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Risk stratification in short QT syndrome: Findings from a pooled analysis.

BACKGROUND: In long QT syndrome, longer QT intervals indicate increased arrhythmic risk, and a rate-corrected QT interval (QTc) of ≥500 ms denotes high risk. Establishing similar associations in short QT syndrome (SQTS) remains elusive. OBJECTIVE: This study aimed to demonstrate that shorter QT intervals denote a higher risk of malignant arrhythmias in SQTS and to define the "high-risk" QTc value in SQTS. METHODS: Pooled analysis of patients treated in our institutions or those reported in the literature revealed 162 patients with SQTS and known symptomatic status; 57 of them (35.2%) had arrhythmic symptoms (sudden death, cardiac arrest, or malignant syncope). RESULTS: There was a significant inverse association between the QTc and arrhythmic symptoms (with a median QTc of 315.0 ms [interquartile range 300.5-338.0] among symptomatic patients vs 330.0 ms [interquartile range 312.5-355.0] among asymptomatic patients; P = .0023). Receiver operator characteristics analysis showed that shorter QTc values were associated with a higher risk (area under the curve 0.64 ± 0.04; P = .0024). When patients were grouped by QTc range, most of those with a QTc of ≤320 ms had malignant arrhythmic symptoms, whereas the reverse was true for those with a QTc of ≥320 ms. Male patients were overrepresented in the SQTS cohort and more so in the subgroup with malignant symptoms. CONCLUSION: This pooled analysis of patients with SQTS demonstrates that, among patients with congenital SQTS, a shorter QTc is associated with a higher risk of malignant ventricular arrhythmias. A QTc shorter than 320 ms correlates with a higher arrhythmic risk. Men seem to be at higher risk.

Humans

Whole-exome Sequencing Identifies Novel Candidate PCNT Variants in a Child With Overlapping MOPD II Features: A Case Report.

A 7-year-old Chinese boy presented with severe postnatal growth failure (height <3rd percentile at age 7 years), global developmental delay, moderate intellectual disability, and characteristic dysmorphic features including hypertelorism, short palpebral fissures, low-set ears, and a broad nasal bridge. A single electrocardiogram demonstrated a borderline corrected QT interval (QTc = 450 ms). No arrhythmias, QT-prolonging medications, electrolyte abnormalities, or relevant family cardiac history were identified. This finding warrants longitudinal cardiology follow-up and should not be interpreted as definitive Long QT syndrome. Whole-exome sequencing identified two novel missense variants in the PCNT gene (NM_006031.5): c.5675A>G (p.Glu1892Gly) in exon 28 and c.9734G>T (p.Arg3245Ile) in exon 45. Both variants were absent from gnomAD, ExAC, the 1000 Genomes Project database, and Chinese population databases, fulfilling ACMG criterion PM2. Although classified as variants of uncertain significance (VUS) because of limited functional evidence and conflicting in silico predictions, the variants occur in a gene associated with primordial dwarfism and are accompanied by partial phenotypic overlap with Microcephalic Osteodysplastic Primordial Dwarfism Type II (MOPD II). However, parental segregation analysis was unavailable; therefore, the variant phase could not be confirmed, and a recessive disease mechanism could not be established. These findings support the presence of candidate PCNT variants in an atypical primordial dwarfism phenotype and illustrate the utility of whole-exome sequencing for generating testable molecular hypotheses in genetically heterogeneous growth disorders. A definitive molecular diagnosis cannot be established at present, and the isolated borderline QTc finding requires further clinical evaluation.

Humans

Ventricular tachycardia and ventricular fibrillation in a young population.

In this study, we describe the findings in 18 young patients (age range 4 days to 24 years, mean 16.6 years) who had ventricular tachycardia and/or ventricular fibrillation and were followed for 4--70 months (mean 22.4 months). Patients had a variety of problems associated with their arrhythmia, including mitral valve prolapse, cardiomyopathy, myocarditis, prolonged QT syndrome and hypokalemia. Six patients had no clinically recognizable cardiac abnormality. The ventricular tachycardia showed a left bundle branch block contour in 10 of 17 patients, right bundle branch block in four, was multiform in two and had an indeterminate contour in one. Sustained ventricular tachycardia was initiated and terminated reproducibly by atrial and ventricular stimulation in three of seven patients who did not have spontaneous episodes of ventricular tachycardia during the electrophysiologic study. In one other patient, short bursts of ventricular tachycardia were induced. Patients who had ventricular fibrillation, those who died, and those who are still symptomatic with poorly controlled ventricular arrhythmias had significant heart disease. In one patient, a ventricular tachyarrhythmia that had required more than 100 electrical cardioversions spontaneously disappeared after requiring 1 year of antiarrhythmic therapy.

Adolescent