I-85
DIGITAL TECHNOLOGY IN DAILY CLINICAL
CARDIAC PACING PRACTICE
Bert T. C. F. van Dalen
Vitatron B. V. Arnhem, The Netherlands
The new digital C-series and T-series pacemakers from Vita-
tron, are the first in the world to process heart signals digi-
tally, and are better at analyzing the signals and diagnosing
them than their analogue predecessors that are currently the
standard in the pacing community. Although digital techno-
logy has been around us for some time in consumer electro-
nics and PC’s, achieving the specific design challenges to in-
corporate this technology in an implantable device represents
a significant step forward bringing important advantages to
the daily practice of pacing clinicians.
The biggest design challenge in converting from analogue to
digital was to keep power consumption down in the new di-
gital devices. The challenge of microchip power consumpti-
on becomes apparent when the pacemaker chip is compa-
red to the Pentium 4, the chip at the heart of the newest gene-
ration of PCs. The leakage current alone from these consu-
mer electronics is ten times higher than the current that is
needed to operate a pacemaker.
In addition, the added »Therapy Advisor« functionality analy-
ses, alerts, and suggests programming recommendations in
the first seconds of follow-up if needed, reducing follow-up
time, and eliminating the need for the clinician to examine all
diagnostic data for trouble-shooting.
The digital pacemaker samples the intracardiac signal 800 ti-
mes per second as compared to the current analog standard
of 125 Hz. The processor parts of the chip are designed to
measure and compare each signal against the preceding si-
gnal extremely quickly, a mandatory requirement for a chip
used for intracardiac signal analysis.
The ability to store these high-resolution intra-cardiac signals
much more precisely, make the diagnostics much more reli-
able, and therapy adjustments can be made with more confi-
dence by the clinician.
Since the digital storage of intra cardiac signals in a fully digi-
tal device consumes less than 1% of battery capacity, compa-
red to 20% for a analog device, it can be left on during the
complete lifetime of the device.
Figure 1. C 60DR; familiar physical shape and size, but con-
taining a new technology for implantable pacemakers.
Figure 2. Exploded view of the digital C-series pacemaker with
the electronics module that incorporates the digital signal
processor.
A patented design of the digital signal processor incorpora-
ted has implemented the field of cardiac pacing.
In daily clinical practice, the new digital pacemakers offer
substantial benefits.
Communication between the implanted digital pacemaker
and the external computer takes a matter of seconds, rather
than minutes in the case of most analog pacemakers. The re-
port produced by the digital pacemaker is also much clearer
and easier to interpret by the clinician.
Storage of historical data and subsequent trending of data in
the C- and T-series allows the clinican to monitor treatment
success, including the efficacy of administered drugs.
Especially in the field of atrial arrythmias there has been a
clinician’s demand for more specific and more precise atrial
sensing and signal interpretation. This need is met to large
extent in the digital Vitatron T-series variant, where auto-
matic analysis of atrial arrhythmia’s and automatic advice on
the programming of preventive pacing therapies greatly
reduces the workload of clinicians for these difficult to treat
patients.
Recent clinical data has identified that reduction of ventricu-
lar pacing to a necessary minimum, reduces the risk on deve-
ZDRAV VESTN 2005; 74: I-85–7
I-86 ZDRAV VESTN 2005; 74: SUPPL I
loping atrial fibrillation and heartfailure in bradycardia pati-
ents. Automatic analysis of AV conduction development over
follow-up periodin the new digital devices by may lead to the
suggestion to switch a reduced ventricular pacing algorithm
on, if applicable.
Additonally, the digital design is much more robust to handle
electronic interference from the day-to-day world a patient
lives in.
Conclusion
The new digital technology now applied in cardiac pacema-
kers today, allows to make the daily practice of pacemaker
clinicians faster, and with more confidence. In the future, furt-
her development of digital pacemaker software will open up
exiting fields of clinical research. Continuing our long tradi-
tion for research with cardiac clinicians from Slovenia and
other countries worldwide will lead to the delivery of new dia-
gnostics for physicians and new therapies for their patients.
BEAT BY BEAT AUTOCAPTURE™ PACING SYSTEM
Friedrich Rauscha
Department of Cardiology, General Hospital Vienna, Austria
Background
St. Jude Medical’s ventricular AutoCapture™ algorithm veri-
fies capture on a beat-by-beat basis to ensure the highest pa-
tient safety available. It combines several years of clinical ex-
perience with ease of use to become the premier algorithm
of choice. AutoCapture™ insures maximum patient comfort
with programmable polarity (unipolar or bipolar) for the
higher output back-up pulse. AutoCapture™ provides safety
on a beat-by-beat basis by automatically adjusting the ventri-
cular output to the patient’s changing threshold needs. The
AutoCapture™ algorithm effectively controls the device out-
put therefore increasing longevity and potentially decreasing
the number of replacement devices needed by the patient.
AutoCapture™ saves time during follow-up. There is no need
to measure, calculate, and program ventricular pacing thre-
shold safety margins.
Methods
After the pacing pulse, an initial waiting period of approxi-
mately 14 ms is followed by an Evoked Response Detection
Window of approximately 47 ms in length. If the device sen-
ses an evoked response in this detection window, capture is
confirmed. The timing cycle is reset, and pacing resumes at
the Automatic Pulse Amplitude and the programmed pulse
width.
The absence of an evoked response during the detection win-
dow (47 ms) results in the delivery of a 4,5 V back-up safety
pulse within 80–100 ms of the primary pacing pulse.
It is the algorithm’s method of determining the current cap-
ture threshold. It is automatically initiated after 2 consecutive
loss of capture beats, every 8 hours, after magnet and/or tele-
metry wand removal and as desired via the programmer. Du-
ring a threshold search, the AV/PV delay shortens to 50/25 ms
respectively in a dual chamber device, and the pacemaker
automatically adjusts the output to determine the new captu-
re threshold. When capture is confirmed for 2 consecutive
beats, a 0,25 V working margin is then added to the new thres-
hold value.
Results
Implantation Discharge 1 month 3 months
Patients 134 131 116 60
Paced events 4472 3709 2721 1314
Loss of capture 176 168 232 133
Loss of capture followed
by safety pacing 176 168 232 133
Success rate 100% 100% 100% 100%
* This report is based on PMA data corresponding to the FDA report dated
December 23, 1996, and summarizes the results of the Microny SR+, Model
2425T and Regency SR+ model 2400L clinical investigation conducted in
North America.
Conclusions Steven Greenberg et al. at Cardiostim 2000
1) AutoCapture™ provides enhanced longevity when com-
pared to conventional pacing systems.
2) Cost savings per year for single and dual chamber pace-
maker were 52% and 28% less, respectively.
3) AutoCapture™ shows a clear benefit in cost/patient/year
when compared to conventional pacing systems while pro-
viding enhanced safety and similar efficacy.
4) AutoCapture™ appears to be the most cost-effective form
of pacing at present.
I-87
TO STIMULATE OR NOT TO STIMULATE
Ed van der Veen
Institute for Therapy Advancement, Guidant, Belgium
The very first implanted pacemaker used the VOO mode for
stimulation. With this method of pacing there was 100% stimu-
lation. Soon this system was improved and the VVI mode was
used in the majority of patients. The percentage of pacing
reduced to a lower value, off course completely dependent
on the conduction and intrinsic rhythm of the patient. Most
manufacturers started to develop features and special algo-
rithms to decrease the percentage of stimulation to reduce
energy consumption, and secondly, to improve hemodynamic
effects. In the late 70-ties, atrio-ventricular synchrony  mainte-
nance gained special attention in pacemaker design.
Early study results showed improvements in cardiac output,
blood pressure, and ejection fraction. Maintaining AV synchro-
nization (Atrial based pacing) was considered superior to VVI
(Ventricular based) pacing.
Early studies showed that atrial based pacing might reduce
mortality especially after longer periods. Recent studies (PASE,
MOST, CTOPP) have however failed to show this.
In patients with Sinus Node Disease, studies now focus on the
prevention of stroke, and the reduction of Pacemaker syn-
drome, atrial fibrillation, quality of life and Heart Failure (HF).
In the modern approach we have to take into consideration
that stimulation might have a direct impact on the develop-
ment or progression of Heart Failure. Therefore, the crucial
dilemma in the pacemaker treatment is currently: to stimu-
late or not to stimulate.
The MOST study demonstrated a progressive risk for HF
hospitalizations in proportion to the cumulative percentage
of ventricular paced beats. The result is the application of
features to reduce the number of ventricular stimulated beats
or “Pacing avoidance”.
Right ventricular stimulation results in the same depolariza-
tion pattern as left bundle branch block (LBBB). A feature
that gives priority to the intrinsic rhythm is “Rate hysteresis”.
This allows the intrinsic rhythm to be slower than the pacing
rate. Only if there is an episode with a need for stimulation,
the pacemaker will start pacing at the lower rate limit. A search
mechanism prevents pacing for a too long episode.
In a dual chamber system a patient might develop fusion of
pseudo fusion beats. First of all, this is a waste of energy,
secondly this might lead to an inappropriate depolarization
of the ventricles. In clinical practice, a normal approach is
the extension of the AV delay.
However, this has an influence on the upper rate behaviour.
The system will show the 2:1 block at a lower atrial rate, possi-
bly resulting in a potentially reduced exercise capability of
the patient. The solution is AV hysteresis (preferably with a
search mechanism) to avoid fusion beats, but to be able to
stimulate with an appropriate AV delay when necessary. In
modern devices a feature called “Early Detection” can pre-
vent the occurrence of fusion beats by extending the sensing
window upon early sensed cardiac signals.
In the devices for Cardiac Resynchronization Therapy (CRT)
especially in patients with a LBBB, the goal is synchronous
stimulation of both ventricles with an optimized AV delay and
optimized ventricular timing (VV offset). This synchronization
is mandatory, even during episodes of atrial fibrillation with
conduction to the ventricles.
The “biventricular trigger” mechanism will stimulate the left
ventricle in case of a sensed event in the right ventricle, to
ensure synchronization. Ventricular Rate Regulation (VRR)
stabilizes the ventricular rate during episodes of AF. Together
with the biventricular trigger it restores biventricular pacing
as much as possible.
In some of the current CRT devices there is no, or limited use
of left ventricular sensing. This might lead to the induction of
ventricular arrhythmia due to stimulation in the vulnerable
period of a left ventricular premature ventricular contraction
(PVC). A feature like “Left Ventricular Protection Period”
(LVPP) will prevent left ventricular stimulation after a left
sided PVC.
In conclusion, in the last 40 years, pacemaker therapy has
changed from 100% pacing to the avoidance of pacing when
applicable. Nevertheless, when there is a real need for stimu-
lation, all the tools for pacing optimization with improved
safety features are now available.
ABSTRACTS