Early repolarization ER is characterized by elevation of the

Early repolarization (ER) is characterized by elevation of the QRS-ST junction (J point) and QRS notching or slurring (J wave) in multiple leads, especially the inferior and/or left precordial leads. Although this finding has been considered to be a benign ECG manifestation, Haïssaguerre et al reported that the ER pattern was found in 31% (64/206) of IVF patients compared to 5% (21/412) of matched control subjects [21]. An ER pattern in the inferior or inferolateral leads has been reported to be associated with an increased risk for life-threatening arrhythmias, termed ER syndrome. ER has also been reported to coexist with other arrhythmogenic disorders such as BrS, short QT syndrome, and arrhythmogenic right ventricular cardiomyopathy; therefore, ER may be viewed as one of many arrhythmogenic factors that is rarely solely responsible for clinical events [22]. Aizawa et al. first reported a patient with ER-like QRS notching and VF without any apparent cause, which were suppressed by catheter ablation for the VPCs triggering the VF [23]. Recently, a case was reported of a patient with recurrent VF storm and inferoposterior ER in whom catheter ablation guided by pace mapping of the triggering VPCs successfully abolished the clinical event and caused the ER to disappear [24].
Long QT syndrome LQTS is characterized by prolonged ventricular repolarization and susceptibility to syncope and SCD through VT (TdP), which can deteriorate into VF [25]. A clinical diagnosis is made from a combination of clinical history, family history, and 12-lead ECG, which typically reveals a heart rate-corrected QT interval (QT interval divided by the square root of the RR interval in seconds=QTc) of greater than 0.46s in women and 0.45s in men [25]. LQTS is most commonly inherited in an autosomal hedgehog signaling fashion and has been associated with mutations in 15 genes. Among these, more than 75% of the mutations in congenital LQTS were of the KCNQ1 (LQT1), KCNH2 (LQT2), or SCN5A (LQT3) genes [26]. β-blocker therapy is associated with a 50% reduction in risk of cardiac events, and mexiletine is effective in LQT3 patients [27]. ICD implantation is recommended for patients with resuscitated cardiac arrest/VF or recurrent syncope who are on β-blockers. Several studies have suggested that early afterdepolarizations arising from the Purkinje network and/or myocardial fibers are the primary triggering beats in TdP [7,28–31]. For example, Haïssaguerre et al. reported four symptomatic LQTS patients diagnosed on the basis of a corrected QT interval of > 460ms who underwent catheter ablation [7]. In one patient, VPCs originating from the RVOT were ablated by RF energy applications. In three patients, VPCs originated from the left Purkinje system and were eliminated by ablation at multiple sites. During a mean follow-up period of 24±20 months, there was no recurrence of syncope, VF, or SCD in any patient, although one patient with LQTS was maintained on a β-blocker, and another had a late recurrence of VPCs. The authors concluded that the triggers from the Purkinje network or the RVOT play a crucial role in initiating TdP or VF in LQTS, and these can be eliminated by focal ablation. Other groups also reported that VPCs originating from the RV free wall and RV inferoseptal wall could trigger VT/VF and could be eliminated by focal ablation [30,31].
Catecholaminergic polymorphic ventricular tachycardia Catecholaminergic polymorphic VT (CPVT) is an inherited arrhythmogenic disorder characterized by polymorphic VT induced by physical or emotional stress with no detectable morphological abnormalities in the heart [32]. To date, five genes, cardiac ryanodine type 2 receptor (RYR2), calsequestrin 2 (CASQ2), KCNJ2 (which encodes Kir2.1), calmodulin 1 (CALM1), and triadin (TRDN), have been identified as being involved in CPVT [33]. Typical arrhythmias include bidirectional VT and polymorphic VT that can degenerate into VF and thus SCD. β-blockers and additional administration of flecainide or verapamil have been reported to be effective for the prevention of VT/VF [34]. An ICD is considered the definitive therapy for the prevention of SCD, although failure of the ICD to prevent SCD has been reported in several cases because the ICD shock delivery might lead to catecholamine release, resulting in an electric storm [35].