The QT interval is an electrical measurement of the heart’s repolarization process seen on an electrocardiogram. Long QT syndrome can cause dangerous arrhythmias and is associated with sudden death, while some medications can lengthen the interval and should be avoided by those with the syndrome. The interval is due to electrical signals in the ventricles of the heart, which can have errors that cause longer repolarization times. Some drugs that can prolong the QT interval include albuterol, Adderall®, Lexapro®, Geodon®, Benadryl®, Paxil®, Prozac®, Celexa®, fluconazole, ketoconazole, and Mexitil®. It is important to note that not all individuals will develop long QT syndrome or lengthen the QT interval when taking these medications.
The QT interval is an electrical measurement of some aspect of the heart’s functioning. It is seen on an electrocardiogram or EKG and is a measurement of a process called repolarization. In repolarization, the heart has a single contraction, followed by the ventricles receiving new blood. The whole process, when measured on an ECG, is the QT interval. This interval is exceptionally important because a condition in which repolarization takes much longer than average, called long QT syndrome, can cause dangerously rapid arrhythmias; it is associated with sudden death, especially among adolescent and young adult athletes. A slightly longer interval that does not represent the syndrome is also important to note because it may contraindicate the use of some medications that can lengthen the interval.
Those trying to understand the QT interval may mistakenly think that repolarization is primarily influenced by the formation of the heart. This is not the case. The interval is due to electrical signals in the ventricles of the heart. These are the lower two chambers of the heart and they may be perfect shape and form but still have errors in the way they electrically transmit information to the heart. When there are errors, repolarization time can be longer than average. Some people are born with a predilection for a long QT syndrome, but others can acquire it later in life.
Medical research has identified a number of drugs that can alter QT intervals in some individuals. The alteration could create a slightly longer repolarization or could induce long QT syndrome. While this is not an exhaustive list, some drugs that can prolong the QT interval include albuterol, Adderall®, Lexapro®, Geodon®, Benadryl®, Paxil®, Prozac®, Celexa®, fluconazole, ketoconazole and Mexitil®. When reviewing this list, it’s easy to see that these medications treat a wide variety of conditions. They are used to treat attention deficit disorder, allergies, depression, fungal infections, bacterial infections, and heart rhythm disorders. Most of these medications listed here and others not mentioned are antidepressants or other behavioral medications.
It is important to note that these drugs will not necessarily create long QT syndrome or even lengthen the QT interval. Those who have long QT syndrome may need to avoid these medications so they don’t make their condition worse. Most people can use these drugs safely, although some drugs such as Geodon® require an ECG before use and even a slight prolongation of the QT interval contraindicates their use.
For the lay physician, an EKG is difficult to understand, but knowing a little about the QT interval makes sense. It’s certainly something people can ask their doctors about when they get an EKG. Because there are so many common medications that can lengthen repolarization, it might be wise to ask doctors if the QT interval on an ECG is within normal limits.
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