Question

If high ECF potassium alters cardiac resting membrane potential, then:

1. How does the change in RMP affect sodium channel activation?
2. What does this do to conduction through the ventricular myocardium?
3. What happens to the duration of the QRS complex (QRS width)?

Answer 1

Potassium channel blockers slow down the repolarization phase, leading to delayed sodium channel activation and slowed conduction through the ventricular myocardium. This results in a longer duration of the QRS complex on the ECG.

Step-by-step explanation:

Potassium channel blockers, such as amiodarone and procainamide, impede the movement of K+ through voltage-gated K+ channels. This affects the action potential by prolonging the repolarization phase, as potassium channels are responsible for allowing outflux of K+. With prolonged repolarization, it takes longer for the resting membrane potential to be restored, resulting in delayed sodium channel activation. This affects conduction through the ventricular myocardium by slowing down the propagation of the action potential, leading to a longer duration for the QRS complex on the electrocardiogram (ECG).