LQT8

Long QT Syndrome Microchapters
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2]; Associate Editor(s)-in-Chief: Charmaine Patel, M.D. [3]

Overview

LQT8 subtype of long QT syndrome, also known as Timothy's syndrome is due to mutations causing abnormalities in calcium channels. LQT8 is associated with the finding of syndactyly.

LQT8 Subtype

Type	OMIM	Mutation	Notes
LQT8	601005	alpha subunit of the calcium channel Cav1.2 encoded by the gene CACNA1c.	Leads to Timothy's syndrome.

Timothy's syndrome is due to mutations in the calcium channel Cav1.2 encoded by the gene CACNA1c. Since the Calcium channel Cav1.2 is abundant in many tissues, patients with Timothy's syndrome have many clinical manifestations including congenital heart disease, autism, syndactyly and immune deficiency.

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.

Physical Exam

• Physical exam may show syndactyly.

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.
• Placement of a pacemaker may be indicated.
• 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.