Spurious mode-switch due to atrial oversensing of EMI in a patient with a dual-chamber Guidant ICD. Stored atrial (A), near-field (NF), and far-field (FF) electrograms in a patient who presented for routine ICD follow-up. Non-physiologic, high-frequency, pulsed activity is seen in the 3 channels, although with higher amplitude in the atrial and far-field. Very little ventricular oversensing occurs, so ventricular fibrillation is not detected. However, atrial oversensing results in transient mode-switch. The patient could not recall a potential source of EMI.
Signal amplitude versus frequency. This plot shows the approximate characteristics of the P and R waves that pacemakers and ICDs are intended to sense and the approximate characteristics of the electromagnetic interference (EMI, muscle potentials), T waves, and far-field R waves that they are intended not to sense. The sense amplifier's filters are designed to sense signals that are above the U-shaped amplifier threshold curve and to reject signals that are below the curve. P waves and R waves have similar frequency characteristics, but usually R waves have higher dominant frequency than P waves. Muscle potentials usually have higher-frequency components than intracardiac signals. T waves and far-field R waves have lower frequencies. As shown, there are some overlaps in these amplitude-frequency characteristics that cause oversensing or undersensing in particular situations. The ellipses representing the amplitude-frequency characteristics in this figure are conceptual and are not based on quantitative measurements.
Typically each catheter is protected by1) an EMI filtering capacitor (~ 500pF) in reference to the Titanium case ;2) 2 Zener diodes mounted in opposition to limit the voltage inputs to ~ +/- 9V.
Present solutions to the problem of electromagnetic interference final
Present Solutions to the Problem ofElectromagnetic Interference: AreThey Good Enough? Sergio L. Pinski, MD Cleveland Clinic Florida Weston, FL, USA
Presenter Disclosure Information BostonScientific, 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
ResultsEpisode Adjudication 5,248 Episodes with Rhythm Classification 3678 (70%) 1570 (30%) Estimated incidence Appropriate Inappropriate 1 year 5 year (MVT / PVT / (non-VT / VF) 6% 17% VF) 820 (27.4%) 134 (2.6%) Estimated incidence Atrial Fib, SVT, Noise, Artifact, 1 year 5 year sinus tach, or Oversensing 1.1% 1.8% non-sustained Page 12
ResultsEpisode Classification Percent Percent of of all NAO Classification Episodes Patients Episodes 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 7 3 0.1% 5.2% oversensing of atrium T wave oversensing 2 2 0.1% 1.5% Other noise, 1 1 0.1% 0.7% oversensing Total 134 101 2.6% 100.0% Page 13
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 Example with noise reduction post shock no change post shock Page 14
Mitigation of EMI Shielding Bipolar sensing (lower frequencies) Electronic filtering (passive and active) Noise rejection algorithms Noise reversion mode
Design Constraints• 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
EMI Filter InstallationIn order to function properly at high frequencies, the EMI filter must beinstalled (laser welded) so that it forms an integral part of the overall EMIshield: Filtered Hermetic Seal Titanium Can (EMI Shield)
Example of Passive EMI Filter Performance Cardiac Sense Leadwithout EMI filter with EMI filter 100 MHz to 10 GHz 100 MHz to 10 GHz
Noise rejection algorithm Clinical example of DNA in action: Identical noise and 5 mV R-wave in both devices Legacy Device COGNIS & TELIGENLegacy devices could have sensed this noise as a COGNIS-TELIGEN recognizes the low level signal as noise physiologic signal and appropriately adjusts sensitivity
– 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 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.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. Page 25
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 RP V P 95 30 220 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 AVD 95 ms 95 ms 95 ms 125 ms 125 msNoise level 0.2 mV stepsSensitivity level Ventricular pacing can be inhibited (parameter “V pacing on noise”) Graphic representation of noise sensing to the point of decreasing V sensing See example on the following slide 29
ICD Ventricular Noise Circuit Example 30 15 Cycles with noise circuit off after fast cycle 30
Noise Reversion Modes ProgrammableManufacturer Noise detection window response Additional featuresBoston Scientific XOO (nominal), Inhibit Non programmableICDs 40 ms retriggerable window pacing Dynamic Noise Algorithm Programmed Non programmableMedtronic PMs atrial/ventricular refractory asynchronous pacingMedtronic ICDs Not available RV lead noise detection Inhibit (nominal), pace Reduced sensitivity by 0.2Sorin Paradym 125-188 ms asynchronous ms q 16 msSt Jude PMs 30 Hz XOO (nomimal), off XOO 50 BPM (nomimal),St Jude ICDs 100 Hz off
Determinants of the ClinicalConsequences 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 6ISO 14708-2/EN 45502-2-1 Connection of tissue equivalent interfacecircuit (left) and multichannel bipolar cardiac pacemaker (right).
“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 dont know we dont 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
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Beginning of oversensing Furrer et al. NEJM 2004;350:1689
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