Syndrome du QT court congénital

Intervalle QT court d’origine génétique à transmission autosomique dominante (canalopathie) compliqué de trouble du rythme.

Cette pathologie exceptionnelle touche le sujet jeune (plutôt masculin), de façon sporadique ou familiale, et est responsable d’accès de fibrillation atriale ou ventriculaire, syncopes et/ou morts subites par exemple en cas de peur soudaine.[1] L’âge médian du diagnostic est de 30 ans (extrêmes 4-80).[2]

Le syndrome associe un intervalle QTc < 350 ms avec soit des symptômes, des troubles du rythme, des antécédents familiaux, soit une analyse génétique contributive. Les valeurs du QTc sont souvent faibles (ex. 250 ± 15 ms).[3] L’intervalle QT s’adapte mal à la fréquence cardiaque et reste constamment court (risque de faux négatif en cas de mesure lors d’une fréquence > 80/mn). Les ondes T sont pointues, amples et symétriques dans les dérivations précordiales, mais leur aspect varie selon le génotype responsable.

L’exploration électrophysiologique révèle des périodes réfractaires atriales et ventriculaires courtes et des arythmies ventriculaires sont fréquemment déclenchées par la stimulation ventriculaire. Après stratification pronostique, un défibrillateur peut être proposé. Des recommandations USA 2017 sont téléchargeables en ligne.[4]

[1] Gaita F et al. Short QT Syndrome: a familial cause of sudden death. Circulation 2003; 108(8): 965-70 (téléchargeable)
[2] Giustetto C et al. Short QT syndrome: clinical findings and diagnostic-therapeutic implications. Eur Heart J. 2006; 27(20):2440-7.
[3] Gollob MH, Redpath CJ, Roberts JD. The short QT syndrome: proposed diagnostic criteria. J Am Coll Cardiol. 2011; 57(7):802–812
[4] Al-Khatib SM, Stevenson WG, Ackerman MJ, et al. 2017 AHA/ACC/HRS Guideline for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart rhythm Society. J Am Coll Cardiol. 2018;72(14):e91–e220.

1. The prevalence of short QTc ≤ 340 ms is estimated to be 5 in 10,000 in persons < 21 years of age and is more common in males. An incidental finding of a short QTc ≤ 320 ms in an asymptomatic patient warrants monitoring and follow-up without prophylactic medication treatment. In asymptomatic patients with a short QTc interval, observation without treatment is recommended

2. Patients with cardiac arrest in the setting of short QT syndrome are known to be at increased risk for recurrent cardiac arrest. Approximately 18% of the small number of reported patients with short QT and implanted ICDs have experienced appropriate ICD therapies during short-term follow-up. In asymptomatic patients with a short QTc interval, observation without treatment is recommended

3. Markedly shortened QTc values ≤300 ms are associated with increased risk of SCD, especially during sleep or rest, in young persons, in whom the median QTc was 285 ms. A clinical score including QTc duration, clinical history of documented polymorphic VT or VF, unexplained syncope, family history of autopsy-negative SCD or sudden infant death syndrome, and positive genotype results has been proposed to identify patients at increased risk for SCD. Treatment with quinidine results in lengthening of the QTc and, in selected patients, may be an alternative to ICD implantation

4. In the setting of electrical storm with refractory VF and short QT syndrome, infusion of isoproterenol can be effective in restoring/maintaining sinus rhythm

5. Pathogenic mutations in potassium channels have been identified in approximately 10% to 20% of patients with short QT syndrome including in KCNH2 (SQT1), KCNQ1 (SQT2), and KCNJ2 (SQT3) (S7.9.1.5-4). Due to the rarity of the disease, genotype/phenotype correlations are unavailable, limiting the use of knowledge of genotype status. In patients with short QT syndrome and VT/VF storm, isoproterenol infusion can be effective

Lire aussi

A Novel Familial Cardiac Arrhythmia Syndrome with Widespread ST-Segment Depression NEJM 2018

Mazzanti A, Kanthan A, Monteforte N, et al. Novel insight into the natural history of short QT syndrome. J Am Coll Cardiol. 2014 Apr 8;63(13):1300-8. –> In this study, we showed that having survived a first occurrence of CA is a strong predictor of recurrences. This information is important because it supports the need to consider implanting an ICD for secondary prevention of CA even in young SQTS patients.

Anttonen O, Junttila J, Giustetto C, et al. T-Wave morphology in short QT syndrome. Ann Noninvasive Electrocardiol. 2009 Jul;14(3):262-7.