How Is Long QT Syndrome Diagnosed?
Doctors' Considerations
Doctors called cardiologists diagnose and treat long
QT syndrome (LQTS). Cardiologists are doctors who specialize in treating
problems and diseases of the heart. To diagnose LQTS, doctors consider:
- EKG
(electrocardiogram) results
- Medical history and physical exam
- Genetic test results
EKG
An EKG is a simple test that detects and records the
electrical activity of the heart. This test may reveal a long QT interval and
other signs that make it more likely that you have LQTS. Often your doctor
first discovers you have a long QT interval when an EKG is done for another
suspected heart problem.
Not all people with LQTS will always have a long QT
interval on an EKG. The QT interval may change from time to time, sometimes
being long and other times normal. Because of this, your doctor may want you to
have several EKG tests over a period of days or weeks. Or your doctor will have
you wear a device called a Holter monitor.
A Holter monitor, also called an ambulatory EKG,
records the electrical activity of your heart for a full 24-hour period. For
this test, you wear patches called electrodes on your chest that are connected
by wires to a small, portable recorder. The recorder may be clipped to a belt,
kept in a pocket, or hung around your neck. During the 24 hours, you do your
usual daily activities. You then return the recorder to the doctor to read the
results. The purpose of a Holter monitor EKG is to detect heart problems that
may occur for only a few minutes out of the day.
Some people will only have a long QT interval on an
EKG recording while they exercise. For this reason, your doctor may recommend
that you have an exercise
stress
test.
For this test, a machine records your EKG while you
exercise. If you're unable to exercise, a medicine may be injected through an
intravenous line into your bloodstream to make your heart work harder and beat
faster as if you were exercising.
Medical History and Physical Exam
Your doctor will ask whether you have had any
symptoms of an irregular heartbeat. These include:
- Unexplained fainting
- A fluttering feeling in your chest, which is the
result of your heart beating too fast
- Loud gasping during sleep
Your doctor will ask what over-the-counter,
prescription, or recreational drugs you take.
Your doctor also will want to know whether anyone in
your family was diagnosed with or shows signs of LQTS. Signs of LQTS include
unexplained fainting or seizures, drowning,
sudden
cardiac arrest, or sudden death.
Your doctor will examine you and will look for the
presence of conditions that may lower blood levels of potassium or sodium.
These conditions include the eating disorder anorexia nervosa, excess vomiting
or diarrhea, and certain thyroid disorders.
Genetic Tests
Genetic blood tests can detect some forms of
inherited LQTS. If your doctor suspects that you have LQTS, he or she may
recommend genetic testing. Genetic blood tests are usually also suggested for
family members of people with LQTS. But about one-third of LQTS cases aren't
detected with genetic testing. Even if you do have LQTS, the tests may not show
it.
Also, as many as one-third of the people who test
positive for LQTS don't have any signs or symptoms of the disorder. These
people may have silent LQTS. Fewer than 1 out of 10 of these people will
faint or suddenly die from an irregular heartbeat.
But even if you have silent LQTS, you may be more at
risk than most people for developing an irregular heartbeat while taking
medicines that affect potassium ion channels or blood levels of potassium.
Types of Inherited LQTS
If you have inherited LQTS, it may be helpful to
know which of the seven inherited types of the syndrome you have. That way, you
and your doctor can better target the treatment and lifestyle measures you need
to take. To figure out your LQTS type, your doctor will consider:
- Genetic test results
- The types of situations that trigger an irregular
heartbeat
- How well you respond to medicine
|