature-controlled radiofrequency and high-voltage pulsed field trains, with impedance, temperature and voltage feedback governing delivery. The catheter maps with the same tip it ablates with, so lesions can be created at the exact site of signal acquisition without a catheter exchange. Approvals cover the EU and USA. (sources/pfa-af-ehra-2026, rating: very high)
Under the 2026 consensus classification the device is a large-tip focal catheter (largest tissue-contact dimension >4 and ≤12 mm). (sources/pfa-af-ehra-2026)
Key Facts
The RF mode — why the geometry matters
- At 40 W into a 28 mm² tip, current is roughly 600 mA at ~20 mA/mm²; the lattice can deliver up to 3,700 mA at a maximum of 13 mA/mm². Higher total current at lower current density is the entire design rationale: more resistive heating spread over a larger footprint, and therefore deeper conductive heating, without the surface overheating that causes steam pops. (sources/lattice-tip-rf-lesion-circep-2019, rating: medium)
- Direct intramuscular thermometry in a perfused swine thigh preparation showed identical temperatures at 3 mm but +15.1 ± 2.4 °C higher at 7 mm with the lattice — evidence of deeper heating rather than a hotter surface. Steam pops in that preparation occurred in 92% of linear-catheter applications and none with the lattice.
- The spherical shape makes contact almost angle-independent (imprint area 101.5 / 92.6 / 130.7 mm² at 0° / 45° / 90°, versus 27.5 / 18.5 / 10.8 mm² for a linear tip), reducing hot spots when the catheter approaches tissue obliquely.
- The device's own caveat: surface thermocouples read the endocardium, not the subendocardium where maximal heating and steam pops occur, so surface temperature underestimates tissue temperature and the 60 °C limit may need adjusting for duration and tissue.
RF lesion performance versus a conventional irrigated tip
| Model | Setting | Lattice | Conventional | Comparator |
|---|---|---|---|---|
| Ex vivo bovine/porcine, unipolar, 30 s | Tmax 60 °C vs 40 W | 6.7 ± 1.3 mm deep | 4.8 ± 1.2 mm | CF 10 g |
| Ex vivo, unipolar, 60 s | " | 8.3 ± 1.4 mm | 5.4 ± 0.8 mm | |
| Ex vivo, unipolar, 120 s | " | 10.0 ± 1.6 mm, 2.4 ± 1 mL | 6.1 ± 1.6 mm, 0.5 ± 0.3 mL | |
| Ex vivo, bipolar, 60 s | two lattice tips | 15.8 ± 4.1 mm, 80% transmural | 10.5 ± 1.4 mm, 0% transmural | |
| In vivo swine ventricle, 60 s | " | 10.5 ± 1.4 mm deep, 27.3 ± 5.2 mm wide | 6.5 ± 0.8 mm, 9.2 ± 1.3 mm | |
| Ovine LV, unipolar, 60–120 s | 2.7 A / 60 °C / 30 mL/min | 10.3 ± 2.9 mm deep, 1,707 ± 771 mm³ | 5.5 ± 2.4 mm, 563 ± 398 mm³ | 30–35 W / 60 s |
(All: sources/lattice-tip-rf-lesion-circep-2019, rating: medium) (sources/lattice-tip-rf-lesion-jce-2019, rating: medium)
- Steam pops were consistently less frequent with the lattice than with conventional irrigated catheters (5.7% vs 18.4% ex vivo; 0% vs 14% in vivo). (sources/lattice-tip-rf-lesion-circep-2019)
- In the ovine LV, local bipolar electrograms recorded from the catheter surface disappeared during delivery in 17 of 20 (85%) lesions, and the same tip was used to map, ablate and confirm effect. (sources/lattice-tip-rf-lesion-jce-2019)
The PF mode
- Monopolar biphasic pulsed field delivery, 2 kV/µs, 4 s per application. In swine, papillary-muscle lesions reached 5.8 ± 1.0 mm with intact chordae and no mitral regurgitation at 21 days, moderator bands were ablated transmurally, epicardial monopolar lesions were 30.4 × 23.5 × 9.1 mm but only 20% transmural, and bipolar tip-to-tip PFA achieved 87% transmurality at 14.3 mm, the deepest PFA lesion reported. (sources/lattice-tip-preclinical-circep-2024, rating: medium)
- In patients, epicardial PF was explicitly not transmural on endocardial signal assessment. (sources/lattice-tip-vt-europace-2024, rating: medium)
Clinical performance in ventricular arrhythmia
| Study | Design | Key results |
|---|---|---|
| Peichl 2024 | Prospective, 18 patients, 66% prior failed ablation, 22% electrical storm | ~4,500 mapping points in ~18 min; 89% acute non-inducibility; 78% ventricular-arrhythmia-free at 3 months; coronary spasm in 3 of 4 epicardial patients; no phrenic palsy; hsTnT 36 → 995 ng/L |
| AVAAR 2025 | Multicentre registry, 126 patients at 18 centres, 64% redo | 84% acute success; 72% free of recurrence at 5.6 months (de novo 80% vs redo 68%); 6% major acute complications and 6% major events day 1–30 including 3 deaths |
(sources/lattice-tip-vt-europace-2024, rating: medium) (sources/avaar-registry-europace-2025, rating: high)
- Practical penalties documented in humans: pace mapping and entrainment are often impossible with the small surface pacing electrodes; PF delivery causes myocardial capture that can pace-terminate VT and be mistaken for isthmus elimination; and the large tip cannot reach narrow spaces — one inferior basal RV VT required a 4-mm catheter under the tricuspid leaflet at redo. (sources/lattice-tip-vt-europace-2024)
- Coronary spasm occurred at a tip-to-artery distance of 7 ± 3 mm and not at 21 mm, all resolving with intracoronary nitrates; no phrenic nerve palsy occurred in three patients with epicardial delivery on or within 1–2 cm of the nerve. (sources/lattice-tip-vt-europace-2024)
Atrial use
- Approved for AF ablation; the lattice tip is the device in the SPHERE Per-AF randomised trial of persistent AF (n=420; freedom from AF/AT 73.8% vs 65.8% with RF, safety 1.4% vs 1.0%, procedure 101 vs 126 minutes), and the dual-energy focal catheter platform is covered by the smartFIRE study. (sources/pfa-af-ehra-2026, rating: very high)
- The committee notes that dual-energy systems promise tailored depth — PF for thin-walled structures, RF for thick myocardium and near coronary arteries — but comparative outcome data against single-energy PFA are awaited, and that dual-energy access is what makes "lesion stacking" (repeat RF→PF on one trajectory) possible.
Contradictions / Open Questions
- Preclinical superiority has not been converted into a randomised clinical advantage. Lesion depth roughly doubles and bipolar transmurality reaches 80% in animals, yet the human evidence is a 18-patient feasibility series and a 126-patient registry, both without controls and with 3–6 months of follow-up. (sources/lattice-tip-rf-lesion-circep-2019, rating: medium) (sources/avaar-registry-europace-2025, rating: high)
- The volume data are not strictly comparable. The ovine study estimated spherical lesion volume from a single cross-section and surface area because the three-dimensional distribution was unverified, while conventional lesions used a half-ellipsoid formula — so the headline three-fold volume difference rests on different assumptions for each arm. (sources/lattice-tip-rf-lesion-jce-2019, rating: medium)
- Which energy is responsible for clinical success is unknown. In the Prague series RF was primary and PF consolidatory; in AVAAR 42% of procedures used both energies. No study isolates the contribution of either mode to efficacy or to harm, and the atrial experience makes the same point. (sources/lattice-tip-vt-europace-2024, rating: medium)
- "Epicardial ablation may become anecdotal" remains a hypothesis. The 10-mm ovine lesions prompted the claim that transmural endocardial ablation could replace pericardial access, but epicardial PF is not transmural, epicardial RF still terminates circuits that PF cannot reach, and the clinical series report no epicardial-versus-endocardial comparison. (sources/lattice-tip-rf-lesion-jce-2019) (sources/lattice-tip-vt-europace-2024)
- Safety is device-specific and still being characterised. Coronary spasm with epicardial and RVOT delivery, transient complete heart block with bipolar septal delivery near the aortic cusp, haemolysis without renal failure, LVAD electromagnetic interference preventing mapping, and one catheter-shaft insulation rupture causing simultaneous VF and AF have all been reported in small numbers. (sources/avaar-registry-europace-2025) (sources/lattice-tip-preclinical-circep-2024)
- Manufacturer involvement is pervasive. Both 2019 biophysical studies were funded by or involved equity in Affera; the clinical registry has extensive Medtronic relationships, and the AF statement notes that waveforms remain undisclosed. (sources/pfa-af-ehra-2026)
Connections
- Related to concepts/Ventricular-PFA — the pulsed-field mode and the ventricular evidence base
- Related to concepts/VT-Ablation — lesion depth as the limitation of conventional RF ablation
- Related to concepts/VT-Ablation-Nonischemic-Cardiomyopathy — intramural septal substrate the device targets
- Related to concepts/Epicardial-VT-Ablation — the approach larger endocardial lesions were proposed to reduce
- Related to concepts/PFA-Atrial-Arrhythmias — the dual-energy concept and atrial approval
- Related to concepts/PVC-Mapping-Ablation — papillary muscle and moderator band targets
- Related to concepts/Late-Gadolinium-Enhancement — imaging lesion extent
- Related to entities/ICD — device interaction during ventricular procedures