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NOTE
Chapter 6
EFFECTIVE PACING
Note the inverted T-waves
and the absence of
P-waves.
Changing ECG leads and size can sometimes be helpful in determining capture.
Shape and size of the stimulated waveforms can vary depending on lead chosen;
variation from patient to patient can be expected.
DETERMINING OPTIMUM THRESHOLD
The ideal output current is the lowest value that will maintain capture. This is
usually about
10%
above threshold. Typical threshold currents are usually be-
tween
40
and
80
mA. The electrode placement that offers the most direct current
pathway to the heart while avoiding large chest muscles will usually produce the
lowest threshold. Low stimulation currents produce less skeletal muscle contrac-
tion and are better tolerated. Placement of the electrodes will affect the current
required to obtain ventricular capture.
Testing for optimum electrode location may be done with electrodes with a two-
part protective cap (NTP
2000
only). Remove the center cap from the front
electrode to expose the gelled area while keeping the adhesive covered. Once the
best location has been determined, the electrode should be removed and the area
cleansed of salt or other conductive materials (such as defibrillator gel). The
electrode may then be secured after removing the adhesive backing.
4:l TEST MODE
The
4 : l
test mode can be used optionally to test
Iml
in, ,al
for threshold. In this mode a stimulus is delivered
I
to the patient approximately every fourth pace
beat. (The stimulus is demand-synchronized to
the patient's intrinsic beat.) Releasing the control
causes the instrument to resume normal
PACER
OUTPUT~A
PACER
RATE
rn
operation.
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