The Danger of Prolonged QT Interval: Causes, Symptoms, and Treatment

What is a Prolonged QT Interval?

A prolonged QT interval is a dangerous finding on an EKG, or electrocardiogram. It can cause abnormal heart rhythms (arrhythmias) and fainting spells.

Rufinamide, a new anticonvulsant, was recently shown in formal cardiac ECG studies to shorten the QTc interval. This is a proarrhythmic drug effect that needs further exploration.


During each heartbeat, electrical signals cause your heart’s muscle cells to squeeze (contract) and relax to pump blood. After each beat, your heart’s electrical system recharges, preparing for the next contraction. If the system resets more slowly than normal, your EKG may show that the QT interval is prolonged (increasing your risk for arrhythmia). Long QT syndrome can lead to a life-threatening arrhythmia called torsades de pointes. This can cause syncope (fainting) or sudden cardiac death.

Gehi: When a person has LQTS, it’s usually due to a change in one of at least fifteen different genes. This gene change is passed from parent to child in 50 percent of cases.

People can also develop LQTS from conditions, medications or certain foods (like grapefruit). Many drugs can prolong the QT interval. It’s important that doctors use an EKG to help determine which medicines might increase your risk of a dangerous heart rhythm. A QT interval-heart rate chart known as the QT nomogram helps to do this.


People with inherited long QT syndrome have episodes of life-threatening arrhythmias, especially when they exercise or experience emotional stress. Inherited LQT syndrome may cause sudden death, even in young adults.

Health care providers use a medical history and physical exam to diagnose long QT syndrome. They may also order an electrocardiogram (ECG, or EKG) to record your heart’s electrical activity over time. The EKG can show how well your heart’s lower chambers, called the ventricles, beat during each heartbeat. It can also show the length of time your heart cells take to recharge after each heartbeat, known as the QT interval.

The doctor may ask about your family’s history of LQT and any medications you are taking. Certain medicines — including over-the-counter drugs and herbal remedies — can prolong the QT interval, increasing your risk for arrhythmias. The doctor may suggest a blood test to check your levels of potassium and magnesium. The doctor may also suggest a surgical procedure to implant a device in your chest that monitors your heart’s rhythm and delivers an electric shock to stop dangerous heartbeats.


Your doctor can diagnose long QT syndrome with an electrocardiogram (ECG) test. This is a simple test that records your heart’s electrical activity.

Normally, tiny holes in your heart’s cells open and close as electrically charged sodium, calcium and potassium ions pass in and out of the cell. This creates the electrical impulses that cause your heart to beat. A defect in these ion channels can lead to the QT interval lasting longer than it should. This delays the heart’s recharging between beats, which can increase your risk of having a dangerous abnormal heart rhythm called ventricular fibrillation that can lead to fainting and sudden death.

A prolonged QT interval may not cause symptoms, so it’s sometimes difficult to detect. Your doctor can identify it with an ECG test, though, especially if you have a family history of LQTS or have experienced unexplained fainting spells. Your doctor will also ask about your medical, family and personal history and perform a physical exam.


People who have inherited long QT syndrome want to avoid exercise that makes their heart beat faster, and they might take medicine to lower blood levels of potassium or magnesium. They might also need to eat a balanced diet to prevent electrolyte imbalances that can lengthen the QT interval. They should always check with a doctor or pharmacist before starting any new medications, including over-the-counter drugs and supplements.

Inherited long QT syndrome raises the risk of dangerous arrhythmias, such as torsades de pointes, which can lead to fainting or sudden death. People who have the condition may show signs of it on an electrocardiogram (EKG).

Heart muscle cells have tiny holes, called ion channels, that open and close to create electrical impulses for beating the heart. The time it takes for these channels to reopen after a contraction is measured on an EKG as the QT interval. A prolongation of the QT interval increases the risk of a deadly arrhythmia called polymorphic ventricular tachycardia, or torsades de pointes.

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