Medical Glossary


Acquired Long QT Syndrome

A similar condition to Inherited Long QT syndrome, except the electrical abnormalities are not genetic, but caused by medications, strokes, and chemical imbalances in the body, among others. This condition caused the highly publicized withdrawal of the prominent drugs, Seldane and PropulcidÓ, among others.


Automatic External Defibrillator (see Defibrillator)


An abnormal heart rhythm

Arrhythmogenic Right Ventricular Dysplasia ARVD

A familial (runs in families) cardiomyopathy. Progressive damage to the right ventricle muscle.


The upper chambers in the heart, they receive blood from the veins and store it prior to each heartbeat.

Autosomal dominant

A genetic term, referring to the mode of transmission of the genetic trait from a parent to a child. Autosomal means that it is non-sex linked, so both males and females inherit the gene equally. Dominant means that a person who inherits just one abnormal copy of the gene (all people have two copies of each gene) manifests the trait. The gene is “dominant” so that only one copy is necessary to exhibit the trait.


Beta blocker

A class of drugs that block beta receptors, chemical receptors in the body that effect a particular physiologic action. Beta-blockers relieve the stress on the heart by slowing the heartbeat and lessening the force with which the heart contracts, therefore reducing blood vessel contraction in the heart and throughout the body. They are used to treat abnormal cardiac arrhythmias, angina pectoris, hypertension, and the prevention of migraines.


Slow heart rate (less than 60 bpm)

Brugada Syndrome

A genetic condition that affects the electrical system of the heart and renders affected individuals susceptible to sudden cardiac death. In this condition the deaths tend to occur to adults between ages 20 and 40 years. It is usually evident on the electrocardiogram, but no abnormalities are detected at autopsy.



A cardiomyopathy is a disease of the heart muscle, and predisposes patients to sudden death from heart rhythm abnormalities. Cardiomyopathies are common causes of sudden cardiac death in the young as well as adults. The diagnosis is usually evident during life and at autopsy. There are a variety of causes. The most common form is known as hypertrophic cardiomyopathy, or HCM.

Catacholaminergic Polymorphic Ventricular Tachycardia CPVT

A genetic condition affecting the electrical system of the heart, with no specific abnormalities on the routine electrocardiogram, and none at autopsy, to assist in the diagnosis. Affected patients are prone to very fast heart rhythms and sudden death.


The filament-like structures in the nucleus of each cell that contain the genetic material. Genes are located on the chromosomes.


Meaning present at birth



A process in which an electrical shock is administered to the heart to stabilize an irregular heartbeat or restore a normal heart beat after cardiac arrest.


A device that delivers an electrical shock to the heart in order to restore normal heart rhythm or to start the heart beating after a cardiac arrest. These particular devices are designed to convert the life-threatening arrhythmia, ventricular fibrillation, to a normal rhythm. There are internal, implantable defibrillators (ICD) which require a surgical procedure; external defibrillators, machines that are used by paramedics and other medical personnel, in which an electrical shock is applied to the chest through paddles and automatic external defibrillators (AED) designed to be used by the general public.


That part of the electrical cycle of a cell, including heart cells, in which the electrical signal is discharged. This is just like discharging a battery.



These two abbreviations are the same. They stand for electrocardiogram. The ECG is a measure of the electrical activity of the heart.

Electrophysiologist (EP)

A cardiologist or Ph.D. scientist whose specializes in the electrical activity of the heart. Clinical electrophysiologists are MD Cardiologists who deal with patients who have electrical abnormalities.



A rapid, uncoordinated heart rhythm that can originate in either the atrium or the ventricle of the heart.



The area on chromosomes that contains the genetic signals for everything that happens in the body, including our physical structure and our chemical and physiologic make up. It is currently estimated that each person has approximately 100,000 genes on our 46 chromosomes.


Inherited characteristic and the science dealing with the interaction of the genes in producing similarities and differences between individuals related by descent.


A term that refers to the specific gene which causes a disease process. In Long QT syndrome, five different genes have been discovered to cause Long QT syndrome when mutations occur in those genes.


Hypertrophic Cardiomyopathy (HCM)

When a heart muscle thickening occurs without any apparent cause.



Internal Cardioverter-Defibrillator (see Defibrillator)


A term which means the cause is unknown.

Idiopathic Ventricular Tachycardia

A fast heart rhythm that has no known cause.

Inherited Long QT syndrome

A genetic condition affecting the electrical system of the heart, often abbreviated as LQTS, followed by the number for the type of LQTS (1, 2, 3, etc,). Individuals with this condition are at risk for serious heart rhythm abnormalities (arrhythmias) that can lead to loss of consciousness, cardiac arrest and sudden cardiac death. These events most commonly occur in children and young adults. It is a common cause of unexplained sudden death in the young. No abnormalities are evident at autopsy. It is usually recognized by an abnormality on the electrocardiogram known as a prolonged QT interval.

Ion channel

A protein structure in many cells, including heart cells, through which chemical particles known as ions pass. The passage of these ions effects changes in the cell. In Long QT syndrome, the disease is caused by abnormalities of ion channels.


Jervell Lange-Nielsen

A form of Long QT syndrome associated with severe deafness at birth. In this rare form of Long QT syndrome, both parents pass the defective gene to their child.


Modifier genes

These are genes that modify other genes and gene processes. It is assumed that there are genes that modify the effect of the Long QT syndromes genes, and help to produce the diverse presentation of patients with Long QT syndrome.


Neurocardiogenic Syncope

See vasovagal syncope



An electrical device that is placed into the body to regulate the heart rhythm.


The patient feels an abnormal heart rhythm in the chest, this may be racing, fluttering fast arrhythmia or a slow heavy rhythm.


A family health history diagrammed with a set of international symbols to indicate the individuals in a family, their relationships to one another and those with a disease or syndrome etc.


A term that describes the observable manifestations of our genetic makeup. For example, eye color is a phenotype, such as blue, brown, hazel, etc.


QT Interval

A time duration between certain beats in the heart measured from the electrocardiogram.



A complementary term to depolarization. Depolarization is the discharging of an electrical circuit, and repolarization is the re-charging of that electrical circuit so that the circuit can be discharged again. The depolarization of heart cells causes the heart to beat.

Right and left bundle branch

The heart contains electrical wires which transmit the electrical signal rapidly and precisely throughout the heart muscle. This is necessary to assure uniform and very rapid discharging (depolarization) of heart muscle cells, in order to provide a uniform contraction of the heart muscle. The two ‘electrical wires’ that transmit electricity quickly to the right and left ventricles of the heart are the right and the left bundle branches.

Romano Ward Syndrome

One of the forms of Long QT syndrome, named after Drs. Romano and Ward, two physicians who independently described Long QT syndrome families. Romano Ward Syndrome is the most common form of Long QT syndrome, making up well over 95% of families and subjects with Long QT syndrome.



Sudden Arrhythmia Death Syndromes


An electrical disturbance of the brain. It leads to alterations of consciousness and often to motor movements, sometimes confused with Long QT syndrome loss of consciousness. Seizures come in a variety of forms. Most recognized is the “grand mal” which is associated with loss of consciousness, rhythmic jerking of the extremities, often biting of the tongue and drooling at the mouth. Another common form is “petite mal” which does not have much in the way of motor movements but is manifest by a passing loss of consciousness.


The medical term for loss of consciousness or fainting. Usually reserved for loss of consciousness due to alterations of the blood pressure, heart rate, heart rhythm, etc.


The occurrence, in combination of a number of symptoms that are characteristic of a particular ailment or condition.



A fast heart rhythm, usually above 100 bpm.

Timothy's Syndrome

A rare form of Long QT syndrome discovered by Katherine Timothy. People with Timothy’s often have a spectrum of complicated health concerns including a very prolonged QT and syndactyly (webbed fingers).

Torsades Des pointes

A French term, literally meaning “turning about a point”, which describes the visual characterization of the heart rhythm which is typical for the Long QT syndrome


Vasovagal syncope (event)

A physical event which is usually associated with loss of consciousness, and is due to excessive discharging of the vagal nerves in the body, part of the parasympathetic nervous system. These events cause a discharge of the vagal nerves, leading to a slowing of the heart rate and a lowering of the blood pressure. They cause dizziness, blurring of the vision, and often loss of consciousness. A vasovagal event is the most common cause of fainting. They are often confused with Long QT syndrome events, and Long QT syndrome events are often misdiagnosed as vasovagal events.


A chamber of the heart that receives blood from the atrium and pumps it into the arteries.

Ventricular fibrillation VF or V-Fib

A disorganized fast rhythm of the lower chambers, it is often the cause of sudden death.

Ventricular tachycardia VT or V-Tach

This arrhythmia causes a high (200/300bpm) heart beat which prevents the ventricles filling correctly, this effectively stops the heart pumping and is potentially life threatening. The tachycardia generally starts from the edge of scar tissue from a previous heart attack. 


Wolff-Parkinson-White (WPW) Syndrome

This is a particular form of PSVT that can be life-threatening, the electrical signal short-circuits and bypasses the AV node, this causes the QRS complex to become abnormal. The WPW Syndrome has been associated with sudden death in young people.