An emerging role for DPP6: reciprocal regulation of INa-Ito and implications for arrhythmogenesis

Background

Since the association of a chromosomal risk haplotype harboring dipeptidyl peptidase-like protein-6 (DPP6) to familial idiopathic ventricular fibrillation (iVF), a growing number of DPP6 missense variants has been reported in patients with ventricular tachyarrhythmias. The mechanisms underlying DPP6 mediated-arrhythmogenesis are not yet fully elucidated. DPP6 is a subunit of the transient outward potassium (Ito) channel complex in Purkinje cells (PC) and ventricular myocytes (VM).

Purpose

Since other Ito-channel subunits (Navβ1, KChIP2, KCNE4 and DPP10) are also known to antagonize INa, we examined whether DPP6 could play a broader role in the inter-regulation of Kv4.3 and Nav1.5 channels. We identified two novel DPP6 variants (p.Arg274His and p.His213Tyr), each segregating in families with QT/QU prolongation. DPP6 p.Arg274His carriers suffered from iVF, ectopic beats from the conduction system, and mitral valve prolapse. Other DPP6 variants (p.Ala751Val identified in this study; p.Gln526His and DPP6-T p.His332Arg published) are associated with Brugada syndrome (BrS). We hypothesized that DPP6 has opposing effects on INa and Ito displaying a reciprocal regulation of these currents.

Methods and results

First, we determined the effect of the DPP6 variants on INa and Ito in transfected CHO cells. Ito density was significantly reduced only when PC subunits were co-expressed with the DPP6 p.Arg274His or p.His213Tyr variants. Indeed, DPP6 modulates Nav1.5 channels in CHO cells by reducing INa Peak and INa Late, whereas DPP6 mutants p.Arg274His or p.His213Tyr resulted in an increase of both components compared to WT. Co-immunoprecipitation experiments in human endocardium confirmed an interaction between DPP6 and Nav1.5 channels. Computing of mutant DPP6-driven Ito-INa changes in a published human PC model led to significant prolongation of the action potential duration, mainly caused by increased INa Late.

On the other hand, the DPP6 p.Gln526His and p.Ala751Val variants, linked to BrS, led to a decreased INa Peak compared to the WT, while there was a tendency towards increased Ito density in both PC and VM molecular setups.

DPP6 (p.Arg274His and p.Ala751Val) transfection experiments in hiPSC cardiomyocytes, expressing endogenous INa and Ito, confirmed the reciprocal results obtained in CHO cells.

Conclusions

DPP6 regulates INa and Ito in a reciprocal manner. The cardiac phenotype of DPP6 variants could encompass a spectrum between two opposite poles: 1) QT/QU prolongation by DPP6 variants causing loss of Ito and gain of INa, like p.Arg274His and p.His213Tyr versus 2) BrS by DPP6 variants leading to gain of Ito and loss of INa, like p.Gln526His and p.Ala751Val.

Funding Acknowledgement

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): ESC Personal research grant, obtained in 2019

Modeling of an SCN5A founder mutation in iPSC-derived cardiomyocytes

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Research Foundation - Flanders (FWO)

Introduction

SCN5A encodes the α-subunit of voltage-gated cardiac sodium channel Nav1.5. Mutations in SCN5A are identified in about 20% of patients with Brugada syndrome (BrS), an inherited cardiac arrhythmia. We have identified an SCN5A founder mutation (c.4813+3_4813+6dupGGGT), leading to a loss-of-function of Nav1.5 in 25 different families. Mutation carriers show variable expression of the phenotype: from asymptomatic to syncopes and sudden cardiac death. We used induced pluripotent stem cell derived cardiomyocytes (iPSC-CM) to investigate the underlying pathophysiology.

Material & Methods

Dermal fibroblasts of six patients with different disease severity, and two unrelated healthy control individuals were reprogrammed using a commercially available reprogramming kit. iPSC-CMs were differentiated following a published protocol. We performed several differentiation rounds and investigated expression of cardiac markers using qPCR and immunocytochemistry and electrophysiological properties using patch-clamping.

Results

All iPSC-CMs expressed the tested markers. We observed reduction in sodium current density in patient iPSC-CMs compared to the control cells. However, our data display variability in AP characteristics between the differentiation batches, as well as between clones generated from one donor.

Conclusions

We established iPSC-CM models for a unique Belgian SCN5A founder mutation. Despite the observed variability, we could detect expected differences in electrophysiological properties of patient cells compared to controls.

A new prediction model for left ventricular systolic function recovery after catheter ablation of atrial fibrillation in patients with heart failure and reduced ejection fraction, The ANTWOORD Study

Funding Acknowledgements

Type of funding sources: None.

Background

In patients with heart failure with reduced ejection fraction (HFrEF) and atrial fibrillation (AF), pulmonary vein isolation (PVI) improves left ventricular ejection fraction (LVEF), along with prognosis, in a variable percentage of patients.

Aim

To investigate the predictors of LVEF recovery after PVI and to develop a prediction model for individualized assessment.

Methods

We conducted an observational, retrospective, single-center study on 111 consecutive patients with AF and HFrEF undergoing PVI. Patients were divided into Responder vs. Non-Responder according to the "Universal definition of HF". Clinical predictors were evaluated by multivariate logistic regression analysis and cross-validation technique. Independent predictors were used to build an internally validated prediction model.

Results Responders (54%) had significantly shorter QRS duration and less dilated left atria. Persistent AF and absence of a known etiology more frequent among Responders. AF recurrence was non-significantly different between the two groups (p=0.2), although clinical AF burden was lower in Responders, after PVI (p<0.001). Absence of known etiology, presence of persistent AF, left atrial volume index<50ml/m2, and QRS<120msec were independent predictors of LVEF recovery and composed the "Antwerp Score". Patients with Antwerp Score ≤1 had 90% likelihood of LVEF recovery, compared to 5% in patients with 3-6.

Conclusions Patients with wide QRS complex, known HF etiology, dilated left atria, and paroxysmal AF were less likely to recover LVEF after PVI. A new score system based on the above-mentioned parameters adequately predict LV function recovery after PVI. These results warrant confirmation and prospective validation.

App based monitoring of heart rate via FibriCheck to facilitate teleconsultations: from COVID-19 to clinical practice?

Funding Acknowledgements

Type of funding sources: Public Institution(s). Main funding source(s): Part of this project was realized with financial support from the city of Antwerp in the context of the call "Innovative solutions for Corona”

Background

During the first peak of the COVID-19 pandemic, face-to-face cardiology visits had to be replaced by teleconsultations but lacking the standard performed electrocardiogram. Instead, app-based monitoring of patients’ heart rate and rhythm using photoplethysmography (PPG) technology was available as an alternative to aid these teleconsultations.

Purpose

Evaluation of the feasibility to initiate remotely PPG recordings with FibriCheck (Qompium, Hasselt, Belgium) and of the value of using FibriCheck before and after teleconsultation to substitute in-person arrhythmia consultations in three Belgian hospitals (Antwerp University Hospital, Heilig-Hart Hospital Lier and Jessa Hospital Hasselt).

Methods

Patients known with AF or with suspected arrhythmia symptoms during teleconsultation were contacted for the activation of FibriCheck seven days before or after a teleconsultation respectively, as shown in Figure 1. Instructions and a QR code were sent to the patients to download and activate FibriCheck. The code automatically links the application to an online platform available for the treating physician. Patients were asked to record their heart rhythm three times a day and when they experienced symptoms.

Results

In total, 92 patients (mean age: 64.7 ± 17.4) were contacted during the first COVID-19 peak, of which a total of 22 patients declined because not owing a smartphone or tablet (n = 11) or they were not willing or not capable to use FibriCheck (n = 11). A significant age difference was seen between the 22 non-participants versus the 70 participants (mean age 73.8 ± 18.7 vs. 61.9 ± 15.9; p = 0.004). Half of the patients, eligible for PPG monitoring (n = 38, 54.9%), were initiated before a planned (tele)consultation. Of these, four patients (10.5%) were diagnosed with an arrhythmia by using FibriCheck, of which two had frequent extrasystoles and two had a recurrence of AF and rate control was adapted. Of the 32 patients who used FibriCheck after a teleconsultation due to symptomatic palpitations, extrasystoles (n = 3) or high suspicion for a new AF diagnosis (n = 2) was established via FibriCheck. Early in-office evaluation was organised for the patients with a new diagnosis of AF, and rhythm control was initiated. In the majority of patients (57.1%), teleconsultation with FibriCheck was reassuring so that they could be followed-up according to their normal schedule.

Conclusion

During the COVID-19 pandemic, cardiologists were able to obtain important additional information using the FibriCheck application when performing teleconsultations. The possibility to successfully complete teleconsultations using the FibriCheck data, and its broad applicability, create opportunities to implement FibriCheck in standard clinical practice as an easy tool to monitor patients before or after in-person consultations or even hospitalisations.

Mitral regurgitation attenuates thrombotic risk in nonrheumatic atrial fibrillation: a new CHA2DS2-VASc score risk modifier?

Funding Acknowledgements

Type of funding sources: None.

Background/Introduction: Atrial fibrillation (AF) carries a thrombotic risk related to left atrial blood stasis. Many risk scores, such as the CHA2DS2-VASc score, have been developed to guide physicians in initiating anticoagulant therapy. However, the risk prediction with these models is modest at best (C-statistic = 0.6). The presence of mitral regurgitation (MR) has been shown to reduce thrombotic risk in patients with rheumatic AF. In nonrheumatic AF, direct evidence of a lower thrombotic risk in patients with MR is still controversial.

Purpose

The current study assessed the effect of MR on thrombotic risk in nonrheumatic AF patients.

Methods

The prevalence of atrial thrombosis, defined as the presence of left atrial appendage thrombus (LAAT) and/or left atrial spontaneous echo contrast (LASEC) grade >2, was determined in 686 consecutive nonrheumatic AF patients without (adequate) anticoagulation scheduled for transoesophageal echocardiography before electrical cardioversion and was related to the severity of MR adjusted for the CHA2DS2-VASc score. The independent predictors of atrial thrombosis were assessed by stepwise multiple logistic regression analysis.

Results

A total of 103 (15%) patients had severe MR, 210 (31%) had moderate MR, and 373 (54%) had no-mild MR; the median CHA2DS2-VASc score was 3.0 (IQR 2.0-4.0). Atrial thrombosis (LAAT and/or LASEC grade >2) was observed in 118 patients (17%). The prevalence of atrial thrombosis decreased with increasing MR severity: 19.9% versus 15.2% versus 11.6% for no-mild, moderate, and severe MR, respectively (p for trend = 0.03) (Figure 1). Patients with moderate and severe MR had a lower risk of atrial thrombosis than patients with no-mild MR, with adjusted odds ratios (ORs) of 0.51 (95% CI 0.31-0.84) and 0.24 (95% CI 0.11-0.49), respectively. The other independent predictors of atrial thrombosis were: the CHA2DS2-VASc score with an adjusted OR of 1.25 (95% CI 1.10-1.42), poor left ventricular ejection fraction (LVEF, <40%) with an adjusted OR of 4.08 (95% CI 2.56-6.50), and large left atrial volume index (LAVI, >37 ml/m²) with an adjusted OR of 1.90 (95% CI 1.19-3.03) (Figure 1, upper right corner). The C-statistic of the regression model increased significantly (p = 0.0003) from 0.62 to 0.75 by adding MR grade, LVEF, and LAVI to the univariate CHA2DS2-VASc score model. The protective effect of MR was present across all levels of the CHA2DS2-VASc score and the presence of moderate-severe MR in patients with an intermediate CHA2DS2-VASc score (2-3) lowered the atrial thrombotic risk to the level of patients with a low CHA2DS2-VASc score (0-1).

Conclusion

Our data show that the presence of MR attenuated the atrial thrombotic risk by more than 50% in patients with nonrheumatic AF, independent of the CHA2DS2-VASc risk score. Moderate to severe MR can therefore be considered a new risk modifier of the CHA2DS2-VASc score, which might help refine the indication of anticoagulants in AF patients. Abstract Figure 1. Thrombotic risk per MR grade.

P435Reproducibility and predictive value of a simple novel method to measure pulmonary vein activity in persistent atrial fibrillation FARS AF CL study

Funding Acknowledgements

No disclosure

Introduction. Pulmonary vein (PV) firing can trigger or act as a rapid driver to maintain atrial fibrillation (AF). Automated 1-minute measurement of fragmented and non-fragmented PV activity cycle length (CL) showed contradictory results to predict ablation outcome in persistent AF. 

Purpose. This study investigated the reproducibility of a novel non-automated simple method to measure non-fragmented fastest discrete consecutive AF signal cycle length and the value of this measurement in the PVs to predict long-term success after pulmonary vein isolation (PVI) only ablation in persistent AF. 

Methods. Consecutive 75 patients with persistent AF undergoing first-time PVI between 2015 and 2018 were included. The mean of 10 FAstest Repetitive Similar morphology discrete signal cycle lengths (FARS-AF CL) were measured twice with > 2 minutes between in the coronary sinus (CS), superior vena cava (SVC), left and right atrial appendage (LAA, RAA) and PVs. FARS discrete AF signals were defined as (I) signal duration ≤80 msec; (II) repetitive similar morphological characteristics; (III) fastest consecutive 10 intervals during 1-minute observation. The reproducibility of the FARS–AF CL measurement was compared to traditional 10 consecutive interval measurements of fragmented CS signals. The CL gradient between the PV and the LA was quantified by the computing the ratio of the PV and LAA or CS CL. 

Results.  Good correlation was found between two FARS CL measurements in the CS, PVs, LAA and RAA (Correlation Kendall area: 0.882, 0.675-0.941, 0.859, 0.944, respectively). The correlation between two traditional CL measurements of fragmented CS signals was low (Correlation Kendall area:-0.006). After a mean follow-up of 20 months, freedom from atrial arrhythmias was achieved in 50 (66%) patients after the single PVI procedure with or without the use of AADs. Patient without recurrence were more likely to have FARS CL ≤140 msec (8 vs. 42%, p= 0.002), higher FARS PV CL/LAA CL and FARS PV CL/CS CL ratio (96 ± 13% vs. 86 ± 23 %, p= 0.04; 95 ± 13% vs. 82 ± 22%, p= 0.036). Patients with recurrence at follow-up had more dilated left atria (LAVI: 44 ± 12 vs. 38 ± 9 ml/m2, p= 0.02; LA diameter: 49 ± 6 vs. 45 ± 6 mm, p= 0.01), less AF termination during the procedure (16 vs. 37%, p= 0.049) and less first pass isolation (44 vs. 68%, p= 0.04). Multivariable Cox regression analysis showed that LAVI (p = 0.035) and FARS-PV CL (0.011) were significant predictors of arrhythmia free survival. After adjusting for LAVI, FARS-PV CL remained a significant predictor of AF recurrence (p = 0.028).

Conclusions. Traditional non-automated AF CL measurement of fragmented CS signals is poorly reproducible.  FARS-AF CL measurements in the PVs, RA and LA structures are highly reproducible. FARS-AF CL measurement in the PVs could predict the success of PVI-only procedure in persistent AF independent of left atrial size.

P1878Long-term effect of atrial fibrillation on the evolution of mitral and tricuspid valve regurgitation

Background

While severe mitral regurgitation is a well-established risk factor for atrial fibrillation (AF), it is less known whether atrial fibrillation induces mitral/tricuspid valve regurgitation (MR/TR). The present study aims to identify the long-term effects of permanent or non-permanent AF on atrial remodelling and on the progression of MR/TR.

Methods

The severity of MR/TR was assessed at baseline and after a period of 65±10 months in 37 patients with permanent AF, in 80 patients with non-permanent AF (of whom 43 were treated with ablation) and in 53 control patients with persistent sinus rhythm. MR/TR was qualitatively assessed by the multi-integrative approach, and quantitatively by measurement of the colour jet area.

Results

At baseline, AF patients had larger MR jet areas than control patients. At follow up, progression of MR, expressed as delta MR jet area, was 0.05±1.3 cm2 in the control group, 0.73±2.1 cm2 in the non-permanent AF group and 1.95±3.6 cm2 in the permanent AF group (p=0.001). Severe MR at follow up was observed in 0%, 2.5%, 8%, respectively. After adjustment for baseline clinical and echocardiographic parameters, permanent AF remained independently associated with the progression of MR. There was a significant positive correlation between a progression of MR and an increase in left atrial volume index (r=0.31, p<0.001). Although rhythm control in non-permanent AF patients was better with AF ablation than with medical treatment only, the MR evolution was similar (delta MR jet area: 0.85±2.05 cm2 vs 0.61±2.12 cm2, p=0.6). Comparable findings, albeit less pronounced, were observed for the association between of AF and TR progression.

MR jet area

Conclusions

The presence of longstanding AF is associated with a significant progression of MR/TR mainly due to atrial remodelling. Our data showed a beneficial effect of sustained rhythm control, either medically or by ablation, on MR/TR progression.

Long-term effect of atrial fibrillation on the evolution of mitral and tricuspid valve regurgitation

Objective: The present study aims to identify the long-term effects of atrial fibrillation (AF) on atrial remodelling and on the progression of mitral/tricuspid valve regurgitation (MR/TR). Methods: The severity of MR/TR was assessed by the colour jet area and by multi-integrative approach at baseline and after a period of 65 ± 10 months in 37 patients with permanent AF, in 80 patients with non-permanent AF (of whom 43 were treated with ablation) and in 53 control patients with sinus rhythm. Results: At baseline, AF patients had larger MR jet areas than control patients. At follow up, progression of MR, expressed as delta MR jet area, was 0.05 ± 1.3 cm² in the control group, 0.73 ± 2.1 cm² in the non-permanent AF group and 1.95 ± 3.6 cm² in the permanent AF group (p = .001). Severe MR at follow up was observed in 0%, 2.5%, 8%, respectively. There was a significant positive correlation between progression of MR and increase of left atrium volume (r = 0.31, p < .001). After adjustment for baseline clinical and echocardiographic parameters, permanent AF remained independently associated with the progression of MR. Although rhythm control was better with AF ablation than with medical treatment only, the MR evolution was similar. Comparable findings, albeit less pronounced, were observed for the association between of AF and TR progression. Conclusions: The presence of longstanding AF is associated with a significant progression of MR/TR mainly due to atrial remodelling. Our data showed a beneficial effect of sustained rhythm control, either medically or by ablation, on MR/TR progression.