Drug-induced or Acquired Long QT
Not all cases of Long QT are caused by genetics. Around 15% of all Long QT cases are caused by medications which can prolong the QT interval. The definition of diLQTS varies but generally refers to patients who have developed marked prolongation of the QTc interval to ≥ 500 ms or a change of >60 ms from their baseline.
For clinical trials sometimes the fact that medication prolongs the QT can be very useful. It means that the QT can be artificially prolonged in healthy subjects so the efficacy of new therapies can be tested in a relatively safe way.
Often medications will create a Long QT type 2 phenomenon, making the potassium voltage gate Ikr go glitchy.
QT prolongation has been found in almost every class of therapeutic agent, including antiarrhythmic, antihistamines, antibiotics, anticancer drugs, gastrointestinal prokinetics, antipsychotics, etc.
Typically the QT interval returns to normal when the patient stops taking the QT prolonging medication but there is always a benefit to risk analysis.
Some medications are so important that they are a necessity even though they cause QT prolongation. In healthy people i.e. not congenital Long QT these medications are safe to take as it is unlikely they will cause the QTc to move into a dangerous territory over 500msec. One of the biggest challenges amongst the Long QT community can be the need to balance effective antidepressants/anxiety medications and QT prolongation.