Functional Descriptions B: Theory of Operation
201
Shock Delivery
The discharging cycle (shock delivery) is initiated by any of the following three events:
• Pressing the front panel Shock button when using pads or switchless internal paddles. (The button is
disabled when using external paddles or switched internal paddles). This button press is then
detected and processed by the Processor PCA.
• Simultaneously pressing the Shock buttons on both the external Sternum and Apex paddles. These
button presses are transferred from the buttons to the Processor PCA that detects and processes the
signal.
•Pressing the Shock button on the switched internal paddles. This button press is transferred from
the button to the Processor PCA that detects and processes the signal.
In any case, the Processor PCA directs the Therapy PCA to deliver the shock. Patient resistance is derived
from the current and voltage delivered during the initial portions of the waveform, and the biphasic
waveform timing is then adjusted as needed to deliver the correct shock energy, duration, and shape.
The Therapy PCA aborts delivery of the shock if during the impedance measurement, the impedance is
outside of operating limits (too high or too low).
If this condition is detected, the Therapy PCA terminates delivery of the waveform and disarms the
capacitor. The problem is reported to the Processor PCA, which displays and/or prints the appropriate
messages.
Another safety feature is the presence of an identification resistor in the pads and paddles cables. If the
device does not sense that resistance, it generates a Cable Off message and does not charge the capacitor.
Synchronized Cardioversion Delivery
Synchronized cardioversion operates the same as delivering a shock, except that the shock must be
synchronized to the R wave of the ECG. The Processor PCA is responsible for detecting the R wave and
placing markers on the printed strip and on the display to indicate the timing of the proposed
cardioversion shock.
A synchronized shock can be delivered in either of two ways:
• First, when using pads, by pressing and holding the Shock button until the next time an R wave is
detected.
• Second, by simultaneously pressing and holding the Shock buttons on both the Sternum and Apex
paddles until the next time an R wave is detected.
When both events occur (either type of button press and detection of an R wave), then the Processor
PCA directs the Therapy PCA to deliver the shock.
Transcutaneous Pacing
Pacing is initiated and controlled by pressing front panel buttons. These button presses are transferred
from the buttons to the Processor PCA via a flex circuit. The button presses are detected and processed
by the Processor PCA.
The Processor PCA directs the Therapy PCA to deliver the pacing pulses at the rate and output current
selected by the user. The Therapy PCA controls the output current and the pulse duration, and the
Processor PCA provides the rate setting and the R-wave indications to the Therapy PCA, which controls
the timing of the delivered pulses. The pacing pulses are delivered via the pads cable to the multifunction
electrode pads. The pacing current delivered is reported back to the Processor PCA, which sends the
information to the display and activates the printouts and messages as needed.
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