Feasibility of functional substrate mapping with a novel lattice-tip catheter: Implications for ventricular tachycardia ablation

Key Findings.

• ▪Functional mapping with the lattice-tip catheter is feasible, enabling the recording of high-quality near-field signals displaying decremental properties.
• ▪Decrement-evoked potentials were colocalized with local activation time maps and the critical isthmus of the ventricular tachycardia.
• ▪Despite its larger profile, this spherical catheter may permit effective entrainment mapping and/or pace mapping to accurately delineate the critical components of the tachycardia circuit.
• ▪81.8% of patients remained free of arrhythmia during a short follow-up period.

Functional mapping refers to a variety of mapping approaches for ventricular tachycardia (VT) ablation that aim to reveal dynamic substrate changes related to conduction discontinuity within the abnormal scar tissue owing to source-sink mismatch and nonuniform anisotropic propagation.^1,2 Data regarding the feasibility of functional substrate mapping with a large-footprint lattice-tip catheter that allows both mapping and ablation with dual energy (radiofrequency [RF] high energy or pulsed field energy) are missing.

11 consecutive patients with ischemic cardiomyopathy (11 of 11 men; mean age 68.3 ± 9.3 years; mean ejection fraction 38.2% ± 9%) and monomorphic VT documented on the 12-lead electrocardiogram (ECG) were referred for catheter ablation and included for analysis in a prospective fashion. The study complied with the Declaration of Helsinki and was approved by the local ethics committee.

After patients’ informed consent, left ventricular (LV) endocardial VT mapping and ablation were performed under conscious sedation (9 of 11 cases) or under general anesthesia (2 of 11 cases). Unfractionated heparin was administered before LV mapping, aiming for an activated clotting time of 350–400 seconds. A quadripolar diagnostic catheter was placed in the right ventricle (RV) to perform the decrement-evoked potential (DeEP) mapping protocol. High-density 3-dimensional electroanatomic mapping and ablation were performed with a 9-mm lattice-tip catheter (Sphere-9 Catheter, Medtronic Inc., Minneapolis, MN) via transseptal (9 of 11 cases) or transaortic (2 of 11 cases) access. No other catheters were used for mapping and ablation.

Standard voltage thresholds (<0.5 mV for the core and <1.5 mV for the border zone) were used to define the scar. Scar dechanneling for delineation of potential conduction channels was additionally performed by adjustment of the voltage window. Local abnormal ventricular activities (LAVAs) and late potentials were initially evaluated during sinus rhythm and manually annotated. Local activation time (LAT) maps during sinus rhythm and RV pacing were developed for localizing the latest activation within the scar. DeEP mapping was performed during RV pacing (S1, a drive train of 6 beats at 500–600 ms) with a short-coupled extrastimulus (S2, 20–30 ms above the ventricular refractory period) to evaluate those LAVAs and late potentials with decremental conduction properties. Isolated near-field signals with >10-ms decrement were manually delineated as DeEPs.³ Activation mapping and entrainment mapping of the clinical VT were performed in cases with hemodynamic tolerance. In the setting of hemodynamic intolerance, a QRS axis–based ECG algorithm was applied to identify the segment most likely related to the VT exit.⁴ Potential corridors within the LAT areas exhibiting DeEPs were considered targets for ablation when pace mapping led to a perfect or near-perfect match (>90% correlation).

Based on the ECG morphology of the VT, mapping was more meticulous in the area of interest. The mean points acquired during mapping in sinus rhythm and during RV pacing were 2448 ± 974 and 2253 ± 1048, respectively. The mean mapping time was 11.2 ± 5.3 and 9.4 ± 4.8 minutes, respectively.

DeEP mapping was feasible in all cases. Low-amplitude, high-frequency DeEPs of excellent quality were colocalized with LAT maps both in sinus rhythm and during RV pacing as well as with the critical isthmus during activation mapping (Figure 1). Activation mapping of the clinical VT was performed in 5 cases (Figure 1). The mean points acquired during activation mapping were 630 ± 248. High-quality near-field signals, forming part of the diastolic pathway and characterizing the critical isthmus, were recorded in these cases (Figure 1). The allocation of the critical isthmus was correlated with LAT maps and DeEPs during substrate mapping in all cases. Entrainment mapping was achieved in 2 cases (Figure 1). Pace mapping in DeEP areas was feasible in 10 of 11 cases.

Figure 1.

Procedural images of a patient with ischemic cardiomyopathy who underwent ventricular tachycardia (VT) ablation because of recurrent implantable cardioverter-defibrillator shocks for sustained monomorphic VT episodes. The upper left part demonstrates an example of decrement-evoked potential (DeEP) mapping. A local abnormal ventricular activity potential (yellow bar) becomes a split potential during right ventricular pacing (green bar), displaying decremental properties during a short-coupled extrastimulus (orange bar). The upper right part shows the voltage map with scar dechanneling performed by adjustment of the voltage window and the local activation time (LAT) map during sinus rhythm. DeEPs were manually annotated. The lower right part demonstrates activation mapping with very-low-amplitude, high-frequency signals recorded at the critical isthmus as well as entrainment mapping at the area of interest, with concealed fusion and measurements compatible with pacing at the central isthmus.

All patients (11 of 11) underwent RF energy ablation (30 seconds per lesion) while 2 of 11 underwent pulsed field ablation to homogenize areas displaying DeEPs that correlated with either isthmus allocation during activation mapping or a perfect/near-perfect match during pace mapping in cases with hemodynamic intolerance. Programmed ventricular stimulation from the RV apex at 3 different drive trains—600, 500, and 400 ms—and up to 3 extrastimuli down to ventricular refractoriness or to 200 ms (if ventricular refractoriness <200 ms) was performed in all patients. Noninducibility of the clinical VT at the end of the procedure was the end point. Nonclinical VTs induced during the procedures were not ablated. The mean number of RF applications was 11.7 ± 8 (RF time 288.3 ± 283.4 seconds). In 2 patients, pulsed field ablation lesions (2 ± 2) were additionally delivered because of insufficient LAVA abolition with RF. All but 1 patient became noninducible after ablation (91% acute success rate for the clinical VT). Nonclinical monomorphic VTs were induced in 2 patients and ventricular fibrillation in 1 patient (73% acute success rate for any VT). The mean procedural duration was 110.3 ± 32.9 minutes, with a fluoroscopy time of 11.2 ± 4.4 minutes.

During a mean follow-up of 4 ± 3 months, 2 patients experienced VT recurrences (18.2%). None of the patients had major complications. Decompensated heart failure occurred in 1 patient 3 days postablation, possibly related to a transient reduction of LV systolic function. No ST-segment alterations were noticed in this cohort.

The main findings of the present study are as follows:

• 1.Functional mapping with the lattice-tip catheter is feasible, enabling the recording of high-quality near-field signals displaying decremental properties.
• 2.DeEPs were colocalized with LAT maps and the critical isthmus of the VT.
• 3.81.8% of patients remained free of arrhythmia during a short follow-up period.

Limited data exist regarding the efficacy of the lattice-tip catheter in VT ablation procedures. The recent multicenter European registry AFFERA Ventricular Arrhythmia Ablation Registry demonstrated an efficacy rate of 72% after a follow-up period of 5.6 ± 3.7 months.⁵ In this study, where a heterogeneous protocol for mapping and ablation of the arrhythmogenic substrate was used, the mean total RF duration was 428 ± 354 seconds. Based on our findings, functional mapping enables selective ablation with shorter RF delivery times (288.3 ± 283.4 seconds) and similar efficacy rates.

High-density multielectrode mapping has become standard practice in substrate-based VT ablation. Contemporary systems such as the HD Grid Advisor catheter (16 electrodes, 1-mm electrode size, 3-mm interelectrode spacing) integrated with EnSite Precision (Abbott, St. Paul, MN) and the Optrell catheter (48 microelectrodes, 0.9-mm² electrode size, 2.4-mm interelectrode spacing) with CARTO 3 (version 8, Biosense Webster, Diamond Bar, CA) enable rapid, high-resolution electroanatomic mapping. In contrast to these mapping catheters, which acquire bipolar electrograms between relatively large electrodes, the Sphere-9 catheter incorporates 9 substantially smaller mini-electrodes (0.7 mm in diameter, 3- to 4-mm interelectrode spacing) integrated within a compliant lattice structure.

The Sphere-9 uses a close-unipolar recording configuration, wherein each mini-electrode is referenced to the catheter’s central reference rather than to a distant indifferent electrode. This configuration differs from traditional bipolar recordings and may result in differences in electrogram morphology and wavefront directionality. The extent to which these design features affect signal characteristics requires systematic evaluation.

Mapping with the Sphere-9 catheter and AFFERA system (Medtronic, Minneapolis, MN) displays certain limitations compared to other multielectrode high-density mapping catheters. The major difference is related to the mapping point density, which is lower with Sphere-9 than with HD Grid Advisor and Optrell catheters. This finding appears to reflect differences in catheter geometry and electrode configuration as well as in annotation of signals by the navigation systems, rather than limitations in signal quality per se. The effective mapping surface area of the Sphere-9 catheter is smaller than the planar configuration of the HD Grid Advisor and Optrell catheters, influencing acquisition efficiency and leading to longer acquisition times for high-density mapping. Mapping time is also expected to be shorter with other navigation systems that permit automatic annotation of signals during sinus rhythm, ventricular pacing, or short-coupled extrastimulus at the same time, and not manually as in the AFFERA system. Another important consideration is that the AFFERA system does not incorporate tissue contact criteria during electrogram annotation. This may therefore influence voltage assessment in areas with heterogeneous ventricular tissue. Finally, in our practice, certain difficulties can be seen when mapping the areas around the papillary muscles, particularly the anterolateral papillary muscle via a transseptal approach. However, the latter also remains an issue with the planar configuration catheters.

In conclusion, the AFFERA platform offers the practical advantage of an “all-in-one” approach, enabling mapping, ablation, and validation with a single catheter, reducing the need for catheter exchanges. We demonstrated that substrate mapping with the Sphere-9 catheter provides high spatial resolution and excellent electrogram quality, which allows detailed delineation of low-amplitude near-field electrograms displaying decremental conduction properties during DeEP mapping or those that define the diastolic pathway during activation mapping of VT. Despite its larger profile, this spherical catheter may permit effective entrainment mapping and/or pace mapping to accurately delineate the critical components of the tachycardia circuit.

Disclosures

The authors have no conflicts of interest to disclose.