What may cause a lengthened QT interval?

What may cause a lengthened QT interval?

• A. Excess digitalis
• B. Antiarrhythmic drugs, such as quinidine and amiodarone
• C. Elevated blood pressure
• D. Dehydration

Answer: (B)

A lengthened QT interval can indeed be caused by antiarrhythmic drugs such as quinidine and amiodarone. These medications can affect the cardiac action potential duration by altering the ion channels responsible for cardiac repolarization. Specifically, they can inhibit potassium channels, which extends the time it takes for the heart's electrical system to reset after each heartbeat—thereby lengthening the QT interval on the ECG. Monitoring the QT interval is crucial because a significantly prolonged QT can increase the risk of life-threatening arrhythmias such as Torsades de Pointes. Hence, recognizing the impact of these medications on the QT interval is important for safe patient management and to mitigate potential complications associated with this prolongation. Other factors may contribute to a lengthened QT interval, but in the context of this question, the focus on specific drugs as a causative factor highlights the significant role that certain antiarrhythmics play in affecting cardiac repolarization.

A lengthened QT interval can indeed be caused by antiarrhythmic drugs such as quinidine and amiodarone. These medications can affect the cardiac action potential duration by altering the ion channels responsible for cardiac repolarization. Specifically, they can inhibit potassium channels, which extends the time it takes for the heart's electrical system to reset after each heartbeat—thereby lengthening the QT interval on the ECG.

Monitoring the QT interval is crucial because a significantly prolonged QT can increase the risk of life-threatening arrhythmias such as Torsades de Pointes. Hence, recognizing the impact of these medications on the QT interval is important for safe patient management and to mitigate potential complications associated with this prolongation.

Other factors may contribute to a lengthened QT interval, but in the context of this question, the focus on specific drugs as a causative factor highlights the significant role that certain antiarrhythmics play in affecting cardiac repolarization.