Long QT Syndrome medical and device therapy

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

Overview

Beta-blockers are first line treatment in LQTs along with electrolyte repletion, and avoidance of triggers (drugs, supplements, loud noises). LQTs is one of the few diseases where genetic testing actually can provide important guidance such as who to put a AICD (defibrillator) in for primary prevention. Left stellectomy) is not a cure, but is second line therapy to reduce the risk of sudden cardiac death and is indicated if the patient does not tolerate beta blockers or breaks through beta blockers, as well as in young patients under the age of 12 where beta blockers are not deemed protective enough and where the morbidity of an AICD seems excessive. Patients with Long QT syndrome should undergo secondary prevention with AICD implantation for secondary prevention if they sustain an aborted cardiac arrest or sudden cardiac death.

Primary Prevention

Withdrawal of Drugs and Supplements

Certain medications should be avoided in persons with long QT syndrome, to avoid worsening the condition. These medications include certain appetite suppressants, decongestants, and antibiotics such as erythromycin. Illicit drugs such as cocaine and amphetamines can be even more dangerous in persons with long QT syndrome.

Correct Electrolyte Disturbances

Illness that cause hypokalemia due to vomiting and diarrhea can aggravate long QT syndrome. Medications that can lower the levels of potassium in the blood should also be avoided.

Postassium Administration

The use of potassium supplementation is experimental and is not evidence based. The hypothesis is that ff the potassium content in the blood rises, the action potential shortens and it is for this reason that increasing potassium concentration may minimize the occurrence of arrhythmias. It should work best in LQT2 since the HERG channel is especially sensible to potassium concentration, but potassium supplementation is experimental and not evidence based.

Beta Blockers

Beta blockers are first line therapy in the treatment of Long QT syndrome.

Arrhythmia suppression involves the use of medications or surgical procedures that attack the underlying cause of the arrhythmias associated with LQTS. Since the cause of arrhythmias in LQTS is after depolarizations, and these after depolarizations are increased in states of adrenergic stimulation, steps can be taken to blunt adrenergic stimulation in these individuals. beta receptor blocking agents decrease the risk of stress or catecholamine induced arrhythmias. Nadolol and propranolol are recommended, and caution should be used with atenolol.

Nadolol

Nadolol at a dose of 1.0 to 1.5 mg/kg/day or 50 mg/m2/day QD or BID is the dose

Propranolol

3-4 mg/kg/day BID for the long acting form and TID for the liquid. Often preferred in LQT3.

Mexiletine

Mexiletine is a sodium channel blocker. In LQT3 the problem is that the sodium channel does not close properly. Mexiletine closes these channels and is believed to be potentially of use when other therapies fail. It should be especially effective in LQT3 but there is limited evidence to support this recommendation.

AICD Implantation

Genotype and QT interval duration are independent predictors of recurrence of life-threatening events during beta-blockers therapy. Specifically the presence of QTc >500ms and LQT2 and LQT3 genotype are associated with the highest incidence of recurrence. In these patients primary prevention with ICD (Implantable Cardioverster Defibrilator) implantaion can be considered.

An AICD should be implanted if:

• The QTc is > 550 ms and if it is not LQT1
• LQT2 in women and the QTc is > 500 ms, with or without symptoms
• In infants with 2:1 AV block (controversial)
• In JLNS (LQTS with deafness) given its malignant propensity (controversial)

Sympathetic Denervation

Videoscopic Left Cardiac Sympathetic Denervation Surgery (left stellectomy) is not a cure, but reduces the risk of sudden cardiac death and is indicated if:

• The patient does not tolerate beta blockers or breaks through beta blockers
• The patient faints while on beta blockers
• There is a history of VF terminating AICD shocks
• In young patients under the age of 12 where beta blockers are not deemed protective enough and where the morbidity of an AICD seems excessive.

Secondary Prevention

Patients with Long QT syndrome should undergo secondary prevention with AICD implantation if they sustain an aborted cardiac arrest or sudden cardiac death.