Distinct Electrogram Features and Ventricular Arrhythmia Induction Modes Between Repolarization and Conduction Heterogeneities

BACKGROUND

Recent clinical studies have indicated the presence of localized electrical abnormalities in idiopathic ventricular fibrillation and J-wave syndrome patients.

OBJECTIVES

This study aims to characterize the specific electrical signatures of localized repolarization and conduction heterogeneities and their respective role in vulnerability to arrhythmias.

METHODS

Optical mapping was performed in porcine right ventricles with local: 1) repolarization shortening; 2) conduction slowing; or 3) structural heterogeneity induced by locally perfusing: 1) pinacidil (20 μmol/L, n = 13); or 2) flecainide (2 μmol/L, n = 13) via an epicardial catheter; or 3) by local epicardial tissue destruction (9 radiofrequency lesions n = 12). Electrograms were recorded (n = 5 in each group) and spontaneous and induced arrhythmias were quantified and optically mapped.

RESULTS

Electrograms were normal in (1) but showed local fragmentation in 40% of preparations in (2) with greater effects observed at high pacing frequencies dependent on the wavefront direction. In (3), the structural substrate alone increased the width and number of peaks in the electrograms, and addition of flecainide induced pronounced fragmentation (≥3 peaks and ≥70 ms) in all cases. Occurrence of spontaneous arrhythmias was significantly increased in (1) and (2) (P < 0.0001 and 0.05, respectively, vs baseline) and were triggered by ectopies. Vulnerability to arrhythmias at high pacing frequencies (≥2 Hz) was the lowest in (1) and greatest in (2).

CONCLUSIONS

Microstructural substrates have the most pronounced impact on electrograms, especially when combined with sodium channel blockers, whereas local action potential duration shortening does not lead to electrogram fragmentation even though it is associated with the highest prevalence of spontaneous arrhythmias.

Mitral Annular Disjunction in Idiopathic Ventricular Fibrillation Patients: Just a Bystander or a Potential Cause?

AIMS

Previously, we demonstrated that inferolateral mitral annular disjunction (MAD) is more prevalent in patients with idiopathic ventricular fibrillation (IVF) than in healthy controls. In the present study, we advanced the insights into the prevalence and ventricular arrhythmogenicity by inferolateral MAD in an even larger IVF cohort.

METHODS AND RESULTS

This retrospective multicentre study included 185 IVF patients (median age 39 [27, 52] years, 40% female). Cardiac magnetic resonance images were analysed for mitral valve and annular abnormalities and late gadolinium enhancement. Clinical characteristics were compared between patients with and without MAD. MAD in any of the 4 locations was present in 112 (61%) IVF patients and inferolateral MAD was identified in 24 (13%) IVF patients. Mitral valve prolapse (MVP) was found in 13 (7%) IVF patients. MVP was more prevalent in patients with inferolateral MAD compared with patients without inferolateral MAD(42% vs. 2%, p < 0.001). Proarrhythmic characteristics in terms of a high burden of premature ventricular complexes (PVC) and non-sustained ventricular tachycardia (VT) were more prevalent in patients with inferolateral MAD compared to patients without inferolateral MAD (67% vs. 23%, p < 0.001 and 63% vs 41%, p = 0.046, respectively). Appropriate implantable cardioverter defibrillator therapy during follow-up was comparable for IVF patients with or without inferolateral MAD (13% vs. 18%, p = 0.579).

CONCLUSION

A high prevalence of inferolateral MAD and MVP is a consistent finding in this large IVF cohort. The presence of inferolateral MAD is associated with a higher PVC burden and non-sustained VTs. Further research is needed to explain this potential interplay.

The Prevalence and Characteristics of Arrhythmic Mitral Valve Prolapse in Patients With Unexplained Cardiac Arrest

BACKGROUND

There is growing evidence that mitral valve prolapse (MVP) is associated with otherwise unexplained cardiac arrest (UCA). However, reports are hindered by the absence of a systematic ascertainment of alternative diagnoses.

OBJECTIVES

This study reports the prevalence and characteristics of MVP in a large cohort of patients with UCA.

METHODS

Patients were enrolled following an UCA, defined as cardiac arrest with no coronary artery disease, preserved left ventricular ejection fraction, and no apparent explanation on electrocardiogram. A comprehensive evaluation was performed, and patients were diagnosed with idiopathic ventricular fibrillation (IVF) if no cause was found. Echocardiography reports were reviewed for MVP. Patients with MVP were divided into 2 groups: those with IVF (AMVP) and those with an alternative diagnosis (nonarrhythmic MVP). Patient characteristics were then compared. The long-term outcomes of AMVP were reported.

RESULTS

Among 571 with an initially UCA, 34 patients had MVP (6%). The prevalence of definite MVP was significantly higher in patients with IVF than those with an alternative diagnosis (24 of 366 [6.6%] vs 5 of 205 [2.4%]; P = 0.03). Bileaflet prolapse was significantly associated with AMVP (18 of 23 [78%] vs 1 of 8 [12.5%]; P = 0.001; OR: 25.2). The proportion of patients with AMVP who received appropriate implantable cardioverter-defibrillator therapies over a median follow-up of 42 months was 21.1% (4 of 19).

CONCLUSIONS

MVP is associated with otherwise UCA (IVF), with a prevalence of 6.6%. Bileaflet prolapse appears to be a feature of AMVP, although future studies need to ascertain its independent association. A significant proportion of patients with AMVP received appropriate implantable cardioverter-defibrillator therapies during follow-up.

Ventricular fibrillation induced by fever in structurally normal hearts

Ventricular fibrillation (VF) is a life-threatening arrhythmia that usually happens in patients with structural heart diseases. However, fever-induced ventricular fibrillation in structurally normal hearts was reported, and the four main diseases associated with these cases were Brugada syndrome, long QT syndrome, idiopathic ventricular fibrillation, and non-cardiovascular diseases. In this review, we analyzed this phenomenon and its clinical characteristics.

Genetics in Probands With Idiopathic Ventricular Fibrillation: A Multicenter Study

BACKGROUND

Different genes have been associated with idiopathic ventricular fibrillation (IVF); however, there are no studies correlating genotype with phenotype.

OBJECTIVES

The aim of this study was to define the genetic background of probands with IVF using large gene panel analysis and to correlate genetics with long-term clinical outcomes.

METHODS

All consecutive probands with a diagnosis of IVF were included in a multicenter retrospective study. All patients had: 1) IVF diagnosis throughout the follow-up; and 2) genetic analysis with a broad gene panel. All genetic variants were classified as pathogenic/likely pathogenic (P+), variants of unknown significance (VUS) or no variants (NO-V), following current guidelines of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology. The primary endpoint was occurrence of ventricular arrhythmias (VA).

RESULTS

Forty-five consecutive patients were included. A variant was found in 12 patients, 3 P+ and 9 VUS carriers. After a mean follow-up time of 105.0 months, there were no deaths and 16 patients (35.6%) experienced a VA. NO-V patients had higher VA free survival during the follow-up, compared with both VUS (72.7% vs 55.6%, log-rank P < 0.001) and P+ (72.7% vs 0%, log-rank P = 0.013). At Cox analysis, P+ or VUS carrier status was a predictor of VA occurrence.

CONCLUSIONS

In probands with IVF, undergoing genetic analysis with a broad panel, the diagnostic yield for P+ is 6.7%. P+ or VUS carrier status is a predictor of VA occurrence.

Novel SCN5A frame‑shift mutation underlying in patient with idiopathic ventricular fibrillation manifested with J wave in inferior lead and prolonged S‑wave in precordial lead

Mutations in the SCN5A gene has been recognized as resulting in a series of life-threatening arrhythmias. However, it also causes idiopathic ventricular fibrillation (IVF) with J wave in inferior leads and prolonged S-wave upstroke in precordial leads, which has not been previously reported. The present study aimed to study the mechanisms of a patient with IVF manifested with J wave in inferior leads and prolonged S-wave upstroke in precordial leads. The electrocardiograms (ECG) of the proband were recorded and genetic testing was conducted. Patch-clamp and immunocytochemical studies were performed in heterologously transfected 293 cells. The VF attacks was documented in a 55-year-old male proband with syncope episodes. 12-lead ECG shown the transient J wave in the inferior leads and prolonged S-wave upstroke in precordial V1-V3 leads in the same timeframe. Genetic analysis revealed a novel 1 base deletion (G) at position 839 in exon 2 in SCN5A gene (C280S*fs61), which causes a severe truncation of the sodium channel. The functional study revealed that in 293 cells transfected with mutant channel, no sodium current could be recorded even though the immunocytochemical experiment confirmed the truncated sodium channel existed in cytosol. The kinetics of the wild-type (WT) channel were not altered when co-transfected with C280S*fs61 mutant which suggested a haploinsufficiency effect of sodium channel in the cells. The present study identified a novel C280Sfs*61 mutation that caused the 'loss of function' of the sodium channel by haploinsufficiency mechanism. The reduced sodium channel function in the heart may cause conduction delay that may underlie the manifestation of J wave and prolonged S-wave upstroke associated with IVF.

Ventricular Conduction Stability Noninvasively Identifies an Arrhythmic Substrate in Survivors of Idiopathic Ventricular Fibrillation

Background Idiopathic ventricular fibrillation (VF) is a diagnosis of exclusion following normal cardiac investigations. We sought to determine if exercise-induced changes in electrical substrate could distinguish patient groups with various ventricular arrhythmic pathophysiological conditions and identify patients susceptible to VF. Methods and Results Computed tomography and exercise testing in patients wearing a 252-electrode vest were combined to determine ventricular conduction stability between rest and peak exercise, as previously described. Using ventricular conduction stability, conduction heterogeneity in idiopathic VF survivors (n=14) was compared with those surviving VF during acute ischemia with preserved ventricular function following full revascularization (n=10), patients with benign ventricular ectopy (n=11), and patients with normal hearts, no arrhythmic history, and negative Ajmaline challenge during Brugada family screening (Brugada syndrome relatives; n=11). Activation patterns in normal subjects (Brugada syndrome relatives) are preserved following exercise, with mean ventricular conduction stability of 99.2±0.9%. Increased heterogeneity of activation occurred in the idiopathic VF survivors (ventricular conduction stability: 96.9±2.3%) compared with the other groups combined (versus 98.8±1.6%; P=0.001). All groups demonstrated periodic variation in activation heterogeneity (frequency, 0.3-1 Hz), but magnitude was greater in idiopathic VF survivors than Brugada syndrome relatives or patients with ventricular ectopy (7.6±4.1%, 2.9±2.9%, and 2.8±1.2%, respectively). The cause of this periodicity is unknown and was not replicable by introducing exercise-induced noise at comparable frequencies. Conclusions In normal subjects, ventricular activation patterns change little with exercise. In contrast, patients with susceptibility to VF experience activation heterogeneity following exercise that requires further investigation as a testable manifestation of underlying myocardial abnormalities otherwise silent during routine testing.

Sinus Rhythm Electrocardiographic Abnormalities, Sites of Origin, and Ablation Outcomes of Ventricular Premature Depolarizations Initiating Ventricular Fibrillation

BACKGROUND

Ventricular fibrillation (VF) can be initiated by ventricular premature depolarizations (VPDs) in the absence of obvious structural abnormalities.

OBJECTIVE

To determine the prevalence of 12-lead ECG sinus rhythm reduced QRS amplitude, QRS fractionation (QRSf) and early repolarization (ER) pattern, and the outcome of catheter ablation and VPD anatomic distribution in patients with VPDs initiating VF.

METHODS

We compared a cohort with no apparent structural heart disease and VPDs initiating VF (Group 1, n=42) to a reference cohort (Group 2, n=61) of patients with no structural heart disease and symptomatic unifocal VPDs.

RESULTS

A reduced QRS amplitude (<.55 mV) in aVF (59 % vs 10%, p<0.001), QRSf in ≥2 contiguous leads (50% vs 16%, p<0.001) and early repolarization pattern (21.4% vs 1.6%, p=0.01) were more common in Group 1 vs Group 2. At least one abnormal ECG finding was present in 34 (81%) Group 1 vs 17 (28%) Group 2 patients, (p<0.001). VPD origin included RV and LV distal Purkinje system and moderator band/ papillary muscles, in 83% Group 1 vs 18% Group 2 patients, p<0.001. VF was eliminated with single ablation procedure in 77% of Group 1 patients with at least 2 years of follow-up.

CONCLUSIONS

A reduced QRS amplitude (<.55 mV) in aVF, QRS fractionation in ≥2 contiguous leads and/or an early repolarization pattern are frequently observed in patients with VPDs initiating VF. VPDs initiating VF typically originate from the distal Purkinje system and papillary muscles and can be successfully eliminated with catheter ablation.

Idiopathic ventricular fibrillation associated with long-coupled Purkinje ectopy

INTRODUCTION

Idiopathic ventricular fibrillation (IVF) is mainly associated with and triggered by short-coupled (R-on-T) ventricular ectopics. However, little is known about the risk of VF associated with long-coupled premature ventricular complexes (LCPVCs).

OBJECTIVE

To examine the prevalence and characteristics of IVF patients presenting with LCPVCs.

METHODS

Consecutive patients with IVF and PVCs from five arrhythmia referral centers were reviewed. We included patients presenting LCPVCs, defined as PVCs falling after the end of the T wave, with a normal QTc interval. We evaluated demographics, medical history, and clinical circumstances associated with PVCs and VF episodes. The origin of PVCs was determined by invasive mapping.

RESULTS

Seventy-nine patients with IVF were reviewed. Among them, 12 (15.2%) met the inclusion criteria (8 women, age 36 ± 14 years). Eleven patients had documented LCPVCs initiating repetitive PVCs or sustained VF, whereas 1 had only documented isolated PVCs. In 10 of 12 patients, PVCs were recorded showing both long and short coupling intervals of 418 ± 46 and 304 ± 33 ms, respectively. Mapping showed that PVCs originated from the left Purkinje in 10 patients, from the right Purkinje in 1 patient, and both in 1 patient. Compared to other patients from the initial cohort, IVF with LCPVCs was associated with a left-sided origin of PVCs (92% in long-coupled IVF vs. 46% of left Purkinje PVCs in short-coupled IVF, p = .004).

CONCLUSION

Long-coupled fascicular PVCs, traditionally recognized as benign, can be associated with IVF in a subset of patients. They can induce IVF by themselves or in association with short-coupled PVCs.

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

BACKGROUND

Idiopathic ventricular fibrillation (iVF) is a diagnosis of exclusion. Systematic diagnostic testing is important to exclude alternative causes for VF. The early use of "high yield" testing, including cardiac magnetic resonance (CMR), exercise testing, and sodium channel blocker provocation, has been increasingly recognized.

OBJECTIVES

The purpose of this study was to investigate the importance and consistency of systematic diagnostic testing in iVF.

METHODS

This study included 423 iVF patients from 11 large secondary and tertiary hospitals in the Netherlands. Clinical characteristics and diagnostic testing data were ascertained.

RESULTS

IVF patients experienced the index event at a median age of 40 years (IQR: 28-52 years), and 61% were men. The median follow-up time was 6 years (IQR: 2-12 years). Over the years, "high yield" diagnostic tests were increasingly performed (mean 68% in 2000-2010 vs 75% in 2011-2021; P < 0.001). During follow-up, 38 patients (9%) originally labeled as iVF received an alternative diagnosis. Patients in whom "high-yield" diagnostic tests were consistently performed during the initial work-up received an alternative diagnosis less frequently during follow-up (HR: 0.439; 95% CI: 0.219-0.878; P = 0.020). Patients who received an alternative diagnosis during follow-up had a worse prognosis in terms of cardiac death (P = 0.012) with a trend toward more implantable cardioverter-defibrillator therapy (P = 0.055).

CONCLUSIONS

Although adherence to (near) complete diagnostic testing in this population of iVF patients increased over the years, patients with iVF still undergo varying levels of diagnostic evaluation. The latter leads to initial underdiagnosis of alternative conditions and is associated with a worse prognosis. Our results underscore the importance of early systematic diagnostic assessment in patients with apparent iVF.

Prevalence of Mitral Annulus Disjunction and Mitral Valve Prolapse in Patients With Idiopathic Ventricular Fibrillation

Background

Idiopathic ventricular fibrillation (IVF) is diagnosed in patients with ventricular fibrillation of which the origin is not identified after extensive evaluations. Recent studies suggest an association between mitral annulus disjunction (MAD), mitral valve prolapse (MVP), and ventricular arrhythmias. The prevalence of MAD and MVP in patients with IVF in this regard is not well established. We aimed to explore the prevalence of MAD and MVP in a consecutive cohort of patients with IVF compared with matched controls.

Methods and Results

In this retrospective, multicenter cohort study, cardiac magnetic resonance images from patients with IVF (ie, negative for ischemia, cardiomyopathy, and channelopathies) and age‐ and sex‐matched control subjects were analyzed for the presence of MAD (≥2 mm) and MVP (>2 mm). In total, 72 patients (mean age 39±14 years, 42% women) and 72 control subjects (mean age 41±11 years, 42% women) were included. MAD in the inferolateral wall was more prevalent in patients with IVF versus healthy controls (7 [11%] versus 1 [1%], P=0.024). MVP was only seen in patients with IVF and not in controls (5 [7%] versus 0 [0%], P=0.016). MAD was observed in both patients with (n=4) and without (n=3) MVP.

Conclusions

Inferolateral MAD and MVP were significantly more prevalent in patients with IVF compared with healthy controls. The authors advocate that evaluation of the mitral valve region deserves extra attention in the extensive screening of patients with unexplained cardiac arrest. These findings support further exploration of the pathophysiological mechanisms underlying a subset of IVF that associates with MAD and MVP.

Atrial Fibrillation-triggered Ventricular Fibrillation in a Patient with Early Repolarization Syndrome

A 54-year-old man with early repolarization syndrome (ERS) implanted with an implantable cardioverter-defibrillator (ICD) developed persistent atrial fibrillation (AF) three years after the implantation. Similarly, the remote monitoring system begun frequently detecting ventricular fibrillation (VF) and polymorphic ventricular tachycardia (PVT). Longer RR intervals were repeatedly observed just before the initiation of PVT/VF. Catheter ablation for AF successfully diminished both the PVT and VF events.

Short-Coupled Idiopathic Ventricular Fibrillation: A Literature Review With Extended Follow-Up

Idiopathic ventricular fibrillation is responsible for approximately 10% of cases of aborted cardiac arrest. Recent studies have shown that short-coupled ventricular premature complexes are present at the onset of idiopathic ventricular fibrillation in 6.6%-17% of patients. The present review provided information on 86 patients with short-coupled malignant ventricular arrhythmias that were reported as case reports or small patient series during the last 70 years. In 75% of the 81 cases published during the last 40 years, extended information and follow-up (from 2.63 ± 4.5 to 10.67 ± 7.8 years; P < 0.001, between the original publication to the latest update) could be obtained from the authors. The review shows that short-coupled malignant ventricular arrhythmias occurred almost equally in males and females, at the mean age of 40 years. A tendency for later occurrence of the arrhythmia by 4 years was observed in females. A prior history of syncope was noted in 45.3% of the patients, whereas arrhythmic storm occurred in 42% at presentation. The most common mode of revelation of short-coupled malignant ventricular arrhythmias was syncope (53.5%), followed by aborted cardiac arrest (26.7%) and recurrent arrhythmic event after prior implantable-cardioverter defibrillator implantation for idiopathic ventricular fibrillation (17.4%). For the first time, short-coupled malignant arrhythmias exhibiting "not-so-short" coupling intervals (≥350 ms) were found in a significant proportion of patients (17.4%). During long-term follow-up, quinidine yielded a slightly higher success rate in arrhythmia control than ablation. Larger studies are necessary to assess the best strategy for the management of this potentially lethal arrhythmia.

Dopamine in Idiopathic Polymorphic Ventricular Tachycardia/Ventricular Fibrillation

The role of medical therapy in the treatment of idiopathic polymorphic ventricular tachycardia (IPMVT) and idiopathic ventricular fibrillation (IVF) is not well established. Current medications in use include amiodarone, lidocaine, isoproterenol, verapamil, and quinidine. However, the use of dopamine for controlling such arrhythmias has never been described. We present an interesting case of IPMVT/IVF storm induced by short-coupled premature ventricular contractions. The arrhythmia was terminated acutely using dopamine infusion and was suppressed chronically using verapamil.

Empirical Ablation to Prevent Sequential Purkinje System Recruitment: A Novel Therapy for Idiopathic Ventricular Fibrillation

We report 3 cases (mean age 48.3 ± 11.6 years) of idiopathic ventricular fibrillation (IVF), in which a triggering premature ventricular complex leading to IVF could not be identified. All patients underwent posterior fascicle transection with empirical linear ablation of the mid-Purkinje potentials identified along the left ventricular interventricular inferior septum, and no ventricular fibrillation recurrence was documented in any of the patients. (Level of Difficulty: Advanced.)

Diagnostic Impact of Repeated Expert Review & Long-Term Follow-Up in Determining Etiology of Idiopathic Cardiac Arrest

Background

Recognizing the etiology of sudden cardiac arrest (SCA) has an enormous impact on the management of victims and their immediate families. A significant proportion of SCA survivors with a structurally normal heart are not offered a diagnosis and there is no clear consensus on the type and duration of follow‐up. We aimed to assess the utility of a multidisciplinary approach in optimizing diagnosis of cardiac arrest etiology during follow‐up.

Methods and Results

We retrospectively assessed 327 consecutive SCA survivors (mean age 61.9±16.2 years, 80% men) who underwent secondary prevention implantable cardioverter defibrillators between May 2015 and November 2018. The initial diagnosis was recorded at the time of admission and follow‐up diagnosis was deduced from subsequent clinic records, investigations, and outcomes of multidisciplinary team meetings. Structural heart disease accounted for 282 (86%) of SCAs. Forty‐five (14%) patients had a structurally normal heart and underwent comprehensive testing and follow‐up (mean duration 93±52 weeks). On initial evaluation, 14/45 (31%) of these received a diagnosis, rising to 29/45 (64%) with serial reviews during follow‐up. Discussion in multidisciplinary team meetings and imaging reassessment accounted for 47% of new diagnoses. No additional diagnoses were made beyond 96 weeks. Nineteen (5.8%) fatalities occurred in the entire cohort, exclusively in patients with structural heart disease.

Conclusions

Systematic comprehensive testing combined with multidisciplinary expert team review of SCA survivors without structural heart disease improves the yield and time to diagnosis compared with previously published studies. This approach has positive implications in the management of SCA survivors and their families.

Three-dimensional mapping discovered arrhythmic substrate missed in the initial diagnosis of idiopathic ventricular fibrillation

During an initial diagnosis of IVF, an arrhythmic substrate may be missed for several reasons such as lack of information; thus, a careful follow-up is important. A three-dimensional mapping may identify a possible missed arrhythmic substrate in IVF.

Why Ablation of Sites With Purkinje Activation Is Antiarrhythmic: The Interplay Between Fast Activation and Arrhythmogenesis

Ablation of sites showing Purkinje activity is antiarrhythmic in some patients with idiopathic ventricular fibrillation (iVF). The mechanism for the therapeutic success of ablation is not fully understood. We propose that deeper penetrance of the Purkinje network allows faster activation of the ventricles and is proarrhythmic in the presence of steep repolarization gradients. Reduction of Purkinje penetrance, or its indirect reducing effect on apparent propagation velocity may be a therapeutic target in patients with iVF.

The Electrophysiological Substrate of Early Repolarization Syndrome: Noninvasive Mapping in Patients

Background

The early repolarization (ER) pattern is a common ECG finding. Recent studies established a definitive clinical association between ER and fatal ventricular arrhythmias. However, the arrhythmogenic substrate of ER in the intact human heart has not been characterized.

Objectives

To map the epicardial electrophysiological (EP) substrate in ER syndrome patients using noninvasive Electrocardiographic Imaging (ECGI), and to characterize substrate properties that support arrhythmogenicity.

Methods

Twenty-nine ER syndrome patients were enrolled, 17 of which had a malignant syndrome. Characteristics of the abnormal EP substrate were analyzed using data recorded during sinus rhythm. The EP mapping data were analyzed for electrogram morphology, conduction and repolarization. Seven normal subjects provided control data.

Results

The abnormal EP substrate in ER syndrome patients has the following properties: (1) Abnormal epicardial electrograms characterized by presence of J-waves in localized regions; (2) Absence of conduction abnormalities, including delayed activation, conduction block, or fractionated electrograms; (3) Marked abbreviation of ventricular repolarization in areas with J-waves. The action potential duration (APD) was significantly shorter than normal (196±19 vs. 235±21 ms, p<0.05). Shortening of APD occurred heterogeneously, leading to steep repolarization gradients compared to normal control (45±17 vs.7±5 ms/cm, p<0.05). Premature ventricular contractions (PVCs) were recorded in 2 patients. The PVC sites of origin were closely related to the abnormal EP substrate with J-waves and steep repolarization gradients.

Conclusions

Early Repolarization is associated with steep repolarization gradients caused by localized shortening of APD. Results suggest association of PVC initiation sites with areas of repolarization abnormalities. Conduction abnormalities were not observed.

Early Repolarization Syndrome: Diagnostic and Therapeutic Approach

An early repolarization pattern can be observed in 1% up to 13% of the overall population. Whereas, this pattern was associated with a benign outcome for many years, several more recent studies demonstrated an association between early repolarization and sudden cardiac death, so-called early repolarization syndrome. In early repolarization syndrome patients, current imbalances between epi- and endo-cardial layers result in dispersion of de- and repolarization. As a consequence, J waves or ST segment elevations can be observed on these patients' surface ECGs as manifestations of those current imbalances. Whereas, an early repolarization pattern is relatively frequently found on surface ECGs in the overall population, the majority of individuals presenting with an early repolarization pattern will remain asymptomatic and the isolated presence of an early repolarization pattern does not require further intervention. The mismatch between frequently found early repolarization patterns in the overall population, low incidences of sudden cardiac deaths related to early repolarization syndrome, but fatal, grave consequences in affected patients remains a clinical challenge. More precise tools for risk stratification and identification of this minority of patients, who will experience events, remain a clinical need. This review summarizes the epidemiologic, pathophysiologic and diagnostic background and presents therapeutic options of early repolarization syndrome.

Electrophysiological Basis for Early Repolarization Syndrome

During last centuries, Early Repolarization pattern has been interpreted as an ECG manifestation not linked to serious cardiovascular events. This view has been challenged on the basis of sporadic clinical observations that linked the J-wave with ventricular arrhythmias and sudden cardiac death. The particular role of this characteristic pattern in initiating ventricular fibrillation has been sustained by clinical descriptions of a marked and consistent J-wave elevation preceding the onset of the ventricular arrhythmia. Until now, Early Repolarization syndrome patients have been evaluated using ECG and theorizing different interpretations of the findings. Nonetheless, ECG analysis is not able to reveal all depolarization and repolarization properties and the explanation for this clinical events. Recent studies have characterized the epicardial substrate in these patients on the basis of high-resolution data, in an effort to provide insights into the substrate properties that support arrhythmogenicity in these patients. An overview for the current evidence supporting different theories explaining Early Repolarization Syndrome is provided in this review. Finally, future developments in the field directed toward individualized treatment strategies are examined.

Mapping and Ablation of Idiopathic Ventricular Fibrillation

Idiopathic ventricular fibrillation (IVF) is the main cause of unexplained sudden cardiac death, particularly in young patients under the age of 35. IVF is a diagnosis of exclusion in patients who have survived a VF episode without any identifiable structural or metabolic causes despite extensive diagnostic testing. Genetic testing allows identification of a likely causative mutation in up to 27% of unexplained sudden deaths in children and young adults. In the majority of cases, VF is triggered by PVCs that originate from the Purkinje network. Ablation of VF triggers in this setting is associated with high rates of acute success and long-term freedom from VF recurrence. Recent studies demonstrate that a significant subset of IVF defined by negative comprehensive investigations, demonstrate in fact subclinical structural alterations. These localized myocardial alterations are identified by high density electrogram mapping, are of small size and are mainly located in the epicardium. As reentrant VF drivers are often colocated with regions of abnormal electrograms, this localized substrate can be shown to be mechanistically linked with VF. Such areas may represent an important target for ablation.

Impaired Mental Health-Related Quality of Life in Patients with Idiopathic Ventricular Fibrillation

BACKGROUND

Idiopathic ventricular fibrillation (iVF) is diagnosed in cardiac arrest survivors without an identifiable cause. Data regarding the health-related quality of life (HRQoL) in iVF patients are lacking. The purpose of this study was to investigate the HRQoL of iVF patients and to compare it to patients with an implantable cardioverter defibrillator (ICD) diagnosed with an underlying disease and healthy subjects.

METHODS

In 61 iVF patients with an ICD (iVF-ICD) and 59 ICD patients with a diagnosis (diagnosis-ICD), HRQoL was assessed using the 12-item Short-Form Health Survey (SF-12), the EuroQoL-5 dimensions (EQ-5D), the 9-item Patient Health Questionnaire, and the ICD Patient Concerns (ICDC) Questionnaire. In addition, 860 healthy subjects completed the SF-12.

RESULTS

IVF-ICD showed similar SF-12 physical summary scores compared with diagnosis-ICD patients (50.8 [interquartile range (IQR) = 42.1-53.9] vs 54.1 [IQR = 46.5-58.3]; P = 0.080) and healthy subjects (51.8 [IQR = 45.9-54.1]; P = 0.691). The mental summary score was impaired in iVF-ICD patients compared with diagnosis-ICD patients (45.9 [IQR = 40.7-49.4] vs 54.6 [IQR = 46.0-57.9]; P < 0.001) and healthy subjects (47.7 [IQR = 43.0-50.4]; P = 0.027). Scores on all five EQ-5D domains were similar between iVF-ICD patients and diagnosis-ICD patients, as well as symptoms of severe depression (19% vs 12%; P = 0.101). ICD concerns were similar between iVF-ICD and diagnosis-ICD patients (ICDC-scores 2 vs 2; P = 0.494).

CONCLUSIONS

Data suggest that there is a reduced mental HRQoL in patients with iVF compared to other cardiac arrest survivors. Screening and treatment of psychological distress should therefore be considered in iVF patients.

Sudden death and cardiac arrest without phenotype: the utility of genetic testing

Approximately 4% of sudden cardiac deaths are unexplained [the sudden arrhythmic death syndrome (SADS)], and up to 6-10% of survivors of cardiac arrest do not have an identifiable cardiac abnormality after comprehensive clinical evaluation [idiopathic ventricular fibrillation (IVF)]. Genetic testing may be able to play a role in diagnostics and can be targeted to an underlying phenotype present in family members following clinical evaluation. Alternatively, post-mortem genetic testing (the "molecular autopsy") may diagnose the underlying cause if a clearly pathogenic rare variant is found. Limitations include a modest yield, and the high probability of finding a variant of unknown significance (VUS) leading to a low signal-to-noise ratio. Next generation sequencing enables cost-efficient high throughput screening of a larger number of genes but at the expense of increased genetic noise. The yield from genetic testing is even lower in IVF in the absence of any suggestion of another phenotype in the index case or his/her family, and should be actively discouraged at this time. Future improvements in diagnostic utility include optimization of the use of variant-calling pipelines and shared databases as well as patient-specific models of disease to more accurately assign pathogenicity of variants. Studying "trios" of parents and the index case may better assess the yield of sporadic and recessive disease.

Early Repolarisation - What Should the Clinician Do?

The early repolarisation (ER) pattern is a common ECG finding. Most individuals with the ER pattern are at minimal risk for arrhythmic events. In others, ER increases the arrhythmic risk of underlying cardiac pathology. Rarely ER syndrome will manifest as a primary arrhythmogenic disorder causing ventricular fibrillation (VF). ER syndrome is defined as syncope attributed to ventricular arrhythmias or cardiac arrest attributed to ER following systematic exclusion of other etiologies. Some ECG features associated with ER portend a higher risk. However, clinically useful risk-stratifying tools to identify the asymptomatic patient at high risk are lacking. Patients with asymptomatic ER and no family history of malignant ER should be reassured. All patients with ER should continue to have modifiable cardiac risk factors addressed. Symptomatic patients should be systematically investigated, directed by symptoms.

Some Controversies about Early Repolarization: The Haïssaguerre Syndrome

Controversy has followed the groundbreaking and cornerstone paper of Haïssaguerre et al. Much of this controversy has been due to the use of the term "early repolarization pattern" and possible waveform morphologies on the standard 12-lead ECG ( it is 10 second strip) that could predict who will manifest the malignant arrhythmogenic syndrome described by Haïssaguerre et al. The standard ECG definition of early repolarization pattern (ERP) or early repolarization variant (ERV) since then has changed its clinical meaning for a surface electrocardiographic waveform from benign to malignant. The new definition of ERP/ERV contains only J wave but ST-segment elevation is no more obligatory. In the old definition, early repolarization pattern (ERP) or early repolarization variant (ERV) 3 is a well-recognized idiopathic electrocardiographic phenomenon considered to be present when at least two adjacent precordial leads show elevation of the ST segment, with values equal or higher than 1 mm. In the new electrocardiographic ERP concept, the ST segment may or may not be elevated and can be up-sloping, horizontal or down-sloping while in the old ERP/ERV concept it must be elevated at least 1 mm in at least two adjacent leads and the variant is characterized by a diffuse elevation of the ST segment of upper concavity, ending in a positive T wave of V2 to V4 or V5 and prominent J wave and ST-segment elevation predominantly in left precordial leads. The phenomenon constitutes a normal variant; it is almost a rule in athletes (present in 89% of the cases in this universe).

Early repolarization, acute emotional stress and sudden death

We herein report the case of a 36-year-old man who died suddenly after a fight with another man. Forensic investigations included unenhanced computed tomography, postmortem angiography, autopsy, histology, neuropathology, toxicology, and biochemistry and allowed a traumatic cause of death to be excluded. An electrocardiogram recorded some years prior to death revealed the presence of an early repolarization pattern. Based on the results of all investigations, the cause of death was determined to be cardiac arrhythmia and cardiac arrest during an emotionally stressful event associated with physical assault. Direct third party involvement, however, was excluded, and the manner of death was listed as natural. The case was not pursued any further by the public prosecutor.

Evolution of clinical diagnosis in patients presenting with unexplained cardiac arrest or syncope due to polymorphic ventricular tachycardia

BACKGROUND

A systematic evaluation of patients with unexplained cardiac arrest (UCA) yields a diagnosis in 50% of the cases. However, evolution of clinical phenotype, identification of new disease-causing mutations, and description of new syndromes may revise the diagnosis.

OBJECTIVE

To assess the evolution in diagnosis among patients with initially UCA.

METHODS

Diagnoses were reviewed for all patients with UCA recruited from the Cardiac Arrest Survivors with Preserved Ejection Fraction Registry with at least 1 year of follow-up.

RESULTS

After comprehensive investigation of 68 patients (age 45.2 ± 14.9 years; 63% men), the initial diagnosis was as follows: idiopathic ventricular fibrillation (n = 34 [50%]), a primary arrhythmic disorder (n = 21 [31%]), and an occult structural cause (n = 13 [19%]). Patients were followed for 30 ± 17 months, during which time the diagnosis changed in 12 (18%) patients. A specific diagnosis emerged for 7 patients (21%) with an initial diagnosis of idiopathic ventricular fibrillation. A structural cardiomyopathy evolved in 2 patients with an initial diagnosis of primary electrical disorder, while the specific structural cardiomyopathy was revised for 1 patient. Two patients with an initial diagnosis of a primary arrhythmic disorder were subsequently considered to have a different primary arrhythmic disorder. A follow-up resting electrocardiogram was the test that most frequently changed the diagnosis (67% of the cases), followed by genetic testing (17%).

CONCLUSIONS

The reevaluation of patients presenting with UCA may lead to a change in diagnosis in up to 20%. This emphasizes the need to actively monitor the phenotype and also has implications for the treatment of these patients and the screening of their relatives.

Early repolarization syndrome: electrocardiographic signs and clinical implications

Early repolarization syndrome (ERS) was previously considered as a benign variant, but it has recently emerged as a risk marker for idiopathic ventricular fibrillation (VF) and sudden death. As measured by electrocardiogram (ECG), early repolarization is characterized by an elevation of the J point and/or ST segment from the baseline by at least 0.1 mV in at least two adjoining leads. In particular, early repolarization detected by inferior ECG leads was found to be associated with idiopathic VF and has been termed as ERS. This condition is mainly observed in young men, athletes, and blacks. Also, it has become evident that electrocardiographic territory, degree of J-point elevation, and ST-segment morphology are associated with different levels of risk for subsequent ventricular arrhythmia. However, it is unclear whether J waves are more strongly associated with a depolarization abnormality rather than a repolarization abnormality. Several clinical entities can cause ST-segment elevation. Therefore, clinical and ECG data are essential for differential diagnosis. At present, the data set is insufficient to allow risk stratification in asymptomatic individuals. ERS, idiopathic VF, and Brugada syndrome (known as J-wave syndromes) are three clinical conditions that share many common ECG features; however, their clinical consequences are remarkably different. This review summarizes the current electrocardiographic data concerning ERS with clinical implications.

A mutation in CALM1 encoding calmodulin in familial idiopathic ventricular fibrillation in childhood and adolescence

OBJECTIVES

This study aimed to identify the genetic defect in a family with idiopathic ventricular fibrillation (IVF) manifesting in childhood and adolescence.

BACKGROUND

Although sudden cardiac death in the young is rare, it frequently presents as the first clinical manifestation of an underlying inherited arrhythmia syndrome. Gene discovery for IVF is important as it enables the identification of individuals at risk, because except for arrhythmia, IVF does not manifest with identifiable clinical abnormalities.

METHODS

Exome sequencing was carried out on 2 family members who were both successfully resuscitated from a cardiac arrest.

RESULTS

We characterized a family presenting with a history of ventricular fibrillation (VF) and sudden death without electrocardiographic or echocardiographic abnormalities at rest. Two siblings died suddenly at the ages of 9 and 10 years, and another 2 were resuscitated from out-of-hospital cardiac arrest with documented VF at ages 10 and 16 years, respectively. Exome sequencing identified a missense mutation affecting a highly conserved residue (p.F90L) in the CALM1 gene encoding calmodulin. This mutation was also carried by 1 of the siblings who died suddenly, from whom DNA was available. The mutation was present in the mother and in another sibling, both asymptomatic but displaying a marginally prolonged QT interval during exercise.

CONCLUSIONS

We identified a mutation in CALM1 underlying IVF manifesting in childhood and adolescence. The causality of the mutation is supported by previous studies demonstrating that F90 mediates the direct interaction of CaM with target peptides. Our approach highlights the utility of exome sequencing in uncovering the genetic defect even in families with a small number of affected individuals.

Electrical storm in idiopathic ventricular fibrillation is associated with early repolarization

OBJECTIVES

This study sought to characterize patients with idiopathic ventricular fibrillation (IVF) who develop electrical storms.

BACKGROUND

Some IVF patients develop ventricular fibrillation (VF) storms, but the characteristics of these patients are poorly known.

METHODS

Ninety-one IVF patients (86% male) were selected after the exclusion of structural heart diseases, primary electrical diseases, and coronary spasm. Electrocardiogram features were compared between the patients with and without electrical storms. A VF storm was defined as VF occurring ≥3 times in 24 h and J waves >0.1 mV above the isoelectric line in contiguous leads.

RESULTS

Fourteen (15.4%) patients had VF storms occurring out-of-hospital at night or in the early morning. J waves were more closely associated with VF storms compared to patients without VF storms: 92.9% versus 36.4% (p < 0.0001). VF storms were controlled by intravenous isoproterenol, which attenuated the J-wave amplitude. After the subsidence of VF storms, the J waves decreased to the nondiagnostic level during the entire follow-up period. Implantable cardioverter-defibrillator therapy was administered to all patients during follow-up. Quinidine therapy was limited, but the patients on disopyramide (n = 3), bepridil (n = 1), or isoprenaline (n = 1) were free from VF recurrence, while VF recurred in 5 of the 9 patients who were not given antiarrhythmic drugs.

CONCLUSIONS

The VF storms in the IVF patients were highly associated with J waves that showed augmentation prior to the VF onset. Isoproterenol was effective in controlling VF and attenuated the J waves, which diminished to below the diagnostic level during follow-up. VF recurred in patients followed up without antiarrhythmic agents.

Prognostic significance of early repolarization in inferolateral leads in Brugada patients with documented ventricular fibrillation: a novel risk factor for Brugada syndrome with ventricular fibrillation

BACKGROUND

Little is known about the clinical and prognostic impact of early repolarization (ER) on patients with Brugada syndrome (BrS), especially those with documented ventricular fibrillation (VF).

OBJECTIVE

To investigate the prevalence and prognostic significance of ER in inferolateral leads in patients with BrS and documented VF.

METHODS

We investigated 10 different 12-lead electrocardiograms (ECGs) recorded on different days to identify the presence of ER, which was defined as J-point elevation ≥0.1 mV in inferior (II, III, aVF) or lateral leads (I, aVL, V₄-V₆), in 49 individuals (46 men; age 46 ± 13 years) with a type 1 ECG of BrS and previous history of VF.

RESULTS

ER was observed persistently (in all ECGs) in 15 patients (31%; P group), intermittently (in at least one but not in all ECGs) in 16 patients (33%; I group), and not observed in 18 patients (37%; N group), yielding an overall ER incidence of 63% (31/49). During the follow-up period (7.7 years), recurrence of VF was documented in all 15 patients (100%) in the P group, and less in 12 patients (75%) in the I group and in 8 patients (44%) in the N group. The P group showed a worse prognosis than N group (P = .0001) by Kaplan-Meier analysis. Either persistent or intermittent ER in an inferolateral lead was an independent predictor of fatal arrhythmic events (hazard ratio 4.88, 95% confidence interval 2.02-12.7, P = .0004; and hazard ratio 2.50, 95% confidence interval 1.03-6.43, P = .043, respectively).

CONCLUSION

The prevalence of ER in inferolateral leads was high and an especially persistent form of ER was associated with a worse outcome in BrS patients with documented VF.

Genetic, molecular and cellular mechanisms underlying the J wave syndromes

An early repolarization (ER) pattern in the ECG, distinguished by J-point elevation, slurring of the terminal part of the QRS and ST-segment elevation has long been recognized and considered to be a benign electrocardiographic manifestation. Experimental studies conducted over a decade ago suggested that some cases of ER may be associated with malignant arrhythmias. Validation of this hypothesis was provided by recent studies demonstrating that an ER pattern in the inferior or inferolateral leads is associated with increased risk for life-threatening arrhythmias, termed ER syndrome (ERS). Because accentuated J waves characterize both Brugada syndrome (BS) and ERS, these syndromes have been grouped under the term "J wave syndromes". ERS and BS share similar ECG characteristics, clinical outcomes and risk factors, as well as a common arrhythmic platform related to amplification of I(to)-mediated J waves. Although BS and ERS differ with respect to the magnitude and lead location of abnormal J wave manifestation, they can be considered to represent a continuous spectrum of phenotypic expression. Although most subjects exhibiting an ER pattern are at minimal to no risk, mounting evidence suggests that careful attention should be paid to subjects with "high risk" ER. The challenge ahead is to be able to identify those at risk for sudden cardiac death. Here I review the clinical and genetic aspects as well as the cellular and molecular mechanisms underlying the J wave syndromes.

J wave syndromes

The J wave, also referred to as an Osborn wave, is a deflection immediately following the QRS complex of the surface ECG. When partially buried in the R wave, the J wave appears as J-point elevation or ST-segment elevation. Several lines of evidence have suggested that arrhythmias associated with an early repolarization pattern in the inferior or mid to lateral precordial leads, Brugada syndrome, or arrhythmias associated with hypothermia and the acute phase of ST-segment elevation myocardial infarction are mechanistically linked to abnormalities in the manifestation of the transient outward current (I(to))-mediated J wave. Although Brugada syndrome and early repolarization syndrome differ with respect to the magnitude and lead location of abnormal J-wave manifestation, they can be considered to represent a continuous spectrum of phenotypic expression that we propose be termed J-wave syndromes. This review summarizes our current state of knowledge concerning J-wave syndromes, bridging basic and clinical aspects. We propose to divide early repolarization syndrome into three subtypes: type 1, which displays an early repolarization pattern predominantly in the lateral precordial leads, is prevalent among healthy male athletes and is rarely seen in ventricular fibrillation survivors; type 2, which displays an early repolarization pattern predominantly in the inferior or inferolateral leads, is associated with a higher level of risk; and type 3, which displays an early repolarization pattern globally in the inferior, lateral, and right precordial leads, is associated with the highest level of risk for development of malignant arrhythmias and is often associated with ventricular fibrillation storms.

Quinidine depresses the transmural electrical heterogeneity of transient outward potassium current of the right ventricular outflow tract free wall

BACKGROUND#ENTITYSTARTX02014;: Electrical heterogeneity of the right ventricular outflow tract (RVOT) is regarded as one of the main electrophysiological substrates for Brugada syndrome. Recently quinidine has shown efficacy in patients with Brugada syndrome due to its ability to inhibit potassium current especially 4-aminopyridine-sensitive, non-Ca(2+) -dependent transient outward potassium current (Ito). However, much less is known on how extent quinidine in clinical therapeutic concentration range can inhibit this kind of electrical heterogeneity of RVOT Ito. METHODS AND RESULTS#ENTITYSTARTX02014;: Single RVOT free wall epicardial (Epi) cell, midmyocardial (M) cell and endocarcial (Endo) cells were used for whole-cell voltage clamping and Ito was recorded at 37°C, 0.2 Hz depolarization pulse. Evident Ito tranmural heterogeneity existed in RVOT free wall. Under the condition of baseline, of 10 μM quinidine perfusion 5 minutes (mins), and of 10 μM quinidine perfusion 7-10 mins, from 0 mV to 70 mV the whole transmural average Ito values of RVOT free wall were 10.2 pA/pF, 5.5 pA/pF and 3.5 pA/pF, respectively (between groups, P< 0.01). The inhibitory percentage of 10 μM quinidine at 5 mins and 7-10 mins steady-state level on the the whole Ito transmural heterogeneity of RVOT free wall were 46.3%±6% and 66.5%±11%, respectively. CONCLUSIONS#ENTITYSTARTX02014;: There exists a robust Ito transmural electrical heterogeneity in RVOT free wall and quinidine in clinical therapeutic concentration can depress this kind of heterogeneity effectively.