What is a sign that indicates capturing the heart outside of the natural refractory period?

When assessing heart capture during pacing, "capture" refers to the successful stimulation of the heart muscle, resulting in a contraction. The capture threshold is the minimum level of electrical output required to achieve this response. When the pacing output meets or exceeds the capture threshold, it indicates that the heart muscle is being activated effectively outside of its natural refractory period, affirming that the device is functioning correctly.

This concept is crucial in cardiac pacing because if the pacing output is below the threshold, the heart will not respond, which could lead to inadequate cardiac function. Recognizing the adequacy of the pacing output through the capture threshold helps ensure that the pacing leads are properly stimulating the heart, thereby maintaining stable cardiac rhythms and hemodynamics.

While other factors such as electrical interference, stable hemodynamics, and adequate pacing output can reflect varying aspects of pacing efficiency, they do not specifically indicate the success of capturing the heart muscle in relation to the refractory period. Meeting the capture threshold is the definitive sign that confirms effective pacing outside the refractory period.