LQT9

LQT9 subtype is a variant of long QT syndrome, which causes abnormalities in a membrane protein called caveolin.

This newly discovered variant is caused by mutations in the membrane structural protein,caveolin-3. Caveolins form specific membrane domains called caveolae in which among others the Na_V1.5 voltage-gated sodium channel sits. Similar to LQT3, these particular mutations increase so-called ‘late’ sodium current which impairs cellular repolarization.

• 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.

• 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. ^[1]
• 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.