Overview of SQTS
Short Q-T interval syndrome (SQTS) is a clinical syndrome of electrocardiographic disorders with autosomal dominant inheritance, characterized by shortened QT intervals (generally ≤300 ms), markedly shortened ventricular or atrial effective response time, symmetric hyperextension of the T wave in the thoracic leads, recurrent syncope and sudden cardiac death without obvious structural abnormalities of the heart. It is a new clinical syndrome characterized by no obvious structural abnormality of the heart. Sudden death is common in young people and carries a lifelong risk of death. It is also common in infants and young children.
Etiology
Recent studies have revealed that short Q-T interval syndrome is a genetically heterogeneous disorder, and to date, three genotypes of short Q-T interval syndrome have been identified, namely short Q-T interval syndrome 1, short Q-T interval syndrome 2, and short Q-T interval syndrome 3. These three different genotypes are functionally acquired mutations in genes encoding different potassium channel subunits. They result in either an increase in the strength or density or a speeding up of the kinetic process of outward potassium ion flow during repolarization of cardiomyocytes or a decrease in the strength or density or a slowing down of the kinetic process of inward potassium ion flow, which causes a shortening of the Q-T interval and thus an increase in the electrical susceptibility of atrial and ventricular myocardium. Further studies are needed to determine whether other genetic alterations are present in short Q-T interval syndrome. Therefore, the main cause of short Q-T interval syndrome is a genetic abnormality. There is a family history of short Q-T interval syndrome, with occasional disseminated cases. Both male and female members of the same family can be affected, suggesting autosomal dominant inheritance.
Symptoms
1. The clinical manifestations of patients with short Q-T interval syndrome are variable, ranging from no symptoms or only palpitations and dizziness in mild cases to syncope and sudden death in severe cases. In severe cases, syncope and sudden death may occur. Moreover, patients begin to show clinical symptoms at a very young age. It can even lead to sudden cardiac death in newborns. This disease may be one of the causes of sudden neonatal death syndrome.
2. The majority of patients with short Q-T interval syndrome have shortened ventricular shortening, ventricular fibrillation induced by electrophysiology, and a positive family history of sudden death or atrial fibrillation; short Q-T interval syndrome is characterized by the presence of very short QT intervals on the electrocardiogram; the T-wave is always upright and upward, and the intervals between the peaks of the T-wave and the ends of the T-wave do not lengthen.
3. Widening of the interbrow space has been reported as a manifestation of short Q-T interval syndrome.
Examination
1. Electrocardiogram (ECG): Conventional ECG shows obvious shortening of QT interval; high sharp T wave in chest lead; often accompanied by ventricular tachycardia/ventricular fibrillation or atrial fibrillation ECG, and high incidence of atrial fibrillation is one of the characteristics of SQTS.
2. Electrophysiological examination: shortening of the effective response period of atrial and ventricular muscles; increased susceptibility of atria and ventricles. Electrophysiological examination is valuable for risk stratification and prognosis judgment of short Q-T interval syndrome.
3. Physical examination and blood biochemical examination without organic heart disease.
4. Secondary factors leading to QT interval shortening, such as hyperthermia, hyperkalemia, hypercalcemia, sympathetic excitation, digitalis effect, etc., should be excluded.
Treatment
The treatment of short Q-T interval syndrome is still under investigation. The goal of treatment is to prolong the QT interval and eliminate the risk of arrhythmia and sudden death.
The treatment of patients with the syndrome is as follows
1. Implantable cardioverter-defibrillator (ICD) is the treatment of choice for short Q-T interval syndrome, especially in patients who have been rescued from sudden cardiac death or have a history of syncope. Implantable cardioverter-defibrillators (ICDs) are the only effective treatment and prevention of sudden death. However, the main problem is that implantable cardioverter defibrillators over-sense high-tip T waves leading to false discharges, and it is important to carefully regulate their sensing and therapeutic parameters.
2. Radiofrequency ablation: reported to be effective, but few cases.
3. Drugs: strong sodium channel blockers fluocaine, quinidine, propafenone, etc.
4. Treatment of offspring: gene therapy is a promising treatment.
Prognosis
Those with shortened QTc have a 2-fold increase in the risk of sudden death compared with those with normal QTc. Short QT intervals during and after cardiopulmonary resuscitation is a serious electrocardiographic phenomenon that predicts the soon development of second- and third-degree atrioventricular block and ventricular arrest, and it is one of the end-of-life electrocardiographic manifestations.
Prevention
The syndrome often affects young, healthy individuals without organic heart disease. In people with a family history of short Q-T interval syndrome, active testing of genotype and Q-T interval should be performed to detect occult patients.