Biomedical Engineering Reference
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Fig. 13.2 Measurement of the right atrium voltage threshold in AAI mode
constant pacing pulse width. The monitored quantity values
are decreased automatically by the implanted device, which
is controlled by the programmer. The first unsuccessful or the
last successful pacing pulse is identified, which represents the
voltage pacing threshold. In addition, a pacing pulse width
threshold can be measured at a constant voltage; this method
is, however, not in use today.
and an AV interval or changes in morphology are monitored,
even though identification of these may also be insufficient if
a less detailed ECG record lacking time markers is used.
13.1.2 Measuring the Threshold in the Right
Ventricle
The VVI or V00 modes are applied advantageously for mea-
suring threshold in the right ventricle. On a surface ECG,
ventricular depolarization is usually more apparent than
atrial depolarization. If the surface ECG is not used, shock
lead electrograms may be used in ICD systems because there
is a good signal due to a larger distance between the shock
electrodes (Fig. 13.3 ). Provided that a high pacing threshold
is measured in the right ventricle, certain pacing systems
may allow unipolar/bipolar configuration reprogramming;
ICDs, however, lack this option.
13.1.1 Measuring the Threshold in the Right
Atrium
In case of intact AV conduction, the AAI or A00 mode is
to be applied temporarily to measure the threshold in the right
atrium. Nevertheless, if a higher AV block (second or third
degree) is diagnosed, measuring in the atrial mode could be
dangerous because pulses could fail to be conducted to ven-
tricles, which would result in a cardiac arrest. In such cases,
the atrial threshold must be measured in the DDD mode. In
the atrial mode (Fig. 13.2 ), the first unsuccessful atrial pacing
pulse is identified while the amplitude is decreased gradually.
Provided that a high pacing threshold is measured, certain
pacing systems allow unipolar/bipolar configuration repro-
gramming; ICDs, however, lack this option.
In the DDD mode, the first unsuccessful atrial pacing pulse
may not be apparent. Thus, prolongation of the cardiac cycle
13.1.3 Measuring the Threshold in the Left
Ventricle
The VVI or V00 modes also are applied for the purpose of
measuring threshold in the left ventricle (Fig. 13.4 ). Provided
that a high pacing threshold is measured in the left ventricle,
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