What must the amplitude of a pacemaker be to ensure successful myocardial capture?

The amplitude of a pacemaker pulse must be large enough to ensure successful myocardial capture by causing depolarization of the cardiac tissue. This is essential because myocardial capture occurs when the electrical impulse generated by the pacemaker stimulates the cardiac muscle fibers sufficiently to initiate a contraction. The pulse must exceed a certain threshold to depolarize the myocardial cells and achieve this effect.

In this context, the resting membrane potential of myocardial cells is typically around -90 mV, and the pacemaker output must effectively overcome this threshold to evoke a response. Ensuring that the amplitude is at least at this level is vital, but simply stating "at least equal to the resting membrane potential" is not enough. The pacemaker amplitude must specifically be sufficient to cause depolarization to confirm successful capture.

The concept of a safety margin and threshold voltage also plays a role in pacemaker settings, but the critical factor for capturing the myocardial fibers is ensuring that the pulse is strong enough to provoke depolarization, which aligns with the correct answer.