More detailed description about long QT interval

Electrocardiogram (EKG) measures the electrical activity of the heart. It is used to record the conduction of electrical impulses within the heart muscle. Based on characteristic waves in the signal, the physician is able to conclude whether the heart rhythm is adequate, whether the heart muscle is healthy and whether the electrical conduction system in the heart functions well or not. The Q and T waves are characteristic features of an EKG, and the time period between them is called the QT interval. This interval indicates the time needed by the heart muscle to repolarize after the electrical impulse had spread through the muscle and triggered a contraction. If the length between Q and T is prolonged in an EKG, the phenomenon is called the long QT syndrome. This condition is associated with a sudden arrhythmia preventing the heart muscle to pump enough blood to match the needs of the body, thus leading to death.

Long QT interval development

Long QT interval is a consequence of a disorder in the function of the ion channels in the heart muscle. These channels play a pivotal role in the spread of the electrical impulses across the heart muscle. They are proteins that form openings in the cellular membrane of the heart muscle fibers and allow the passage of ions through the cell membrane. The syndrome of long QT is characterized by a disturbance in the sodium and potassium channels.

Currently, over 10 genes that encode these ion channels are known. Several mutations of these genes are responsible for the long QT syndrome. Apart from these mutations, the mentioned genes more commonly display small variants in the genetic code or polymorphisms. These variants increase the predisposition to dangerous arrhythmias, especially with the concomitant use of certain medications.

Prevention

Individuals who were found to suffer from a congenital long QT syndrome due to a minor genetic variation should avoid excess physical activity, professional and extreme sports as well as emotional stress. It is also important for them to avoid certain medications that tend to prolong the QT interval including primarily antibiotics such as erythromycin, asthma medication such as salbutamol and certain anti-arrhythmic drugs used to treat cardiac arrhythmias.

Of utmost importance is also the prevention and therapy of disease states that can lead to a low level of serum potassium. The prime examples include vomiting and diarrhoea. Drugs that influence the level of blood electrolytes, such as some diuretics, may also prolong the QT interval. Some illicit drugs such as amphetamines and cocaine are also dangerous.

An implantable cardioverter-defibrillator is a distinct option for patients with a very long QT. This is a device that monitors the heart rhythm and triggers electrical activity when an arrhythmia is detected; such electrical impulse re-establishes the normal heart function.

Therapy

The aim of the therapy is to prevent lethal cardiac arrhythmias and sudden death that may follow.

Basically, the therapy includes:

• Medicinal products such as primarily beta blockers that slow down the heart rate and prevent arrhythmias from developing. The mineral potassium is essential for the correct rhythmical heart function.
• Electronic implants such as a pace-maker and cardioverter-defibrillator. These devices monitor the heart rhythm and act in case of an arrhythmia. They are primarily used in critical, syncope-prone patients despite pharmacotherapy, and in patients that have a cardiac arrest in their history.
• Left cardiac sympathetic denervation (LCSD) where surgeons cut certain sympathetic nerves leading to the heart.
• Lifestyle change, including avoidance of excess physical activity and excessive emotionally-stressful situations.

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