QT prolongation: Definition, causes, treatment, and more

QT prolongation occurs when the heart muscle takes longer to contract and relax than usual. Various health factors and medications can increase the risk. QT prolongation can affect heart rhythms and lead to sudden cardiac arrest.

The heart is a muscle that contracts and relaxes to pump blood around the body. Electrical signals trigger the process of contraction and relaxation, thereby regulating the rate and rhythm of the heart.

This article discusses the potential causes, risk factors, and symptoms associated with QT prolongation. It also provides information on how to diagnose QT prolongation and discusses options for its treatment and management.

What are QT intervals?

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Infographic by Diego Sabogal.

An electrocardiogram (ECG) is a test that measures the electrical activity of the heart and depicts the information in the form of a graph.

Spikes and bumps on an ECG reading indicate the heart contracting and relaxing. Healthcare professionals label these spikes and bumps “P-wave” through to “U-wave.”

In simple terms, a QT interval measures the length of time between the start of the Q-wave and the end of the T-wave. This interval represents the time it takes for the lower chambers, or ventricles, of the heart to contract and relax.

Mineral concentrations in the blood control the process of contraction and relaxation. The minerals responsible are:

• sodium
• calcium
• potassium

What is a normal QT interval?

The length of a normal QT interval varies by age and sex.

For males and females below 15 years of age:

• Normal QT interval: 0.35–0.44 seconds
• Borderline QT interval: 0.44–0.46 seconds
• Prolonged QT interval: More than 0.46 seconds

For adult males:

• Normal QT interval: 0.35–0.43 seconds
• Borderline QT interval: 0.43–0.45 seconds
• Prolonged QT interval: More than 0.45 seconds

For adult females:

• Normal QT interval: 0.35–0.45 seconds
• Borderline QT interval: 0.45–0.47 seconds
• Prolonged QT interval: More than 0.47 seconds

Medications that cause QT prolongation

QT prolongation may occur as a result of:

• certain genetic conditions
• hormonal imbalances
• incorrect concentrations of minerals in the blood

Certain medications can also cause QT prolongation, including some belonging to the following groups:

• antibiotics
• antifungals
• diuretics
• antidepressants
• antipsychotics
• antiarrhythmics

A person is more likely to develop medication-induced QT prolongation if they already have underlying risk factors for the condition.

Symptoms

People with QT prolongation do not usually experience any symptoms. A doctor typically detects the condition during a routine medical check.

When symptoms are present, they may include:

• heart palpitations
• dizziness
• sudden fainting
• seizures

Diagnosis

Using an ECG is the most common way to diagnose QT prolongation. A doctor may administer a resting ECG, in which a person lies on a bed while sensors measure their heart activity. The doctor may also administer an ECG while the person is exercising.

In some cases, the doctor may recommend that the person wears a portable ECG device called a Holter monitor. The person can wear the monitor around their neck or on a belt. The device typically records heart activity over a 24-hour period.

Manufacturers are also developing newer technologies, including a patch that can continuously monitor heart activity for 14 days.

If a doctor suspects congenital long QT syndrome, they may request a genetic test to check for the condition.

Treatment options

There are several treatment options available for QT prolongation. These include medications, lifestyle changes, and surgery.

The following sections will look at each of these options in more detail.

Medications

Several medications may help treat QT prolongation. A doctor may prescribe beta-blockers to help slow the heart rate or antiarrhythmic drugs to help shorten the QT interval.

People may also consider dietary supplementation with potassium.

Diuretics are one class of drugs that may cause QT prolongation. If a person requires diuretics, a doctor may prescribe potassium-sparing diuretics. Some research suggests that these medications shorten the QT interval.

Lifestyle changes

The cardiovascular system benefits from moderate exercise. However, doctors do not recommend strenuous or prolonged exercise for people who have QT prolongation.

Eating a healthy diet is good for the heart, and eating a well-balanced diet can help prevent electrolyte imbalances.

Consuming potassium-rich foods may help treat QT prolongation that results from low potassium levels.

Also, drinking plenty of water every day can reduce the risk of dehydration.

Surgery

Some people may require surgical treatment for QT prolongation. Some examples of surgical procedures for this condition include the following.

Left cardiac sympathetic denervation surgery

This type of surgery can help reduce the risk of sudden death due to arrhythmia. It also provides an effective option for people who experience adverse side effects while taking beta-blockers.

Implantable cardioverter defibrillator surgery

This type of surgery involves implanting a battery powered device called an implantable cardioverter defibrillator (ICD) under the skin. ICDs can detect abnormal heart rhythms and respond by delivering electric shocks to correct the arrhythmia.

This surgery is an alternative option for people with long QT syndrome who faint while taking beta-blockers.

Summary

QT prolongation is the medical term for an extended interval between the heart contracting and relaxing. This condition can increase a person’s risk of experiencing abnormal heart rhythms and sudden cardiac arrest.

QT prolongation can be present from birth, or it may develop later in life. People with QT prolongation do not usually experience any symptoms of the condition. In most cases, a doctor discovers the condition during a routine medical exam. An ECG can usually confirm the diagnosis.

Treatment for QT prolongation may include medications, lifestyle changes, and surgery. A person can discuss all the potential treatment options with a doctor.