The existence of J wave on sECG is considered a benign finding observed in approximately 2–10% of the general population [8]. However, following the findings reported by Haissaguerre et al. [9] and Nam et al. [10] the J wave syndrome has emerged as a significant cause of idiopathic ventricular fibrillation. The concept has now expanded to include other structural heart disease such as acute myocardial infarction, variant angina and even some forms of cardiomyopathy, such as arrhythmogenic right ventricular dysplasia/cardiomyopathy and noncompaction cardiomyopathy. In addition, two important J wave syndromes, the ER and Brugada syndromes (BS) are also considered to be of clinical importance.
J wave on the sECG is believed to originate from the generation of a transmural voltage gradient between the endocardium and epicardium during repolarization or depolarization, due to decreased inward sodium or calcium channel currents, or an increase in outward potassium currents mediated through the Ito, IK-ATP, and IK-Ach channels. These outward current shifts and heterogeneous loss of the action potential (AP) dome result in a marked dispersion of repolarization, which is followed by phase 2 reentry and gives rise to polymorphic VT or VF. Transient ischemia, caused by multivessel coronary spasm or neurological stress, [11] has been suggested as an additional mechanism triggering J wave and VT.
Masato et al. [12], reported a prevalence of J wave of approximately 30% (9 of 30 patients), and of VT/VF in the J wave and non-J wave group of approximately 22% (2 of 9 patients) and 9% (2 of 22 patents), respectively, in patients with TTC. Similarly, in our study, we found J wave prevalence of 37.5% (30 of 80 patients), and VT prevalence of 53% (15 of 30 patients) and 8% (5 of 50 patients) in the J wave and non-J wave group, respectively.
Samuelov-Kinori et al. [13] reported longer QTc intervals in patients with TTC who developed TdP. The mechanisms of QT prolongation in TTC appear to be similar to those of AMI resulting from autonomic dysregulation [14], and the intracardial gradient (apicobasal) of myocardial edema leads to transient inhomogeneity and gives rise to regional dispersion of AP duration [15]. These mechanisms may explain the prolonged QT interval in TTC, and the even longer QT interval seen in the VT and J wave groups, compared with that in the non-VT and non-J wave groups. Results from univariate and multivariate logistic analyses also showed that a prolonged QT interval appears to be an independent risk factor for VT. Multivariate logistic analyses also indicated that male sex is a risk factor for VT, in agreement with previous studies suggesting that male sex is strongly associated with the ER pattern observed on the ECG [16].
A relationship between the magnitude of the J point elevation and a higher occurrence of VF episodes has been previously reported [9]. Antzelevitch et al. [17] classified the ER pattern into three subtypes to estimate the risk for the development of malignant arrhythmia, according to the ECG leads in which the ER pattern appears. An ER pattern in the lateral leads; inferior or inferolateral leads; and globally, in the inferior, lateral and right precordial leads; is associated with a low, moderate, and high risk, respectively. However, Tikkanen et al. [18] proposed another classification based on the shape of the ST segment after the J wave, with a rapidly ascending ST, and a horizontal or descending ST segment being considered benign and malignant forms. Likewise, we found that the prevalence of J wave with an amplitude ≥ 0.2 mV, seen in the inferior leads, or in the inferolateral leads with a J point elevation ≥ 0.2 mV as well as horizontal/descending ST segments seen after the J point, was significantly higher in the VT group than in the non-VT group.
Our results suggest that the presence of a J wave on the sECG is significantly associated with the occurrence of polymorphic VT or TdP during TTC. Therefore, the identification of a J wave on sECG during TTC may help to distinguish patients who are susceptible to developing VT, especially in men with a prolonged QT interval, in whom close monitoring and primary prevention of VT should be considered. Additionally, evidence on the genetic basis for ER is currently limited, but recent reports suggest that mutations in candidate genes such as KCNJ8 which encode a pore-forming subunit of the ATP-sensitive potassium channel, as well as CACNA1C, CACNB2, and CACNA2D1 which encode a L-type calcium channel, and SCN5A related to INa, may be implicated in ER pathophysiology [19,20,21]. Hence, further studies are needed to clarify the relationship between genetic susceptibility and VT in TTC patients with J wave on sECG.
Our study had several limitations. Firstly, this was a retrospective study, with a small sample size, and limited to a single center. Secondly, since we could not perform stress tests or cardiac magnetic resonance imaging to verify the presence of myocardial scar, which is known to have arrhythmogenic potential, it could not be objectively ruled out. Thirdly, although we monitored cardiac rhythm thoroughly in patients hospitalized in the intensive care unit, this level of monitoring could not be achieved in the general ward. Nevertheless, our results provide valuable evidence of clinical implications of J wave in predicting the development of lethal arrhythmia during TTC. Further multi-center, prospective studies in larger groups of patients, are necessary to confirm the predictive value of J wave.
