Biomedical Engineering Reference
In-Depth Information
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Sensor data
8.5
Hysteresis
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Heart rhythm histograms
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Real-time intracardial EGMs
Pacing hysteresis is an feature allowing the patient's intrinsic
rhythm below the programmed LRL to be supported by tem-
porarily prolonging the escape interval; the intrinsic heart
rate is thus given preference. As a consequence, the hystere-
sis can extend the longevity of the device by decreasing the
number of pacing pulses and optimize the patient's hemody-
namics by supporting the intrinsic rhythm. Hysteresis is
applied if the intrinsic heart rate is between the LRL and the
LRL decremented by the set offset value.
In single-chamber pacing modes, hysteresis is available in
VVI or AAI modes. The device delivers pacing at the pro-
grammed LRL. After a sensed event, the device prolongs the
escape interval by the hysteresis interval. Programmed hys-
teresis then determines the lowest heart rate to occur before
the pacing commences. Hysteresis is activated by one nonre-
fractory sensed event.
In dual-chamber devices, the function is available in
DDD, VDD, and DDI modes. Here, hysteresis is usually
activated by one nonrefractory sensed atrial event and is
deactivated by an atrial or ventricular pacing pulse [65, 66].
Upon the activation of the search hysteresis function, the
device prolongs the escape interval periodically by a pro-
grammed hysteresis offset value to detect possible intrinsic
cardiac activity below the LRL. During the search hysteresis,
the pacing decreases by the offset value over several cardiac
cycles. When the search ends, hysteresis remains active if
intrinsic activity is sensed during this interval. Failing that,
pacing is restored at the LRL. If intrinsic cardiac activity
occurs, the function allows the pacing to be inhibited until
the LRL value decreased by the hysteresis offset value is
reached.
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Annotated event markers
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Automatically stored EGMs
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Patient-triggered stored EGMs
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Daily P and R wave amplitude measurements and trend
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Daily A and V lead impedance measurements and trend
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Condition of atrioventricular conduction
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Search histogram of intrinsic AV conduction
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Sensor-indicated pacing pro fi le
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Tachycardia episodes
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Bradycardia episodes
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Atrial arrhythmia trend
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Duration of atrial arrhythmias
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Ventricular rhythm during atrial arrhythmias
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Change history of the most important parameters
Certain types of data are deleted during an ambulatory
device follow-up, while others are not. With the exception of
lead replacement, long-term data concerning the lead condi-
tion should not be deleted. Collection of data stops at the end
of the device's longevity. Nevertheless, the collected data
can be downloaded even afterward for a certain period of
time [ 67, 68 ] .
8.6.1
Arrhythmia Records
Data concerning tachycardia in both heart chambers include
the date and time of an episode, the maximum and average
rate, and the total duration of the episode. Moreover, upon
the detection of an episode, a sensor-indicated pacing rate
can be stated in printed reports. A programmed method of
data collection determines whether episodes are updated and
older episodes are rewritten, or whether collection is termi-
nated once a set limit is reached. When displaying recorded
arrhythmias, the intracardial signal time base can be adjusted;
it can be rolled right or left, and electronic rulers can be used
for measuring on the display.
In addition to short atrial and ventricular arrhythmia epi-
sodes, atrial tachycardia also triggers daily recording of their
duration. On a long-term basis, the data allow the trend of
this arrhythmia type to be identified as increasing or decreas-
ing. The ventricular rhythm during atrial arrhythmia is dis-
played in the profile of a ventricular action recorded during
atrial arrhythmias sensed since the last patient's follow-up.
Based on the information, the extent of the ventricular pac-
ing during atrial arrhythmias can be identified.
Arrhythmia recording can be triggered automatically (at a
set triggering heart rate) or by the patient. A patient may
commence recording data on EGMs, intervals, and annotated
markers during a symptomatic episode by placing a magnet
on the device. If the function is activated, the device stores
8.6
Diagnostic Features of Pacemakers
Storing diagnostic information in the pacemaker helps moni-
tor the patient's condition between follow-ups and on a long-
term basis. The diagnostics also suggest which pacemaker
parameters are to be adjusted to provide optimum treatment.
The pacemaker records various information relating to the
patient's heart rhythm and some device functions. The infor-
mation is either recorded automatically or certain functions
must be activated. Using the programmer, the recorded infor-
mation may be downloaded, displayed, and printed.
The data normally recorded within the diagnostic func-
tions are as follows:
Results of automatic threshold measurement
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Current measure of P wave and R wave amplitude
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Current measure of lead impedance
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Paced and sensed event counters
