LQTS (Long QT syndrome) (Acquired LQTS (MANAGEMENT ( nonsynchronized…
LQTS (Long QT syndrome)
The primary symptoms include palpitations, syncope, seizures, and SCD.
Normal QT interval
- similar in males and females until late adolescence (0.37 to 0.44 sec).
- In adults QT interval of more than 0.45 sec is considered prolonged in men; the normal range generally is extended to 0.45 to 0.47 seconds in women
- Bazett formula: QTc = QT interval ÷ √RR interval (in sec) QTc = QT at HR 60 bpm
- Electrolyte abnormalities: hypokalaemia, hypomagnesemia and hypocalcemia
- Drug-induced LQTS
Antiarrhythmic drugs: class IA, III,
Macrolide antibiotics: Azithromycin, erythromycin, clarithromycin, roxithromycin
Psychotropic drugs: Chlorpromazine, haloperidol, thioridazine
Antiemetics: Ondansetron, granisetron, dolasetron,
Other: methadone, cisapride (restricted availability), domperidone, metoclopramide, diuretics
- Bradyarrhythmias (avb, sss)
- Metabolic disorders: Hypothyroidism, Anorexia nervosa
- Myocardial ischemia or infarction, especially with prominent T- wave inversions
- Intracranial disease
- HIV infection
- nonsynchronized electric defibrillation in patients with hemodynamically unstable Torsades de pointes.
- In the conscious patients with TdP:
Intravenous magnesium is first-line therapy
Temporary transvenous overdrive pacing (atrial or ventricular) at about 100 bpm (for pts who do not respond to Mg iv).
Isoproterenol can be used as a temporizing measure to achieve a heart rate of 100 bpm prior to pacing(contraindicated for congenital long QT syndrome).
terminate spontaneously but may degenerate to ventricular fibrillation, resulting in sudden death.
- Autosomal dominant LQTS (Romano–Ward syndrome; prevalence 1 in 2500), includes LQT1–6 and
LQT9–13 and is characterized by an isolated prolongation of the QT interval;
- Autosomal dominant LQTS with extracardiac manifestation,
- LQT7 (Andersen–Tawil syndrome) prolonged QT interval with prominent U wave, VT, facial dysmorphisms and hyper-/hypokalaemic periodic paralysis
- LQT8 (Timothy syndrome), prolonged QT, syndactyly, cardiac malformations, autism spectrum disorder and dysmorphisms;
- Autosomal recessive LQTS (Jervell and Lange–
Nielsen syndrome) an extremely prolonged QT with congenital deafness.
Genetics of LQTS
- Mutations in 13 genes have been associated with LQTS, most encoding for subunits of potassium, sodium or calcium voltage-dependent ion channels.
- Genetic screening identifies a disease-causing
- mutation in 75% of LQTS cases and three main genes (KCNQ1, KCNH2 and SCN5A) account for 90% of positively genotyped cases
(a) Avoidance of QT-prolonging drugs
(b) Correction of electrolyte abnormalities that may occur during diarrhoea, vomiting or metabolic conditions.
(c) Avoidance of genotype-specific triggers for arrhythmias (strenuous swimming, especially in LQTS1, and exposure to loud noises in LQTS2 patients).
- Class I Recommendations
ICD implantation with the use of betablockers is recommended in LQTS patients with previous cardiac arrest
Nadolol – 1-1.5 mg/kg/day
Propranolol – 3-4 mg/kg/day
Propranolol and/or Mexiletine/Ranolazine (LQT3)
- Class IIa Recommendations
Beta-blockers should be considered in carriers of a causative LQTS mutation and normal QT interval.
ICD implantation in addition to beta-blockers should be onsidered in LQTS patients who experienced syncope and/or VT while receiving an adequate dose of beta-blockers.
LCSD Left cardiac sympathetic denervation should be considered in patients with symptomatic LQTS when
(a) Beta-blockers are either not effective, not tolerated or contraindicated;
(b) ICD therapy is contraindicated or refused;
(c) Patients on beta-blockers with an ICD experience multiple shocks.
- Class IIb Recommendations
Sodium channel blockers (mexiletine, flecainide or ranolazine) may be considered as add-on therapy to shorten the QT interval in LQTS3 patients with a QTc >500 ms.
Implant of an ICD may be considered in addition to beta- blocker therapy in asymptomatic carriers of a pathogenic mutation in KCNH2 or SCN5A when QTc is >500 ms.
- disorder of myocardial repolarization characterized by a prolonged QT interval on the ECG.
- associated with an increased risk of torsade de pointes (TdP)