When Prescribing Pain Medications, Think About Qtc Index

The QT interval in the electrocardiogram is the expression of ventricular repolarisation, it is variable in the general population and highly dependent upon heart frequency; therefore, in clinical practice, the QTc index is used, to correct for heart frequency through the well-known Bazzett’s correction formula (QTc=QT/ RR0.5) for heart frequencies below 90 bpm. The QTc index is considered normal when below 450 milliseconds (ms) in men and 470 in women, a considerable risk to develop polymorphic ventricular tachycardia named “Torsade de pointes” (TdP) is possible when QTc is over 500 milliseconds. Symptoms can be either dramatic, like loss of consciousness or seizures, or mild like vertigo, lypothymia, palpitations or sensation of lightheadedness. In both cases there is a sensible risk of ventricular fibrillation and sudden death. Nevertheless, TdP does not always lead to ventricular fibrillation, but is more often so when QTc prolongation is reached in a short amount of time, therefore it is very important to check baseline ECG before prescribing drugs with know QTc prolongation effect. In fact, although the congenital long-QT syndrome, a genetic disease with mutation of the potassium cardiac channels, is rare, still it could affect 1 in 10000 individuals and cause as many as 3000 deaths (mostly children and young adults) in the USA per year [1].