research activities in 2007 - CSEM

Prediction of Neurocardiovascular Events
R. Vetter, N. Virag •
In order to improve acceptability and quality of life related to a medical diagnostic test, CSEM developed in a joint collaboration with Medtronic
Europe a system based on computer supported prediction of the test outcome. The results of the retrospective study on 1155 patients are very
promising and show that if the diagnostic test was stopped at the instant of event prediction only five percent of the patients would have had to
experience the traumatic neuro-cardiovascular event associated with a positive test outcome.
Patients with unexplained neuro-cardiovascular disorders
often represent diagnostic dilemmas due to the difficulty to
gather the pre-current signs of significant events. The rarity of
such events brings about that limited time period monitoring
using external Holter may be ineffective and not record the
pre-current signs and cause of the disorders. More advanced
monitoring devices such as implantable loop recorders may
gather the pre-current signs and causes of the disorder but
only if a dedicated automatic event detection exists.
Nevertheless, such devices require invasive procedure and
thus cause increased diagnostic costs. To approach this
problem, diagnostic medicine designed dedicated
experimental protocols which will provoke the specific neurocardiovascular
events through external controlled stimulus
and conditions. The inconvenience of these approaches
consists in the fact that the patient has to experience the
neuro-cardiovascular event during the diagnostic assessment.
This is often traumatic and is a reason why some patients
prefer not to undergo such a test.
As an example, tilt table testing is recognized as a standard
test to diagnose vasovagal syncope and establish the neurocardiovascular
dysfunction. The test is illustrated in Figure 1.
After 5 minutes supine rest, the patient is tilted to a 60 degree
head-up position. If symptoms do not develop after 20 min of
tilt, sublingual glyceryl trinitrate is administered to further
provoke syncope. The test ends successfully if syncope
develops or is stopped unsuccessfully after 35 min. Thus,
each successful tilt test allowing an establishment of the
neuro-cardiovascular dysfunction and yielding further medical
insights ends with a traumatic fainting of the patient.
In order to make this test more acceptable to the patient,
shorten the tilt testing experience and decrease the diagnostic
costs, a method which allows an early prediction of a
successful outcome of the tilt test [1] has been developed. The
algorithm exploits the trend of blood pressure, the trend of the
heart rate and an indicator of the autonomic nervous
modulation to continuously process a cumulative risk of the
positive outcome of the tilt test. The algorithm yields an alert
when a threshold is crossed. This suggests that the tilt table
test will be positive, that syncope will occur in very soon and
that the test should be stopped to avoid the traumatic
experience of fainting for the patient.
The performance of the algorithm was assessed on a large
control database of 1155 patients where tilt table tests were
conducted to their end. The successful outcome of the tilt
table test was predicted in 719 of 759 patients (95%) whereas
29 false alarms were generated in 396 unsuccessful tilt table
tests. On average the successful outcome was predicted 60
seconds before fainting leaving sufficient time to stop the
experience before the traumatic outcome.
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In other words, if the test had been stopped at the alert
processed by the computer, out of 759 patients only
40 patients would have had to experience the traumatic
fainting experience engendered by vasovagal syncope while
for 719 patients the establishment of the autonomic
dysfunction would have been performed without traumatic
psychological stress.
The proposed system may open a novel area in diagnostic
medicine where traumatic events due to systemic dysfunction
would not have to be experienced to further establish and
assess a pathological situation. The clinical validity of the
proposed application of prediction of vasovagal syncope is
limited due to the retrospective nature of the study. However,
a prospective clinical study is currently being designed.
In conclusion, computer supported sensing and processing of
vital signals in a diagnostic protocol could increase the
acceptability of the tilt test protocol and improve the patient
quality of life. In medicine there are few parallels for which
standard tests are replaced by mechanisms predicting
outcomes midway through a laboratory study. The present
development concerns a first step in such a process.
Figure 1: Illustration of tilt table test setup used in medical diagnostic
to establish neuro-cardiovascular dysfunction together with the
developed system predicting the test outcome.
The work was partly funded by the CTI Medtech Initiative and
CSEM would like to thank them for their support.
•
Swiss R&D Medtronic Europe
[1] N. Virag, R. Sutton, R. Vetter, T. Markowitz, M. Erickson,
“Prediction of vasovagal syncope from heart rate and blood
pressure trend and variability: Experience in 1,155 patients”,
Heart Rhythm, vol. pp. 1377-1382, November 2007.