Epsilon waves: Milestones in the discovery and progress

The Epsilon wave was first identified in 1977. Four decades of progress help people to better understand its pathological electrogenesis and diagnostic value. Currently, the Epsilon wave is on the list of the 2010 Task Force recommendations for the diagnosis of arrhythmogenic right ventricular dysplasia (ARVD). In this review, we provide the history of the first recording of the Epsilon wave in coronary artery disease and Uhl's anomaly, subsequently leading to the signal averaging technique to record late potentials. Based on our experience, we discuss some existing controversies. When we look back at the decades of progress of the Epsilon wave, we conclude that the Epsilon wave is only the tip of the iceberg of ECG abnormalities in ARVD.

Naxos disease: from the origin to today

Naxos disease, first described by Dr. Nikos Protonotarios and colleagues on the island of Naxos, Greece, is a special form of arrhythmogenic right ventricular dysplasia (ARVD). It is an inherited condition with a recessive form of transmission and a familial penetrance of 90%. It is associated with thickening of the skin of the hands and sole, and a propensity to woolly hair. The cardiac anomalies characterized by ventricular arrhythmias with ventricular extrasystoles and tachycardia and histologic features of the myocardium are consistent with ARVD, but in a more severe form of dysplasia with major dilatation of the right ventricle. The identification of the responsible first gene on chromosome 17, and its product plakoglobin as the responsible protein for Naxos disease proved to be a milestone in the study of ARVD, which opened a new field of research. Thanks to those with the determination to discover Naxos disease, there is and will be more clarity in understanding the mechanisms of juvenile sudden death in the young who have an apparently otherwise normal heart.

Electrocardiographic features of disease progression in arrhythmogenic right ventricular cardiomyopathy/dysplasia

BACKGROUND

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is considered a progressive cardiomyopathy. However, data on the clinical features of disease progression are limited. The aim of this study was to assess 12-lead surface electrocardiographic (ECG) changes during long-term follow-up, and to compare these findings with echocardiographic data in our large cohort of patients with ARVC/D.

METHODS

Baseline and follow-up ECGs of 111 patients from three tertiary care centers in Switzerland were systematically analyzed with digital calipers by two blinded observers, and correlated with findings from transthoracic echocardiography.

RESULTS

The median follow-up was 4 years (IQR 1.9-9.2 years). ECG progression was significant for epsilon waves (baseline 14% vs. follow-up 31%, p = 0.01) and QRS duration (111 ms vs. 114 ms, p = 0.04). Six patients with repolarization abnormalities according to the 2010 Task Force Criteria at baseline did not display these criteria at follow-up, whereas in all patients with epsilon waves at baseline these depolarization abnormalities also remained at follow-up. T wave inversions in inferior leads were common (36% of patients at baseline), and were significantly associated with major repolarization abnormalities (p = 0.02), extensive echocardiographic right ventricular involvement (p = 0.04), T wave inversions in lateral precordial leads (p = 0.05), and definite ARVC/D (p = 0.05).

CONCLUSIONS

Our data supports the concept that ARVC/D is generally progressive, which can be detected by 12-lead surface ECG. Repolarization abnormalities may disappear during the course of the disease. Furthermore, the presence of T wave inversions in inferior leads is common in ARVC/D.

Different prognostic value of functional right ventricular parameters in arrhythmogenic right ventricular cardiomyopathy/dysplasia

BACKGROUND

The value of standard 2-dimensional transthoracic echocardiographic parameters for risk stratification in patients with arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is controversial.

METHODS AND RESULTS

We investigated the impact of RV fractional area change (FAC) and tricuspid annulus plane systolic excursion (TAPSE) for the prediction of major adverse cardiovascular events (MACE) defined as the occurrence of cardiac death, heart transplantation, survived sudden cardiac death, ventricular fibrillation, sustained ventricular tachycardia, or arrhythmogenic syncope. Among 70 patients who fulfilled the 2010 ARVC/D Revised Task Force Criteria and underwent baseline transthoracic echocardiography, 37 (53%) patients experienced MACE during a median follow-up period of 5.3 (interquartile range, 1.8-9.8) years. Average values for FAC, TAPSE, and TAPSE indexed to body surface area (BSA) decreased over time (P=0.03 for FAC, P=0.03 for TAPSE, and P=0.01 for TAPSE/BSA, each versus baseline). In contrast, median RV end-diastolic area increased (P=0.001 versus baseline). Based on the results of Kaplan-Meier estimates, the time between baseline transthoracic echocardiography and experiencing MACE was significantly shorter for patients with FAC <23% (P<0.001), TAPSE <17 mm (P=0.02), or right atrial short axis/BSA ≥25 mm/m(2) (P=0.04) at baseline. A reduced FAC constituted the strongest predictor of MACE (hazard ratio, 1.08 per 1% decrease; 95% confidence interval, 1.04-1.12; P<0.001) on bivariable analysis.

CONCLUSIONS

This long-term observational study indicates that TAPSE and dilation of right-sided cardiac chambers are associated with an increased risk for MACE in patients with ARVC/D with advanced disease and a high risk for adverse events. However, FAC is the strongest echocardiographic predictor of adverse outcome in these patients. Our data advocate a role for transthoracic echocardiography in risk stratification in patients with ARVC/D, although our results may not be generalizable to lower-risk ARVC/D cohorts.

Desmosomal cadherins are decreased in explanted arrhythmogenic right ventricular dysplasia/cardiomyopathy patient hearts

Aims

Arrhythmogenic right ventricular Dysplasia/cardiomyopathy (ARVD/C) is an autosomal dominant inherited cardiomyopathy associated with ventricular arrhythmia, heart failure and sudden death. Genetic studies have demonstrated the central role of desmosomal proteins in this disease, where 50% of patients harbor a mutation in a desmosmal gene. However, clinical diagnosis of the disease remains difficult and molecular mechanisms appears heterogeneous and poorly understood. The aim of this study was to characterize the expression profile of desmosomal proteins in explanted ARVD/C heart samples, in order to identify common features of the disease.

Methods and Results

We examined plakophilin-2, desmoglein-2, desmocollin-2, plakoglobin and β-catenin protein expression levels from seven independent ARVD/C heart samples compared to two ischemic, five dilated cardiomyopathy and one healthy heart sample as controls. Ventricular and septum sections were examined by immunoblot analysis of total heart protein extracts and by immunostaining.

Immunoblots indicated significant decreases in desmoglein-2 and desmocollin-2, independent of any known underlying mutations, whereas immune-histochemical analysis showed normal localization of all desmosomal proteins. Quantitative RT-PCR revealed normal DSG2 and DSC2 mRNA transcript levels, suggesting increased protein turn-over rather than transcriptional down regulation.

Conclusion

Reduced cardiac desmoglein-2 and desmocollin-2 levels appear to be specifically associated with ARVD/C, independent of underlying mutations. These findings highlight a key role of desmosomal cadherins in the pathophysiology of ARVD/C. Whether these reductions could be considered as specific markers for ARVD/C requires replication analysis.