Value of genotyping and scar‐phenotyping for VT ablation procedures in patients with nonischemic left ventricular cardiomyopathies

Variants of cardiomyopathy genes in patients with nonischemic cardiomyopathy (NICM) generate various phenotypes of cardiac scar and delayed enhancement cardiac magnetic resonance (DE‐CMR) imaging which may impact ventricular tachycardia (VT) management.


| INTRODUCTION
Ventricular tachycardia (VT) can occur in patients with nonischemic cardiomyopathy (NICM), especially in the presence of extensive scarring.The scar pattern is often located in the midwall of the myocardium and may be difficult to reach in patients undergoing VT ablation procedures for recurrent VT.NICM though is a heterogeneous disease including forms of familial cardiomyopathy and patients with idiopathic dilated cardiomyopathy.Patients with pathogenic variants (PV) have been found to have a more extensive disease and worse outcomes after VT ablation procedures 1 .The purpose of this study was to assess scar phenotypes and outcomes after VT ablation in patients with and without PVs causative for predominant left ventricular cardiomyopathy.

| Study population
This was a retrospective evaluation of consecutive patients from 2010 to 2022, with a history of predominantly left-sided NICM and VT, who underwent ablation procedures.Genetic testing was performed in all patients.All patient's underwent stress testing or coronary angiography to exclude significant coronary artery disease.
Among 27 patients without PVs, further workup including positron emission tomography scan (n = 14) and cardiac biopsy (n = 2) were performed at the discretion of the treating physician, yielding a final T A B L E 1 Patients characteristics.diagnosis of idiopathic NICM (n = 26) or premature ventricular contraction cardiomyopathy.
The study was approved by the Institutional Review Committee.

| Cardiac magnetic resonance (CMR) imaging and processing
Delayed enhancement CMR (DE-CMR) studies were performed on In patients with an implantable cardiac defibrillator (ICD), pre-and post-CMR interrogation and programming of the device was performed according to institutional protocol and the CMR was limited to the sequence of delayed enhancement and to a specific absorption rate of 2.0.A modified broad band CMR sequence 3 was used to avoid artifacts in patients with an ICD.
Scar location was classified based on the location of the predominant scar as subendocardial, intramural, epicardial, or transmural.Septal scar was defined as ring-like if it was visible in at least three contiguous segments in the same short axis slice 4 (Figure 1).Nonring-like septal scar was defined as focal scar in a single or two contiguous septal segments (Figure 1).
Using proprietary software (MUSIC, Lyric, Université de Bordeaux/Inria), regions of interest were drawn to segment the myocardium and the histogram of pixel intensities within the myocardium was analyzed.For scar quantification, we used the area encompassing pixels with signal intensities ≥50% of the maximal value (method of full width half maximum) 5 and defined this as core scar.The area with a signal intensity of 30%-50% of the maximal signal intensity was defined as the total scar.Both volumes were quantified and reported in cm 3 .In two patients, there were artifacts related to the ICD generator that made the CMR nondiagnostic.
Posthoc, the scar depth index (SDI) was determined as previously described. 6In brief, the area of the intramural scar was projected on that surface and the % of the scar area within a depth of 0-3, 3-5, and >5 mm was determined on the projected surface.The later measurement was defined as the SDI and is a reflection of the % of the entire scar surface located at the indicated depths.The different depths were arbitrarily chosen with the notion that an ablation lesion will be complete at a scar depth of 0-3 mm but may not complete at a depth of 3-5 mm, and is likely to be incomplete at a depth >5 mm.

| Genetic testing
Patients with infiltrative disorders, cardiac sarcoidosis, hypertensive heart disease, valvular heart disease, and congenital heart disease were excluded.All patients had the opportunity to receive genetic counseling.Genetic testing was performed for cardiomyopathy genes (Supporting Information: Table 1) in all patients  Programmed stimulation was repeated at the conclusion of the procedure using the same protocol as at the onset of the procedure.
A VT was considered successfully ablated if the VT terminated during radiofrequency energy delivery for tolerated VTs and could not be induced subsequently, or for nontolerated VTs if a VT that was readily inducible before ablation was no longer inducible after ablation.

| Results of genetic testing
The specific genetic defects are shown in the Supporting Information: Table 1.A total of 16 PVs were identified in the 43 patients in either channelopathy genes or cardiomyopathy genes.All patients had leftsided cardiomyopathy with either a LMNA variant (n = 5) or a Titin (n = 1), and SCN5A variants (n = 1).A total of 21 patients had no PVs but VUSs.A total of 38 VUSs were observed in the patients with only VUSs.In 6 patients genetic testing was negative.

| Imaging and scar distribution
In two patients, artifact related to the ICD generator made the CMR The intramural scar had a ring-like distribution involving the septum in 14/40 (35%) patients with diagnostic CMRs (Figure 1).Patients with ring-like scar pattern had a similar total scar burden as those without a ring-like pattern (9.8 ± 5.1 cc vs. 7.8 ± 7.0 cc, p = .35);however, these patients had a greater % of scar located in depths >5 mm (scar depth index >5 mm 30.6 ± 22.6% vs. 12.4 ± 16.2%, p = .005).
Patients with either LMNA and TTN variants had a similar amount of total and dense scar compared to other patients (total scar: 9.7 ± 6.3 vs. 6.6 ± 5.4 mL, p = .17,core scar: 3.6 ± 2.5 vs.

| Ablation outcomes and genotype
Over a follow-up period of 3.4 ± 2.9 years, VT occurred in 15 patients.The VT recurrence rate was higher in patients with PVs compared with patients with VUS, and, or negative testing (11/17 (65%) vs. 4/26 (15%, p = .002)(Figure 3).There were survival differences among patients with no variants, patients with VUSs and patients with PVs (log rank p < .001).Patients without known PVs had greater survival free from recurrent VT than those with PVs (HR: 3.93, 95% CI: [1.34-11.5],p = .01,log rank p = .007)(Figure 3).After adjustment for age, sex, EF, and total scar burden, the presence of a PV remained an independent predictor of worse survival free from VT (HR: 4.7, 95% CI: [1.22-18.0],p = .02).Patients with VUS had statistically similar outcomes compared to patients with negative genetic testing (log rank p = .21).

| Follow-up
Over a follow-up period of 3. T A B L E 2 Scar characteristics among patients with and without pathogenic variants.

| Genetic testing, imaging, and outcomes
All but one of the patients with LMNA or TTN variants had VT recurrence after the initial ablation procedure.A deeper location of scarring most likely was the reason for the high prevalence of VT recurrence, which is consistent with prior reports of patients with LMNA or TTN mutations. 8,9We could demonstrate in another series of patients with NICM that the SDI is a reliable indicator of VT recurrence. 6A cut-off value of >17% of the projected scar surface being located at a depth of >5 mm was associated with VT recurrence. 6The mean scar percentage of the projected scar at a depth >5 mm in this series was 32% in patients with LMN or TTN variants.It therefore is not surprising that a large portion of the scar could not be reached with radiofrequency ablation lesions that rarely reach a depth >5 mm.Based on the high recurrence rate Kumar et al. 9 suggested that ablation procedures in patients with LMNA variants should be considered as a palliative procedure.Similar disappointing ablation results with frequent VT recurrences have been reported in patients with TTN variants. 8DE-CMR is beneficial in identifying patients in whom VT recurrence is high, 6 and in whom early considerations for advanced heart failure therapies may be appropriate.Periprocedural planning in these patients may help to target deeper seated arrhythmias with bipolar, simultaneous unipolar ablation technologies or needle catheter ablation.
The potential of genetic testing to help determine ablation outcomes is a new concept and has been recently reported on by Ebert et al. 1 The use of DE-CMR to plan ablation procedures is well known but it's use to predict ablation outcomes is a more recent observation 6 .Taken together scar phenotyping and genotyping for PVs will likely further enhance the prediction of VT ablation outcomes and thereby help to improve outcomes by focusing on improvement of current ablation catheter technology and technique.
There is incremental value to genetic testing compared with definition of a scar pattern by DE-CMR.Knowledge of a particular PV with its prognostic implications helps to identify patients who may require expedited advanced heart failure treatment due to heightened risk.Furthermore, genetic testing helps to identify family members with pathogenic mutations allowing for the possibility of early disease recognition and preventive treatment initiation.

| Limitations
This is a single center study of a small series of patients with genetic testing, and DE-CMR who underwent VT ablation procedures.A larger patient population is required before generalizing the results of this study.Off-label procedures such as needle ablation, transcoronary ethanol ablation, and bipolar ablation procedures were not performed in these patients, but might have improved outcomes in patients with deep seated scar.

a 1 . 5
Tesla scanner (1.5 T Achieva Philips MR) with an eightelement phased array coil placed over the chest of patients in the supine position.Images were acquired with electrocardiogram gating during breath-holds.Ten to 15 min after administration of 0.1-0.15mmol/kg of intravenous gadobenate dimeglumine (Multi-Hance, Bracco Diagnostics), two-dimensional late gadoliniumenhanced imaging was performed using an inversion-recovery sequence 2 (repetition time: 6.7 ms, echo time: 3.2 ms, in-plane spatial resolution: 1.4 × 2.2 mm, slice thickness: 8 mm) in the shortaxis and three long-axis views of the left ventricle.The inversion time (250-350 ms) was optimized to null the normal myocardium.
from 2012 to 2021 using standard clinical genetic testing.A comprehensive combined arrhythmia and cardiomyopathy panel was used for all cases.Variants were classified as pathogenic or likely pathogenic based on ClinGen guidelines 7 and included as a combined category of pathogenic variants.Variants of unknown significance (VUSs) were considered separately for a secondary analysis.F I G U R E 1 Ring-like septal scar pattern and nonring-like septal scar: Cross-sectional delayed gadolinium enhanced cardiac magnetic resonance imaging is shown, demonstrating intramural septal scarring.Left panel: A ring-like pattern can be seen displaying continuous areas of delayed enhancement extending throughout the anterior, mid, and inferior septal segments (yellow arrows).Right panel: Intramural scarring in a nonring-like pattern is shown (red arrows).

2. 4 |
Programmed stimulation, mapping, and ablationAblation procedures were performed for VT refractory to antiarrhythmic medications.Multipolar catheters were positioned at the His bundle and the right ventricular apex.After arterial access was obtained, heparin was administered and an activated clotting time of >250 s was targeted.Programmed ventricular stimulation was performed with up to four extrastimuli at two right ventricular sites.All inducible VTs were targeted for ablation.If hemodynamically tolerated, entrainment mapping and activation mapping were performed.Thorough pace-mapping was performed in every patient, covering the entire scar area.Sites with matching pace maps were noted if ≥10/12 leads matched a VT morphology.Radiofrequency energy was delivered at sites showing concealed entrainment for tolerated VTs, sites with matching pace-maps for nontolerated VTs and sites with myocardial capture in the presence of fragmented electrograms or isolated potentials.In the endocardium, radiofrequency energy was delivered for 60-120 s at a power of 30-50 watts titrated to achieve an impedance drop of 10 Ohms or noncapture with high output pacing (20 mV at 5.0 ms).Within the coronary venous system, radiofrequency energy was delivered for 30-60 s beginning at 10 watts and titrated to achieve an impedance drop of 10 Ohms or noncapture with high output pacing (20 mV at 5.0 ms).In the pericardial space, only irrigated tip catheters were used with a targeted impedance drop of 10 Ohms or noncapture with high output pacing (20 mV at 5.0 ms), starting at a power of 20 W and titrated up to 50 W.

3 | RESULTS 3 . 1 |
Ablation procedure A total of 37 patients had endocardial ablation procedures involving the left and/or right ventricles, and six patients underwent a combined epicardial and endocardial ablation including three patients with PVs (lamin AC [LMNA], sodium channel [Na 1.5] [SCN5A], and desmoplakin [DSP]) and three without.The total procedure time (437 ± 139 min) and fluoroscopy times (43 ± 25 min) were similar between patients with and without PVs (p > .05).Patients with PVs had longer radiofrequency ablation times (112 ± 70 min vs. 69 ± 44 min, p = .01).A total of 165 VTs were induced (4.9 ± 4.4 per patient), with an average cycle length of 342 ± 89 ms including 78 VTs with a left bundle-branch-block morphology and 87 with right bundle branch block morphology.Complete procedural success was achieved in 33 patients; six patients remained inducible for VT post ablation and four did not undergo final programmed ventricular stimulation due to hemodynamic concerns.There were two major procedural complications including an atrioventricular fistula and one pericardial tamponade treated with epicardial drain placement.

| DISCUSSION 4 . 1 |
4 ± 2.9 years, VT occurred in 15 patients.A second ablation was performed in eight patients over the follow up period.Two patients underwent heart transplantation (both LMNA variants) due to worsening heart failure (n = 1) and intractable VT (n = 1).One patient underwent left ventricular assist device placement for worsening heart failure.Two patients died due to COVID infection (n = 1) and due to failure to thrive after cardiac transplantation (n = 1).Antiarrhythmics were discontinued in 22/43 patients.Four patients remained on two antiarrhythmics, 15 remained on one antiarrhythmic.Five patients in total remained on amiodarone, three of which had dose-reductions post ablation.4 Main findings A pathogenic variant was discovered in more than one-third of patients with predominately left-sided NICM undergoing VT ablation procedures.Patients with left ventricular cardiomyopathy due to specific pathogenic cardiomyopathy variants had different scar characteristics than patients without PVs, although the scar size was similar.The presence of a PV was independently associated with worse arrhythmia free survival after VT ablation procedures.Patients with LMNA or TTN variants had larger components of deep-seated scar, often displayed a ring-like pattern of septal scarring, and had higher rates of VT recurrence post ablation.
Genetic testing and DE-CMR are both beneficial to determine outcomes of VT ablation procedures in patients with left-sided NICM.Ring-like intramural scarring was the predominant phenotype of PV in the patients with NICM referred for VT ablation The presence of deeper-seated scarring in LMNA and TTN variants was associated with increased VT recurrence post ablation.
Categorical variables were reported as frequencies and percentages, whereas continuous variables were reported using mean ± SD if normally distributed or median (interquartile range Q1-Q3) otherwise.Categorical baseline characteristics, procedural, and imaging variables were compared by the Fisher's exact or χ 2 testing, as appropriate.Group comparisons for continuous variables were performed with two-sided Student's t test or Wilcoxon rank-sum test as appropriate.The clinical long-term event of interest was survival free from recurrent VT in patients with or without known PVs.Additional analysis on patients with VUSs was also performed.Kaplan-Meier curves were created and a log-rank test was used to compare hazard of clinical outcome.Hazard ratios (HRs) and the corresponding 95% confidence intervals (CIs) were obtained based on Cox regression models, outcomes were adjusted a priori for age, sex, EF, and total scar size.A two-sided p < .05 was considered to indicate statistical significance.All statistical analyses were performed using R version 4.1.1(R Foundation for Statistical Computing).
ablation procedure in the device clinic every 6 months for device interrogation, or earlier if clinically indicated.Recurrent VT was defined as sustained VT documented electrocardiographically or by ICD electrograms, regardless of whether or not ICD therapies were delivered.2.6 | Statistical analysis Survival free from VT post ablation in patients with vs without pathogenic mutations.VT, ventricular tachycardia.