An increase in QRS duration of how much indicates the need to stop Procainamide administration?

The correct choice indicates that an increase in QRS duration by 50% or more signals the need to discontinue Procainamide administration. This is essential in clinical practice because Procainamide, an antiarrhythmic medication, can have proarrhythmic effects, meaning that it can potentially exacerbate or induce new arrhythmias. Monitoring the QRS duration is a critical part of patient assessment when administering this drug.

When the QRS duration increases significantly, particularly by 50% or more, it suggests a risk of electrical conduction disturbances which can lead to serious complications like sustained ventricular tachycardia or ventricular fibrillation. Thus, stopping the administration of Procainamide at this threshold is a precautionary measure to ensure patient safety and prevent adverse cardiac events.

In practice, healthcare professionals are trained to monitor QRS duration closely, and knowing that a 50% increase is the cutoff for cessation helps in making timely and informed clinical decisions.