Which condition increases the ventricular capture threshold, potentially jeopardizing pacing during anesthesia?

Which condition increases the ventricular capture threshold, potentially jeopardizing pacing during anesthesia?

• A. Acute hypokalemia
• B. Acute hyperkalemia
• C. Metabolic acidosis
• D. Hypovolemia

Answer: (A)

The key idea is how electrolyte balance, especially potassium, affects the heart’s excitability and the energy needed for pacing. Acute hypokalemia makes the resting membrane potential more negative (hyperpolarized), so the myocardium is farther from the threshold. A pacemaker then has to deliver more energy to reach that threshold, increasing the ventricular capture threshold and risking loss of capture during anesthesia. The other options don’t consistently raise the threshold in the same direct way: mild-to-moderate hyperkalemia depolarizes cells and, while it can impair conduction, it doesn’t reliably increase the capture threshold; metabolic acidosis and hypovolemia influence perfusion and overall conduction but aren’t as direct at elevating the pacing energy requirement as hypokalemia.

The key idea is how electrolyte balance, especially potassium, affects the heart’s excitability and the energy needed for pacing. Acute hypokalemia makes the resting membrane potential more negative (hyperpolarized), so the myocardium is farther from the threshold. A pacemaker then has to deliver more energy to reach that threshold, increasing the ventricular capture threshold and risking loss of capture during anesthesia. The other options don’t consistently raise the threshold in the same direct way: mild-to-moderate hyperkalemia depolarizes cells and, while it can impair conduction, it doesn’t reliably increase the capture threshold; metabolic acidosis and hypovolemia influence perfusion and overall conduction but aren’t as direct at elevating the pacing energy requirement as hypokalemia.