LQT5

Long QT Syndrome Microchapters
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2]

Overview

LQT5 subtype of long QT syndrome is an autosomal dominant mutation that leads to a defect in the potassium channel. In its rare homozygous form it can cause Jervell and Lange-Nielsen syndrome.

LQT5 Subtype

Type	OMIM	Mutation
LQT5	176261	beta subunit MinK (or KCNE1) which coassembles with KvLQT1

Genetics and Pathophysiology

LQT5 is an autosomal dominant relatively uncommon form of LQTS. It involves mutations in the gene KCNE1 which encodes for the potassium channel beta subunit MinK. In its rare homozygous forms it can lead to Jervell and Lange-Nielsen syndrome. As in LQT1, LQT5 can lead to a decreased excretion of potassium from the cell and will show prolongation of the QT interval on EKG.

History and Symptoms

• Seizures - due to oxygen deprivation that occurs during arrhythmia.
• Fainting - fainting or syncope is the most common symptom LQTS.
• A prodrome may occur before losing consciousness, which may consist of lightheadedness, heart palpitations, blurred vision or weakness.
• Sudden death - a fatal arrhythmia that is not quickly intervened on, may cause sudden death.
• History of sensorineural deafness as occurs in Jervell and Lange-Nielsen syndrome.

Therapy

• Beta-blockers are the first line treatment in LQTS, even in asymptomatic carriers, as they reduce the incidence of syncope and sudden cardiac death.
• Other medications to control non-malignant arrhythmias.
• Electrolytes should be repleted as neccesary.
• Avoidance of triggers (drugs, supplements, loud noises, exercise).
• LQTs is one of the few diseases where genetic testing can provide important guidance, such as in whom to place an AICD (defibrillator) for the primary prevention of cardiac events.
• Left stellectomy is not a cure, but is a second line therapy to reduce the risk of sudden cardiac death and is indicated if the patient does not tolerate beta blockers, as well as in young patients under the age of 12 where beta blockers are not deemed protective enough and AICD is not appropriate.
• Patients with long QT syndrome should undergo secondary prevention with AICD implantation if they sustain an aborted cardiac arrest or sudden cardiac death.