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.

Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT)
Like LQTS, CPVT is an inherited disorder that causes abnormal electrical activity in the heart.  This abnormal activity often occurs during exercise, physical activity or in stressful or emotional situations.

Causes of CPVT
Like LQTS, CPVT is caused by abnormal ion channels in the heart.  This can cause ventricular tachycardia, an extremely rapid heart beat that originates in the ventricles of the heart. This ventricular tachycardia is felt to be triggered by the release, under stress, of certain hormones, called catecholamines. Ventricular tachycardia is a potentially life-threatening arrhythmia because it may lead to ventricular fibrillation and possibly sudden death.  CPVT is hereditary, so it’s important for both you and your family members to be tested.

Diagnosis of CPVT
Your doctor may suspect that you have CPVT based on your symptoms and specific abnormal findings on an exercise stress test.  Unlike LQTS, a resting ECG for an individual with CPVT will almost always be normal. This may lead your physician to recommend that you undergo an exercise stress test.  A specific abnormal arrhythmia on the exercise stress test will often confirm a CPVT diagnosis, however, in some cases, the exercise stress test will lack this specific rhythm.  FAMILION can help your doctor confirm this diagnosis for you and your family members, including those who may not show any symptoms of the disease.

Treatment of CPVT

• Medication prescribed by your doctor may help control your heart beat. It is very important that you take your medication as directed, and never stop taking a medication without talking to your doctor first.
• Sometimes, your doctor may want to recommend implantation of a device called an implantable cardioverter defibrillator (ICD).

Brugada Syndrome (BrS)
Like LQTS and CPVT, BrS causes abnormal electrical activity in the heart. The most common symptom is fainting, but not all people with Brugada Syndrome have symptoms. It is seen in both men and women, but it is more common in men.

Causes of Brugada Syndrome
Like LQTS, BrS is caused by abnormal ion channels in the heart. This can cause a fast, disorganized beating of the heart called “ventricular fibrillation.” Ventricular fibrillation interferes with blood flow to the body, and if not corrected, it can result in death. BrS is hereditary, so it’s important for both you and your family members to get tested.

Diagnosis of Brugada Syndrome
Your doctor may suspect that you have BrS based on your symptoms and specific abnormal findings in your ECG. He or she may recommend that you undergo a “provocative test,” which involves taking a drug to produce the typical ECG findings. FAMILION can also help your doctor confirm this diagnosis for you and your family members.

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