Basic cardiac pacing, pacemaker functions and settings

Basic cardiac pacing, pacemaker functions and settings

Stimulation threshold As previously discussed, myocardium may be excited by external electrical stimuli that drive the cells to threshold.  Stimulation threshold  is the minimum amount of energy required to reach threshold and evoke an  action potential . The intensity of the electrical stimulus is described by its  amplitude  (measured in volts) and  duration  (measured in milliseconds). The amplitude and duration of the pulse must be optimized to ensure depolarization while minimizing battery consumption. Amplitudes are normally below 1.5 V and pulse duration (width) is usually set to 0.5 ms. The relationship between current (I), voltage (V) and resistance (R) is described by Ohm’s law: V = I • R Pacemakers generate a constant voltage (V). The current that is delivered by the pulse generator can be calculated as follows: I = V/R Given that voltage (V) is constant and battery depletion must be minimized, most pacemakers use lead tips with high resistance (400 to 1200 Ω). The higher the resistance …

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