Catecholaminergic polymorphic ventricular tachycardia: risk modulators in patients treated with beta-blockers

Background

Due to the catecholaminergic nature of arrhythmias that define the Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT), beta-blockers (BBs) represent the first line therapy for this severe arrhythmogenic syndrome. Despite optimal BB therapy, a proportion of patients continue to suffer breakthrough life-threatening arrhythmias (LAE).

Purpose

To evaluate the role different classes of BBs (β1-selective vs. non-selective) in LAE reduction and to identify risk factors for breakthrough LAE while on BB monotherapy.

Methods

We studied 238 consecutive patients with CPVT and treated with BB monotherapy followed-up prospectively. CPVT was diagnosed according to the 2015 European Society of Cardiology Guidelines. The endpoint was the occurrence of the first LAE (sudden cardiac death, aborted cardiac arrest, or hemodynamically non-tolerated ventricular tachycardia) in BB monotherapy. The follow-up for each patient was calculated from BB therapy start to the occurrence of the endpoint, death from non-arrhythmic cause, the date of last visit, or the initiation of other treatments (i.e.: other antiarrhythmics or left cardiac sympathetic denervation [LCSD]), whichever occurred first.

Multivariable Cox proportional hazards model was used to evaluate the effects of history of LAE before diagnosis of CPVT, occurrence of unexplained syncope before diagnosis of CPVT, genotype, and type of BB therapy, as a time-dependent variable, on the risk of experiencing an LAE during BB monotherapy.

Results

We enrolled 238 CPVT patients (135 probands, 135 females): 226 with typical CPVT (n=216 RYR2; n=10 CASQ2) and 12 with atypical CPVT (n=5 RYR2-Loss-of-Function, n=4 TRDN and n=3 TECRL).

Prior to BB monotherapy, 48/238 (20%) patients had survived an LAE, and 110/238 (46%) patients had experienced an unexplained syncope.

During 1,629 person-years of follow-up during BB monotherapy, 35 patients experienced an LAE (annual LAE rate 2.1%, 95% CI: 1.5%–3.0%; Figure A). Five-year cumulative probability of experiencing an LAE during BB monotherapy was 11.9% (95% CI: 7.0%-16.6%). In this population, multivariable analysis showed that history of LAE before diagnosis (HR 3.6; 95% CI: 1.6–8.1; p=0.002) and syncope before diagnosis (HR 6.1; 95% CI: 2.5–14.9; p<0.001) were clinical risk factors for LAE occurrence. Patients with TRDN mutations were significantly more likely to suffer LAE (HR 20.9; 95% CI: 2.2–196.3; p=0.008). Using nadolol as the gold standard, the use of β1-selective BBs (HR 3.4; 95% CI: 1.4–8.6; p=0.009), but not propranolol (HR: 0.9; 95% CI: 0.2–3.8; p=0.887), was associated with poorer outcome during BB monotherapy (Figure B).

Conclusions

In patients with CPVT, selective BBs are associated with a higher risk of LAE as compared to nadolol. Patients who have survived an LAE and/or experienced an unexplained syncope prior to diagnosis, as well as carriers of TRDN mutations are at high risk of BB failure.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Ricerca Corrente Funding scheme of the Italian Ministry of Health and Italian Ministry of Research and University Dipartimenti di Eccellenza 2018–2022 grant to the Molecular Medicine Department (University of Pavia).

Natural History of Patients with Typical and Atypical Catecholaminergic Polymorphic Ventricular Tachycardia

Background

Recently, a novel genetic-based classification for Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT) has been proposed to distinguish “typical” (RYR2 and CASQ2 genes) and “atypical” (TRDN, TECRL, CALM1–3, RYR2 loss-of-function [RYR2-LoF]) CPVT variants. Although some genetic forms were reported as malignant forms of CPVT, natural history data comparing typical and atypical CPVT variants are lacking.

Purpose

We compared the natural history of “typical” and “atypical” forms of CPVT in a large cohort of patients with genetically confirmed CPVT.

Methods

CPVT was diagnosed according to the criteria defined in the 2015 European Society of Cardiology Guidelines. Based on the genetic background, we classified the patients in two groups: 1) “Typical” CPVT (i.e., carriers of pathogenic or likely pathogenic mutations in RYR2 and CASQ2 genes); 2) “Atypical” CPVT (i.e., carriers of pathogenic or likely pathogenic mutations in TRDN, TECRL, CALM1–3 and RYR2-LoF). Patients with mutations in the CALM1, CALM2 or CALM3 were not identified in our cohort. The outcome was the occurrence of a life-threatening arrhythmic event (LAE), defined as: sudden cardiac death, aborted cardiac arrest or hemodynamically non-tolerated ventricular tachycardia. The Kaplan-Meier life-table method was used to determine the cumulative probability of experiencing a first LAE before the age of 40 years and in the absence of treatment. Outcomes in two groups were compared using the log-rank test.

Results

The study cohort included 238 patients (56% females, median age at diagnosis 14 years [IQR: 9–28 years]), of whom 226/238 (95%) patients with “typical” CPVT (216 RYR2, 10 CASQ2), and 12/238 (5%) patients with “atypical” CPVT (5 RYR2-LoF, 4 TRDN, 3 TECRL). In the entire population, the cumulative probability of experiencing a first LAE between birth and the diagnosis of CPVT was 2.3%, 21.2 and 40.8% at 5, 20, and 40 years, respectively. At any given age, the probability of a first LAE in the absence of therapy was significantly higher in patients with atypical CPVT (25%, 36%, and 100% at 5, 20, and 40 years, respectively), as compared to patients with typical CPVT (1%, 20%, and 39% at 5, 20, and 40 years, respectively; p=0.003, Figure 1). Patients with atypical CPVT suffered LAEs in early childhood (i.e., by the age of 5 years) significantly more often than patients with typical CPVT (3/5 patients [60%] in atypical CPVT vs. 2/43 patients [5%] in typical CPVT, p<0.001; Figure 2).

Conclusions

The natural history of CPVT is modulated by the genetic cause. Atypical CPVT variants are rare but are characterized by a worse outcome and a greater likelihood of experiencing an LAE since the early childhood, as compared to typical CPVT.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Ricerca Corrente funding scheme of the Italian Ministry of Health

Efficacy and safety of the ICD in patients with catecholaminergic polymorphic ventricular tachycardia

Background

Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT) is a potentially fatal genetic arrhythmia syndrome and, despite optimal beta-blocker (BB) therapy, patients often experience life-threatening arrhythmic events (LAE). The role of implantable cardioverter defibrillators (ICD) on reducing mortality in patients with CPVT is debated.

Purpose

1) To assess the survival benefit of ICD in the overall CPVT population; 2) to investigate the benefit-to-harm ratio in the population of CPVT patients carriers of ICD.

Methods

We followed-up consecutive patients with genetically-proven CPVT, treated with optimal BB mono-therapy. The probability of surviving at the occurrence of a first LAE (defined as: sudden cardiac death, aborted cardiac arrest or hemodynamically non-tolerated ventricular tachycardia) during BB mono-therapy was compared between ICD carriers and non-ICD carriers.

In the cohort of ICD carriers, we assessed the rate of a first major complication (i.e., a complication requiring surgical intervention) and we calculated the benefit-to-harm ratio of ICD (defined as rate of appropriate shocks on LAE over rate of major complications).

Results

We enrolled 228 CPVT patients with a pathogenic RYR2 (n=216) or CASQ2 (n=12) mutation, of whom 87 (38%) had an ICD implanted. Overall, during 1,558 person-years of follow-up, 31/228 (14%) patients experienced a first LAE on BB mono-therapy (annual LAE rate 2.0%, 95% CI: 1.4–2.8%).

Of the 31 individuals who experienced an LAE, 21 patients had an ICD when the LAE occurred, and all survived after ICD intervention. Of the remaining 10 patients who were not carriers of an ICD, 6/10 (60%) survived after external defibrillation or spontaneous arrhythmia termination, while 4/10 (40%) died suddenly. The probability of surviving at the occurrence of a first LAE in BB mono-therapy was thirty-fold higher (Odds Ratio: 30.0, 95% CI: 1.4–629.0; p=0.029) in patients with an ICD, as compared to patients without an ICD.

Overall, 15/87 (17%) patients with an ICD experienced a first major complication over 602 person-years of follow-up (2.5% per year, 95% CI: 1.4%-4.1%). Importantly, no patient died for a pro-arrhythmic effect or complications related to ICD. Comparing the rate of major complications to the rate of appropriate ICD shocks on LAE (LAE rate 4.7% per year, 95% CI: 3.1–7.0%), the benefit-to-harm ratio was 1.9, thus favouring the benefit of ICD therapy.

Conclusions

In our population, ICD therapy conferred a significant survival benefit in patients with CPVT at the occurrence of a first LAE. Overall, the benefit of ICD implant outweighed the harm, as shown by almost two times greater benefit-to-harm ratio. This study provides evidence supporting ICD implantation in patients with high-risk CPVT.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Ricerca Corrente Funding Scheme of the Italian Ministry of Health

Is mexiletine ready for prime time in patients with Type 2 Long QT Syndrome?

Background

Mexiletine has been proven effective in shortening the duration of ventricular repolarization and reducing the arrhythmic events in type 3 Long QT Syndrome (LQT3). Initial reports indicate that mexiletine might also be effective in patients with type 2 Long QT Syndrome (LQT2, caused by loss-of-functions variants on KCNH2 gene, coding for HERG potassium channel), but this issue has not been investigated in detail.

Purpose

We quantified the electrocardiographic (ECG) effects of mexiletine in a cohort of LQT2 patients.

Methods

Twelve-lead ECGs were collected before and after the administration of mexiletine to evaluate the drug's effect on the heart rate-corrected QT interval (QTc). QTc intervals were classified as being (1) at “high-risk” if >500 ms or (2) “normal” if <460 ms, before and after the administration of the drug. KCNH2 variants were defined as (1) trafficking-deficient or (2) non-trafficking-deficient, based on functional studies.

Results

We tested the maximum tolerated dose of mexiletine in 20 patients (11 males, 55%), who were 17±16 years old at diagnosis, affected by genetically established LQT2. The mean age at the beginning of mexiletine administration was 23±15 years and the mean daily dose administered was 9±2 mg/kg/day.

Before mexiletine, the mean QTc interval was 527±53 ms and 10/20 (50%) patients had high-risk QTc values (i.e. QTc >500 ms).

After mexiletine, the mean QTc interval shortened to 484±47 ms in the overall population (p=0.001). In the majority of patients (18/20, 90%; Figure 1) QTc interval shortened, with a mean shortening of 42±28 ms, and a high-interindividual variability (range of shortening from 86 ms to 8 ms). Just 2 (10%) patients did not show any reduction of the QTc, despite receiving the highest adult dosages of mexiletine in our cohort (up to 10 mg/kg/day).

As compared to baseline conditions, after mexiletine the proportion of patients with high risk QTc values (>500 ms) decreased non-significantly from 50% to 35% (p=0.52). Furthermore, in only 6/20 (30%) patients the QTc normalized (i.e. QTc <460 ms) after the initiation of treatment.

The effect of mexiletine was not influenced by gender (p=0.89) or by the functional effect of the KCNH2 mutation (trafficking-deficient vs. non-trafficking-deficient variants, p=0.41).

The effect of mexiletine in LQT2 patients was inferior to the one previously observed in a cohort of 34 LQT3 patients, who had similar QTc values at baseline and received similar dosages of mexiletine, but showed a significantly higher reduction of the average QTc interval (63±37 ms in LQT3 vs. 42±28 ms in LQT2, p=0.02).

Conclusions

Mexiletine induces a reduction of the QTc interval in most LQT2 patients, but many patients remain with high-risk QTc values after receiving the drug. The demonstration that an average QTc shortening of 42 ms is enough to reduce arrhythmic events is necessary, before the introduction of mexiletine in clinical practice for LQT2.

Figure 1

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): Italian Ministry of Research and University Dipartimenti di Eccellenza 2018–2022 grant to the Molecular Medicine Department (University of Pavia)

Automated screening tool for Subcutaneous Implantable Defibrillator in Brugada syndrome has a high eligibility rate which is predicted by simple electrocardiographic parameters

Background

Manual electrocardiographic (ECG) screening tools for the use of subcutaneous cardiac defibrillator (S-ICD) have been associated with high ineligibility rates in Brugada syndrome patients (BrS). Although recent works identified ECG parameters for S-ICD eligibility in general population, automated screening tool (AST) for S-ICD eligibility have not even been assessed in large series of patients with BrS.

Purpose

This study evaluates the AST-derived eligibility rates for an S-ICD in patients with BrS, and ECG parameters associated with S-ICD eligibility.

Methods

Screening for S-ICD eligibility was performed using AST in 194 consecutive patients with BrS. Eligibility was defined when at least one of the three vectors was acceptable both in supine and standing position. Twelve-lead ECGs were registered during the screening. ECG parameters associated with AST eligibility were identified using multivariable logistical regression.

Results

Our study population consisted of 194 patients, with male preponderance (n=165/194; 85%); and were 43±12 years old at the time of screening. Majority of patients presented a spontaneous type 1 pattern during screening (n=128/194; 66%), with an average pattern height of 3±3 mm.

Remarkably, 93% of patients passed the screening with AST. No differences in eligibility rates in terms of gender (93% males vs. 93% females eligible; p=1) and age (48±9 years non-eligible vs. 42±12 eligible; p=0.07) existed. Notably, our eligibility rate was 2.5 times higher than rates reported in literature when using manual screening tools (p=0.023). Independent 12-lead ECG parameters (Table) associated with AST eligibility were duration of S wave <80 ms in aVF and R/T ratio ≥3 in lead II (Figure), which have a high positive predictive value (97% and 99%, respectively) for screening eligibility.

Conclusions

Most BrS patients (93%) are eligible for S-ICD when AST is used. S wave <80 ms in aVF, and R/T ratio ≥3 in lead II have a high positive predictive value for S-ICD eligibility.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): The Italian Ministry of Research and University Dipartimenti di Eccellenza 2018–2022 grant to the Molecular Medicine Department (University of Pavia)

Characterization of arrhythmic presentation in patients with arrhythmogenic cardiomyopathy

Background/Introduction

Arrhythmogenic cardiomyopathy (ACM) is one of the most arrhythmogenic conditions known to man. ACM is caused by desmosomal mutations in most cases, resulting in progressive replacement of the myocardium by adipose and fibrous tissue. It comes as no surprise that ACM is one of the leading causes of sudden cardiac death (SCD). Nonetheless, the characteristics of arrhythmic manifestations have not dissected after the release of most recent criteria.

Purpose

This study investigates different types of ventricular tachyarrhythmias which had occurred at first arrhythmic event in patients with ACM.

Methods

We investigated 91 consecutive patients with documented evidence of sustained ventricular tachyarrhythmias from 291 ACM patients followed at our center up to this date. Diagnosis of ACM was made using 2010 Task Force Criteria, and patients were defined as having an advanced disease if they had more than 4 TFC points at diagnosis. Presenting ventricular tachyarrhythmias were divided into (1) life-threatening arrhythmic event (LAE; ventricular fibrillation or hemodynamically unstable polymorphic ventricular tachycardia) and (2) hemodynamically stable monomorphic ventricular tachycardia (MMVT). Right ventricular (RV) involvement was defined as a presence of RV wall motion abnormalities and RV dilation at transthoracic echocardiography or cardiac magnetic resonance.

Results

Our study population was constituted of a predictably higher number of males (n=68; 75%), with an average age at the first arrhythmic event of 38±15 years of age.

At first documented arrhythmia, majority of patients studied experienced a stable MMVT (n=53; 58%), while 38 patients experienced an LAE (n=38; 42%). The patients suffering an LAE as first arrhythmic event were slightly younger than the patients who experienced a stable MMVT (35±14 years vs. 40±15 years; p=0.076) but there were no statistically significant gender differences (28/38 males with LAE vs. 40/53 males with stable MMVT; p= n.s.).

Interestingly, patients who presented with stable MMVT were more likely to have an advanced disease at diagnosis (OR=6.52; 95% CI 2.02–20.99; p=0.002). This is supported by the fact that RV involvement was significantly more common in patients presenting with stable MMVT (OR=4.38; 95% CI 1.26–15.26; p=0.021). Additionally, patients with stable MMVT were more commonly carriers of variants on PKP2 gene (OR=3.6; 95% CI 1.1–11.91; p=0.021).

Conclusions

Our data suggest that two types of arrhythmia reflect the two different stages of the disease. The early stage of the ACM is characterized by LAE in absence of RV structural involvement; while, stable MMVT is typical of PKP2 carriers and advanced stage of ACM with RV involvement.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): The Italian Ministry of Research and University Dipartimenti di Eccellenza 2018–2022 grant to the Molecular Medicine Department (University of Pavia)

Mutation site-specific risk profile in patients with Type 1 Long QT Syndrome

Background

Type 1 Long QT Syndrome (LQT1) is an arrhythmogenic disorder, caused by loss-of-function mutations on KCNQ1 gene, coding for Kv7.1 potassium channel. Although LQT1 is described as the most benign form of LQTS, patients still experience arrhythmic events and there is an unmet need for personalized risk stratification. Attempts have been made to correlate the location of mutations with outcome, but the results are unequivocal.

Purpose

We provide in the present study a new mutation site-specific risk profile obtained from a large cohort of LQT1 patients.

Methods

We gathered data on 963 patients with the diagnosis of LQT1 and divided the Kv7.1 channel into 5 functional regions: the N-terminus (NT), the voltage sensor (VS, including transmembrane segments S1 to S4), the cytoplasmic loops (CL), the pore (PO, including the transmembrane segments S5, S6 and the S5-S6 extracellular linker), the C-terminus (CT).

Results

We studied 963 LQT1 patients: 518 (54%) females; average age 20±17 years; mean QTc at baseline ECG 465±38ms. During a mean follow-up of 8±7 years, 172 (18%) patients experienced arrhythmic events: 31 (3%) experienced one or more cardiac arrests, while 141 (15%) experienced one or more syncopal spells. We identified 188 different variants in the KCNQ1 gene, with the following distribution: 15 (8%) in the NT, 33 (18%) in the VS, 27 (14%) in the CL, 43 (23%) in the PO, 70 (37%) in the CT. The frequency of pathogenic variants per number of amino acids (a.a.) was higher in the CL region, as compared to the other domains (1 mutation every 1.4 a.a.). The duration of QTc interval was significantly longer for patients with mutations in the PO region (473±40 ms) and in the CL region (468±38 ms) as compared to the other regions (p<0.01).

Importantly, in a multivariate analysis PO and CL regions were associated with a higher probability of experiencing arrhythmic events (OR 2.89, 95% CI 1.95–4.29, p=0.019 and OR 1.61, 95% CI 1.0–2.49, p=0.05, respectively. Figure) than the other regions. Interestingly, the risk was independent from QTc interval duration.

Conclusions

Mutations affecting the PO and the CL region of the Kv7.1. channel are associated with a higher probability of experiencing arrhythmic events. This finding is clinically relevant, because it will allow for a more personalized, mutation site-specific risk stratification.

Mutation site and arrhythmic events

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): Italian Ministry of Research and University Dipartimenti di Eccellenza 2018–2022 grant to the Molecular Medicine Department (University of Pavia)