Which factors influence the capture threshold in cardiac pacing?

The capture threshold in cardiac pacing is influenced primarily by the integrity of the pacemaker circuit, the characteristics of the electrodes used, and their specific placement within the heart. The pacemaker circuit integrity ensures that the device functions properly and delivers the correct amount of energy required to stimulate myocardial cells.

Electrode characteristics, such as charge delivery capacity, surface area, and impedance, also play a vital role. These factors determine how effectively the electrical impulses can stimulate the heart muscle. In addition, the placement of the electrodes within the heart can significantly affect the capture threshold. Optimal positioning ensures that the electrical stimulation reaches the myocardial tissue effectively, thus allowing for consistent capture of cardiac contractions.

The other options touch on factors that may influence cardiac function or overall patient health but do not directly pertain to the mechanisms that determine the capture threshold in pacing. For instance, although heart rate variability and blood pressure changes can affect cardiac output and rhythm, they don't influence the specific thresholds required for capture in pacing therapy.