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Available online at www.sciencedirect.com
Clinical aspects of inherited J-wave syndromesy Heikki V. Huikurin and M. Juhani Junttila Department of Internal Medicine, Medical Research Center, University Hospital and University of Oulu, P.O. Box 5000, Oulu 90014, Finland
abstract Presence of J-point elevation with rapidly ascending ST segment in the anterior leads of the 12-lead electrocardiogram has been generally considered a benign phenomenon. The concept of benign nature of J-waves has changed as data emerged on variants of J-waves that were associated with the increased risk of sudden cardiac death. Two speciﬁc inherited arrhythmia syndromes, such as Brugada syndrome and early repolarization syndrome, have been recognized that carry an increased risk for ventricular ﬁbrillation. The current review is aimed at discussing the clinical aspects of these syndromes and the implications of incidental recognition of the J-waves in a randomly recorded electrocardiogram of asymptomatic subjects. & 2015 Elsevier Inc. All rights reserved.
Introduction The J-point on the electrocardiographic (ECG) waveform is deﬁned as the junction between the end of the QRS complex and the beginning of the ST segment [1,2]. In 1953, Osborn  described the classic J-wave in experimental hypothermia. Dogs subjected to hypothermia developed spontaneous ventricular ﬁbrillation (VF) that was preceded by the development of J-waves . Despite these early observations, the presence of J-point elevation followed by rapidly ascending ST-segment pattern in the chest leads V2–V4, commonly observed in young adults, designated as early repolarization (ER), has generally been considered to be a benign phenomenon [4,5]. The concept of the benign nature of J-waves has changed in more recent years as data emerged on variants of J-point elevation and J-waves that were associated with an increased risk of sudden cardiac death (SCD) . These included the ECG patterns observed in the right precordial leads in Brugada syndrome (BrS)  and the ECG pattern of ER or J-waves in the inferior and/or lateral leads, which associated with increased risk of idiopathic ventricular ﬁbrillation (VF) and SCD in case– control and general population studies [8,9]. y
The variations in the ECG patterns of J-point elevations in conjunction with disparities in associated risk of SCD have led to a recognition of the need to carefully classify the spectrum of these observations. Many questions about the pathogenesis, nomenclature, and deﬁnitions of J-wave patterns, as well as associated magnitudes of risk, remain partly unanswered. Interest in these ECG patterns has grown dramatically in recent years, in large part because of the frequency with which these patterns are observed on routine ECGs of asymptomatic subjects. In this review, we discuss the current knowledge of the clinical aspects of different J-point/ J-wave patterns.
J-waves in the Brugada syndrome Diagnosis, epidemiology, and etiology of Brugada syndrome Brugada syndrome (BrS) is characterized by J-waves, STsegment elevation, and inversion of the terminal part of T-wave in the right precordial leads V1 and V2 . Current ECG criteria of BrS proposed in the recent consensus report of
This article is Open Access as the January’s Editor’s Choice selection. The authors have indicated there are no conﬂicts of interest. Supported in part by Grants from the Finnish Academy of Science, Finland, and Sigrid Juselius Foundation, Finland. n Corresponding author. Tel.: þ358 400 892 330; fax: þ358 831 555 99. E-mail address: heikki.huikuri@oulu.ﬁ (H.V. Huikuri). http://dx.doi.org/10.1016/j.tcm.2014.08.008 1050-1738/& 2015 Elsevier Inc. All rights reserved.
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Table 1 – Diagnostic criteria of electrocardiographic pattern of Brugada syndrome.a (1) BrS is diagnosed in patients with ST-segment elevation with type 1 morphology 42 mm in 41 lead among the right precordial leads V1 and V2, positioned in the 2nd, 3rd, or 4th intercostal space occurring either spontaneously or after provocative drug test with intravenous administration of Class I antiarrhythmic drugs (2) BrS is diagnosed in patients with type 2 or type 3 ST-segment elevation in Z1 lead among the right precordial leads V1 and V2 positioned in the 2nd, 3rd, or 4th intercostal space when a provocative drug test with intravenous administration of Class I antiarrhythmic drugs induces a type 1 ECG morphology BrS ¼ Brugada syndrome, ECG ¼ electrocardiogram. Modiﬁed with permission from Priori et al. .
Priori et al.  are summarized in Table 1. The ECG patterns within the spectrum of BrS phenotype are classiﬁed into three categories. J-point elevations are characteristic of all three patterns of Brugada-associated ECGs; the distinctions between the patterns reﬂected primarily in the ST segment and T waveforms following the J-points (Fig. 1). In general, type 1 pattern is considered as a BrS ECG with a worse prognosis while types 2 and 3 are considered as more benign variants of BrS. The J-wave pattern may vary from time-to-time within series of ECGs in individual patients and tends to become evident or accentuated by increased vagal tone, fever, and by sodium channel blocking drugs, such as ajmaline or ﬂecainide [11–13]. Exercise, catecholamine stimulation, and quinidine have been shown to normalize the Brugada ECG pattern . The differential diagnosis includes a number of diseases and conditions that can lead to Brugada-like ECG abnormality, including atypical RBBB, left ventricular hypertrophy, acute pericarditis, acute myocardial ischemia or infarction, acute stroke, pulmonary embolism, Prinzmetal angina, dissecting aortic aneurysm, various central and autonomic nervous system abnormalities, Duchenne muscular dystrophy, thiamine deﬁciency, hyperkalemia, hypercalcemia, pectus excavatum, hypothermia, and mechanical compression of the right ventricle . BrS can be deﬁnitely diagnosed in type 1 ECG pattern in the presence of symptoms, such as aborted SCD, syncopal episodes, or ECG documented polymorphic ventricular tachycardia . Many subjects displaying a type 1 ECG, spontaneous or drug-induced, are asymptomatic. In asymptomatic patients, the diagnosis of
BrS should be ideally based on additional risk factors (see below) and follow-up of the patients. The prevalence of the diagnostic Brugada ECG is ethnicitydependent. Among the Asian population, the prevalence of the type 1 Brugada pattern has been estimated to be 0.4% and in European populations at 0–0.01% . BrS seems to be more prevalent in Southern than in Northern European countries (personal communication). There is also a considerable male predominance in the prevalence of ECG pattern of BrS . BrS is generally considered as an inherited arrhythmia syndrome, the inheritance occurring via an autosomal dominant mode of transmission . Overall, 12 responsible genes have been reported so far . In all 12 genotypes, either a decrease in inward sodium or calcium current or an increase in outward potassium current has been proposed to be responsible for Brugada phenotype. Genetic mutation can be found in approximately one-third of BrS patients. Genetic testing is not generally recommended in the absence of a diagnostic ECG but may be useful otherwise and is recommended for family members of a successfully genotyped proband. While most investigators consider the pathophysiology of BrS-associated J-waves to be regional early repolarization caused by monogenic mutation, recent data suggest the possibility of delayed depolarization in the right ventricular outﬂow tract as a contributing mechanism to J-waves, arrhythmia expression, or perhaps both . It is possible that the pathophysiologic background of BrS is heterogeneous, and various causes can actually result in ECG phenotype of BrS and arrhythmia risk.
Risk stratiﬁcation and treatment
Fig. 1 – ECG patterns of Brugada syndrome. Type 1 is diagnostic for Brugada syndrome. Types 2 and 3 are benign variants of Brugada syndrome.
There is a common consensus on the high risk of recurrence of cardiac arrest among BrS patients who have survived a ﬁrst VF. Accordingly, there is general agreement that these patients should be protected with an implantable cardioverter deﬁbrillator (ICD) irrespective of the other risk factors . There is also a common agreement that the presence of syncopal episodes in patients with spontaneous type 1 ECG at baseline has a high risk of arrhythmia events. The risk of lethal or near-lethal arrhythmic episodes among previously asymptomatic patients with BrS phenotype varies according to the published series from 1% to 8% event rate within a follow-up of 3–4 years [10,14]. Several factors have been recognized as risk factors of arrhythmic events in asymptomatic patients, such as attenuation of ST-segment elevation at peak exercise followed by its appearance during recovery phase, presence of ﬁrst degree AV block and left axis deviation
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of the QRS, presence of atrial ﬁbrillation, late potentials in signal-averaged ECG, fragmented QRS complex, ST–T alternans, spontaneous LBBB, frequent ventricular premature beats during prolonged ECG recording, and short effective refractory period of the ventricle (o200 ms) recorded during electrophysiological (EP) testing [10,14]. Male gender has consistently been shown to present more arrhythmic events . The coexistence of ECG pattern of ER in the inferolateral leads also has been shown to be associated with worse outcome of patients with BrS even in those with non-type 1 BrS ECG [16,17]. Although large registries agree that inducibility of sustained ventricular tachyarrhythmia during the EP testing is greatest among BrS patients with aborted SCD or syncope , there is no consensus on the value of the EP study in predicting outcome in asymptomatic subjects. The largest series of BrS patients published so far found that inducibility of sustained ventricular arrhythmias was signiﬁcantly associated with a shorter time to ﬁrst arrhythmic event in the univariate analysis, but in the multivariate analysis, inducibility did not predict arrhythmic events . These results were conﬁrmed in a recent prospective study in previously asymptomatic patients . A positive history of SCD or the presence of SCN5A mutation has not proven to be risk markers of arrhythmic events . To date, the only proven effective therapeutic strategy for the prevention of SCD in BrS patients is the ICD . The indications of ICD implantation are summarized in Table 2. It should be noted that ICDs are not free from several disadvantages, especially in young individuals facing a long-lasting coexistence with the device and multiple device replacements. Some series have reported low rates of appropriate shocks (8– 15%, median follow-up 45 months) and high rates of complications, mainly inappropriate shocks . All attempts to avoid inappropriate shocks should be done by adequate
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programming of the ICDs in the BrS patients. Asymptomatic BrS patients do not generally qualify for an ICD as their risk for life-threatening events is very low . In this group of patients, individual assessment of associated risk factors should be performed (see above). The decision concerning the implantation of an ICD or treatment with quinidine should be based on individual decision making of arrhythmia experts together with the patient after thorough discussion about the risks and beneﬁts of the various treatment options. Careful follow-up of individuals with type 1 BrS without any treatment is essential. Quinidine has shown to prevent induction of VF and suppress spontaneous ventricular arrhythmias in a clinical setting, being currently used in patients with ICDs and multiple shocks, cases in which ICD implantation is contraindicated, or for the treatment of supraventricular arrhythmias . It has been suggested that it could also be useful in children with BrS, as a bridge to an ICD or as an alternative to it . Radiofrequency ablation also has been proposed as a therapeutic approach in BrS patients. Nademanee et al.  have presented the ﬁrst series showing that epicardial substrate ablation of the right ventricular outﬂow tract can prevent VF inducibility in a high-risk population and abolish the ECG pattern of BrS. Large studies of the efﬁcacy of catheter ablation are lacking, however.
Inferior and/or lateral J-waves After some case reports pointing to the arrhythmogenic potential of ST-segment elevation accompanied by J-waves in the inferior and/or lateral leads of the ECG , an ECG variant called early repolarization (ER), a case–controlled study of Haissaguerre
Table 2 – Recommendations on Brugada syndrome therapeutic interventions.a (1) The following lifestyle changes are recommended in all patients with diagnosis of BrS: (a) Avoidance of drugs that may induce or aggravate ST-segment elevation in right precordial leads (e.g., those listed on Brugadadrugs.org) (b) Avoidance of excessive alcohol intake (c) Immediate treatment of fever with antipyretic drugs (2) ICD implantation is recommended in patients with a diagnosis of BrS who (a) are survivors of a cardiac arrest and/or (b) have documented spontaneous sustained VT with or without syncope. (3) ICD implantation can be useful in patients with a spontaneous diagnostic type 1 ECG who have a history of syncope judged to be likely caused by ventricular arrhythmias
(4) Quinidine can be useful in patients with a diagnosis of BrS and history of arrhythmic storms deﬁned as more than two episodes of VT/VF in 24 h
(5) Quinidine can be useful in patients with a diagnosis of BrS (a) who qualify for an ICD but present a contraindication to the ICD or refuse it and/or (b) have a history of documented supraventricular arrhythmias that require treatment. (6) Isoproterenol infusion can be useful in suppressing electrical storms in BrS patients (7) ICD implantation may be considered in patients with a diagnosis of BrS who develop VF during programmed electrical stimulation (inducible patients)
(8) Quinidine may be considered in asymptomatic patients with a diagnosis of BrS with a spontaneous type 1 ECG (9) Catheter ablation may be considered in patients with a diagnosis of BrS and history of arrhythmic storms or repeated appropriate ICD shocks BrS ¼ Brugada syndrome, ECG ¼ electrocardiogram, ICD ¼ implantable cardioverter deﬁbrillator, VF ¼ ventricular ﬁbrillation, VT ¼ ventricular tachycardia. a Modiﬁed with permission from Priori et al. .
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Fig. 2 – Examples of ECG pattern of early repolarization with a rapidly ascending ST segment following the J-wave (A) and a horizontal/downsloping ST segment following the J-point (B). et al.  described an apparent over-presentation of ER in patients with unexplained VF. Numerous cases of patients with idiopathic VF who have the ER pattern in the inferior and/or lateral ECG leads have now been described, involving more than 300 patients [24–26]. Subsequently, several epidemiological studies observed that the ECG pattern of ER is associated with an increased risk of arrhythmic death and mortality either as a primary cause of sudden death in the general population or in conjunction with concurrent cardiac disease [9,27–29]. A recent meta-analysis summarized the reported studies and showed that individuals with the ER had a relative risk of 1.7 of experiencing an arrhythmia death .
Diagnosis and epidemiology of ER ECG pattern The criteria for ECG pattern of ER are J-point elevation Z0.1 mV of either notched or slurred morphology in at least two consecutive inferior or lateral leads. Another cutoff value of Z0.2 mV J-point elevation also has been used. In additional analysis, the ST-segment morphology in adjunction with the
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ECG pattern of ER has been divided into rapidly ascending (100 ms after J-point elevation of Z0.1 mV) and horizontal/ descending (100 ms after J-point ST-segment elevation o0.1 mV)  (Fig. 2). The diagnostic criteria of ER syndrome and ECG pattern of ER are summarized in Table 3. It is important to note that the terms ER syndrome and ECG pattern of ER should be separated from each other. The ER syndrome can be diagnosed only in patients with resuscitated cardiac arrest, documented VF, or polymorphic ventricular tachycardia, or possibly in the relatives of the ER syndrome in whom a genetic mutation can be documented [10,24]. Since the ECG pattern of ER is relatively common even in patients with otherwise unexplained VF, additional diagnostic tests are needed, such as echocardiogram, coronary angiography, magnetic resonance imaging, and endocardial biopsies, to exclude other causes of VF. Consideration also should be given to provocative drug infusion with epinephrine and with a sodium channel blocker, such as ajmaline or ﬂecainide, to unmask latent inherited causes of cardiac arrest, such as the BrS. The possible presence of the short QT syndrome should also be noted. There are no validated techniques to provoke the ECG pattern of ER . The correct diagnosis of the ER syndrome and its separation from idiopathic VF has clinical importance, since available data show that patients with the ER syndrome are prone to frequent ICD shocks and electrical storms after the implantation of the ICD and that these events can be prevented by quinidine treatment [10,24]. Genetic testing of the family members of the ER syndrome patients may also become available in the near future. Some controversy exists in the ECG deﬁnitions of the ECG patterns of ER and its nomenclature as well as deﬁnitions of the “malignant” vs. “benign” ER patterns [32,33]. The magnitude of the J-point elevation may have some prognostic signiﬁcance. Either slurred or notched J-point elevations Z0.2 mV is relatively rare in the general population, but appears to be associated with an increased risk . Furthermore, there is greater amplitude and wider ECG lead distribution of J-point elevation in idiopathic VF patients compared to those with an established cause of cardiac arrest . The available data also suggest that transient changes in the presence and amplitude of J-point elevation portends a higher risk for VF . Short-coupled ventricular premature beats preceded by an augmented J-wave also suggest an increased risk. A horizontal or descending ST segment following J-point elevation is associated with a worse outcome in the general population . This ECG pattern also has been helpful in distinguishing idiopathic VF patients from matched controls, and is a key aid in clinical decision making
Table 3 – Recommendations on the diagnosis of early repolarization.a (1) ER syndrome is diagnosed in the presence of J-point elevation Z1 mm in Z2 contiguous inferior and/or lateral leads of a standard 12-lead ECG in a patient resuscitated from otherwise unexplained VF/ Polymorphic VT
(2) ER syndrome can be diagnosed in a SCD victim with a negative autopsy and medical chart review with a previous ECG demonstrating J-point elevation Z1 mm in Z2 contiguous inferior and/or lateral leads of a standard 12-lead ECG
(3) ECG pattern of ER pattern can be diagnosed in the presence of J-point elevation Z1 mm in Z2 contiguous inferior and/or lateral leads of a standard 12-lead ECG ECG ¼ electrocardiogram, ER ¼ early repolarization, VF ¼ ventricular ﬁbrillation, VT ¼ ventricular tachycardia. a Modiﬁed with permission from Priori et al. .
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Table 4 – Recommendations on early repolarization therapeutic interventions.a (1) (2) (3) (4) (5)
ICD implantation is recommended in patients with a diagnosis of ER syndrome who have survived a cardiac arrest Isoproterenol infusion can be useful in suppressing electrical storms in patients with a diagnosis of ER syndrome Quinidine in addition to an ICD can be useful for secondary prevention of VF in patients with a diagnosis of ER syndrome ICD implantation may be considered in symptomatic family members of ER syndrome or patients with a history of syncope in the presence of ECG pattern of ER and horizontal/downsloping ST-segment elevation 41 mm in two or more inferior or lateral leads (6) ICD implantation or quinidine treatment may be considered in asymptomatic individuals who demonstrate a high-risk ER ECG pattern, such as high J-wave amplitude, widespread J-waves, association with BrS ECG or short QT interval, dynamic changes in J-waves and shortcoupled ventricular premature beats preceded by augmented J-waves, and high J-wave amplitude followed by a horizontal/descending STsegment in the presence of a strong family history of juvenile unexplained sudden death with or without a pathogenic mutation (7) ICD implantation is not recommended for asymptomatic patients with an isolated ECG pattern of ER ECG ¼ electrocardiogram, ER ¼ early repolarization, VF ¼ ventricular ﬁbrillation, VT ¼ ventricular tachycardia. a Modiﬁed with permission from Priori et al. .
. These early observations may be of some help in separating the benign ER patterns from potentially more malignant forms. The prevalence of the ECG pattern of ER in the inferior and/ or lateral leads has been reported to be in a range between 3% and 24% in general population [14,24]. The prevalence seems to vary considerably, depending on the demographic features of the studied population, age, race, gender, and physical activity. In the Finnish community sample of middle-aged subjects, the dominant form of ST segment in those with J-waves was horizontal or descending (71.5%), conversely to that observed in young adults or athletes . ECG pattern of ER is overrepresented among young males compared to females, but the higher prevalence in males declines rapidly during middle age . This suggests a potential inﬂuence of testosterone as a modiﬁer of J-wave/ ER expression , an association also observed in Brugada syndrome . This male preponderance as a function of age is primarily attributable to the high frequency of the benign ascending ST-segment pattern of ER in young males. Family studies have suggested inheritance of propensity to ECG patterns of ER as well as for ER syndrome [35,37]. A candidate gene approach in idiopathic VF patients with ER has identiﬁed monogenic mutations in six different genes so far . A recent genome-wide association meta-analysis in three independent populations of European ancestry found eight loci associated with ER, the strongest association being found in genes that encode transient outward potassium channel . Similar to BrS, it is likely that many factors, both structural and genetic, can cause the ECG phenotype of ER.
idiopathic VF in an individual younger than 45 years is 3:100,000. The risk increases to 11:100,000 when J-waves are present . From a meta-analysis, the estimated absolute difference of subjects with the ER is seven cases of arrhythmic death per 100,000 subjects per year . Although ER increases the relative risk of VF, the absolute risk is still very low. Therefore, the incidental identiﬁcation of the ER should not be interpreted as a high-risk marker for arrhythmic death due to relatively low odds. However, there are some rare exceptions that may need to be considered on an individual basis. It may be difﬁcult to ignore the ECG pattern of ER and not recommend therapeutic interventions such as prophylactic implantation of an ICD or quinidine treatment when the ECG of ER is not considered benign. This scenario may be present in a subject with a strong family history of juvenile unexplained sudden cardiac death, e.g., in two affected subjects, and/or ER in a subject with evidence of frequent arrhythmic syncopal episodes, deﬁned as sudden witnessed loss of consciousness without prodromal or postictal symptoms in a patient with high-risk ECG pattern of ER (Table 4). In the latter case, implantation of an ECG loop recorder may be considered. Because current data also suggest that the presence of the ECG pattern of ER increases the vulnerability to sudden death during an acute ischemic event [24,39], a plausible implication stemming from the population studies is that middle-aged subjects with the ER pattern on the ECG should target prophylactic reduction of their long-term risk for acute coronary events in accordance with current practice guidelines.
Conclusions and recommendations Prognosis and clinical signiﬁcance of inferior and/or lateral early repolarization ICD is generally recommended for patients with ER syndrome (Table 4). Electrical storm is relatively common after ICD implantation in these patients [10,24]. Case series evidence supports the acute use of isoproterenol for suppression of recurrent VF, and quinidine for long-term suppression [10,24]. The clinical implications of an ECG pattern of ER of an asymptomatic subject are not clear. The presence of ER triples the risk of developing VF, but the overall risk is still negligible because idiopathic VF itself is a rare disorder. Viskin et al. have estimated that the risk of developing
A key issue in the diagnosis of both BrS and ER syndrome is the correct ECG diagnosis of these syndromes in patients resuscitated from cardiac arrest, or in those with documented polymorphic ventricular tachycardia, or recurrent syncopal episodes of presumed arrhythmic etiology. The risk stratiﬁcation and selection of proper treatment for asymptomatic subjects with ECG patterns of BrS are a challenge for future research. Although the terminology surrounding the terms of J-point elevation and J-waves, vs. ER in the inferior or lateral ECG leads, can be misleading in many ways, part of the intent in this review is to clarify the implications of such ECG ﬁndings,
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blending historical concepts with contemporary observations. The speciﬁc patterns that have been explored in recent years have been shown to convey risk for arrhythmic death in separate general population-based studies. Therefore, regardless of the terminology, this variant has the potential for arrhythmia prediction that can be seen in an ECG tracing several years or even decades before the actual intermittent risk for sudden death. The patterns of J-point elevations and J-waves or ER pattern appear to reﬂect a continuum of risk for arrhythmias. Regardless of whether the patterns have their origins in variants of depolarization or repolarization processes, or contributions by either or both, the patterns appear to have usefulness for risk prediction in a number of clinical circumstances. However, we are still at the early phase of understanding the pathophysiology of J-wave syndromes and their clinical consequences in asymptomatic subjects. Meanwhile, clinicians and patients should not be alarmed if the ECG pattern of ER, even with horizontal/downsloping ST segment, or BrS (type 2 or 3), is observed in a randomly recorded ECG of an asymptomatic subject without a strong family history of SCD or history of syncopal episodes of probable arrhythmic origin.
re fe r en ces
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