At the time of ventricular pacemaker implantation, lead resistance is determined at a voltage near that of the pacemaker's output. The calculated resistance at 5 volts should range from:

C. 300 to 800 ohms.

DISCUSSION: At the time of pacemaker implantation, in addition to measuring pulse amplitude (voltage and current) and pulse width, resistance is also determined. As described by Ohm's law, resistance is calculated by dividing voltage by current. Resistance calculations are made at a voltage near that of the pacemaker's output. The calculated resistance at 5 volts should range from 300 to 800 ohms. An unsatisfactorily low resistance is unsatisfactory because current is wasted and battery life is shortened. Conversely, excessively high resistance (more than 800 ohms) increases battery life but decreases the current delivered to the heart for pacing.