Long QT syndrome. QBANK SESSION. CLINICAL SCIENCES. LEARNED. Summary. FEEDBACK. Etiology. Congenital LQTS. Acquired LQTS

Long QT syndrome

Last updated: Dec 16, 2019

QBANK SESSION

CLINICAL SCIENCES

LEARNED

Summary

Long QT syndrome (LQTS) is a congenital or acquired heart condition in which the QT interval (i. e., ventricular depolarization and repolarization) is prolonged. Most patients with LQTS are asymptomatic, but some present with seizures, syncope, or even life-threatening arrhythmias and sudden death. Treatment depends on the underlying cause: Beta blockers and implantable cardioverter defibrillator (ICD) insertion are commonly used for congenital LQTS, whereas treatment of the underlying cause (drug, electrolyte abnormality, etc. ) is the first-line therapy for acquired LQTS.

NOTES

FEEDBACK

Etiology

A prolonged QT interval may be congenital or acquired.

Congenital LQTS

· Congenital LQTS arises from mutations in genes that code for ion channels within myocytes

· These mutations all cause ventricular action potentials to be prolonged, resulting in a lengthened QT interval on ECG. ^[1]

· LQTS type 1

o Most common type of congenital LQTS

o Defect: loss of function mutation on the KCNQ1 gene located on chromosome 11p → defective slow delayed rectifier voltage-gated potassium channel

o Subtypes

§ Jervell and Lange-Nielsen syndrome ^[2]

§ Associated with congenital deafness

§ Autosomal recessive

§ Associated with ventricular tachyarrhythmias

§ Romano-Ward syndrome ^[3]

§ No associated deafness

§ Autosomal dominant

§ Associated with ventricular tachyarrhythmias

Acquired LQTS

· Drugs: Usually substances that block potassium outflow during the rapid repolarization phase ^[4]

o Antiarrhythmics: especially class IA and class III antiarrhythmics

§ Compared to other class III antiarrhythmics, amiodarone rarely causes torsades de pointes.

o Psychiatric medications: especially tricyclic antidepressants and haloperidol

o Antibiotics (e. g., macrolides, fluoroquinolones)

o Antihistamines (e. g., diphenhydramine)

o Antimalarial medications

o Antiparkinson medications

o Opioids

· Electrolyte imbalances (e. g., hypokalemia, hypomagnesemia, hypocalcemia)

· Endocrine disorders (e. g., hypothyroidism)

· Nutritional deficiencies (e. g., anorexia nervosa)

· Ischemic stroke or intracranial hemorrhage

References: ^{[5][6][7][8][9][10][11]}

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