Drug-induced QT Prolongation

Drug-induced QT prolongation is a significant alteration in cardiac electrophysiology, which can lead to an increased risk of life-threatening arrhythmias, most notably Torsades de Pointes (TdP). This condition occurs when the duration of the QT interval, measured on an electrocardiogram (ECG), is extended beyond the normal range due to the influence of certain medications. The QT interval represents the time it takes for the heart's ventricles to depolarize and repolarize, essentially the period from the start of the Q wave to the end of the T wave in the heart's electrical cycle.

Causes[edit | edit source]

Drug-induced QT prolongation can be caused by a wide variety of pharmaceutical agents, including but not limited to antiarrhythmic drugs, antibiotics, antihistamines, antipsychotic drugs, and antidepressants. The mechanism behind this adverse effect often involves the blockade of the hERG (human Ether-à-go-go-Related Gene) potassium channels, which are crucial for the repolarization phase of the cardiac cycle. This blockade leads to a delay in repolarization, thereby prolonging the QT interval.

Risk Factors[edit | edit source]

Several factors can increase the risk of drug-induced QT prolongation, including:

Female gender
Advanced age
Existing heart conditions, such as congenital long QT syndrome
Electrolyte imbalances, particularly low levels of potassium (hypokalemia) or magnesium (hypomagnesemia)
Use of multiple medications that prolong the QT interval (polypharmacy)

Symptoms and Diagnosis[edit | edit source]

Symptoms of drug-induced QT prolongation may not be apparent until a significant arrhythmia, such as Torsades de Pointes, occurs. Symptoms of TdP include dizziness, palpitations, syncope (fainting), or seizures. In severe cases, it can lead to sudden cardiac death.

Diagnosis is primarily based on the measurement of the QT interval on an ECG. A prolonged QT interval is generally considered to be over 440 milliseconds for men and 460 milliseconds for women. However, the risk of arrhythmias increases significantly with QT intervals exceeding 500 milliseconds.

Management and Prevention[edit | edit source]

Management of drug-induced QT prolongation involves the discontinuation of the offending medication and correction of any electrolyte imbalances. In cases where discontinuation of the medication is not possible, close monitoring of the QT interval and adjustment of the drug dosage may be necessary.

Prevention of drug-induced QT prolongation involves careful selection of medications, especially in patients with known risk factors. Healthcare providers should assess the risk-benefit ratio of prescribing medications known to prolong the QT interval and consider alternative treatments when possible.