The Dutch Idiopathic Ventricular Fibrillation Registry: progress report on the quest to identify the unidentifiable

BACKGROUND

Idiopathic ventricular fibrillation (iVF) is a rare cause of sudden cardiac arrest and, by definition, a diagnosis of exclusion. Due to the rarity of the disease, previous and current studies are limited by their retrospective design and small patient numbers. Even though the incidence of iVF has declined owing to the identification of new disease entities, an important subgroup of patients remains.

AIM

To expand the existing Dutch iVF Registry into a large nationwide cohort of patients initially diagnosed with iVF, to reveal the underlying cause of iVF in these patients, and to improve arrhythmia management.

METHODS

The Dutch iVF Registry includes sudden cardiac arrest survivors with an initial diagnosis of iVF. Clinical data and outcomes are collected. Outcomes include subsequent detection of a diagnosis other than 'idiopathic', arrhythmia recurrence and death. Non-invasive electrocardiographic imaging is used to investigate electropathological substrates and triggers of VF.

RESULTS

To date, 432 patients have been included in the registry (median age at event 40 years (interquartile range 28-52)), 61% male. During a median follow-up of 6 (2-12) years, 38 patients (9%) received a diagnosis other than 'idiopathic'. Eleven iVF patients were characterised with electrocardiographic imaging.

CONCLUSION

The Dutch iVF Registry is currently the largest of its kind worldwide. In this heterogeneous population of index patients, we aim to identify common functional denominators associated with iVF. With the implementation of non-invasive electrocardiographic imaging and other diagnostic modalities (e.g. echocardiographic deformation, cardiac magnetic resonance), we advance the possibilities to reveal pro-fibrillatory substrates.

Molecular genetic screening after non-ischaemic sudden cardiac arrest and no overt cardiomyopathy in real life: A major tool for the aetiological diagnostic work-up

BACKGROUND

With the development of advanced sequencing techniques, genetic testing has emerged as a valuable tool for the work-up of non-ischaemic sudden cardiac arrest (SCA).

AIMS

To evaluate the effectiveness of genetic testing in patients with unexplained SCA, according to clinical phenotype.

METHODS

All patients who underwent molecular genetic testing for non-ischaemic SCA with no left ventricular cardiomyopathy between 2012 and 2021 in two French university hospitals were included.

RESULTS

Of 66 patients (mean age 36.7±11.9years, 54.5% men), 21 (31.8%; 95% confidence interval 22.4-45.3%) carried a genetic variant: eight (12.1%) had a pathogenic or likely pathogenic (P/LP) variant and 13 (19.7%) had a variant of uncertain significance (VUS). Among 37 patients (56.1%) with no phenotypic clues, genetic testing identified a P/LP variant in five (13.5%), mainly in RYR2 (n=3) and SCN5A (n=2), and a VUS in nine (24.3%). None of the nine patients with phenotypic evidence of channelopathies had P/LP variants, but two had VUS in RYR2 and NKX2.5. Among the 20 patients with suspected arrhythmogenic cardiomyopathy, three P/LP variants (15.0%) and two VUS (10.0%) were found in DSC2, PKP2, SCN5A and DSG2, TRPM4, respectively. Genetic testing was performed sooner after cardiac arrest (P<0.001) and results were obtained more rapidly (P=0.02) after versus before 2016.

CONCLUSION

This study highlights the utility of molecular genetic testing with a genetic variant of interest identified in one-third of patients with unexplained SCA. Genetic testing was beneficial even in patients without phenotypic clues, with one-fourth of patients carrying a P/LP variant that could have direct implications.

Comparing adolescent- and adult-onset unexplained cardiac arrest: Results from the Dutch Idiopathic VF Registry

BACKGROUND

Current cohorts of patients with idiopathic ventricular fibrillation (IVF) primarily include adult-onset patients. Underlying causes of sudden cardiac arrest vary with age; therefore, underlying causes and disease course may differ for adolescent-onset vs adult-onset patients.

OBJECTIVE

The purpose of this study was to compare adolescent-onset with adult-onset patients having an initially unexplained cause of VF.

METHODS

The study included 39 patients with an index event aged ≤19 years (adolescent-onset) and 417 adult-onset patients from the Dutch Idiopathic VF Registry. Data on event circumstances, clinical characteristics, change in diagnosis, and arrhythmia recurrences were collected and compared between the 2 groups.

RESULTS

In total, 42 patients received an underlying diagnosis during follow-up (median 7 [2-12] years), with similar yields (15% adolescent-onset vs 9% adult-onset; P = .16). Among the remaining unexplained patients, adolescent-onset patients (n = 33) had their index event at a median age of 17 [16-18] years, and 72% were male. The youngest patient was aged 13 years. In comparison with adults (n = 381), adolescent-onset patients more often had their index event during exercise (P <.01). Adolescent-onset patients experienced more appropriate implantable cardioverter-defibrillator (ICD) therapy during follow-up compared with adults (44% vs 26%; P = .03). Inappropriate ICD therapy (26% vs 17%; P = .19), ICD complications (19% vs 14%; P = .41), and deaths (3% vs 4%; P = 1) did not significantly differ between adolescent-onset and adult-onset patients.

CONCLUSION

IVF may occur during adolescence. Adolescent-onset patients more often present during exercise compared with adults. Furthermore, they are more vulnerable to ventricular arrhythmias as reflected by a higher incidence of appropriate ICD therapy.

Surviving the Shocks: A Contemporary of Short-coupled Ventricular Fibrillation

A young man presented following successful cardiac resuscitation after an out-of-hospital cardiac arrest. During his admission, he had multiple runs of short-coupled ventricular fibrillation with a similar morphology premature ventricular complex (PVC) trigger. He was brought to the electrophysiology laboratory, and, with a high dose of isoprenaline, the PVC was localised to the moderator band. Ablation induced short runs of ventricular tachycardia before elimination of the PVC. He subsequently underwent subcutaneous implantable cardiac defibrillator implantation before his discharge.

Outcome of patients with idiopathic ventricular fibrillation and correlation with ECG markers of early repolarization

BACKGROUND

Early repolarization pattern (ERP) has been associated with idiopathic ventricular fibrillation (IVF) and with cardiovascular mortality in the general population. As there is limited data about long- term outcome of IVF, the aim of our study was to observe ventricular arrhythmia (VA) recurrences in these patients and to identify a possible correlation of VA with ECG markers of early repolarization.

METHODS AND RESULTS

We investigated 56 consecutive IVF patients who received an implantable cardioverter-defibrillator for secondary prevention. ERP was defined as a J-point elevation ≥ 0.1 mV in two or more contiguous inferior or lateral leads. Markers of early repolarization were present in 32.1% of cases with a preponderance of QRS slurring (77.8%). During a mean follow-up of 41.2 months, 11 patients (19.6%) received in total 18 adequate ICD-therapies. VF was most the common cause for ICDtherapy (61.1%) but monomorphic VT also occurred in four patients. Presence of ERP was associated with a significant trend towards arrhythmia recurrences. 38.9% patients with ERP received appropriate ICD-therapies whereas only 10.5% of patients without ERP had arrhythmia recurrence (p = 0.05). Inappropriate ICD-therapies occurred in seven patients (12.5%) with a non-significant trend towards a higher incidence in patients with a transvenous ICD (p = 0.15).

CONCLUSION

A significant correlation between ERP and VA recurrences in patients with IVF could be observed. Though monomorphic VA also play a role in the studied IVF-population, our data support the use of the S-ICD in this collective.

Identification of concealed cardiomyopathy using next-generation sequencing-based genetic testing in Korean patients initially diagnosed with idiopathic ventricular fibrillation

AIMS

Idiopathic ventricular fibrillation (IVF) is a disease in which the cause of ventricular fibrillation cannot be identified despite comprehensive clinical evaluation. This study aimed to investigate the clinical yield and implications of genetic testing for IVF.

METHODS AND RESULTS

This study was based on the multi-centre inherited arrhythmia syndrome registry in South Korea from 2014 to 2017. Next-generation sequencing-based genetic testing was performed that included 174 genes previously linked to cardiovascular disease. A total of 96 patients were clinically diagnosed with IVF. The mean age of the onset was 41.2 ± 12.7 years, and 79 patients were males (82.3%). Of these, 74 underwent genetic testing and four (5.4%) of the IVF probands had pathogenic or likely pathogenic variants (each having one of MYBPC3, MYH7, DSP, and TNNI3). All pathogenic or likely pathogenic variants were located in genes with definite evidence of a cardiomyopathy phenotype, either hypertrophic cardiomyopathy or arrhythmogenic right ventricular cardiomyopathy.

CONCLUSION

Next-generation sequencing-based genetic testing identified pathogenic or likely pathogenic variants in 5.4% of patients initially diagnosed with IVF, suggesting that genetic testing with definite evidence genes of cardiomyopathy may enable molecular diagnosis in a minority of patients with IVF. Further clinical evaluation and follow-up of patients with IVF with positive genotypes are needed to unveil concealed phenotypes, such as the pre-clinical phase of cardiomyopathy.

The genetic basis of apparently idiopathic ventricular fibrillation: a retrospective overview

AIMS

During the diagnostic work-up of patients with idiopathic ventricular fibrillation (VF), next-generation sequencing panels can be considered to identify genotypes associated with arrhythmias. However, consensus for gene panel testing is still lacking, and variants of uncertain significance (VUS) are often identified. The aim of this study was to evaluate genetic testing and its results in idiopathic VF patients.

METHODS AND RESULTS

We investigated 419 patients with available medical records from the Dutch Idiopathic VF Registry. Genetic testing was performed in 379 (91%) patients [median age at event 39 years (27-51), 60% male]. Single-gene testing was performed in 87 patients (23%) and was initiated more often in patients with idiopathic VF before 2010. Panel testing was performed in 292 patients (77%). The majority of causal (likely) pathogenic variants (LP/P, n = 56, 15%) entailed the DPP6 risk haplotype (n = 39, 70%). Moreover, 10 LP/P variants were found in cardiomyopathy genes (FLNC, MYL2, MYH7, PLN (two), TTN (four), RBM20), and 7 LP/P variants were identified in genes associated with cardiac arrhythmias (KCNQ1, SCN5A (2), RYR2 (four)). For eight patients (2%), identification of an LP/P variant resulted in a change of diagnosis. In 113 patients (30%), a VUS was identified. Broad panel testing resulted in a higher incidence of VUS in comparison to single-gene testing (38% vs. 3%, P < 0.001).

CONCLUSION

Almost all patients from the registry underwent, albeit not broad, genetic testing. The genetic yield of causal LP/P variants in idiopathic VF patients is 5%, increasing to 15% when including DPP6. In specific cases, the LP/P variant is the underlying diagnosis. A gene panel specifically for idiopathic VF patients is proposed.

Clinical presentation of calmodulin mutations: the International Calmodulinopathy Registry

AIMS

Calmodulinopathy due to mutations in any of the three CALM genes (CALM1-3) causes life-threatening arrhythmia syndromes, especially in young individuals. The International Calmodulinopathy Registry (ICalmR) aims to define and link the increasing complexity of the clinical presentation to the underlying molecular mechanisms.

METHODS AND RESULTS

The ICalmR is an international, collaborative, observational study, assembling and analysing clinical and genetic data on CALM-positive patients. The ICalmR has enrolled 140 subjects (median age 10.8 years [interquartile range 5-19]), 97 index cases and 43 family members. CALM-LQTS and CALM-CPVT are the prevalent phenotypes. Primary neurological manifestations, unrelated to post-anoxic sequelae, manifested in 20 patients. Calmodulinopathy remains associated with a high arrhythmic event rate (symptomatic patients, n = 103, 74%). However, compared with the original 2019 cohort, there was a reduced frequency and severity of all cardiac events (61% vs. 85%; P = .001) and sudden death (9% vs. 27%; P = .008). Data on therapy do not allow definitive recommendations. Cardiac structural abnormalities, either cardiomyopathy or congenital heart defects, are present in 30% of patients, mainly CALM-LQTS, and lethal cases of heart failure have occurred. The number of familial cases and of families with strikingly different phenotypes is increasing.

CONCLUSION

Calmodulinopathy has pleiotropic presentations, from channelopathy to syndromic forms. Clinical severity ranges from the early onset of life-threatening arrhythmias to the absence of symptoms, and the percentage of milder and familial forms is increasing. There are no hard data to guide therapy, and current management includes pharmacological and surgical antiadrenergic interventions with sodium channel blockers often accompanied by an implantable cardioverter-defibrillator.

Short-Coupled Ventricular Fibrillation

Short-coupled ventricular fibrillation (SCVF) is a distinct phenotype among individuals with unexplained cardiac arrest accounting for 7% to 14% of cases of idiopathic ventricular fibrillation (IVF). VF is typically initiated by a trigger premature ventricular contraction with a short-coupling interval of less than 350 milliseconds. In the absence of specific electrocardiographic features or provocative tests, the diagnosis remains challenging and requires documentation of VF onset. Most cases are diagnosed during follow-up at the time of VF recurrence. SCVF is characterized by a high risk of VF recurrence. Insertion of an implantable cardioverter-defibrillator and quinidine are the keystones of SCVF management.

Investigation of Unexplained Cardiac Arrest: Phenotyping and Genetic Testing

Unexplained cardiac arrest (UCA) is a working diagnosis that should be replaced by a final diagnosis once evaluation is completed. Complete evaluation of UCA should include high-yield tests like cardiac magnetic resonance imaging, exercise treadmill test, and sodium-channel blocker challenge to identify latent causes of UCA. If no clear etiology is revealed after complete evaluation, idiopathic ventricular fibrillation may be diagnosed, and the strength of its diagnosis can be divided into definitive, probable, and possible based on the number of high-yield tests performed. Care should be provided by a multidisciplinary team with expertise in this area.

Calcium Release Deficiency Syndrome: A New Inherited Arrhythmia Syndrome

Calcium release deficiency syndrome (CRDS) is a newly described form of inherited arrhythmia caused by damaging loss-of-function variants in the cardiac ryanodine receptor (RyR2). Unlike the prototypical RyR2 gain-of-function channelopathy, known as catecholaminergic polymorphic ventricular tachycardia, patients with CRDS are predisposed to sudden death usually in the absence of any electrical abnormalities at rest or during stress electrocardiography. This makes diagnosis incredibly challenging, however, an invasive electrophysiologic test appears to be effective in unmasking the phenotype, called the long-burst, long-pause, short-coupled ventricular extra-stimulus protocol. Optimal therapies for patients with CRDS remain unestablished, although flecainide appears to be a promising candidate drug.

Outcomes in Dutch DPP6 risk haplotype for familial idiopathic ventricular fibrillation: a focused update

BACKGROUND

The genetic risk haplotype DPP6 has been linked to familial idiopathic ventricular fibrillation (IVF), but the associated long-term outcomes are unknown.

METHODS

DPP6 risk haplotype-positive family members (DPP6 cases) and their risk haplotype-negative relatives (DPP6 controls) were included. Clinical follow-up data were collected through March 2023. Implantable cardioverter-defibrillator (ICD) indication was divided in primary or secondary prevention. Cumulative survival and event rates were calculated.

RESULTS

We included 327 DPP6 cases and 315 DPP6 controls. Median follow-up time was 9 years (interquartile range: 4-12). Of the DPP6 cases, 129 (39%) reached the composite endpoint of appropriate ICD shock, sudden cardiac arrest or death, at a median age of 45 years (range: 15-97). Median overall survival was 83 years and 87 years for DPP6 cases and DPP6 controls, respectively (p < 0.001). In DPP6 cases, median overall survival was shorter for males (74 years) than females (85 years) (p < 0.001). Of the DPP6 cases, 97 (30%) died, at a median age of 50 years. With a prophylactic ICD implantation advise based on risk haplotype, sex and age, 137 (42%) of DPP6 cases received an ICD, for primary prevention (n = 109) or secondary prevention (n = 28). In the primary prevention subgroup, 10 patients experienced a total of 34 appropriate ICD shocks, and there were no deaths during follow-up. DPP6 cases with a secondary prevention ICD experienced a total of 231 appropriate ICD shocks.

CONCLUSION

Patients with the DPP6 risk haplotype, particularly males, are at an increased risk of IVF and sudden cardiac death. Using a risk stratification approach based on risk haplotype, sex and age, a substantial proportion of patients with a primary prevention ICD experienced appropriate ICD shocks, showing the benefit of prophylactic ICD implantation with this strategy.

Atrial fibrillation begets ventricular fibrillation when the AV node fails

Deterioration of atrial fibrillation into ventricular fibrillation has frequently been described in patients with pre-excitation of the ventricles. We report two cases of atrial fibrillation without pre-excitation leading to rapid ventricular tachycardias and recurrent implantable cardioverter defibrillator therapy in young idiopathic ventricular fibrillation patients.

Red Flags in Syncope: Clues for the Diagnosis of Idiopathic Ventricular Fibrillation

Idiopathic ventricular fibrillation is responsible for ≈5%-7% of aborted cardiac arrest, mainly striking subjects in their forties. Syncope caused by short-coupled rapid polymorphic ventricular tachycardia is frequently noted in a patient's past history. However, a diagnosis of neurally mediated syncope, the most frequent cause of syncope in the young, is often erroneously made. Clinical clues suggest that syncope has an arrhythmic rather than a neurally mediated origin. In addition, the presence of premature ventricular contractions on an electrocardiogram recorded shortly after a syncopal event has utmost importance in establishing the cause of syncope. Although such extrasystoles are frequently benign, especially when associated with a long coupling interval, they also may suggest a malignant origin when closely coupled to the preceding complex with short coupling intervals (usually <350 ms). These arrhythmias mainly originate from the Purkinje system (usually the right ventricle in men and the left ventricle in women) and favorably respond to quinidine as well as to ablation therapy targeting Purkinje-fibers ectopic activity.

Malignant Purkinje Ectopy induced by Sodium-channel Blocker

BACKGROUND

Sodium-Channel Blocker (SCB) infusion is used to unmask the ECG pattern of Brugada syndrome. The test may also induce premature ventricular complexes (PVCs) in individuals without Brugada pattern, the clinical relevance of which is little known.

OBJECTIVE

To describe the prevalence of short-coupled (Sc) PVCs induced by ajmaline or flecainide in patients with suspected or documented severe ventricular arrhythmias.

METHODS

We reviewed the SCB tests performed in 335 patients with suspected ventricular arrhythmias and structurally normal hearts in 9 centers. ScPVCs were defined as frequent and repetitive PVCs with an R-on-T pattern on SCB tests. Repeated SCB tests were performed in seven patients and electrophysiological mapping of ScPVCs in nine.

RESULTS

Sixteen patients (8 males, 36±11 years) showed ScPVCs and were included. ScPVCs appeared 229±118 sec after the start of the infusion and displayed coupling intervals of 288±28 ms. ScPVC patterns were monomorphic in 10 and polymorphic in 5 patients, originating from the Purkinje system in mapped patients. Repetitive PVCs were induced in 15 (94%) patients including polymorphic ventricular tachycardias in 9 (56%). SCB was repeated 45 (IQR 0.6-46) months later and induced identical ScPVC in all. SCB test was the only mean to reveal the malignant arrhythmia in six patients. Catheter ablation was performed in 9 patients, resulting in arrhythmia elimination in 8 with a follow-up of 6 (IQR 2-9) years.

CONCLUSION

SCB can induce ScPVC, mostly from Purkinje tissue, in a small subset of patients with idiopathic ventricular arrhythmias. Its high reproducibility suggests a distinct individual mechanism.

Prevalence of Inherited Cardiac Conditions in Pediatric First-Degree Relatives of Patients with Idiopathic Ventricular Fibrillation

Idiopathic ventricular fibrillation (IVF) is diagnosed in out-of-hospital VF survivors after comprehensive investigations have excluded structural heart disease or inherited channelopathies. Current guidelines recommend clinical screening of first-degree relatives of IVF survivors, but this approach has not been validated in children. This study aimed to assess the yield of clinical cardiac screening in child first-degree relatives of IVF victims. A retrospective observational study was conducted of all consecutive pediatric first-degree relatives of IVF patients referred to our center between December 2007 and April 2020. Patients underwent systematic evaluation including medical and family history; 12-lead resting, signal-averaged, and ambulatory electrocardiogram (ECG); echocardiogram; exercise testing; cardiac magnetic resonance imaging; and ajmaline provocation testing. Sixty child first-degree relatives of 32 IVF survivors were included [median follow-up time of 55 months (IQR 27.0-87.0 months); 30 (50%) females]. Eight patients (13.3%) from 6 families (18.8%) received a cardiac diagnosis: long QT syndrome (n = 4); Brugada syndrome (n = 3); and dilated cardiomyopathy (n = 1). There were no deaths during follow-up. This study demonstrates a high yield of clinical screening for inherited cardiac disease in child first-degree relatives of IVF survivors. These findings highlight the variable expression of inherited cardiac conditions and the importance of comprehensive clinical evaluation in pediatric relatives, even when extensive investigations in the proband have not identified a clear etiology. Moreover, our results support the validity of the investigations proposed by current guidelines in family relatives of IVF survivors.

[24-year-old man with successful resuscitation due to ventricular fibrillation without evident cause]

A 24-year-old man was resuscitated successfully after ventricular fibrillation. Structural heart disease and a primary channelopathy could not be identified despite extensive work-up, including molecular genetic testing. Three years after the initial event, ventricular fibrillation recurred and recording of the induction mechanism opened additional therapeutic options.

Short-coupled ventricular fibrillation represents a distinct phenotype among latent causes of unexplained cardiac arrest: a report from the CASPER registry

AIMS

The term idiopathic ventricular fibrillation (IVF) describes survivors of unexplained cardiac arrest (UCA) without a specific diagnosis after clinical and genetic testing. Previous reports have described a subset of IVF individuals with ventricular arrhythmia initiated by short-coupled trigger premature ventricular contractions (PVCs) for which the term short-coupled ventricular fibrillation (SCVF) has been proposed. The aim of this article is to establish the phenotype and frequency of SCVF in a large cohort of UCA survivors.

METHODS AND RESULTS

We performed a multicentre study including consecutive UCA survivors from the CASPER registry. Short-coupled ventricular fibrillation was defined as otherwise unexplained ventricular fibrillation initiated by a trigger PVC with a coupling interval of <350 ms. Among 364 UCA survivors, 24/364 (6.6%) met diagnostic criteria for SCVF. The diagnosis of SCVF was obtained in 19/24 (79%) individuals by documented ventricular fibrillation during follow-up. Ventricular arrhythmia was initiated by a mean PVC coupling interval of 274 ± 32 ms. Electrical storm occurred in 21% of SCVF probands but not in any UCA proband (P < 0.001). The median time to recurrent ventricular arrhythmia in SCVF was 31 months. Recurrent ventricular fibrillation resulted in quinidine administration in 12/24 SCVF (50%) with excellent arrhythmia control.

CONCLUSION

Short-coupled ventricular fibrillation is a distinct primary arrhythmia syndrome accounting for at least 6.6% of UCA. As documentation of ventricular fibrillation onset is necessary for the diagnosis, most cases are diagnosed at the time of recurrent arrhythmia, thus the true prevalence of SCVF remains still unknown. Quinidine is effective in SCVF and should be considered as first-line treatment for patients with recurrent episodes.

Non-invasive detection of exercise-induced cardiac conduction abnormalities in sudden cardiac death survivors in the inherited cardiac conditions

AIMS

Rate adaptation of the action potential ensures spatial heterogeneities in conduction across the myocardium are minimized at different heart rates providing a protective mechanism against ventricular fibrillation (VF) and sudden cardiac death (SCD), which can be quantified by the ventricular conduction stability (V-CoS) test previously described. We tested the hypothesis that patients with a history of aborted SCD due to an underlying channelopathy or cardiomyopathy have a reduced capacity to maintain uniform activation following exercise.

METHODS AND RESULTS

Sixty individuals, with (n = 28) and without (n = 32) previous aborted-SCD event underwent electro-cardiographic imaging recordings following exercise treadmill test. These included 25 Brugada syndrome, 13 hypertrophic cardiomyopathy, 12 idiopathic VF, and 10 healthy controls. Data were inputted into the V-CoS programme to calculate a V-CoS score that indicate the percentage of ventricle that showed no significant change in ventricular activation, with a lower score indicating the development of greater conduction heterogeneity. The SCD group, compared to those without, had a lower median (interquartile range) V-CoS score at peak exertion [92.8% (89.8-96.3%) vs. 97.3% (94.9-99.1%); P < 0.01] and 2 min into recovery [95.2% (91.1-97.2%) vs. 98.9% (96.9-99.5%); P < 0.01]. No significant difference was observable later into recovery at 5 or 10 min. Using the lowest median V-CoS scores obtained during the entire recovery period post-exertion, SCD survivors had a significantly lower score than those without for each of the different underlying aetiologies.

CONCLUSION

Data from this pilot study demonstrate the potential use of this technique in risk stratification for the inherited cardiac conditions.

Idiopathic ventricular fibrillation: the ongoing quest for diagnostic refinement

Prior to the recognition of distinct clinical entities, such as Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, and long QT syndrome, all sudden cardiac arrest (SCA) survivors with ventricular fibrillation (VF) and apparently structurally normal hearts were labelled as idiopathic ventricular fibrillation (IVF). Over the last three decades, the definition of IVF has changed substantially, mostly as result of the identification of the spectrum of SCA-predisposing genetic heart diseases (GHDs), and the molecular evidence, by post-mortem genetic analysis (aka, the molecular autopsy), of cardiac channelopathies as the pathogenic basis for up to 35% of unexplained cases of sudden cardiac death (SCD) in the young. The evolution of the definition of IVF over time has led to a progressively greater awareness of the need for an extensive diagnostic assessment in unexplained SCA survivors. Nevertheless, GHDs are still underdiagnosed among SCA survivors, due to the underuse of pharmacological challenges (i.e. sodium channel blocker test), misrecognition of electrocardiogram (ECG) abnormalities/patterns (i.e. early repolarization pattern or exercise-induced ventricular bigeminy) or errors in the measurement of ECG parameters (e.g. the heart-rate corrected QT interval). In this review, we discuss the epidemiology, diagnostic approaches, and the controversies related to role of the genetic background in unexplained SCA survivors with a default diagnosis of IVF.

[Recurrent torsades and asystole without structural heart disease]

We report on a 67-year-old female patient with recurrent syncope induced by asystole and polymorphic ventricular tachycardia without relevant structural heart disease. After secondary prophylactic ICD implantation, beta-blocker and flecainide therapy, the patient suffered from recurrent syncope and ICD shocks due to ventricular fibrillation. A rare cause of polymorphic ventricular tachycardia in patients without structural heart disease was found and successfully treated.

Sex differences in the origin of Purkinje ectopy-initiated idiopathic ventricular fibrillation

BACKGROUND

Purkinje ectopics (PurkEs) are major triggers of idiopathic ventricular fibrillation (VF). Identifying clinical factors associated with specific PurkE characteristics could yield insights into the mechanisms of Purkinje-mediated arrhythmogenicity.

OBJECTIVE

The purpose of this study was to examine the associations of clinical, environmental, and genetic factors with PurkE origin in patients with PurkE-initiated idiopathic VF.

METHODS

Consecutive patients with PurkE-initiated idiopathic VF from 4 arrhythmia referral centers were included. We evaluated demographic characteristics, medical history, clinical circumstances associated with index VF events, and electrophysiological characteristics of PurkEs. An electrophysiology study was performed in most patients to confirm the Purkinje origin.

RESULTS

Eighty-three patients were included (mean age 38 ± 14 years; 44 [53%] women), of whom 32 had a history of syncope. Forty-four patients had VF at rest. PurkEs originated from the right ventricle (RV) in 41 patients (49%), from the left ventricle (LV) in 36 (44%), and from both ventricles in 6 (7%). Seasonal and circadian distributions of VF episodes were similar according to PurkE origin. The clinical characteristics of patients with RV vs LV PurkE origins were similar, except for sex. RV PurkEs were more frequent in men than in women (76% vs 24%), whereas LV and biventricular PurkEs were more frequent in women (81% vs 19% and 83% vs 17%, respectively) (P < .0001).

CONCLUSION

PurkEs triggering idiopathic VF originate dominantly from the RV in men and from the LV or both ventricles in women, adding to other sex-related arrhythmias such as Brugada syndrome or long QT syndrome. Sex-based factors influencing Purkinje arrhythmogenicity warrant investigation.

Remote Monitoring of the QT Interval and Emerging Indications for Arrhythmia Prevention

QT interval prolongation is a marker of increased risk for life-threatening arrhythmias, and needs to be promptly recognized. Many effective drugs, however, prolong QTc (QT interval corrected for heart rate) in genetically predisposed subjects. The possibility of remote monitoring and QTc measurement for up to 2 weeks, continuously providing physicians with real time data, allows life-saving interventions or changes in drug therapy. This applies especially to patients with the long QT syndrome and to those taking drugs blocking the IKr current and prolonging the QT interval. Patch monitors recording ECG traces continuously are available and contribute to effective arrhythmic prevention.

Echocardiographic deformation imaging unmasks global and regional mechanical dysfunction in patients with idiopathic ventricular fibrillation: A multicenter case-control study

BACKGROUND

Idiopathic ventricular fibrillation (IVF) is diagnosed in patients with sudden onset of ventricular fibrillation of unidentified origin. New diagnostic tools that can detect subtle abnormalities are needed to diagnose and treat patients with an underlying substrate.

OBJECTIVE

The purpose of this study was to explore echocardiographic deformation characteristics in IVF patients.

METHODS

Echocardiograms were analyzed with deformation imaging by 2-dimensional speckle tracking. Global and regional measurements of the left ventricle (LV) and right ventricle (RV) were performed. Regional LV deformation patterns were evaluated for the presence of postsystolic shortening. Regional RV deformation patterns were classified as type I (normal) or type II/III (abnormal).

RESULTS

In total, 47 IVF patients (mean age 45 years; left ventricular ejection fraction [LVEF] 56%) and 47 healthy controls (mean age 41 years; LVEF 60%) were included. IVF patients showed more global deformation abnormalities as indicated by lower LV global longitudinal strain (18.5% ± 2.6% vs 21.6% ± 1.8%; P <.001) and higher LV mechanical dispersion (41 ± 12 ms vs 26 ± 6 ms; P <.001). In addition, IVF patients showed more regional LV postsystolic shortening compared to healthy controls (50% vs 11%; P <.001). Abnormal RV deformation patterns were observed in 16% of IVF patients and in none of the control subjects (P <.001).

CONCLUSION

We were able to show both regional and global echocardiographic deformation abnormalities in IVF patients. This study provides evidence that localized myocardial disease is present in a subset of IVF patients.

Epidemiology of early repolarization pattern in an adult general population

Background: Early repolarization pattern (ERP) is a frequent finding in asymptomatic subjects with controversial implications regarding to its prognosis. This study aims to estimate the prevalence of ERP and its association with sociodemographic characteristics and cardiovascular risk factors among the adult population in the Southern Cone of Latin America.Methods: A sub-sample of 5398 participants of the CESCAS I study was included in the present analysis. ERP was defined as a J peak ≥0.1 mV in two or more contiguous leads with an end-QRS notch or slur on the downslope of a prominent R-wave.Results: The global prevalence of ERP was 8.1%; 11.1% in men and 5.6% in women. The prevalence in women increased with age (odds ratio [OR] 2.5, 95% confidence interval [CI] 1.5-4.2, at >65 years, p < 0.001), current cigarette smoking (OR 1.4, 95%CI 1.0-2.0, p = 0.045) and hypercholesterolaemia (OR 1.4, 95%CI 1.0-2.0, 0 p = 0.036). Conversely, in men, ERP prevalence decreased with age (OR 0.5, 95%CI 0.3-0.9, at >65 years, p = 0.01) and obesity (OR 0.6, 95%CI 0.4-0.8, p = 0.006). We found an increasing ERP prevalence with a higher Sokolow-Lyon index in both sexes (p < 0.001). Inferior location was found in 67.9% of cases, and the most common ERP type was a "slurring" appearance without ST elevation (76.3%).Conclusions: We found an overall prevalence of ERP of 8.1% and a robust association of ERP with normal BMI and higher Sokolow-Lyon index in men and with hypercholesterolaemia, current cigarette smoking and higher Sokolow-Lyon index in women.

Out-of-hospital cardiac arrest due to idiopathic ventricular fibrillation in patients with normal electrocardiograms: results from a multicentre long-term registry

AIMS 

To define the clinical characteristics and long-term clinical outcomes of a large cohort of patients with idiopathic ventricular fibrillation (IVF) and normal 12-lead electrocardiograms (ECGs).

METHODS AND RESULTS

Patients with ventricular fibrillation as the presenting rhythm, normal baseline, and follow-up ECGs with no signs of cardiac channelopathy including early repolarization or atrioventricular conduction abnormalities, and without structural heart disease were included in a registry. A total of 245 patients (median age: 38 years; males 59%) were recruited from 25 centres. An implantable cardioverter-defibrillator (ICD) was implanted in 226 patients (92%), while 18 patients (8%) were treated with drug therapy only. Over a median follow-up of 63 months (interquartile range: 25-110 months), 12 patients died (5%); in four of them (1.6%) the lethal event was of cardiac origin. Patients treated with antiarrhythmic drugs only had a higher rate of cardiovascular death compared to patients who received an ICD (16% vs. 0.4%, P = 0.001). Fifty-two patients (21%) experienced an arrhythmic recurrence. Age ≤16 years at the time of the first ventricular arrhythmia was the only predictor of arrhythmic recurrence on multivariable analysis [hazard ratio (HR) 0.41, 95% confidence interval (CI) 0.18-0.92; P = 0.03].

CONCLUSION 

Patients with IVF and persistently normal ECGs frequently have arrhythmic recurrences, but a good prognosis when treated with an ICD. Children are a category of IVF patients at higher risk of arrhythmic recurrences.

Calmodulin mutations and life-threatening cardiac arrhythmias: insights from the International Calmodulinopathy Registry

AIMS

Calmodulinopathies are rare life-threatening arrhythmia syndromes which affect mostly young individuals and are, caused by mutations in any of the three genes (CALM 1-3) that encode identical calmodulin proteins. We established the International Calmodulinopathy Registry (ICalmR) to understand the natural history, clinical features, and response to therapy of patients with a CALM-mediated arrhythmia syndrome.

METHODS AND RESULTS

A dedicated Case Report File was created to collect demographic, clinical, and genetic information. ICalmR has enrolled 74 subjects, with a variant in the CALM1 (n = 36), CALM2 (n = 23), or CALM3 (n = 15) genes. Sixty-four (86.5%) were symptomatic and the 10-year cumulative mortality was 27%. The two prevalent phenotypes are long QT syndrome (LQTS; CALM-LQTS, n = 36, 49%) and catecholaminergic polymorphic ventricular tachycardia (CPVT; CALM-CPVT, n = 21, 28%). CALM-LQTS patients have extremely prolonged QTc intervals (594 ± 73 ms), high prevalence (78%) of life-threatening arrhythmias with median age at onset of 1.5 years [interquartile range (IQR) 0.1-5.5 years] and poor response to therapies. Most electrocardiograms (ECGs) show late onset peaked T waves. All CALM-CPVT patients were symptomatic with median age of onset of 6.0 years (IQR 3.0-8.5 years). Basal ECG frequently shows prominent U waves. Other CALM-related phenotypes are idiopathic ventricular fibrillation (IVF, n = 7), sudden unexplained death (SUD, n = 4), overlapping features of CPVT/LQTS (n = 3), and predominant neurological phenotype (n = 1). Cardiac structural abnormalities and neurological features were present in 18 and 13 patients, respectively.

CONCLUSION

Calmodulinopathies are largely characterized by adrenergically-induced life-threatening arrhythmias. Available therapies are disquietingly insufficient, especially in CALM-LQTS. Combination therapy with drugs, sympathectomy, and devices should be considered.

Prevalence of early repolarization syndrome and long-term clinical outcome in patients with the diagnosis of idiopathic ventricular fibrillation

Idiopathic ventricular fibrillation (IVF) is diagnosed in up to 14% of sudden cardiac death (SCD) survivors. Early repolarization syndrome (ERS) in patients with ventricular tachyarrhythmia is characterized by an elevated J-point in inferior and/or antero-lateral leads. Our objectives were to determine the prevalence of ERS in IVF patients, and to evaluate potential differences in clinical outcome. Out of 3,552 implantable cardioverter defibrillator (ICD) carriers, 758 SCD survivors were retrospectively identified from the databases of the Medical Universities of Vienna and Innsbruck within the last three decades. Early repolarization pattern (ERP) was classified either as "notching" or "slurring". Endpoints were defined as appropriate ICD therapies for ventricular tachyarrhythmia, either anti-tachycardia pacing or shock, and all-cause mortality. After exclusion of recognized reasons for SCD, 50 patients were assigned to the diagnosis of IVF (6.6%). An ERP was identified in 10 patients, most of them with notching (n = 8). After a mean follow-up of 11.2 ± 6.7 years (539.3 patient years), appropriate ICD therapies were found in 50% of ERS and 43% of IVF patients without ERP (p = 0.732). In ERS patients, all ICD therapies were found in patients with notching pattern. Similarly, incidence of inappropriate ICD therapies, and all-cause mortality was comparable (30% vs. 23%, p = 0.707; 10% vs. 5%, p = 0.496, respectively). In 758 SCD survivors, we found a low prevalence of IVF and ERS. Similar event rates were reported concerning all-cause mortality and ICD therapies for ventricular tachyarrhythmia after long-term follow-up in this cohort.

Detection of Variants in Patients with Idiopathic Ventricular Fibrillation by Whole-exome Sequencing

AIMS AND BACKGROUND

Idiopathic ventricular fibrillation (IVF) is a cause of sudden cardiac death (SCD). The frequency of mutations in disease-causing genes ranges, on average, between 16 and 48% in SCD cases. This study aimed to identify novel mutations in IVF patients without KCNQ1, KCNH2, and SCN5A mutations using whole-exome sequencing (WES).

METHODS

Genomic DNA extracted from peripheral blood samples obtained from five patients with IVF and WES was used to identify mutations associated with IVF. Candidate variants were validated by Sanger sequencing.

RESULTS

Four patients harbored suspected mutations in 100 inherited cardiomyopathy-and channelopathy-associated genes (e.g., TCAP, TTN, MYPN, CACNA1C, and TNNT2). All of these genetic variants have been given a dbSNP rs number; however, their clinical significance remains unknown. Bioinformatics tools predicted severe functional disruptions in the loci harboring these suspected mutations, suggesting their pivotal roles in IVF.

CONCLUSIONS

This study revealed the effectiveness of WES for IVF patients without KCNQ1, KCNH2, and SCN5A mutations. Although it is difficult to interpret broad WES results, the analysis can provide insight into the etiology of a heterogeneous disease.

Medium-term outcomes of idiopathic ventricular fibrillation survivors and family screening: a multicentre experience

Aims

Early repolarization (ER) has been linked to poorer outcomes in idiopathic ventricular fibrillation (IVF). The role of family screening in IVF is not clear. Our aim was to review predictors for poorer outcomes and evaluate the role of family screening in IVF.

Methods and results

This was a retrospective multicentre cohort study including all patients diagnosed with IVF. Data were collected on baseline characteristics, ECG findings, and recurrence of ventricular arrhythmia (VA) during follow-up. Electrocardiogram findings were reviewed in first-degree relatives that were screened. A total of 66 patients were included with male predominance (42/66, 64%) and Caucasian ethnicity (47/66, 71%). Mean age at cardiac arrest was 38 years ± 11. Thirty-one patients had ER (47%) predominantly with J-point amplitude ≥2 mm and horizontal ST segments (18/31, 58%). Recurrent VA was seen in 13 patients (20%). Horizontal ST segments were associated with increased rates of VA recurrence (OR 11, 95% CI 2.7-43.7; P = 0.0007). Early repolarization was seen in 20% of the 72 first-degree relatives and was more common if the proband had persistent ER pattern (OR 10.7, 95% CI 2.2-51.5; P = 0.003).

Conclusion

Ventricular arrhythmia recurrence was lower than previously reported. Early repolarization was common in this IVF cohort, and horizontal ST segments were suggestive predictor for poorer outcomes. Persistent ER in proband was associated with ER in first-degree relatives. With better understanding of its predictive value and the relationship to IVF, this information could potentially be used to guide family screening and identify new mutations using family members with persistent ER.

The genetics underlying idiopathic ventricular fibrillation: A special role for catecholaminergic polymorphic ventricular tachycardia?

BACKGROUND

Ventricular fibrillation (VF) is a major cause of sudden cardiac death. In some cases clinical investigations fail to identify the underlying cause and the event is classified as idiopathic (IVF). Since mutations in arrhythmia-associated genes frequently determine arrhythmia susceptibility, screening for disease-predisposing variants could improve IVF diagnostics.

METHODS AND RESULTS

The study included 76 Finnish and Italian patients with a mean age of 31.2years at the time of the VF event, collected between the years 1996-2016 and diagnosed with idiopathic, out-of-hospital VF. Using whole-exome sequencing (WES) and next-generation sequencing (NGS) approaches, we aimed to identify genetic variants potentially contributing to the life-threatening arrhythmias of these patients. Combining the results from the two study populations, we identified pathogenic or likely pathogenic variants residing in the RYR2, CACNA1C and DSP genes in 7 patients (9%). Most of them (5, 71%) were found in the RYR2 gene, associated with catecholaminergic polymorphic ventricular tachycardia (CPVT). These genetic findings prompted clinical investigations leading to disease reclassification. Additionally, in 9 patients (11.8%) we detected 10 novel or extremely rare (MAF<0.005%) variants that were classified as of unknown significance (VUS).

CONCLUSION

The results of our study suggest that a subset of patients originally diagnosed with IVF may carry clinically-relevant variants in genes associated with cardiac channelopathies and cardiomyopathies. Although misclassification of other cardiac channelopathies as IVF appears rare, our findings indicate that the possibility of CPVT as the underlying disease entity should be carefully evaluated in IVF patients.

Next-generation sequencing of a large gene panel in patients initially diagnosed with idiopathic ventricular fibrillation

BACKGROUND

Idiopathic ventricular fibrillation (IVF) is a rare primary cardiac arrhythmia syndrome that is diagnosed in a resuscitated cardiac arrest victim, with documented ventricular fibrillation, in whom no underlying cause is identified after comprehensive clinical evaluation. In some patients, causative genetic mutations are detected that facilitate patient treatment and follow-up. The feasibility of next-generation sequencing (NGS) has increased with its greater availability and decreasing costs.

OBJECTIVE

The aim of this study was to assess the diagnostic yield of NGS in patients with IVF.

METHODS

A total of 33 patients initially diagnosed with IVF were included (mean age 53 ± 15 years; 14(42%) men). In all included patients, NGS of 33 genes and the DPP6 haplotype revealed no pathogenic mutations. Genetic screening comprised NGS of a panel of 179 additional genes. Variants with a minor allele frequency of <0.05% were assessed for pathogenicity by using existing mutation databases and in silico predictive algorithms.

RESULTS

In 1 of 33 patients, a likely pathogenic mutation was detected. The added yield of genetic testing with NGS of 179 additional genes is 3% in patients with IVF. In 15% of patients, 1 or multiple variants of uncertain clinical significance were detected.

CONCLUSION

The added yield of genetic screening of extended NGS panels in patients initially diagnosed with IVF is minimal. Routine analysis of large diagnostic NGS panels is therefore not recommended.

A type 2 ryanodine receptor variant associated with reduced Ca2+ release and short-coupled torsades de pointes ventricular arrhythmia

BACKGROUND

Ventricular fibrillation may be caused by premature ventricular contractions (PVCs) whose coupling intervals are <300 ms, a characteristic of the short-coupled variant of torsades de pointes (scTdP).

OBJECTIVE

The purpose of this study was to analyze the underlying cardiac ryanodine receptor (RyR2) variants in patients with scTdP.

METHODS

Seven patients with scTdP (mean age 34 ± 12 years; 4 men and 3 women) were enrolled in this study. The RyR2 gene was screened by targeted gene sequencing methods; variant minor allele frequency was confirmed in 3 databases; and the pathogenicity was investigated in silico analysis using multiple tools. The activity of wild-type and mutant RyR2 channels was evaluated by monitoring Ca²⁺ signals of HEK293 cells with a [³H]ryanodine binding assay.

RESULTS

The mean coupling interval of PVCs was 282 ± 13 ms. The 12-lead electrocardiogram had no specific findings except PVCs with an extremely short-coupling interval. Genetic analysis revealed 3 novel RyR2 variants and 1 polymorphism, all located in the cytoplasmic region. p.Ser4938Phe was not detected in 3 databases, and in silico analysis indicated its pathogenicity. In functional analysis, p.Ser4938Phe demonstrated loss of function and impaired RyR2 channel Ca²⁺ release, while 2 other variants, p.Val1024Ile and p.Ala2673Val, had mild gain-of-function effects but were similar to the polymorphism p.Asn1551Ser.

CONCLUSION

We identified an RyR2 variant associated with reduced Ca²⁺ release and short-coupled torsades de pointes ventricular arrhythmia. The mechanisms of arrhythmogenesis remain unclear.

Premature Ventricular Complexes in Apparently Normal Hearts

Premature ventricular complexes (PVCs) are consistently associated with worse prognosis and higher morbidity and mortality. This article reviews PVCs and their presentation in patients with an apparently normal heart. Patients with PVCs may be completely asymptomatic, whereas others may note severely disabling symptoms. Cardiomyopathy may occur with frequent PVCs. Diagnostic work-up is directed at obtaining 12-lead ECG to characterize QRS morphology, Holter monitor to assess frequency, and echo and advanced imaging to assess for early cardiomyopathy and exclude structural heart disease. Options for management include watchful waiting, medical therapy, or catheter ablation. Malignant variants of PVCs may induce ventricular fibrillation even in a normal heart.

Silent and Malignant Early Repolarization Syndrome Mimicking Hyper-Acute ST Elevation Myocardial Infarction

A 55-year-old male with underlying type 2 diabetes mellitus and hypertension presented at our emergency department with ventricular fibrillation-related cardiac arrest. Hyper-acute ST elevation myocardial infarction was the preliminary diagnosis by 12-lead electrocardiography, which simultaneously showed J point ST elevation and tall T waves. However, the echocardiography showed concentric left ventricle hypertrophy and preserved left ventricular systolic function with no regional wall motion abnormalities, and coronary angiography did not show any critical coronary artery lesion. Malignant early repolarization syndrome was diagnosed, and an implantable cardioverter defibrillator was implanted. Early repolarization syndrome is associated with J point elevation, and more involved leads and an increased J point elevation amplitude can increase the risk of arrhythmogenicity. In summary, we report a case with asymptomatic type 3 early repolarization syndrome-induced idiopathic ventricular fibrillation mimicking hyper-acute ST elevation myocardial infarction.

Detailed characterization of familial idiopathic ventricular fibrillation linked to the DPP6 locus

BACKGROUND

Familial idiopathic ventricular fibrillation (IVF) is a severe disease entity and is notoriously difficult to manage because there are no clinical risk indicators for premature cardiac arrest. Previously, we identified a link between familial IVF and a risk haplotype on chromosome 7q36 (involving the arrhythmia gene DPP6).

OBJECTIVE

The purpose of this study was to expand our knowledge of familial IVF and to discuss its (extended) clinical characteristics.

METHODS

We studied 601 family members and probands: 286 DPP6 risk-haplotype positive (haplotype-positive) and 315 DPP6 risk-haplotype negative (haplotype-negative) individuals. Clinical parameters, a combination of all-cause mortality and (aborted) cardiac arrest and differences between haplotype-positives and haplotype-negatives, were evaluated.

RESULTS

There were no differences in electrocardiographic indices between haplotype-positives and haplotype-negatives, or between haplotype-positives with or without events. Cardiac magnetic resonance documented slightly larger ventricular volumes in haplotype-positives compared to controls (P <.05), but these were not clinically useful. Mortality and/or cardiac arrest occurred in 85 haplotype-positives (30%) and 18 haplotype-negatives (6%). Twenty-four haplotype-positives (8% male) were resuscitated from ventricular fibrillation (VF). Documented VF was always elicited by monomorphic short-coupled extrasystoles from the right ventricular apex/lower free wall. Median survival in risk-haplotype haplotype-positives was 70 vs. 93 years for haplotype-negatives (P < .01), with a worse phenotype in males (median survival 63 vs. 83 years in females, P < .01). Implantable cardioverter-defibrillators were implanted in 99 patients (76 [77%] for primary prevention). Two arrhythmic events occurred in the primary prevention group during follow-up (5 ± 3 years).

CONCLUSION

Despite our extensive analysis, the complexity in identifying asymptomatic IVF family members at risk for future arrhythmias based on clinical parameters is once more demonstrated.

Malignant conversion of benign right ventricular outflow track ventricular tachycardia 18 years post-ablation

This case report describes the rare phenomenon of malignant conversion of benign right ventricular outflow tract ventricular tachycardia into idiopathic ventricular fibrillation 18 years after successful ablation, in the absence of any type of heart disease. We review the current literature looking at predictors for this event, with the conclusion that there are no reliable risk predictors available. Until clear guidelines exist, we suggest patients be informed and monitored for the possibility of "malignant conversion" following ablation for benign idiopathic outflow tract ventricular tachycardia.