About Cardiac Channelopathies

What are cardiac channelopathies?
The heart has an electrical system that controls the heartbeat and other important functions. It is controlled by pores in the heart called ion channels. Cardiac channelopathies occur when the proteins forming these channels do not function properly. In some patients, cardiac channelopathies cause noticeable symptoms from an early age, but in others they can go undetected for years until unexpectedly causing symptoms.
Symptoms from cardiac channelopathies may occur spontaneously in the hereditary disorders or be caused by reactions to certain drugs. Regardless of the trigger, the heart can beat irregularly causing symptoms such as fainting or seizures and lead to the diagnosis or tentative diagnosis of potentially dangerous conditions, such as:

• Long QT Syndrome (LQTS)
• Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT)
• Brugada Syndrome  (BrS)

Long QT Syndrome (LQTS)

What is Long QT Syndrome?
LQTS is a condition that impairs the electrical system of the heart. Its symptoms may include fainting, seizures, abnormal heartbeats, and even death. For some people, symptoms only occur under certain conditions, for example, when they are startled, under emotional stress, or engaged in vigorous physical activities. Most LQTS deaths can be prevented with early diagnosis and treatment.

What is the QT interval?
Every heartbeat is started by an electrical signal that tells the heart muscle to contract. This signal causes the waves that you see on an ECG. These waves are represented by the letters P, Q, R, S, T, and U.

The QT interval represents the length of time between the beginning of the Q wave and the end of the T wave, when the heart “recharges” before its next beat. People with LQTS have an unusually long QT interval.

Why does it matter if the QT interval is too long?
When the QT Interval is too long, your heart may not beat correctly. This can result in very fast, abnormal heartbeats, causing symptoms such as dizziness, fainting or seizures. The severity and duration of these symptoms depend on how quickly your heart can return to a normal rhythm.

Cause of QT Interval Prolongation:

Familial LQTS
Familial LQTS is an inherited disorder seen in about 1 in 3,000 people. In some families, there may be a history of seizures, fainting, or sudden death from unknown causes. Others may find out that they have LQTS only after taking a medication that causes them to faint or have an unusual heart rhythm.

Familial LQTS is caused by a gene mutation that is passed from one generation to the next. If you have a mutation, one of your parents, your children, and other relatives may also have it. Children of a parent with an LQTS mutation have a 50% chance of inheriting it. The symptoms experienced by family members with the same mutation are likely to vary by severity and age of first occurrence.

For this reason, family members of people with LQTS may benefit significantly from the FAMILION Family Specific Test, even if they have never had any symptoms.

Acquired LQTS
Acquired LQTS also results from abnormal ion channel function. However, people with the disorder do not exhibit symptoms until they take certain medications, which cause them to faint or have seizures. In most cases, their QT interval returns to normal after they stop taking the medication. This is also commonly called “drug-induced LQTS.” Often, an LQTS mutation is involved and the drug acts to worsen the condition to the point where symptoms are observed.

Diagnosis of LQTS
Your doctor may suspect that you have LQTS based on a history of fainting or seizures in you or a family member. They may request an ECG to measure your QT interval. You may also be asked to take an exercise test. These tests may tell you that you have LQTS, but they cannot tell you its cause.

FAMILION can provide this information by analyzing ion channel genes, uncovering the type of mutation or mutations you have. This is a valuable tool that can help your doctor determine the cause of your symptoms and evaluate possible treatment options. The test can also help determine whether your blood relatives are at risk for LQTS.

Treatment of LQTS
Several treatment options are available if you are diagnosed with LQTS:

• Medication prescribed by your doctor may help control your heart beat. It is very important that you take LQTS medication as directed, and never stop taking a medication without talking to your doctor first.
• A medical device called an implantable cardioverter defibrillator (ICD) can be surgically implanted to help control your heart.
• Lifestyle modifications can also help control LQTS. You may be advised not to participate in competitive sports, or you may be given a list of medications to avoid.

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