Presentation on theme: "Pacemaker Automatic Features Module 10"— Presentation transcript:
1 Pacemaker Automatic Features Module 10 Student NotesThis module will teach you the baseline information necessary for working toward more advanced knowledge in pacemaker operation.Depending on your background, this module may allow you to meet the objective of this module. It is possible that you may require additional supplemental materials to enhance your knowledge or provide more practice. If you feel this is necessary, ask your instructor for suggestions on books or other tools.Instructor NotesThis module should take approximately 2 hours to cover.To deliver this module the following materials are recommended:Printed participant guides for each participantOverhead projector and screenOptional: whiteboard or flip chartWhile delivering the module engage the learners by asking questions and getting them to talk based on their previous knowledge.Evaluate the learners by delivering the knowledge check at the end of this module. An acceptable score is 90%.World HeadquartersMedtronic, Inc.710 Medtronic ParkwayMinneapolis, MNUSAInternet:Tel: (763)EuropeMedtronic International Trading SàrlRoute du MolliauCh TolochenazSwitzerlandTel: (41 21)Asia-PacificMedtronic International, Ltd.16/F Manulife PlazaThe Lee Gardens, 33 Hysan AvenueCauseway BayHong KongTel: (852)CanadaMedtronic of Canada Ltd.6733 Kitimat RoadMississauga, Ontario L5N 1W3Tel: (905)Toll-free: 1 (800)Medtronic USA, Inc.Toll-free: 1 (800)(24-hour technical support for physicians and medical professionals)Latin AmericaMedtronic USA, Inc.Doral Corporate Center II3750 NW 87th Avenue Suite 700Miami, FL 33178USATel: (305)UC d ENMedtronic, Inc.Minneapolis, MNFebruary 2008
2 Topics Atrial and Ventricular Capture Management® Sensing Assurance Auto Adjusting SensitivityLead Monitor and Polarity SwitchRate ResponseStudent NotesHere are the topics for this module.Instructor Notes
3 Capture Management® Objectives Describe the value of Atrial and Ventricular Capture Management®Recall the basic operation of ACM and VCMIdentify how to program ACM and VCMStudent NotesHere are the objectives.Instructor Notes
4 Capture Management® Why is it important? How is it conducted? Patient SafetyDevice LongevityTroubleshooting InformationHow is it conducted?Automatic algorithms that mimic what a person would do in a clinicStudent NotesBy now you should be capable of running and obtaining an accurate in-office threshold test for the atrium and ventricle. We now introduce the concept of a pacemaker doing this testing automatically. Why is this important? Patient Safety—Threshold results taken more often can allow for automatic output changes as patients’ conditions changeDevice Longevity—A smaller safety margin may be acceptable if adaptability happens on a more regular basisTroubleshooting Information—If a problem does arise, trended threshold information may help to pinpoint the source of the problemInstructor Notesprompt the class to list reasons as to why this will be importantTransition to next slide with the “how” answer. Ask how. Solicit answers from the class. Come to the consensus that the pacemaker must mimic how an in office threshold test and management of output is performed.
5 Capture Management® - Three Categories Assess Patient’sRhythmDetermineThresholdProgramAppropriatelyStudent NotesAll of these steps can be grouped into 3 general categories:Assess Patient’s RhythmAssess patient’s rhythm (rate, type)Determine ThresholdDecide pacing rate or AV delay to force pacingTell the patient that you are going to start the testStart the test at an output that should definitely achieve captureDecrement the outputLook for loss of captureCall capture 1 step above lossProgram AppropriatelyProgram appropriate safety marginMake the point that the pacemaker does these same steps automatically, but that it must follow rigid pre-defined guidelines.)Instructor NotesSince you agree that the pacemaker must mimic what a follow-up person must do, let’s first walk through those steps.Have different people offer the steps of a threshold test, write them down on a white board or flip chart. Get a good comprehensive list and put it in order. Advance through the list on the slide and agree that this is a pretty good comprehensive list of steps that will achieve an appropriate threshold.
6 Capture Management® Manual Testing Automated Testing Assess Patient’sRhythmDetermineThresholdProgramAppropriatelyManual TestingAutomated TestingAssess patient’s rhythm (rate, type)Stability CheckStudent NotesThe first step to managing capture thresholds is assessing the patient’s rhythm. This may be second nature to a very experienced follow-up person, because you may not even realize that you have already assessed the rhythm. The device has to be very methodical about this and does it by conducting what we will call a stability check.Instructor Notes
7 Capture Management®Assess Patient’sRhythmDetermineThresholdProgramAppropriatelyWhen you get ready to run a threshold test manually:What questions do you ask?Why do you ask these questions?Would you run a ventricular threshold test on a patient whose underlying rhythm is AF with a ventricular response of 120 bpm?NOStudent NotesNow that you see that the Capture Management® Feature obtains a threshold in a similar fashion as running the test manually, let’s walk through each step the pacemaker takes in more detail—starting with the assessment of the patient’s rhythm.First ask the question: “Would you run a ventricular threshold on a patient who’s underlying rhythm is AF with a ventricular response of 120 bpm?”Get the class to answer no, and then discuss why?Too fast to paceNot safe—may induce a ventricular arrhythmiaPatient become more symptomaticWhat questions do you ask when you look at a patient’s rhythm with the purpose of preparing for a threshold test? (be thorough, and realize that these questions may be automatic to you)Try to get at least the following questions out of the class:What is the patient’s heart rate?What is the type of rhythm? (AF, Brady, Block, etc.)Is there pacing?Why do you ask these questions?To know if the test can be ranTo know what rate or AV delay will force pacingPatient safetyInstructor Notestransition to the automated side
8 Capture Management® VCM Stability check Assess Patient’sRhythmDetermineThresholdProgramAppropriatelyVCM Stability checkAre conditions favorable to conduct a search?What is the rate? (typically lower than 90 – 100 bpm)What is rhythm? (defined by few VR/AR/VSP/PVC)Are there feature interaction? (No RDR or Mode Switch in progress)If conditions are unfavorable, what do you think happens?The threshold test is postponedIf conditions are favorableMove on to determining the thresholdStudent NotesThe pacemaker decides in it’s own way if it should run the threshold test. Even though the rules are much more ridged, the pacemaker asks its own set of questions for the same reason you ask you questions.When you are in front of the patient you can end the test if the patient becomes symptomatic. You can also come up with a creative way of getting a threshold even if there are a lot of PVCs or sensing issues. For example, it may be appropriate for you to switch to VOO to force ventricular pacing (feel free as the instructor to bring up other ways that you can get a threshold in difficult situations). The device, on the other hand, does not have this luxury. Since the device has limited ways to conduct its test, the patient’s rhythm must meet certain criteria before it begins its test.Through the Stability Check, the device decides if conditions are favorable to conducting a thresholdVCM Stability checkAre conditions favorable to conduct a search?What is the rate?If USR/UTR >135 then rate must be < 100If USR/UTR then < 95If USR/UTR <125 then <90Sensor < ADL RateWhat is rhythmFew VR/AR/VSP/PVCFeature interaction?No RDR therapy in progressNot transitioning DDDR-DDIR-DDDRIf conditions unfavorable, search is postponedInstructor Notes
9 Capture Management® Manual Testing Automated Testing Assess Patient’sRhythmDetermineThresholdProgramAppropriatelyManual TestingAutomated TestingDecide how to paceChoose the type of test-amplitude decrement, pulse width decrement, or strength durationChoose the type of test-always strength durationStart pacingTest paces, backup paces, and support cyclesThreshold searchIdentify Loss of Capture (LOC)Evoked response sensingCall capture threshold one step above LOCConfirm capture at one step above LOCStudent NotesIt’s now time to learn how the device determines a ventricular threshold on its own. This step involves several different actions. As you can see from the chart, each action that the device does has a correlating action that you could do manually. Now we are going to walk through each action from the prospective of the device and how it is similar to what you do when in the office with the patient.Instructor Notes
10 Capture Management® Decide how to pace Assess Patient’sRhythmDetermineThresholdProgramAppropriatelyDecide how to paceWhy do you need to decide how to pace?To force pacingWhat are your options for forcing pacing?Increase the rate in a non-tracking mode (VVI/R, DDI/R)How much?Decrease the AV delay in a tracking mode (DDD/R)Student NotesWhy do you need to decide how to pace?To force pacing—which ensures that delivered test paces have a chance to stimulate and not compete with intrinsic conductionSo now you are ready to force pacing with the intention of running a threshold test.Different options depending the modeNon-tracking (VVI, DDIR) – the rate must be increasedTracking mode (DDD, DDDR) – the AV delay must be shortened or as short as it is whenIn non-tracking mode—the lower rate on test paces is set to the fastest V-V interval seen on any support cycle or seen during the stable rhythm check plus 15 bpm or minus 150 ms, whichever results in a faster rate.In tracking mode—the AV delay of the test cycle = shortest AV during stability – 15 msInstructor Notes
11 Capture Management® Choose the type of test Assess Patient’sRhythmDetermineThresholdProgramAppropriatelyChoose the type of testThe device runs a strength duration test for Ventricular Capture Management1.50 VPulse Width Threshold1.25 VStudent NotesIn a clinic it is common to manually run only an amplitude auto decrement test. The device runs the strength duration test.Instructor Notes1.0 V0.75 VAmplitude Threshold0.5 V0.4 ms1.0 ms
12 Capture Management® Test paces, backup paces, and support cycles Assess Patient’sRhythmDetermineThresholdProgramAppropriatelyTest paces, backup paces, and support cyclesTest pace- pace delivered to determine captureBackup pace- pace delivered immediately following each test pace to ensure there are no dropped beatsQ: If you start running a threshold test on a pacer dependentpatient, and immediately see Loss of Capture, what do you do?A: Stop the testStudent Notes(Instructor: Ask the question: “If you start running a threshold test on a pacer dependent patient, and immediately see loss of capture, what do you do?”A: Stop the testYou stop the test because you cannot have the patient go without ventricular activity for too long.Explain that the device does not allow for there to be any pause in ventricular activity. It does this by providing a backup pace after each test pace. More specifically, the patient is protected against actual LOC by an automatic back-up pace that occurs 110 ms after each test pace, at programmed outputs.This is step is a little different than the way an in-office threshold test would be run.Instructor Notes
13 Capture Management® Test paces, backup paces, and support paces Assess Patient’sRhythmDetermineThresholdProgramAppropriatelyTest paces, backup paces, and support pacesSupport cycles- a series of three events (paced or sensed) that allow for the heart to function as it would without being testedQ: As you are running a threshold test on a patient atan accelerated rate to force pacing, the patient becomesextremely symptomatic, what do you do?A: Stop the testStudent NotesAnswer: Stop the testYou stop the test because you do not want the patient to feel these symptoms.The device cannot determine if symptoms arise from pacing, so it does not allow for the pacing rate or AV delay to be different for very long. It does this by allowing for support cycles in between each test pace.Instructor NotesAsk the question: “As you are running a threshold test on a patient at an accelerated rate to force pacing, the patient becomes symptomatic, what do you do?”
14 Ventricular Capture Management® Test & Back-up PaceTest & Back-up PaceSupport EventsStudent NotesPacing Threshold Search (PTS)In EnPulse®, the threshold search is conducted by decreasing the amplitude at a 0.4ms pulse width until an evoked response is no longer sensed. The amplitude is increased until the evoked response is confirmed on at least 3 consecutive pacing cycles. This value is doubled. The threshold is reported at 0.4ms pulse width.The clinician controls the test frequency (every 15 min –1/week, nominal 1/day at rest), the minimum adapted output, and the voltage safety margin. The minimum pulse width is 0.4 ms. The patient is protected against actual LOC by an automatic back-up pace that occurs 110 ms after each test pace, at programmed outputs.During the programmable acute phase, thresholds are tested but outputs are not decreased, until this phase has completed.Instructor Notes
15 Capture Management® Threshold Search Starting Output Starting Output Assess Patient’sRhythmDetermineThresholdProgramAppropriatelyThreshold SearchStarting OutputStart at an output that capture should occurCapture Management® starts its threshold search at the previous measured threshold valueStartingOutputDecrementOutputWhen you are performing a threshold,how do you shorten the test?Student NotesThe threshold search includes the output that you start at, the decrement of the output, and the output that you stop the test at.Just like performing a threshold test on a patient in a clinic, the mechanism for finding capture is to first find where loss of capture occurs. To do this the output is decremented in steps until the clinician identifies loss of capture. This also assumes that the starting output has capture.Another goal while searching for the threshold is for the test to run for as little time as possible.Possible answers include: Minimize the number of paces between decrements, start at an output just above the thresholdCapture Management® starts its threshold search at the previous measured threshold value. (more detail: The test Amplitude is set at the last Amplitude result from the previous pacing threshold search or at 0.75 V if no previous search has been done. Pulse Width is set at 0.4 ms.)Instructor NotesWhen you are performing a threshold, how do you shorten the test?Discuss the possible answers: minimize the number of paces between decrement, start at an output close to previous threshold (in the chart, or the listed threshold on the QuickLookTM screen, cut the output in half (this assumes 2x safety margin was programmed).Emphasize that starting at an output of the previous threshold (or very close) will minimize the test time which reduces the amount of time that the patient has to be paced a rate different than normal operation.EndingOutput
16 Capture Management® Threshold Search Decrement Output Assess Patient’sRhythmDetermineThresholdProgramAppropriatelyThreshold SearchDecrement OutputLower output (amplitude or pulse width) one step at a timeVentricular Capture Management® performs Strength Duration TestTests amplitude at 0.4 ms PWTests PW at 2X amplitude thresholdAtrial Capture Management® performs an Amplitude Decrement TestStartingOutputDecrementOutputStudent NotesThe output is then decremented in steps until the clinician identifies loss of capture.Instructor NotesEndingOutput
17 Capture Management® Threshold Search Ending Output Assess Patient’sRhythmDetermineThresholdProgramAppropriatelyThreshold SearchEnding OutputCapture Management® confirms captureStartingOutputWhat do you do when you see Lossof Capture (LOC)?DecrementOutputProgrammerStop the testAnalyzerIncrease output to confirm captureStudent NotesThe output that you stop the test at is one step below the threshold. Therefore, you call capture one step above the first output that you lost at.Since Capture Management® is testing the threshold automatically its mechanism for determining threshold is more like using the analyzer—in that it confirms capture.After Capture Management® sees loss of capture, the output is increased until capture is confirmed on at least 3 consecutive pacing cycles.Instructor NotesAsk, “What do you do when you see loss of capture?”Answer: Stop the test by lifting the programmer pin and letting normal operation start back up.You can also bring up testing thresholds on the analyzer. Ask the question: “what do you do when you lose capture on the analyzer?”Discuss that you come up on the output immediately to confirm captureEndingOutput
18 Capture Management® Identify Loss of Ventricular Capture vs. How do you identify Loss of Capture (LOC) when running a ventricular pacing threshold?VVIDDDvs.Student NotesNow that you know how the device does a capture threshold search, it is time to understand how the device identifies loss of capture.Let’s look at what the device knows:It knows exactly when it delivered a paceLet’s build off that strength. If it knows exactly when the pace occurs—it can make a pretty good judgment about what it should “see” immediately following that pace. That is exactly what it does. It looks for what is called an evoked response.Ventricular capture verification algorithms rely on evoked response sensing to determine if a pacing pulse has captured the myocardium. The characteristics of this evoked response, in a sense it’s shape, is how the pacemaker determines if a test pulse has captured the myocardium.Instructor NotesAsk, “How do you identify loss of capture when running a ventricular pacing threshold?”Look for responses like:See a pacing spike without ventricular activity after itSee a change in rateThere is ventricular activity after the pacing spike, but it is narrow (non-paced looking)
19 Evoked Response Sensing All ventricular capture verification algorithms:Rely on sensing the evoked response to the test paceThe characteristics of this response is how the pacemaker determines if the myocardium is capturedIf the characteristics of the evoked response signal differ from what is expected, the pacemaker assumes LOCEvoked response sensing can be affected byLead tissue interface (acute vs. chronic lead)Lead PolarizationTip-to-Ring spacingLead tip designOther factorsStudent NotesAll capture verification algorithms rely on evoked response sensing to determine if a pacing pulse has captured the myocardium. The characteristics of this evoked response, in a sense it’s shape, is how the pacemaker determines if a test pulse has captured the myocardium. Evoked response sensing can be affected by:The lead tissue interface, for example trauma at the lead tipPolarization – not lead polarity, but polarization at the lead tip- see next slideTip-to-ring spacingLead tip designOther factorsInstructor Notes
20 Capture Management® Identify Loss of Atrial Capture How do you identify capture when you run an atrial pacing threshold?Student NotesAtrial capture can be much more difficult to see on a surface ECG: the p-wave can be difficult to see because it is very small or there is too much baseline noise. Even during a follow-up you may not use the presence of a p-wave as determining capture.If you cannot see a p-wave during follow-up, you can still assess atrial capture implementing these other concepts.ACM does not use evoked response sensing. Rather, ACM finds capture by utilizing the same concepts that you use if seeing a p-wave is difficult.Instructor NotesAsk: How do you identify capture when you run an atrial pacing threshold?Possible answers:P-waveR-wave at the appropriate time after the A-pace (increase in ventricular rate)No intrinsic p-waves competing with the pacing rate
21 No Atrial Sense in the AV Interval (Capture) Capture Management®Atrial Chamber Reset MethodDevice makes sure that there are no intrinsic atrial events competing with the pacing rateTest APStudent NotesThere are two methods for atrial capture management®: Arial Chamber Reset Method and AV Conduction Method. These two algorithms do not compete against one another. The Atrial Chamber Reset method tries to run first, but it requires thePeriods of slow(er) sinus rhythm-or-Periods of intact AV conductionAtrial Chamber Reset (ACR) methodDesigned for patients with stable sinus rhythmAtrial Chamber Reset evaluates capture by observing the response of the intrinsic atrial rhythm to the atrial test pace.A test pace which captures should interrupt the underlying escape rhythm and reset the sinus node.A test pace which fails to capture the atrium will NOT reset the sinus node. An atrial sensed event is observed (after the test pace) falling in its AV delay.In other words, the absence of this atrial sense indicates that the test pace captured the myocardium and reset the sinus node.Instructor NotesNo Atrial Sense in the AV Interval (Capture)
22 Capture Management® AV Conduction Method Device looks for a conducted R-wave at the predicted time after an atrial paceStudent NotesAV Conduction (AVC) methodDesigned for patients with intact AV conductionEach test pace is followed by a back-up pace (AVC only)A captured test pace will result in a VS occurring within an expected “window” based on the intrinsic AV interval from the test paceA non-captured test pace will result in a VS occurring within an expected “window” based on the intrinsic AV interval from the back-up paceThe AV Conduction method (AVC) uses ventricular sensing to determine atrial capture, thus 1:1 AV conduction is required. Since a loss of atrial capture in this methodology could result in a dropped ventricular beat, to reduce symptoms and promote safety, this method also uses a backup atrial safety pace (delivered at programmed polarity and at least 2.5V and 1.0 ms).Instructor NotesNote that the backup pace is delivered after every test pace in AVC, but no marker is recorded for this event. Only a slight change in EGM can be observed.The device algorithm for AVC relies on being able to accurately detect when the VS event occurs, with respect to when it is expected to occur, based upon the timing relationship established during the stability check, and reaffirmed during the Support pacing cycles.AP-VS interval following test pace is monitored; if timing is consistent with support pace “expected” window, device records as capture.AP-VS events that result from back-up paces (LOC) will lag by approximately 70 ms from the “expected” window of a test pace.
23 Capture Management® Manual Testing Automated Testing Assess Patient’sRhythmDetermineThresholdProgramAppropriatelyManual TestingAutomated TestingProgram appropriate safety marginFollow programmed rulesStudent NotesNow that you see that the Capture Management® Feature obtains a threshold in a similar fashion as running the test manually, let’s walk through each step the pacemaker takes in more detail.Instructor Notes
24 Capture Management®Assess Patient’sRhythmDetermineThresholdProgramAppropriatelyAdapts the output downward in one step decrements (0.125V)Never below the programmable Minimum Amplitude (Nominal = 2.5V)Applies the programmable safety margin (Nominal = 2X) to the amplitude at 0.4 ms pulse widthAdapts upward, as needed, to maintain the safety marginAcute PhaseOutput may riseWill not adapt downward until the Acute Phase expires (N=112 days)Student NotesInstructor Notes
26 Sensitivity Management Objectives State a reason why fixed sensing safety margins may not be adequateIdentify three clinical areas affected by inappropriate sensingRecall two of the mechanisms for managing sensing automaticallyStudent NotesSensing Assurance provides clinicians with the confidence that an appropriate sensitivity is programmed in changing conditions. This feature is programmed Nominal - ON.Instructor Notes
27 Sensitivity Management Programming a fixed sensing safety margin may not accommodate for these and other potential changesWhat factors can change a patient’s P- and R-wave amplitudes?Antiarrhythmia MedicationsLead MaturationAtrial ArrhythmiasExerciseVentricular ArrhythmiasMyocardial InfarctionStudent NotesFixed sensing values may not be adequate to manage patients. Advanced pacing systems should be able to accommodate changing patient conditions.Instructor NotesLead off this discussion, ask the class, “what factors can change a patient’s P and R-wave amplitudes?”Answers include:Lead maturationMyocardial infarctionAntiarrhythmia medicationsExerciseAtrial ArrhythmiasVentricular Arrhythmias
28 Sensitivity Management Normal OperationTherapyDiagnosticsStudent NotesYou now know reasons why a fixed sensing safety margin may not be adequate. Now let’s shift our focus to clinical problems with inappropriate sensing. This can be broken down into 3 key areas.Normal OperationUndersensing may result in sub-optimal hemodynamics, for example a loss of AV synchronyOversensing may result in pacemaker inhibition and a return of patient symptoms and/or initiation of a pacemaker mediated tachycardia (PMT)Inappropriate Mode Switch behavior (too often or not at all)TherapyPacemakers designed to utilize intrinsic conduction or modify pacing therapy in response to arrhythmia rely on reliable and accurate sensing to function.DiagnosticsMode Switching relies (in part) on consistent atrial sensing during atrial tachyarrhythmiasTo help guide therapy decisions, accurate arrhythmia detection is necessary for devices to accurately report arrhythmia burden, duration, frequency, etc.Instructor Notes
29 Sensitivity Management Sensing AssuranceAdapts Sensitivity based on target safety margins, to automatically provide safe sensing marginsAdequateHighLow5.6x Sensitivity4x SensitivityAtrial BipolarCurrentSensitivity0.5 mV2.0 mV2.8 mVStudent NotesTwo approaches to automatic sensitivity changes are sensing assurance and auto adjusting sensitivity. If the pacemaker has the capability to automatically change sensing it has either one or the other, not both.Sensing Assurance provides clinicians with the confidence that an appropriate sensitivity is maintained under changing patient conditions. This feature is programmed Nominal - ON.Instructor NotesAt completion of Implant Detection, Sensing Assurance begins monitoring the peak amplitude of sensed signals. Each non-refractory sensed event (AS or VS) is monitored by measuring the ratio of the peak amplitude of the P- or R-wave to the sensitivity setting.For a bipolar, atrial lead, the “Adequate” waveform amplitudes will range between 2.0 and 2.8 mV, (that is, 4.0X - 5.6X of 0.5 mV) at nominal/shipped settings.If the pacemaker detects several “low” waveforms, the operating sensitivity setting is decreased by one step, that is, down to 0.35 mV, in an attempt to shift the Target Sensing Margin downward to place the top of the waveform between the 4.0 and 5.6 X limits.If, on the contrary, the pacemaker detects several “high” waveforms, the operating sensitivity setting is automatically increased by one step in an attempt to place the top of the waveform within the target limits. Adaptation does not occur immediately. 17 consecutive events must be “low” to increase the sensitivity, 36 events to decrease the sensitivity. In the case of a mix of low, adequate, and high events, the adjustments occur more gradually, or if paced events are also intermingled with sensed events. If fewer than 60% of events are high (or low), or if the pace to sense ratio is greater than 5:1, no sensitivity adjustment is made. During periods of infrequent sensing, the pacemaker maintains a long-term running average of the sensitivity adjustments and will adjust sensitivity thresholds toward the long-term average.Note: Sensing Assurance boundaries for an Atrial bipolar lead restrict sensitivity settings to adapt only between the values of 0.18 mV and 0.5 mV. Therefore, at nominal sensitivity of 0.5 mV, Sensing Assurance can only adapt sensitivity to lower numbers (increased sensitivity).ASK: What’s the clinical need for this feature?ANSWER: Pacemakers designed to utilize intrinsic events, or modify pacing therapy in response to an arrhythmia, rely on accurate sensing in order to function properly.
30 Sensitivity Management Auto Adjusting SensitivityAdjusts the sensitivity fence on a beat-by-beat basisStudent NotesAuto Adjusting Sensitivity is applied on a beat-to-beat basis for both paced and sensed events (as shown above). Whether a beat is paced or sensed will determine the level of adjustment and the time decay. For example, a sensed ventricular event will decrease sensitivity to 75% of peak EGM with a maximum of 8X the programmed value and a time decay of 450 ms. A complete description of auto-adjusting sensitivity behavior follows.Note: If the programmed sensitivity value exceeds 0.3 mV in the ventricle or 1.2 mV in the atrial, the threshold is not adjusted.Instructor Notes
32 Rate Response Objectives State the clinical reason for rate response pacingRecall why rate response pacing worksList the implantations industry uses for rate response pacingStudent NotesInstructor Notes
33 Rate Responsive Pacing Introduced in the mid-80’s by MedtronicWhy was it one of the most significant developments in pacing?When one exercises, metabolic demand increases. To meet this demand, cardiac output needs to increase.What contribution does increasing heart rate make to increasing the cardiac output?Click for AnswerStudent NotesIn this context of basic timing and alterations to basic timing, another topic to consider is Rate Responsive Pacing. In terms of adding value to pacemaker therapy it is hard to overstate the importance of this innovation. Prior to rate responsive pacing, pacemaker patients had devices which provided a fixed rate only.If a patient had an unreliable sinus node, whether from chronic AF or SSS, and they got a pacemaker – they received a device which could only provide pacing a preset-programmable rate.Obviously this may not have provided a rate to meet metabolic demands.Instructor NotesUp to a 500% increase over the resting cardiac output. No other component of cardiac output has this significant of a contribution.
34 Rate Responsive Pacing This is designated by the “R” in DDDR, AAIR, or VVIR…It is accomplished by using a sensor to indicate changing metabolic demandThe sensor then modifies the pacing rateThink of it as a dynamic lower rate or dynamic escape intervalDDDR means:The heart will not be paced at rates below 60 bpmThe heart may be paced at rates between bpm, based on the information from the rate response sensorThe heart will not be paced at rates above 130 bpmStudent NotesAt its simplest, rate response is really a dynamic lower rate. The escape rate, the A-A interval, is under the control of a sensor which tries to mimic the sinus node and respond to changing metabolic needs.If metabolic demand rises and the current A-A interval does not meet the programmed criteria for rate at that level of metabolic need, the pacemaker simply begins pacing at a faster rate.Think of it like this:An accelerometer, a common rate response sensor, is similar to a pendulum.As the patient moves about this ‘pendulum’ swings back and forth.The pacemaker is designed to measure the rate of the pendulum swinging and convert that motion into a rate.The pacemaker compares the current rate to the “pendulum’s” rate and uses the faster of the 2.When programming rate response we still program a lower rate, and under normal circumstances the pacemaker will not operate at rates less than this. However, it will operate at faster rates when called upon to do so by its sensor.Instructor Notes
35 Rate Response SensorsMany types have been developed with various advantages and disadvantagesMotion-based SensorsAdvantagesDisadvantagesPiezoelectriccrystalFast to respond, easy to program, less expensive to makeMotion based. May not be as accurate with sustained exercise.AccelerometerMetabolic SensorsMinute Ventilation(MV)Accurate, uses rate and depth of respirationsSlow to respond, increased battery consumptionQ-T intervalAccurateSlow to respond, requires Ventricular PacingTemperatureNot always reliableIncreased battery consumption, special leadStudent NotesOver the years a variety of rate-response sensors have been used. Piezo-electric crystals were among the first and are still used in some devices in operation today. Accelerometers are also very common and probably the most frequently used sensor today. Both of these attempt to mimic the Sinus Node by responding to patient movement or motion.Minute ventilation (MV) is also a common sensor used and can closely match metabolic need however is slower to respond and does consume the battery somewhat to operate. Q-T sensor have been very successfully used by one manufacturer but these are gradually becoming less popular because they require ventricular pacing to establish a QT interval.Other sensors have been tried, most notably thermo-sensors, but were found to be less reliable.Instructor Notes
36 Rate Response Sensors In use today Accelerometer Piezo-electric crystalCombination of MV + Accelerometer or MV + P-E crystalCombination of QT + Piezo-electric crystalStudent NotesA variety of new sensors are under clinical investigation or development however the accelerometer remains popular because it is simple, relatively inexpensive to manufacture and install, reliable, predictable, simple to program and above all, meets the needs of the typical pacemaker patient.Instructor Notes
37 Rate ResponseRate responsive (also called rate modulated) pacemakers provide patients with the ability to vary heart rate when the sinus node cannot provide the appropriate rateRate responsive pacing is for patients who may benefit from increased pacing rates concurrent with increases in activity, such as:Patients who are chronotropically incompetent (heart rate cannot reach appropriate levels during exercise, or meet other metabolic demands)Patients in chronic atrial fibrillation with too slow of a ventricular response to meet metabolic demandsStudent NotesInstructor Notes
38 Rate Responsive Pacing Cardiac output (CO) is determined by the combination of stroke volume (SV) and heart rate (HR)SV X HR = COChanges in cardiac output depend on the ability of the HR and SV to respond to metabolic requirementsStudent NotesInstructor Notes
39 Rate Responsive Pacing SV reserves can account for increases in cardiac output of up to 50%HR reserves can nearly triple total cardiac output in response to metabolic demandsStudent NotesMost of the pacing population relies heavily on rate reserves to increase cardiac output because stroke volume reserves are diminished.Instructor Notes
40 Rate Responsive Pacing When the need for oxygenated blood increases, the pacemaker ensures that the heart rate increases to provide additional cardiac outputAdjusting Heart Rate to ActivityNormal Heart RateRate Responsive PacingFixed-Rate PacingStudent NotesInstructor NotesDaily Activities
41 A Variety of Rate Response Sensors Exist Those most accepted in the market place are:Activity sensors that detect physical movement and increase the rate according to the level of activityMinute ventilation sensors measure the change in respiration rate and tidal volume via transthoracic impedance readingsStudent NotesOther sensors that measure QT interval, central venous temperature, stroke volume, etc., are either not available or have gained limited acceptance.Instructor Notes
42 Rate Responsive Pacing Activity sensors employ a piezoelectric crystal that detects mechanical signals produced by movementThe crystal translates the mechanical signals into electrical signals that in turn increase the rate of the pacemakerPiezoelectric crystalStudent NotesInstructor Notes
43 Rate Responsive Pacing Minute Ventilation (MV) is the volume of air introduced into the lungs per unit of timeMV has two components:Tidal volume - the volume of air introduced into the lungs in a single respiration cycleRespiration rate - the number of respiration cycles per minuteStudent NotesInstructor Notes
44 Rate Responsive Pacing Minute ventilation can be measured by calculating the changes in electrical impedance across the chest cavity to calculate changes in lung volume over timeStudent NotesIncreased tidal volume and rate increase transthoracic impedance, which increases the pacing rate.Instructor Notes
45 Status Check Evaluate this rhythm strip IPG is programmed to 60-130bpm What are the atrial and ventricular rates?What operation is in effect?Click for AnswerStudent NotesInstructor NotesA and V rates are about 79 bpmRate responsive pacing in the atrium with intrinsic AV conduction
46 Brief Statements Indications Implantable Pulse Generators (IPGs) are indicated for rate adaptive pacing in patients who ay benefit from increased pacing rates concurrent with increases in activity and increases in activity and/or minute ventilation. Pacemakers are also indicated for dual chamber and atrial tracking modes in patients who may benefit from maintenance of AV synchrony. Dual chamber modes are specifically indicated for treatment of conduction disorders that require restoration of both rate and AV synchrony, which include various degrees of AV block to maintain the atrial contribution to cardiac output and VVI intolerance (e.g. pacemaker syndrome) in the presence of persistent sinus rhythm.Implantable cardioverter defibrillators (ICDs) are indicated for ventricular antitachycardia pacing and ventricular defibrillation for automated treatment of life-threatening ventricular arrhythmias.Cardiac Resynchronization Therapy (CRT) ICDs are indicated for ventricular antitachycardia pacing and ventricular defibrillation for automated treatment of life-threatening ventricular arrhythmias and for the reduction of the symptoms of moderate to severe heart failure (NYHA Functional Class III or IV) in those patients who remain symptomatic despite stable, optimal medical therapy and have a left ventricular ejection fraction less than or equal to 35% and a QRS duration of ≥130 ms.CRT IPGs are indicated for the reduction of the symptoms of moderate to severe heart failure (NYHA Functional Class III or IV) in those patients who remain symptomatic despite stable, optimal medical therapy, and have a left ventricular ejection fraction less than or equal to 35% and a QRS duration of ≥130 ms.ContraindicationsIPGs and CRT IPGs are contraindicated for dual chamber atrial pacing in patients with chronic refractory atrial tachyarrhythmias; asynchronous pacing in the presence (or likelihood) of competitive paced and intrinsic rhythms; unipolar pacing for patients with an implanted cardioverter defibrillator because it may cause unwanted delivery or inhibition of ICD therapy; and certain IPGs are contraindicated for use with epicardial leads and with abdominal implantation.ICDs and CRT ICDs are contraindicated in patients whose ventricular tachyarrhythmias may have transient or reversible causes, patients with incessant VT or VF, and for patients who have a unipolar pacemaker. ICDs are also contraindicated for patients whose primary disorder is bradyarrhythmia.
47 Brief Statements (continued) Warnings/PrecautionsChanges in a patient’s disease and/or medications may alter the efficacy of the device’s programmed parameters. Patients should avoid sources of magnetic and electromagnetic radiation to avoid possible underdetection, inappropriate sensing and/or therapy delivery, tissue damage, induction of an arrhythmia, device electrical reset or device damage. Do not place transthoracic defibrillation paddles directly over the device. Additionally, for CRT ICDs and CRT IPGs, certain programming and device operations may not provide cardiac resynchronization. Also for CRT IPGs, Elective Replacement Indicator (ERI) results in the device switching to VVI pacing at 65 ppm. In this mode, patients may experience loss of cardiac resynchronization therapy and / or loss of AV synchrony. For this reason, the device should be replaced prior to ERI being set.Potential complicationsPotential complications include, but are not limited to, rejection phenomena, erosion through the skin, muscle or nerve stimulation, oversensing, failure to detect and/or terminate arrhythmia episodes, and surgical complications such as hematoma, infection, inflammation, and thrombosis. An additional complication for ICDs and CRT ICDs is the acceleration of ventricular tachycardia.See the device manual for detailed information regarding the implant procedure, indications, contraindications, warnings, precautions, and potential complications/adverse events. For further information, please call Medtronic at and/or consult Medtronic’s website atCaution: Federal law (USA) restricts these devices to sale by or on the order of a physician.
48 Brief Statement: Medtronic Leads IndicationsMedtronic leads are used as part of a cardiac rhythm disease management system. Leads are intended for pacing and sensing and/or defibrillation. Defibrillation leads have application for patients for whom implantable cardioverter defibrillation is indicatedContraindicationsMedtronic leads are contraindicated for the following:ventricular use in patients with tricuspid valvular disease or a tricuspid mechanical heart valve.patients for whom a single dose of 1.0 mg of dexamethasone sodium phosphate or dexamethasone acetate may be contraindicated. (includes all leads which contain these steroids)Epicardial leads should not be used on patients with a heavily infracted or fibrotic myocardium.The SelectSecure Model 3830 Lead is also contraindicated for the following:patients for whom a single dose of 40.µg of beclomethasone dipropionate may be contraindicated.patients with obstructed or inadequate vasculature for intravenous catheterization.
49 DisclosureNOTE:This presentation is provided for general educational purposes only and should not be considered the exclusive source for this type of information. At all times, it is the professional responsibility of the practitioner to exercise independent clinical judgment in a particular situation.