Final answer:
For a stable patient with WPW in A Fib with RVR, procainamide is the recommended antiarrhythmic medication. Potassium channel blockers like procainamide affect ventricular repolarization, and the atrioventricular node has the slowest rate of firing in the heart's conduction system.
Step-by-step explanation:
In the context of Wolff-Parkinson-White syndrome (WPW) with atrial fibrillation (A Fib) with rapid ventricular response (RVR), one must exercise caution in the selection of antiarrhythmic medication as certain drugs can aggravate the condition. If the patient is stable, procainamide is generally considered the suitable treatment, which is a potassium channel blocker. Potassium channel blockers such as amiodarone and procainamide, which treat cardiac dysrhythmias, would impact ventricular repolarization during the cardiac action potential, as they impede the movement of K+ through voltage-gated K+ channels. In contrast, drugs like adenosine and verapamil should be avoided as they can potentially worsen the conduction abnormality or precipitate more dangerous forms of tachycardia.
The atrioventricular node (AV node) is the component of the heart conduction system that would have the slowest rate of firing compared to the atrioventricular bundle, the bundle branches, and the Purkinje fibers. It is the excitation of cardiac muscle cells at the atrioventricular node that is followed by the sinoatrial node in terms of the firing rate.