Present Solutions to the Problem of Electromagnetic Interference: Are They Good Enough?

Sergio L. Pinski, MD

Cleveland Clinic Florida

Weston, FL, USA

Presenter Disclosure Information

Boston Scientific, Medtronic, St Jude: consultant, member of speaker’s bureau

Pacemaker and ICD Responses to EMI Pacing inhibition Triggering of rapid or premature

pacing Spurious tachyarrhythmia detection Noise reversion mode Electric (power-on) reset Closure of the reed-switch Damage to the generator or the

electrode-myocardial interface

Pinski SL. PACE 2002;25:1367

ResultsEpisode Adjudication

Page 12

5,248 Episodes with Rhythm Classification

3678 (70%) Appropriate

(MVT / PVT / VF)

1570 (30%)Inappropriate (non-VT / VF)

134 (2.6%)Noise, Artifact, Oversensing

Estimated incidence1 year 5 year

6% 17%

Estimated incidence1 year 5 year

1.1% 1.8%

820 (27.4%)Atrial Fib, SVT, sinus tach, or non-sustained

ResultsEpisode Classification

Classification Episodes Patients

Percent of all

Episodes

Percent of NAO

Episodes

External noise / EMI 76 56 1.4% 56.7%

Lead / Connector 37 30 0.7% 27.6%

Muscle noise 11 11 0.2% 8.2%

Ventricular lead oversensing of atrium

7 3 0.1% 5.2%

T wave oversensing 2 2 0.1% 1.5%

Other noise, oversensing

1 1 0.1% 0.7%

Total 134 101 2.6% 100.0%

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ResultsIncidence of NAO Resolution With Shock by Subtype

Category Episodes with Decrease in Noise

External noise / EMI 44 / 76 (58%)

Lead/Connector 13 / 37 (35%)

Muscle noise 3 / 11 (27%)

Other noise/oversensing 0 / 10 (0%)

Total 60 / 134 (45%)

P = .03 comparing External/EMI to Lead/Connector to Muscle – Fisher Exact test.

Example of noise reduction post shock

Example with no change post shock

Page 14

Santucci et al. NEJM 1998;339:1371

Mitigation of EMI

Shielding

Bipolar sensing (lower frequencies)

Electronic filtering (passive and active)

Noise rejection algorithms

Noise reversion mode

• Need to sense very low level biological signals

More ICDs than PMs, more in the atrial than ventricular channel

• Small size is highly desirable by patients and physicians for comfort and appearance but limits size and number of components

• Low power Power used to mitigate EMI reduces the life or

increases the battery size of the device

Design Constraints

Passive Filter Attenuation vs. Frequency

EMI Filter Installation

In order to function properly at high frequencies, the EMI filter must be installed (laser welded) so that it forms an integral part of the overall EMI shield:

Titanium Can(EMI Shield)

Filtered Hermetic Seal

Example of PassiveEMI Filter Performance

Cardiac Sense Lead

without EMI filter with EMI filter

100 MHz to 10 GHz 100 MHz to 10 GHz

Noise rejection algorithmClinical example of DNA in action: Identical noise and 5 mV R-wave in both devices

Legacy Device COGNIS & TELIGEN

Legacy devices could have sensed this noise as a physiologic signal

COGNIS-TELIGEN recognizes the low level signal as noise and appropriately adjusts sensitivity

Page 25

– DNA uses the characteristics of a noise signal—frequency and energy—to identify a signal as noise

– When noise is present, DNA keeps the AGC floor above the noise – DNA is automatically active on all three sensing channels: atrium,

right ventricle and left ventricle

Note: DNA will not make the Boston Scientific devices immune from sensing all noise. The device could still sense EMI or other sources of high amplitude noise.

Note the presence of electroconvulsive therapy noise on the ventricular rate sensing channel and on the shocking egram channel. In this Case Study, DNA keeps AGC sensing floor above noise.

Sorin Group Noise Management - Tachy

• Since 1996 Sorin Group/ELA has had a ventricular noise circuit in all its ICDs

• Based on the premise that human beings cannot sustain intervals in the 188-125 ms range. If intervals consistently in that range are seen they are most likely the result of EMI (noise).

• After several retriggered windows Ventricular Sensitivity is decreased by 0.2 mV on each retriggered window until not retriggered. This process is done on a beat to beat basis

• The circuit is turned off for 15 cycles with an interval of 400 ms to 188 ms to assure arrhythmia detection

• On the 16th cycle, if there has not been an interval larger than 188 ms the noise circuit is turned on again

• Atrial noise circuit similar to Brady function

Sorin Group Noise Management - Tachy

• P

• R

• 95• 30

P V

220 30

Figures show the addition of a 30 ms noise window to the 95 ms (sensed) or the 220 ms (paced) absolute refractory

Sorin Group Noise Management - Tachy

29

Noise level

Sensitivity level0.2 mV steps

95 ms 95 ms

125 ms 125 ms

AVD95 ms

Ventricular pacing can be inhibited (parameter “V pacing on noise”)

Graphic representation of noise sensing to the point of decreasing V sensingSee example on the following slide

30

ICD Ventricular Noise Circuit Example

15 Cycles with noise circuit off after fast cycle

30

Noise Reversion Modes

Manufacturer Noise detection windowProgrammable response Additional features

Boston Scientific ICDs 40 ms retriggerable window

XOO (nominal), Inhibit pacing

Non programmable Dynamic Noise Algorithm

Medtronic PMsProgrammed atrial/ventricular refractory

Non programmable asynchronous pacing

Medtronic ICDs Not available RV lead noise detection

Sorin Paradym 125-188 msInhibit (nominal), pace asynchronous

Reduced sensitivity by 0.2 ms q 16 ms

St Jude PMs 30 Hz XOO (nomimal), off

St Jude ICDs 100 HzXOO 50 BPM (nomimal), off

Determinants of the Clinical Consequences of EMI Intensity of the field Signal spectrum Distance and position of the patient Duration of exposure Nonprogrammable device characteristics Lead configuration Programmed parameters

Sensitivity Mode (baseline, noise reversion, committed)

Patient characteristics Pacemaker-dependency Susceptibility to asynchronous pacing Susceptibility to rapid pacing rates

ANSI/AAMI PC69 standards -2207 Extensive guideline for in vitro testing of pacemaker and ICDs

Typical settings, (eg cellular phone operating at 6 inches)

Different frequencies

Tests also to rule out damage to the generator from electrocautery and external defibrillation

AAMI PC9- Testing for low-frequency EMI via injected current

6

ISO 14708-2/EN 45502-2-1 Connection of tissue equivalent interface circuit (left) and multichannel bipolar cardiac pacemaker (right).

AAMI PC69- Testing for radiated EMI > 450 MHz

“There are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns -- the ones we don't know we don't know."

Donald Rumsfeld, US Secretary of Defense

Cell Phone EMI

• Cellular phone without amplification:

0.3 to 0.6 watts

• Cell phone with 3 watt after market

amplifier and 9 dB gain antenna:

23.8 watts

Garg et al. JICE 2002;7:181

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Furrer et al. NEJM 2004;350:1689

Beginning of oversensing

Wayar et al. PACE 2003;26:1292

Conclusions

Full electromagnetic compatibility has not been achieved yet (and may never be)

Multiple potential sources of EMI exist in daily life, work and medical environments

Conclusions

Improvement in sensing circuits and algorithms together with better awareness of sources of electromagnetic interference have already reduced EMI

Continous surveillance is needed as new emitting sources are introduced

Conclusions

Sources of further minimization

Continuous improvements in device engineering

Awareness of manufacturers of emitters

Patient and public education