Short QT syndrome (SQTS) is a very rare inherited arrhythmia characterized by extremely short QT intervals on electrocardiograms and sudden cardiac death in young patients. Among the genotypes of SQTS, gain-of-function variants in the potassium voltage-gated channel subfamily Q member 1 (KCNQ1) gene are accountable for SQTS type 2 (SQT2). Pathogenic variants for SQT2 are rare and, among them, the p.Val141Met is relatively prevalent. This review summarizes findings for 5 SQTS patients harboring p.Val141Met we recently encountered and compares them to another 14 patients reported in the literature.

Congenital short-QT syndrome (SQTS) is a genetic disorder characterized by short QT interval on electrocardiography (ECG) and a high risk for malignant ventricular tachyarrhythmias. The aim of this study was to describe a new variant in the SQTS-associated gene SLC4A3 at the molecular and clinical levels. Using whole-exome sequencing, a novel missense variant in SLC4A3 was identified, encoding for the cardiac anion exchanger 3. The mutant was characterized using computational structural modeling and functional transport studies in human embryonic kidney 293 cells. Patients were assessed using resting ECG, 12-lead Holter recordings, and a novel diagnostic test termed here the Ippon test. A novel heterozygous SLC4A3 variant (p.R1016G) was detected in a family with 6 cases of sudden cardiac death and a case of documented polymorphic ventricular tachycardia in 5 generations. Functional analyses in human embryonic kidney 293 cells revealed gain of function rather than the loss of function expected on the basis of previously reported SQTS-associated SLC4A3 variants. Although affected family members exhibited shorter corrected QT intervals on resting ECG compared with nonaffected members (360 ± 20 ms vs 380 ± 30 ms; P = 0.0068) and 12-lead Holter monitoring (350 ± 20 ms vs 380 ± 30 ms; P = 0.0013), significant overlap existed. The sudden heart rate deceleration provoked by the Ippon test revealed that the QT interval in carriers failed to prolong in response to the sudden bradycardia, resulting in inappropriately short corrected QT intervals, leading to a better distinction of affected from nonaffected patients (340 ± 30 ms vs 370 ± 10 ms, respectively; P = 0.0003). SLC4A3 p.R1016G is a novel SQTS-associated variant associated with a gain-of-function effect. The Ippon test is a new provocation maneuver that identifies SQTS variant carriers with high diagnostic accuracy.

Congenital short QT syndrome is a very low prevalence inherited primary arrhythmia syndrome first reported in 2000 by Gussak et al., who described two families with a short QT interval, syncope, and sudden cardiac death. In 2004, Ramon Brugada et al. identified the first genetic type of this entity. To date, a total of nine genotypes have been described. The diagnosis is easy from the electrocardiogram (ECG), not only due to the short QT duration, but also based on other aspects covered in this review. During 24-h Holter monitoring, paroxysmal atrial fibrillation spontaneously converting to sinus rhythm may be found. Even though the T wave may appear symmetric on the ECG, the T loop of the vectorcardiogram confirms that the T wave is constantly asymmetric due to the presence of dashes closer to each other in the efferent branch. In this review, we also describe the minus-plus T wave sign that we have described in a previously published article. In addition to congenital causes, we briefly highlight the existence of numerous acquired causes of short QT interval.

The congenital short QT syndrome (SQTS) is a rare condition characterized by abbreviated rate-corrected QT (QTc) intervals on the electrocardiogram and by increased susceptibility to both atrial and ventricular arrhythmias and sudden death. Although mutations to multiple genes have been implicated in the SQTS, evidence of causality is particularly strong for the first three (SQT1-3) variants: these result from gain-of-function mutations in genes that encode K+ channel subunits responsible, respectively, for the IKr, IKs and IK1 cardiac potassium currents. This article reviews evidence for the impact of SQT1-3 missense potassium channel gene mutations on the electrophysiological properties of IKr, IKs and IK1 and of the links between these changes and arrhythmia susceptibility. Data from experimental and simulation studies and future directions for research in this field are considered. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.

The T618I KCNH2-encoded hERG mutation is the most frequently observed mutation in genotyped cases of the congenital short QT syndrome (SQTS), a cardiac condition associated with ventricular fibrillation and sudden death. Most T618I hERG carriers exhibit a pronounced U wave on the electrocardiogram and appear vulnerable to ventricular, but not atrial fibrillation (AF). The basis for these effects is unclear. This study used the action potential (AP) voltage clamp technique to determine effects of the T618I mutation on hERG current (IhERG) elicited by APs from different cardiac regions. Whole-cell patch-clamp recordings were made at 37 °C of IhERG from hERG-transfected HEK-293 cells. Maximal IhERG during a ventricular AP command was increased ∼4-fold for T618I IhERG and occurred much earlier during AP repolarization. The mutation also increased peak repolarizing currents elicited by Purkinje fibre (PF) APs. Maximal wild-type (WT) IhERG current during the PF waveform was 87.2 ± 4.5% of maximal ventricular repolarizing current whilst for the T618I mutant, the comparable value was 47.7 ± 2.7%. Thus, the T618I mutation exacerbated differences in repolarizing IhERG between PF and ventricular APs; this could contribute to heterogeneity of ventricular-PF repolarization and consequently to the U waves seen in T618I carriers. The comparatively shorter duration and lack of pronounced plateau of the atrial AP led to a smaller effect of the T618I mutation during the atrial AP, which may help account for the lack of reported AF in T618I carriers. Use of a paired ventricular AP protocol revealed an alteration to protective IhERG transients that affect susceptibility to premature excitation late in AP repolarization/early in diastole. These observations may help explain altered arrhythmia susceptibility in this form of the SQTS.