Long QT syndrome (LQTS) is an abnormal feature of the heart’s electrical system that can lead to a potentially life-threatening arrhythmia called torsades de pointes (pronounced torsad de pwant). Torsades de pointes may result in syncope (fainting) or sudden cardiac death.

What happens during LQTS?

Electricity is what causes the heart muscle to beat. The electrical current, generated by a chemical process within the muscle cells, makes the heart contract to pump out blood.

The term “long QT” refers to the heart’s electrical activity as graphed on an electrocardiogram (ECG or EKG). Doctors name the different waves on the ECG graph P, Q, R, S and T. Letters Q through T correspond to the heart cells’ “recharging” (repolarizing) after a muscle contraction. Abnormalities in the heart cells can slow the process of electrical recharging, prolonging the QT interval as shown on an ECG.

What are the symptoms of LQTS?

Some people have no symptoms and are only diagnosed when they get an ECG for other reasons. Or they may be diagnosed when family members are found to have genetic LQTS. If symptoms appear, they may include:

• Palpitations (a fluttering in the chest)

• Seizure-like activity caused by lack of blood flow to the brain

• Syncope (dizziness or fainting)

• Sudden cardiac arrest

What are the complications of LQTS?

LQTS can cause torsades de pointes, an irregular rhythm in the ventricles — the lower chambers of the heart. The ventricles beat more than 200 times per minute, resulting in a sudden drop in blood pressure. Though it often stops on its own, torsades de pointes that persists can lead to ventricular fibrillation, which may cause sudden cardiac death.

What causes LQTS?

LQTS can be categorized as congenital (inherited, genetic) or acquired (triggered by some condition, medication or event).

Congenital (Inherited) LQTS

People with congenital LQTS have a genetic mutation that affects sodium or potassium channels in the heart. Sodium and potassium help generate electricity inside the cells.

Children may be diagnosed in infancy or later, either because they go through an episode of seizures or cardiac arrest, or because of family members known to have the mutation. Babies have even been diagnosed in utero. Boys are more likely than girls to have a dangerous cardiac episode from LQTS by age 15.

On the other hand, there are people whose family members have LQTS and who share the genetic mutation, but never have symptoms themselves. This may be because their LQTS is very mild or because they have not been exposed to the “right” combination of triggering conditions or medications.

Anyone diagnosed with congenital LQTS should inform family members so they can be tested.

Acquired LQTS

Acquired long QT syndrome is the result of conditions, medications or events that prolong the QT interval. It is more common in women than men. Stopping the medication and/or correcting the condition causing LQTS often resolves the issue. Sometimes the symptoms are caused by not one but several triggers — for example, a genetic mutation combined with a medication that prolongs the QT interval.

Triggering Conditions

Electrolyte Imbalances

• Potassium deficiency (hypokalemia)

• Magnesium deficiency (hypomagnesemia)

• Blood calcium deficiency (hypocalcemia)

Other Conditions

• Malnutrition

• Hypothyroidism

• A history of heart disease, including heart failure, heart attack, left ventricular hypertrophy or bradycardia

• A history of stroke

Triggering Medications

A wide variety of drugs may lengthen the QT interval. If you have been diagnosed with LQTS, consult your physician about which drugs put you at risk. The most common types of drugs are:

• Antibiotics

• Antifungals

• Antiarrhythmics

Rarely, grapefruit juice may increase the risk of a dangerous cardiac event when combined with a triggering drug.

How is LQTS diagnosed?

Some diagnostic tests take place on site in a doctor’s office or hospital. Other tests provide monitoring at home as you follow your daily routine. Click each method to learn more.

On-site Diagnostic Tests

• Electrocardiogram (ECG or EKG): wires taped to various parts of your body to create a graph of your heart’s electrical rhythm

• Exercise stress test: ECG recorded while strenuously exercising

• Tests of possible trigger medications

• Tests for magnesium, potassium and blood calcium deficiency (electrolyte imbalances)

• Genetic testing

In-home Diagnostic Monitors

• Holter monitor: a portable ECG you wear continuously for one to seven days to record your heart rhythms over time

• Event monitor: a portable ECG you wear for one or two months, which records only when triggered by an abnormal heart rhythm or when you manually activate it

• Implantable monitor: a tiny event monitor inserted under your skin, worn for several years to record events that only seldom take place

Genetic Testing

If congenital LQTS is suspected our genetic counselors can assist you with genetic testing to confirm the underlying cause. Once the genetic cause is identified then at risk family members can consider genetic testing to determine if they are at risk as well.

How is LQTS treated?

Treatment for LQTS will depend on the type and severity of symptoms.

Treating Inherited LQTS

• Taking beta blockers

• Taking medications to control the heart rhythm (antiarrhythmics)

• Avoiding triggers such as swimming or intense exercise

• Inserting a pacemaker

• Inserting an implantable cardio-defibrillator

Treating Acquired LQTS

• Stopping any trigger medications

• Treating any underlying conditions or deficiencies

• Taking medications to control the heart rhythm (antiarrhythmics)

• Inserting a pacemaker or implantable cardio-defibrillator

Learn more about arrhythmias or visit the Johns Hopkins Electrophysiology and Arrhythmia Service