How does the QRS complex respond to anti-arrhythmic medications like procainamide?

• A. Narrow
• B. Wide
• C. No change
• D. Inverted

Answer: (B)

The QRS complex represents the depolarization of the ventricles, and its duration can be indicative of various cardiac conditions. Anti-arrhythmic medications, such as procainamide, are known to affect conduction within the cardiac tissue. Procainamide works primarily as a Class IA anti-arrhythmic agent, which means it functions by blocking sodium channels in the myocardial cell membranes.

When sodium channels are blocked, depolarization becomes slower, which can lead to a prolonged QRS complex. This effect will manifest as a widening of the QRS on the ECG. The widening occurs because it takes a longer time for the electrical impulse to travel through the ventricles due to the altered conduction velocity from the medication's action. Hence, a wide QRS complex indicates that the conduction is impaired, which is consistent with the pharmacological effects of procainamide.

Understanding this mechanism is essential for healthcare professionals as it helps in interpreting the effects of anti-arrhythmic medications on the heart’s electrical activity, allowing for better patient management and monitoring.