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Early repolarization syndrome (ERS) is a rare cardiac condition characterized by J-point elevation (JPE) on the ECG and an increased risk of sudden cardiac death due to polymorphic ventricular tachycardia or ventricular fibrillation. Because of the high prevalence of JPE in the general population, the diagnosis of ERS in presymptomatic patients and the subsequent implementation of primary prevention strategies (e.g., implantable cardioverter-defibrillator insertion) are extremely challenging. In the past decade, electrocardiographic markers for increased risk in individuals with JPE have been investigated in an attempt to improve risk stratification strategies. This chapter focuses on how to diagnose ERS and identify ECG markers of increased arrhythmic risk. Consensus statements and recommendations for the management of these patients will also be discussed.

Early repolarization indicates an electrocardiographic phenotype affecting the junction (J wave) between the QRS complex and the ST segment in inferolateral leads. Here, we report a patient surviving a ventricular fibrillation in whom therapeutic mild hypothermia caused a major increase in J-wave and an arrhythmic storm. Other similar cases in the literature are discussed. Their analysis supports a potential diagnostic role of hypothermic methods in the risk assessment of J- wave syndromes.

Idiopathic ventricular fibrillation (IVF) is a rare condition in which patients without any major structural heart disease develop VF and often suffer from sudden cardiac death (SCD). IVF may contain multiple forms by clinical manifestations and possible pathogenetic backgrounds. In this Chapter, IVF is described as two groups: early repolarization syndrome (ERS), and IVF in a narrow sense excluding ERS. Although the early repolarization pattern in ECG is common, ERS is a very rare but potentially highly malignant. The mechanism and genetic background of ERS have not been fully clarified. Both the impairment of repolarization and conduction are postulated to explain ERS. IVF without ER pattern is also rare, and the understanding of its genetic background is limited. Recent findings indicate that His-Purkinje conduction disturbances are involved in some part of IVF without ER.

Among patients with idiopathic ventricular fibrillation (IVF), we experienced significantly higher prevalence of early repolarization (ER), which had been considered as a benign ECG finding in the past. In addition, recurrence of fatal ventricular arrhythmia was associated with the presence of ER. In analogy to ER seen in Brugada syndrome (BS), recently, a novel concept for J-wave syndrome (JWS) has been proposed by Dr. Antzelevitch and Dr. Yan, which includes both BS and ER syndrome (ERS). Indeed, there are several clinical similarities between them regarding (1) presence of familial cases, (2) male predominance, (3) predominant VF occurrence in night, (4) bradycardia-induced augmentation of J-point elevation, (5) reduction or elimination of J-point elevation during exercise or atrial fibrillation, and (6) pharmacological usefulness of isoproterenol and quinidine. From the point of genetic basis, there reported several candidate genes responsible for ERS, most of which are overlapped with those associated with Brugada syndrome. This chapter will mainly focus on the genetic background of ERS and discuss its similarity and difference to that in BS.

Both Brugada syndrome (BrS) and early repolarization syndrome (ERS) are associated with ST-segment and/or J-point elevation and sudden cardiac death due to ventricular fibrillation. There exist several similarities between BrS and ERS in the genetic, clinical, electrocardiographic, and electrophysiological characteristics, such as causative genes, male dominance, late adulthood onset, pause-dependent augmentation of J-point elevation, and response to drugs. However, the two clinical entities also have certain differences. In this chapter, the currently available evidence for similarities and differences between BrS and ERS in these features will be presented and discussed.