Lack of tissue capture may be a result of what factors?

• A. Insufficient pacing stimulus
• B. Insufficient pacing stimulus or pacing during refractory period
• C. Lead fracture
• D. Excessive pacing energy

Answer: (B)

Tissue capture happens when the pacing stimulus is strong enough to bring the myocardium to the threshold and delivered at a time when the tissue is excitable. If the pacing energy is insufficient, the stimulus won’t reach threshold, so the heart doesn’t depolarize. If the stimulus arrives during the refractory period—the brief time after a beat when tissue cannot be excited—the cells won’t respond regardless of energy. Both of these scenarios explain a lack of tissue capture. Excessive pacing energy would usually ensure capture, and lead fracture represents a hardware issue that can cause pacing loss but isn’t the primary mechanism for failure to capture in this context.