Pacemaker FAQ
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Introduction
This page contains answers to the Frequently Asked Questions about the Pacemaker Challenge. Before asking a new question by contacting Alan Wassyng or Mark Lawford, please Read The Fine Documents listed below. In particular, many questions about the requirements of pacemakers are answered in the recommended reference text Cardiac Pacemakers Step by Step, An Illustrated Guide.
Requirements
The basis of the system requirements are the following Design Input Documents (DID):
- The informal English prose requirements document from Boston Scientific available through the SQRL Pacemaker Challenge website.
- S. Serge Barold, Roland X. Stroobandt, and Alfons F. Sinnaeve, Cardiac Pacemakers Step by Step, An Illustrated Guide, Blackwell Futura, 2004. ISBN 10: 1 4051 1647 1, ISBN 13: 978 1 4051 1647 3
- The Pacemaker Hardware Reference Platform Details - including the general overview document of the hardware reference platform, the circuit schematic and Bill of Materials (BOM).
The questions and answers are generally organized following the structure of the informal requirements document from Boston Scientific. In this section any references to sections or pages are for that document unless explicitly stated otherwise.
Section 2.5.2 Implant Phase
7. Testing the system sensing and pacing efficacy.
- What kind of test is made?
- Which of these parameters are evaluated?
A: See #6 in the section above 2.5.2
Section 2.5.3 Predischarge Follow-up (Page 12)
2. Reprogramming to final pre-discharge value
- Is there any special values for parameters?
A. No. This just means that the doctor can change parameters after implant, but before the patient leaves the hospital.
Section 3.6.1 Permanent State (Page 17)
The normal pacing parameters programmed shall be used in the permanent brady state.
- Which are these normal pacing parameters?
A. The ones that are currently programmed.
Section 3.6.2 Temporary Bradycardia Pacing
The temporary brady parameters programmed shall be used in the temporary brady state.
- Which are these temporary brady parameters?
A. An identical set of parameters to the permanent parameters, but changes in temporary parameters do not affect permanent parameters.
The temporary state shall be capable of being used to temporarily test various system parameters or provide patient diagnostic testing.
- Which parameters are tested?
A. Any or all parameters that the physician wishes to try temporarily. - What is the "patient diagnostic testing".
A. Testing impedance/amplitude/threshold.
3.6.3 Pace-Now State
The first Pace-Now pacing pulse shall be issued within two cardiac cycles plus 500ms from the time of the last user action required to activate the Pace-Now State.
- Can you explain this to me, please?
A. The cardiac cycle is the time between cardiac events. If the Pace-Now-State is activated, the first pulse must occur within the time stated, measured from the time the activating action occurred.
3.6.5 Power-On Reset (POR) State
All functions shall be disabled until the battery voltage exceeds the POR trip voltage.
- What is a POR trip voltage?
A. The minimum battery voltage necessary to pace.
3.7 Magnet Test
3. When the magnet is removed, the device shall automatically assume PRETEST OPERATION.
- What is the “PRETEST OPERATION“?
A. Whatever the PG was doing immediately prior to the application of the magnet.
- What is changed in the pulse generator (PG)?
A. Nothing.
- Do you have any more details for the Magnet Test?
A. Putting a magnet causes a pacing rate indicating energy left (voltage) in the battery:- 100 ppm => beginning of life (new) (no batt voltage stated)
- 85 ppm => elective replacement indicated (old) batt=2.654 V
4.4 Battery Status (Page 21)
1. Monitoring voltage information shall be provided
- How is this made? What kind of information shall be provided?
A. There is an on-board voltmeter. The information provided shall be battery voltage.
2. Battery Status indicator information shall be provided.
- What is this information?
A. How much energy is left in the battery. A typical visual representation is a “gas gauge”.
Section 4.5 Automatic threshold testing
- How does it happen?
A. Loss of capture is observed by the change in shape of the ECG PQRS complex.
Section 4.6 - Bradycardia History (Page 22)
- Which parameters are adjusted in this case?
A. All.
Section 4.6.1 Rate Histograms
- I can’t understand what does mean: "Distributions shall be recorded for all ..."
A. A histogram
- What is a paced event? And a sensed event?
A. A paced event is the issuing of a pacing pulse. A sensed event is the detection of an atrial or ventricular contraction.
Section 4.6.4 Sensor Trending
The system shall provide off-line prediction analysis of sensor indicated rate with or withoutintrisic rate for the synchronized data collected.
- Can you explain this to me, please?
A. Show XL and/or pacing rate derived from it.
Section 5.2 Upper Rate Limit (URL) (page 29)
This section said URI is the min time between a ventricular event and the next ventricular pace.
- Why is URI effective in modes without ventricular pacing nor sensing, such as AAT, AOO (Table 6, page 28)?
A: “URI” should be “URL interval” in the question. For AAT, trigger paces must not be faster than URL. AOO is constant rate pacing at LRL. So long as LRL < URL (one of many implicit parameter constraints) AOO will pace slower than URL.
The requirement could have been broadened to atrial-only modes. Alternatively, strict reading that URL does not apply to atrial-only modes is acceptable as well.
Section 5.3.3 Dynamic AV Delay (page 29)
When using Dynamic AV delay, the delay should stay between a max and a min value. In section 5.3.3, it says the way the new AV delay is calculated as follows:
"The previous cardiac cycle length is multiplied by a factor stored in device memory to create the dynamic AV delay."
The range of values that such a factor can take is not specified in the document. And what happens if we multiply the cardiac cycle length by the factor and get a value outside the max/min range for the dynamic AV.
A. The factor must be calculated to stay within min-max. Hint: consider intervals at LRL and URL.
Section 5.6 Atrial Tachycardia Response (ATR) (page 31)
In section 5.6.1 of the document, explaining the AT detection algorithm, points 1 and 2 do not clearly define the start and stop of AT.
"1. AT onset shall be detected when the intervals between atrial senses are
predominately, but not exclusively, faster than URL.
2. AT cessation shall be detected when the intervals between atrial senses
are mostly, but not exclusively, faster than URL. "
The only difference between start/stop is "predominately" vs. "mostly".
- What is the interpretation of these statements?
A. Both of those def'ns for ATR were deliberately fudged to hide the actual algorithm. In essence, the algorithm allows some slow beats among the fast ones to enter ATR, to leave it's the opposite. "predominately" and "mostly" were carefully chosen.
The implementer gets to define the implementation, but it must be fast. 30s tracking Afib at MTR is really hard on sick patients.
Section 5.9 Rate Smoothing (page 35)
One of the questions we had for the pacemaker was regarding the rate smoothing algorithm. We were wondering if the pacing rate was suppose to increase based on a percentage of the current pacing rate or the rate we are suppose to be pacing at (Lower rate Limit)
A. The percentage is applied to the previous cardiac cycle. Although the physician may define up-rate smoothing of 3%, the period must decrease so that the rate is 1.03x faster => divide by 1.03 instead of multiply by 0.97. Rate smoothing is VERY important, trumping all other rate modifiers.
Hardware Reference Platform
Availability and Cost
- When will the pacemaker boards be available for purchase?
A. Soon! - How much will a pacemaker board cost?
A. Approximately $350 (CDN) plus shipping. We are selling these boards at cost. You are welcome to try to build your own but be forewarned that they use a lot of surface mount parts!
How do I order pacemaker boards?
Send an email to Mark Lawford.
