The Importance of Systematic Diagnostic Testing in Idiopathic Ventricular Fibrillation: Results From the Dutch iVF-Registry

Long-term prognosis of idiopathic ventricular fibrillation: An eighteen-year experience from a tertiary center

INTRODUCTION AND OBJECTIVES

Idiopathic ventricular fibrillation (IVF) is diagnosed in patients who survive sudden cardiac arrest (SCA), preferably with documented ventricular fibrillation (VF), without any identifiable structural or electrical abnormality. Current evidence provides limited guidance on the diagnosis and follow-up of these patients. Our aim was to assess the clinical outcomes of survivors of an aborted SCA attributed to IVF.

METHODS

We retrospectively collected clinical data from all patients who survived SCA and implanted a cardiac defibrillator (ICD) between 2005 and 2023.

RESULTS

A total of 38 patients, 36.8% female, with a mean age of 44±14 years old were included. Median follow-up time was 8.7 years (interquartile range (IQR) 4.7-14.7 years). All patients underwent a comprehensive diagnostic evaluation that excluded structural and coronary disease. During follow-up, underlying diagnoses were established in 34.2% of the whole cohort. Genetic testing, performed in 37.2%, revealed underlying diagnoses in 57.1% of those tested, compared to only 26.3% of patients who did not undergo genetic testing [p=0.035, OR=5.1 (95% confidence interval (CI) 1.2-21.5)]. Mortality was 10.5% (due to non-arrhythmic causes) and 36.8% patients received appropriate therapies with a median time to first ICD therapy of 39 [5.4-47.3] months.

CONCLUSION(S)

Etiological diagnosis and recurrence prediction in patients with IVF remains challenging, even with extensive diagnostic evaluation and long-term follow-up. In our study, genetic testing enhanced diagnostic yield. Consistent with previous findings, our cohort experienced a notable arrhythmic recurrence, with no cardiac deaths, underlining the pivotal role of ICD implantation in these patients.

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.

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.

Idiopathic ventricular fibrillation: is it a case for genetic testing?

Idiopathic ventricular fibrillation (IVF) is a diagnosis of exclusion in sudden cardiac arrest (SCA) survivors. Although there are clear guidelines on the clinical work-up of SCA survivors, less than one in five patients receives a complete work-up. This increases the chances of erroneously labelling these patients as having IVF, while 10-20% of them have an inherited cardiac condition (ICC). Diagnoses of ICC increase over time due to (additional) deep phenotyping or as a result of spontaneous expression of ICC over time. As SCA survivors can also harbor (likely) pathogenic variants in cardiomyopathy-associated genes in the absence of a phenotype, or can have another ICC without a clear cardiac phenotype, the question arises as to whether genetic testing in this group should be routinely performed. Family history (mainly in the case of sudden death) can increase suspicion of an ICC in an SCA victim, but does not add great value when adults underwent a complete cardiological work-up. The diagnosis of ICC has treatment consequences not only for the patient but also for their family. Genetic diagnostic yield does not appear to increase with larger gene panels, but variants of unknown significance (VUS) do. Although VUS can be confusing, careful and critical segregation analysis in the family can be performed when discussed in a multidisciplinary team at a center of expertise with at least a cardiologist as well as a clinical and laboratory geneticist, thereby degrading or promoting VUS. When to introduce genetic testing in SCA survivors remains a matter of debate, but the combination of quick, deep phenotyping with additional genetic testing for the unidentifiable phenotypes, especially in the young, seems preferable.

Explaining the Unexplained: A Practical Approach to Investigating the Cardiac Arrest Survivor

Sudden cardiac arrest (SCA) is a common cause of death. The majority of SCA is caused by ventricular arrhythmia due to underlying CHD. Aborted SCA with no apparent diagnosis after initial assessment with ECG, echocardiography and coronary assessment is referred to as unexplained cardiac arrest (UCA). Systematic evaluation of such patients may reveal a specific diagnosis in up to half of patients before a diagnosis of idiopathic VF is assigned. Specific diagnoses include inherited cardiac conditions, such as latent cardiomyopathies or inherited primary electrical disease. Identifying the cause of UCA is therefore not only critical for appropriate management of the SCA survivors to prevent recurrence, but also for their family members who may be at risk of the same condition. This review provides a tiered, systematic approach for the investigation of UCA.

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.

Appropriate Implantable Cardioverter-Defibrillator Therapy in Patients with Ventricular Arrhythmia of Unclear Cause in Secondary Prevention of Sudden Cardiac Death

In this study, we sought to investigate the occurrence of appropriate implantable cardioverter-defibrillator (ICD) therapies and inappropriate shocks in secondary prevention ICD recipients with ventricular arrhythmia of unclear cause and ventricular arrhythmia in the context of underlying heart disease. In this retrospective study, consecutive patients with an ICD implanted for secondary prevention in the University Medical Center Groningen (UMCG), the Netherlands between 1 January 2012 and 31 December 2018 were included. Patients were classified as having ventricular arrhythmia of unclear cause if no clear cause was found which could explain the index ventricular arrhythmia. The primary outcome was appropriate ICD therapy. The study population consisted of 257 patients. In 220 patients, an underlying heart disease could be identified as the cause of ventricular arrhythmia, while 37 patients had an unclear cause of ventricular arrhythmia. The median age was 64 years (interquartile range (IQR) 53-72 years). Forty-five (18%) patients were women. During a median duration of follow-up of 6.2 years (IQR 4.8-7.8 years), appropriate ICD therapy occurred in 95 (37%) patients. This number was 90 (41%) in the group with a clear etiology and 5 (14%) in the group with an unclear etiology. In multivariable analysis, index ventricular arrhythmia of unclear cause was associated with fewer appropriate ICD therapies (HR 0.37 [95% CI 0.14-0.99]; p = 0.048), as well as an increased risk of inappropriate ICD shocks (HR 3.71 [95% CI 1.17-11.80]; p = 0.026). Index ventricular arrhythmia of unclear cause was significantly associated with fewer appropriate ICD therapies.