Ablation
A technique in which heat (or sometimes cold) is used to destroy abnormal
tissue.
Angiogram
A procedure in which thin tubes are inserted into an artery and threaded
through the artery into the heart. Contrast dye is injected and X-ray
pictures are taken of the heart and its arteries.
Arrhythmia
An abnormal beating of the heart. It can be too fast (tachycardia), too
slow (bradycardia), or simply irregular even though the heart rate is
normal.
Atrial fibrillation
A type of arrhythmia in which the upper chambers of the heart (atria)
have a completely disorganized rhythm, causing them to beat rapidly and
ineffectively.
Brugada syndrome
Brugada syndrome was first described in 1992. The syndrome includes the
findings of an abnormal ECG, ventricular fibrillation, and sudden cardiac
death. It is known to be caused by a genetic abnormality of the cardiac
sodium channel.
Cardiac Catheterization
A procedure in which a catheter (a long, thin tube or wire) is inserted
into a vein or an artery and moved up through the vein or artery into
the heart. Once inside, pictures may be taken of the arteries of the heart,
pressures of the heart chambers measured, or the electrical activity of
the heart evaluated.
Cardiologist
A doctor who specializes in heart diseases.
Cardiac Electrophysiologist
A cardiologist who specializes in diseases of the heart’s electrical
system that may cause arrhythmias.
Catheter Ablation
A technique performed with a catheter (a long, thin tube or wire) in which
abnormal heart tissue is cauterized in an attempt to cure arrhythmias
caused by the abnormality.
Channelopathy
A genetic disease caused by a mutation in one of the genes that codes
for the function of the heart’s electrical system. Each heart cell
has pores, or channels, in its outer covering (cell membrane) that allow
the cell to communicate with other nearby heart cells. The channels pass
ions such as sodium, potassium, calcium and chloride in and out of the
cells. There are many types of channels, but typically, with channelopathies,
either the potassium channels or the sodium channels are defective.
Clinical heterogeneity
Term used to describe a disorder in which mutations of different parts
of the same gene can cause different signs and symptoms of the disorder.
Defibrillator
A device that monitors heart rhythm. If it detects an abnormal rhythm
such as ventricular tachycardia or ventricular fibrillation, it delivers
a shock to the heart to return it back to normal rhythm. See also implantable
defibrillator.
Echocardiogram
An ultrasound examination in which the structure and function of the heart
may be visualized.
Electrocardiogram (ECG, also known as EKG)
The heart generates electrical impulses with each heart beat, and the
electrical signals may be measured on the surface of the body. The ECG
is a test that measures these electrical signals from the heart.
Electrophysiologic Testing (also called
an EP Study or EPS)
A type of heart catheterization in which long, thin wires are passed through
the veins (and sometimes arteries) into the heart, to allow measurement
and testing of the heart’s electrical activity. It is a low-risk
procedure which has a high diagnostic yield in evaluating patients with
known or suspected arrhythmias. It is a helpful test to make diagnoses
and to guide therapy.
Fibrillation
An abnormal heart rhythm in which the normal, rhythmic beating of the
heart is replaced by disorganized, ineffective and extremely rapid electrical
impulses. The state of fibrillation prevents the heart chamber that is
fibrillating from having any effective contractions.
Gene
A hereditary unit of information which carries the instructions to direct
the formation of a specific protein (with a specific function) in the
body.
Genetic Counselor
A health care professional with a specialized graduate degree and experience
in the areas of medical genetics and counseling. Genetic counselors work
as members of a health care team, providing information and support to
individuals and families who may be at risk for a variety of inherited
conditions.
Holter Monitoring
A small, portable recording device that an individual wears while going
about their daily routine, to record the electrocardiogram over a 24-hour
period. The device records every heart beat during the time it is worn,
giving the physician an important view of the heart’s activity over
the course of a full day.
Implantable Defibrillator
A small defibrillator, approximately the size of a beeper, which is implanted
under the skin and monitors heart rhythm. If it detects an abnormal rhythm
such as ventricular tachycardia or ventricular fibrillation, it automatically
delivers a shock to the heart to return it back to normal rhythm.
Invasive testing
Testing that requires a surgical procedure. In general, invasive testing
is associated with some risks, but the risk depends on the type of test
or procedure being performed.
Long QT syndrome (LQTS)
Long QT syndrome was first described in 1957. The syndrome includes the
findings of an abnormal ECG, ventricular fibrillation, and sudden cardiac
death. It is now known to be caused by a genetic abnormality of one of
the cardiac potassium or cardiac sodium channels.
Loop Recording
A small, portable recording device that an individual wears while going
about their daily routine. If a symptom occurs, such as a palpitation
or dizzy spell, the patient activates a button and the device records
the heart rhythm at that time, storing it on a small computer chip inside
the device. The individual then sends this recording over the telephone
to a central station, which faxes the results to the physician. The device
is often used in situations in which the patient has transient or intermittent
symptoms that are not felt to be life-threatening, but nevertheless are
important to record.
(MRI) Magnetic Resonance Imaging
Magnetic Resonance Imaging is a test that is performed utilizing state-of-the-art
MRI equipment with specialized adjustments to allow the heart to be visualized
while it is beating. It is often used to evaluate patients with suspected
Brugada syndrome, and to rule out any other heart abnormalities such as
Arrhythmogenic Right Ventricular Dysplasia.
Mutation
A permanent heritable change in the DNA sequence of an individual. Not
all mutations cause disease; only those mutations that alter the ability
of a gene to create its normal protein will have consequences. Mutations
that are benign are called polymorphisms. Some mutations are of unknown
significance.
Neurocardiogenic Syncope
The medical term for a type of syncope (fainting). Syncope is caused by
an abnormal slowing of the heart rate because of an inappropriate signal
from the brain which tells the heart to slow down.
Noninvasive testing
Testing that does not require a surgical procedure. In general, noninvasive
tests involve minimal or no risk to the individual.
Pacemaker
A device that monitors heart rhythm. If it detects an abnormally slow
heart rhythm, it delivers an electrical impulse to the heart to allow
it to beat at a normal rate.
Penetrance
Penetrance refers to the probability that an individual with a disease-causing
mutation will experience any signs or symptoms of that disease. Penetrance
is an all-or-none concept. See Reduced
penetrance.
Potassium channel
The electrical activity of heart cells depends on ions (sodium, potassium,
calcium, chlorine atoms) that must pass in and out of a heart cell so
the cell can function normally. The ions pass selectively through channels,
which are similar to pores or holes. There are several types of potassium
channels that are encoded by various genes. If there is a mutation in
one of these genes, the structure of the potassium channel may be abnormal
and this in turn can cause the channel to function abnormally. The abnormal
function can often be seen on the surface electrocardiogram.
QT prolongation
Various measurements can be performed on the electrocardiogram to measure
different parts of the electrical activity of the heart. One important
measurement is the QT interval. This is the time it takes for the lower
chambers of the heart to become electrically excited and then return to
the baseline, post-excitation state (repolarization time). The normal
time can be prolonged by various abnormalities of the heart, including
genetic abnormalities, and by many medications. An abnormally long repolarization
time is termed a Prolonged QT Interval.
Reduced penetrance
A disorder is described as having reduced penetrance when less than 100%
of the people who carry a disease-causing mutation for the disorder exhibit
any signs or symptoms of that disorder. See penetrance.
Sodium Channel
The electrical activity of heart cells depends on ions (sodium, potassium,
calcium, chlorine atoms) that must pass in and out of a heart cell so
the cell can function normally. The ions pass selectively through channels,
which are similar to pores or holes. The sodium channel is encoded by
the SCN5A gene. If there is a mutation of this gene, the structure of
the sodium channel may be abnormal and this in turn cause the channel
to function abnormally. The abnormal function can often be seen on the
surface electrocardiogram.
Stress Test
A test in which an individual walks on a treadmill at increasingly faster
speeds, while monitoring the blood pressure and electrocardiogram. Although
the heart may appear to be functioning normally during normal daily activities,
this test causes the heart to beat faster (a type of stress) in an attempt
to bring out any abnormalities of the blood flow or heart rhythm.
Stress Test with Thallium
A type of stress test in which a small dose of radioactive material is
injected at the end of the test and the individual is then placed under
a specialized camera. This allows imaging of areas of the heart to determine
if there are areas of diminished blood flow. If an individual cannot walk
on a treadmill the test may also be performed by giving an intravenous
medication to make the heart beat faster (chemical stress test).
Supraventricular Tachycardia
A type of arrhythmia that affects the upper chambers of the heart and
causes an abnormally fast heart rate. If left untreated, it can cause
palpitations and fainting.
Syncope
A medical term for loss of consciousness, or fainting.
Syndrome
A syndrome is a collection of causally related abnormalities. Examples
include Brugada syndrome and Long QT syndrome.
Tilt Table Test
This test is typically performed to help diagnose the cause of dizziness
and fainting. The individual is placed on a table that tilts upward, and
the table is then placed at an approximately upright position so the individual
is standing. Heart rate and blood pressure are monitored during the test.
If no symptoms occur, a medication may be given to increase the heart
rate in an attempt to reproduce the symptoms.
Variable expressivity
A disorder is said to exhibit variable expressivity when the symptoms
and severity of the disorder differ in people who have the same disease-causing
mutation.
Ventricular Tachycardia
A type of arrhythmia that affects the lower chambers of the heart and
causes a dangerous and abnormally fast heart rate. If left untreated,
it can cause palpitations, fainting, and death.
Ventricular Fibrillation
An arrhythmia which causes complete disorganization of the electrical
activity of the lower chambers of the heart, and is rapidly fatal if not
treated immediately with a shock by a defibrillator to convert the heart
back to normal rhythm.