Overview
 Problem Review
 Solutions Review
 Results
 Assessment and Feedback
 Ethics: “Moral Blindness and the Guidant Recall”
 Closure Writing Pairs
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Problem Review
 The heart can suffer from arrhythmias that disrupt its
normal function.

Ventricular Tachycardia (VT) – heart beats too fast with no
defined rhythm, does not pump enough blood to the body.
Without treatment almost always fatal.

Superventricular Tachycardia (SVT) – heart beats too fast
but with defined rhythm. Unpleasant but rarely fatal.
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Implantable Cardioverter Defibrillator
 ICDs are implanted in high-risk patients
 Uses an algorithm to detect VT and SVT
 When a VT is detected, the
ICD delivers a life-saving
shock to the heart
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Solution Methods
 Two ICD algorithms to classify VT and SVT ECG
signals.

Create a Matlab program, main file and functions,
that will implement the Derivative Method (DM)

Use the EFF Calculator function to distinguish
between VT and SVT
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Overview of the Derivative Method
 Detect three R-peaks from an ECG test signal
 Extract the 80ms interval before each peak
 Calculate the first derivative of each of the three 80ms




intervals
Compute the average of the three derivatives
Rectify the average derivative signal
Normalize the signal to the maximum SR value
Plot these DM results for the ECG test signal against
the DM results for the SR signal
Note the onset time for the ECG test signal by visual
inspection (i.e. looking at it)!
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Derivative Method – continued
 A threshold value is calculated from the analysis of
the known ECG signals.
 The DM algorithm is used to analyze each unknown
ECG signal; the threshold is applied to the resulting
onset time and the ECG is classified as VT or SVT.
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Working in the frequency domain the EFF algorithm can
classify VT and SVT signals.
 First, the EFF algorithm is used to analyze known
ECG signals; one plot provides a quick visual
comparison of EFF values for VT and SVT.
 Next, a threshold value is calculated from the
analysis of the known signals.
 Finally, the EFF algorithm is used to analyze each
unknown ECG signal; the threshold is applied to the
EFF value and classifies the ECG as VT or SVT.
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Results: Some Hints
 A correct implementation of the Derivative Method
will misclassify two unknown signals.
 A correct use of the EFF Calculator will correct one of
these misclassifications.
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Trade Offs
 Speed and Accuracy
 Recall our hypothesis from the Introductory Lecture
 Speed is determined by how long it takes to
calculate a solution
 Hint: cputime command
in Matlab
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Accuracy
 Accuracy is determined based on misclassification
and the cost function.

Misclassifying an SVT as a VT will give the patient
an unnecessary shock: unpleasant but not life
threatening.

However, misclassifying a VT as an SVT and not
giving a shock: likely death of the patient.
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Accuracy Considerations
 Example: An ICD that misclassifies only 1:100
signals may be considered less accurate than one
that misclassifies 2:100 signals.
 This is true if the 1:100 misclassifies a VT as an SVT
while the 2:100 misclassifies SVTs as VT.
 Because the consequence of misclassification of
a VT is severe, the 1:100 is considered less
accurate.
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Report Considerations
 What kind of signal is corrected from the DM to the
EFF method?
 Is the DM or EFF method more accurate?
 Under what conditions?
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Assessment and Feedback
You must demonstrate your team’s project results
to your lab instructor or TA in lab this week
 It is your team’s responsibility to initiate this
demonstration
 All team members must be present
 All team members must participate in the
demonstration
 All team members must be prepared to answer
questions
 Your team’s demonstration should take about 10
minutes
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The accuracy of your team’s results is worth
20% of your project score.
Results
Max
Score
Known DM and EFF results
5
DM and EFF thresholds
2
Unknown DM and EFF
classifications
5
DM and EFF speed differences
3
Code overview and clarity of
explanations
5
Your Team’s
Score
Your team will receive a copy of the scoring
table for your results assessment
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Characteristics of Effective Teams
 Frequent, honest communication
 Divide-and-conquer with expert follow-up
Balance and exploit strengths of individuals AND teams
Weekly meetings outside of lab
EVERY team member present and prepared for meetings
and labs
Use team roles to make expectations and obligations clear
to everyone
Facilitator: it is your job to make sure all team members
are up to speed





Remember the extra credit on the exams—extra 5% if
ALL team members score ≥ 80%!
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Ethics: when dealing with the heart mistakes cost
lives—Guidant ICD recall.
 In 2002 Guidant discovered and fixed a flaw in its
ICD devices. The flaw was a short circuit that drained
the battery and prevented the life saving shock from
being administered.
 There were 20,600 patients implanted with flawed
devices, but Guidant did not expose the flaw until
2005 when it was shamed into issuing an advisory
telling patients not to have the devices replaced.
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Ethics – continued
 Guidant claimed that the probability of the ICD failing
was so low that the surgery to replace the old device
with a new one was more dangerous than the flawed
device.
 However,




Risk = (Probability of harm) x (Severity of harm)
Death is an extremely high severity of harm
Different people have different “utility functions”
Guidant did not warn patients and doctors—so
patients did not get a chance to exercise their utility
functions
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Ethics – continued
 Ultimately the FDA recalled Guidant’s flawed ICDs.
“there is a reasonable probability that if a
particular device is malfunctioning, the
malfunctioning device will cause serious adverse
health consequences or death.”
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Ethical and Legal Issues
 Understand the brief review of ethical theory
 Review the IEEE Code of Ethics
 Intellectual property: what it is and some examples
 How to think about and manage an ethical dilemma
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Closure Writing Pairs
 Team up with one of your neighbors
 Write 2-3 sentences describing the major point you
learned in the project and the main unanswered
question you still have
 Write your paragraph in the online system
 Sign your names and submit
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