heart and blood vessel disorders
Long QT Interval Syndromes
Causes of Long QT Interval Syndromes
Some people are born with a genetic abnormality that causes a long QT interval (called long QT syndrome). These inherited disorders are one type of heart disorder called a Cardiac Channelopathies . In other people, the long QT interval is not inherited but results from disorders such as low serum levels of potassium ( Hypokalemia (Low Level of Potassium in the Blood) ), a very slow heart rhythm, or a drug. Often, drugs used to treat abnormal heart rhythms cause a long QT interval, but certain antidepressants and certain antiviral and antifungal drugs also can cause it. The inherited long QT interval syndromes are classified based on the specific gene that has mutated. More than 15 forms of long QT syndrome have been identified. Many of these are inherited in an Non–X-Linked (Autosomal) Inheritance , in which a person with the disorder has a 50% chance of passing it on to each child they have. However, a specific genetic abnormality is found in only 50 to 75% of people. The likelihood of detecting an abnormality varies depending on the person's symptoms and ECG findings. Sometimes, exercise brings on the ventricular tachycardia (see Sudden Cardiac Death in Athletes ). Other factors that increase the risk of torsades include female sex, older age, an underactive thyroid gland (hypothyroidism), brain disorders such as a stroke, and certain types of heart disease such as a heart attack or inflamed heart (myocarditis). 