Presentation on theme: "Applying Electrical Concepts to Pacemakers Module 4"— Presentation transcript:
1Applying Electrical Concepts to Pacemakers Module 4 Student NotesThis Module covers the clinical application of the basic electrical concepts introduced in Module 3.This module will teach you the baseline information necessary for working toward more advanced knowledge in pacemaker operation.It is possible that you may want additional supplemental materials to enhance your knowledge on this topic. If you feel this is necessary for you, ask your instructor for suggestions on books or other tools.Instructor NotesThis module should take approximately 1.5 hours to complete.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 have them discuss what they already know about this topic.Evaluate the learners by delivering the knowledge check at the end of this module. An acceptable score is 80%.Note: Many of the slides build in this module, so it is recommended that you familiarize yourself with this functionality before you present.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, MNDecember 2007
2Upon completion you will be able to: ObjectivesUpon completion you will be able to:Recognize a high impedance conditionRecognize a low impedance conditionRecognize capture thresholdDetermine which sensitivity value is more (or less) sensitiveStudent NotesMeeting these objectives is imperative so you will have the ability to manage the electric interface between the cardiac device and the patient.Instructor Notes
3Electrical Information Why is this electrical information relevant?A pacemaker is implanted to:Provide a heart rate to meet metabolic needsIn order to pace the heart, it must capture the myocardiumIn order to pace the heart, it must know when to pace, i.e., it must be able to senseA pacemaker requires an intact electrical circuitStudent NotesAs we covered in the second module, cardiac devices are implanted to provide a rate and rhythm adequate to meet metabolic demands. In order to perform this function a pacemaker must:Capture the myocardium when it pacesKnow when (and when not) to paceThis requires an electrical circuit. In order to make informed decisions regarding device evaluation and programming, this basic knowledge is necessary.Instructor Notes
4Ohm’s Law Relevance to Pacemaker Patients High impedance conditions reduce battery current drainCan increase pacemaker battery longevityWhy?R = V/I If “R” increases and “V” remains the same, then “I” must decreaseLow impedance conditions increase battery current drainCan decrease pacemaker battery longevityR = V/I If “R” decreases and “V” remains the same, then “I” must increaseStudent NotesA review of the clinical relevance of Ohm’s law. Since high impedance conditions ultimately conserve the battery, and device costs and longevity are a concern, does it necessarily follow that high impedance conditions are benign?Instructor NotesAsk: So, are all high-impedance conditions a good thing?No, there are conditions that are issues. These will be discussed on upcoming slides.
5The Effect of Lead Performance on Myocardial Capture What would you expect to happen if a lead was partially fractured?Impedance (or Resistance) would riseCurrent would decrease and battery energy conserved- but -Could you guarantee that enough current (I) can flow through this fractured lead so that each time the pacemaker fired the myocardium would beat?Student NotesAre all high impedance conditions a good thing? It might be better said that not all high impedance conditions are a bad thing. However, unless you are using a specially designed high-impedance lead, you have to suspect a problem in the circuit when you see a high impedance condition.This problem may have serious clinical consequences (e.g., result in loss of capture).Instructor Notes
6High Impedance Conditions A Fractured Conductor A fractured wire can cause Impedance values to riseCurrent flow from the battery may be too low to be effectiveImpedance values may exceed 3,000 WLead wire fractureIncreased resistanceStudent NotesAn example of a high impedance condition is when the conductor coil fractures with the insulation remaining intact.Impedance may exceed 3,000 Ohms and the current flow may be too low to be effective.If a complete fracture of the wire occurs:No current will flowImpedance number will be “infinite,” or 9999 OhmsWhen suspecting a wire break, look for a trend of increasing impedance values, rather than a single lead impedance value. The multifilar construction of the leads sometimes means that some of the small conductor filaments fail, while others remain intact. You’ll typically see a trend if increasing impedances over time.Instructor NotesOther reason for high impedance: Lead not seated properly in pacemaker header.
7Lead Impedance Values Change as a Result of: Wire fracturesInsulation breaksTypically, normal impedance reading values range from 300 to 1,000 WSome leads are high impedance by design. These leads will normally show impedance reading values greater than 1,000 ohmsMedtronic High Impedance leads are:CapSure® ZCapSure® Z NovusStudent NotesInsulation failures also have other consequences for patient safety and the pacing system, which we’ll discuss a little later on.Instructor NotesAsk: If an insulation break occurs, but the conductor remains intact, what do you think will happen to the Impedance?The impedance will dropAsk: What effect would this have on the battery longevity and the ability to capture the myocardium?This will compromise battery longevity, and potentially compromise capture thresholds
8Low Impedance Conditions Insulation breaks expose the lead wire to the followingBody fluids, which have a low resistance, orAnother lead wire (in a bipolar lead)Insulation break that exposes a conductor causes the followingImpedance values to fallCurrent to drain through the insulation break into the body, or into the other wirePotential for loss of captureMore rapid battery depletionStudent NotesInsulation around the lead wire prevents current loss from the lead wire.Electrical current seeks the path of least resistance, which is normally the conductor coil.Insulation breaks are often marked by a trend of falling impedance values.An impedance reading that changes suddenly, or one that is >30% lower than previously recorded values for a given patient, is considered significant and should be watched closely.Instructor NotesCurrent will follow the path of LEAST resistance
9Ventricular pacemaker 60 ppm Capture ThresholdThe minimum electrical stimulus needed to consistently capture the heart outside of the heart’s own refractory periodVentricular pacemaker 60 ppmCaptureNon-CaptureStudent NotesLet’s start applying some of this information to clinical situations. Capture threshold is defined as the minimum electrical stimulus required to CONSISTENTLY capture the heart outside of the myocardial refractory period (i.e., outside of the absolute and effective refractory periods – covered in Module 1).In this example of simple ventricular pacing, we see the first 3 pacing “spikes” are followed by QRS complexes, but the fourth is not. This fourth complex is an example of non-capture.Instructor NotesAsk: For review, what rhythm do you think this patient is in?Hard to tell for sure, but it could be:Complete heart block, although there is a P-wave followed by a QRS, the QRS is wide indicating a ventricular originThis may by also normal sinus rhythm with a bundle branch blockAsk: What would explain the reason for the intrinsic QRS after the non-captured beat?If it is complete heart block, then this is an example of the ventricular escape rateIf it is normal sinus rhythm with a bundle branch block, then it is normal AV conduction
10Effect of Lead Design on Capture Lead maturationFibrotic “capsule” develops around the electrode following lead implantationMay gradually raise thresholdUsually no measurable effect on impedanceStudent NotesOnce a pacemaker and its leads are implanted into the body, a maturation process begins. For the leads, there are three phases that make up this process:The acute phase, where thresholds immediately following implant are lowThe peaking phase, where thresholds rise and reach their highest point, usually around one week post-implant. This is followed by a decline in the threshold over the next 6 to 8 weeks1 as the tissue reaction subsides.The chronic phase, where thresholds assume a stable reading to a level somewhat higher than that at implantation, but less than the peak threshold1The lead maturation process occurs due to the trauma to cells surrounding the electrode, which causes edema, and subsequent development of a fibrotic capsule. The unexcitable capsule reduces the current at the electrode interface, requiring more energy to capture the heart.1Hayes DH et al. Cardiac Pacing and Defibrillation: A Clinical Approach. Armonk, NY: Futura Publishing Company; Page 7.Instructor NotesAsk: What fixation mechanism is shown in the graphic?Passive fixation
11Steroid Eluting LeadsSteroid eluting leads reduce the inflammatory processExhibit little to no acute stimulation threshold peakingLeads maintain low chronic thresholdsSilicone rubber plug containing steroidTines for stable fixationPorous, platinized tipfor steroid elutionStudent NotesSteroid eluting leads reduce inflammation by employing a capsule of dexamethasone sodium phosphate This steroid is gradually emitted over time, nearly eliminating the peaking phenomenon of the lead maturation process, and greatly reducing the formation of the fibrotic capsule around the cathode.Medtronic first introduced steroid eluting leads in the mid 1980’s. Today we manufacture and sell steroid eluting leads with active and passive fixation, and even epicardial steroid eluting leads.Instructor Notes
12Effect of Steroid on Stimulation Thresholds Pulse Width = 0.5 msec36Implant Time (Weeks)Textured Metal ElectrodeSmooth Metal Electrode1245Steroid-Eluting Electrode789101112VoltsStudent NotesThis graph compares the stimulation thresholds of contemporary pacing leads. Older, non-steroid electrodes exhibited higher threshold peaking than that of steroid leads shown on the slide.The different types of electrodes exhibit a wide range of threshold peaking.Steroid-eluting electrodes continue to show lower chronic stimulation thresholds and no significant peaking.Threshold changes are shown here over a 12-week period post-implant, where a comparison is made between:• Smooth metal electrode• Textured metal electrode• Steroid-eluting electrodeTraditionally, implant stimulation thresholds are relatively low.Non-steroid-eluting electrodes exhibit a peaking phase from week 1 to approximately week 6, due to the maturation process at the electrode-tissue interface.Steroid-eluting electrodes exhibit virtually no peaking.The chronic phase of stimulation threshold occurs 8-12 weeks post-implant, which is characterized by a plateau. This plateau is higher than the acute phase, due to fibrotic encapsulation of the electrode. Steroid-eluting lead chronic thresholds remain close to implant values.References: Pacing Reference Guide, Bakken Education Center, 1995, UC aEN. Cardiac Pacing, Second Edition, Edited by Kenneth A. EllenbogenInstructor NotesAsk: So, why is this clinically relevant?During the first several weeks after implant, a pacing safety margin is applied than for a chronic leadReferences: Pacing Reference Guide, Bakken Education Center, 1995, UC aEN. Cardiac Pacing, 2nd Edition, Edited by Kenneth A. Ellenbogen
13Myocardial Capture Capture is a function of: Amplitude—the strength of the impulse expressed in voltsThe amplitude of the impulse must be large enough to cause depolarization (i.e., to “capture” the heart)The amplitude of the impulse must be sufficient to provide an appropriate pacing safety marginPulse width—the duration of the current flow expressed in millisecondsThe pulse width must be long enough for depolarization to disperse to the surrounding tissueStudent NotesVoltage has been describes as the force “drawing” the electrons out of the battery, and the size of the voltage certainly affects a pacemakers ability to capture. But another component is involved - the pulse width – or length of time the voltage is applied.The pulse width, expressed in milliseconds, is the duration of time the pacemaker circuit is complete. Electricity flows from the battery down the lead, out the tip (cathode), and back to the anode.Instructor Notes
14Comparison 5.0 Volt Amplitude at Different Pulse Widths Amplitude5.0 V0.25 ms1.0 ms0.5 msStudent NotesThe longer the pulse width, the shorter the battery longevity. An increase in pulse width leads to an increase in total energy delivered (reducing the battery longevity).BUTThe longer the duration of the stimulus, the lower the amplitude required to capture the heart. So when thinking of myocardial capture, the pulse amplitude (voltage) and the pulse width (duration) are related.Instructor Notes
15The Strength-Duration Curve The strength-duration curve illustrates the relationship of amplitude and pulse widthAny combination of pulse width and voltage, on or above the curve, will result in capture.501.01.52.0.25ChronaxieCaptureVoltsRheobaseStudent NotesThe strength-duration curve illustrates the tradeoff of amplitude (think of this as the intensity of stimulation, measured in volts) and duration (the length of time the stimulation is applied, measured in milliseconds).Capture occurs when the stimulus causes the tissue to react. On this graph, capture occurs on or above the strength-duration curve. Anything below the curve will not capture.The lowest voltage on a stimulation curve, which still results in capture at an infinitely long pulse duration, is called rheobase. A voltage programmed below is inefficient and will lead to non-capture.The pulse duration at twice the rheobase value is defined as the chronaxie. Chronaxie time is typically considered most efficient in terms of battery consumption.Don’t worry about these terms for now. The point is to realize that you must balance amplitude and pulse width in making programming choices.Medtronic pacemakers, since the mid-90’s, have been able to measure a strength-duration curve as part of a threshold test. This can be a very useful tool to use when making programming decisions when you are trying to maximize device longevity, but also minimize the risk of non-capture.Instructor NotesNo Capture0.51.01.5Pulse Width
16Clinical Utility of the Strength-Duration Curve By accurately determining capture threshold, we can assure adequate safety margins because:Thresholds may differ in acute or chronic pacing systemsThresholds fluctuate slightly dailyThresholds can change due to metabolic conditions or medications2.0XProgrammed Output1.5Stimulation Threshold (Volts)1.0.50Student NotesThere are several ways to actually perform threshold tests – we’ll cover this a bit later, but the outcome is the same – once you’ve determined the threshold, you must make a programming recommendation.When a threshold is determined by decrementing the pulse width at a fixed voltage, capture or pacing output safety margins have traditionally been selected as follows:At a given voltage, where the pulse width value is < 0.30 ms: Tripling the pulse width is equivalent to providing a two-time voltage safety margin.Pulse widths at a given voltage value, which are > 0.30 ms, are not typically selected because they are less efficient (expend more energy), while not providing further safety. In this case, the voltage should be doubled to provide a two-time safety margin.Appropriate safety margins are programmed because of fluctuations in the capture threshold that can occur due to eating, sleeping, exercise, or other factors. Typically, we will program about a 2-times safety margin on a chronic system.A patient with an acute (new) pacing system will typically be programmed to a setting allowing a higher safety margin, due to the lead maturation process, which can occur within the first 6-8 weeks following implant.Instructor Notes.250.51.01.5DurationPulse Width (ms)
17Programming OutputsPrimary goal: Ensure patient safety and appropriate device performanceSecondary goal: Extend the service life of the batteryTypically program amplitude to < 2.5 V, but always maintain adequate safety marginsA common output value might be 2.0 V at 0.4 msAmplitude values greater than the cell capacity of the pacemaker battery (usually about 2.8 V) require a voltage multiplier, resulting in markedly decreased battery longevityStudent NotesIn most lithium-iodine batteries (those used most often in pacemakers today), the battery voltage is 2.8 V at the beginning of battery life. If an output is programmed above this setting (for example, to 5 V), a voltage multiplier must be used to achieve the higher amplitude. The impact on battery longevity is significant and can reduce longevity by as much as half.The operating voltage of the pacemaker battery is only V. In other words, when the battery reaches 2.5 volts it is almost time to replace the pacemaker. Despite this narrow range, typically, pacemakers can last for up to about 8 years.When you learn about voltage multipliers causing significant battery drain (as when programming outputs to 5.0 V), you might think the reverse is also true—programming low outputs leads to significant gains in battery longevity. Unfortunately – not quite. While longevity can be improved by outputs less than 2.0 V at short pulse widths, most pacemakers also contain diagnostics that also require battery energy.The take-away: When conditions and tests dictate, it is appropriate to program an output and safety margin that keeps the patient safe. When you can, try to program in the 2.0 V range. Less than that and you don’t realize much gain. More than 2.5 V and you start wasting energy, but always keep patient safety in mind.Some clinics may have a pre-established minimum that they allow the output to be programmed down to.Instructor Notes
18Pacemaker SensingRefers to the ability of the pacemaker to “see” signalsExpressed in millivolts (mV)The millivolts (mV) refers to the size of the signal the pacemaker is able to “see”0.5 mV signal2.0 mV signalStudent NotesIntrinsic cardiac activity produces small signals relative to the pacemaker’s output voltage. For example, a P-wave might measure 0.5 millivolts, whereas a pacing spike might measure 5 volts, or 5000 millivolts. Typically, pacemakers are designed to deliver pacing pulses only in the absence of intrinsic activity (also called “demand pacing”), so it is critical for the pacemaker to be able to see or sense these small signals.Instructor Notes
19Sensitivity The Value Programmed into the IPG 5.0 mV2.5 mV1.25 mVStudent NotesThe parameter we program to determine what size signal the pacemaker will sense, is the Sensitivity, which is measured in mV.Increasing this value means the pacemaker is less able to sense smaller signals, or it is less sensitive. For example, if a pacemaker was sensing myopotentials, we might increase the number of the sensitivity setting. The pacemaker will "see less" of the incoming signal (or ‘see’ only bigger signals).If the pacing system is not “seeing” intrinsic cardiac events, decrease the number of the sensitivity setting. The pacemaker will then "see” more of the incoming signal (or “see” smaller signals).Instructor NotesTime
20Sensitivity The Value Programmed into the IPG Time5.0 mV2.5 mV1.25 mV5 mV sensitivityStudent NotesA simple analogy to sensing is a fence.In this example, the sensitivity number is set to 5.0 mV, which is higher than the signal size. Thus, the signal is not sensed.If we programmed the pacemaker so it is unable to see any intrinsic activity, we would call it undersensing.In general, when we refer to undersensing, we mean the pacemaker is unable to “see” intrinsic cardiac events.Instructor NotesAt this value the pacemaker will not see the 3.0 mV signal
21Sensitivity The Value Programmed into the IPG 1.25 mV SensitivityTime5.0 mV2.5 mV1.25 mVBut what about this?Student NotesIn this example, the sensitivity value is much less. In fact, by programming a lower value we’ve made the pacemaker MORE sensitive. But now the pacemaker can sense not only the QRS, but also the T-wave.This is an example of T-wave oversensing.Oversensing can also refer to sensing non-cardiac events, for example, myopotentials.Instructor NotesAsk: If the pacemaker is oversensing, do you increase or decrease the sensitivity?Decrease the sensitivity by programming a higher valueAt this value, the pacemaker can see both the 3.0 mV and the 1.30 mV signal. So, is “more sensitive” better, because the pacemaker sees smaller signals?
22Sensing Amplifiers/Filters Accurate sensing requires that extraneous signals are filtered outBecause whatever a pacemaker senses is by definition a P- or an R-waveSensing amplifiers use filters that allow appropriate sensing of P- and R-waves, and reject inappropriate signalsUnwanted signals most commonly sensed are:T-waves (which the pacemaker defines as an R-wave)Far-field events (R-waves sensed by the atrial channel, which the pacemaker thinks are P-waves)Skeletal muscle myopotentials (e.g., from the pectoral muscle, which the pacemaker may think are either P- or R-waves)Signals from the pacemaker (e.g., a ventricular pacing spike sensed on the atrial channel “crosstalk”)Student NotesThe goal of programming sensing is to provide the pacemaker with accurate information for timing and diagnostics. This information lets the pacemaker know if it needs to pace, when to pace, and what the intrinsic rate is.Keep in mind: Every signal sensed via the atrial lead is a P-wave (according to the pacemaker), just as every signal sensed via the ventricular lead is an R-wave (according to the pacemaker).The pacemaker does not have any ability to discriminate signals on the basis of shape (morphology), or where the signal originates from.So, while we want the pacemaker to sense every P- and R-wave, we want it to sense ONLY P- and R-waves.Instructor NotesIn troubleshooting sensing problems, which we’ll cover later, it is very helpful to keep this simple fact in mind:The pacemaker does not have any ability to discriminate signals on the basis of shape (morphology), or where the signal originates from. Every signal sensed on the atrial lead is, by definition, a P-wave. Every signal sensed on the ventricular lead is, by definition, an R-wave.
23Sensing Accuracy Affected by: Pacemaker circuit (lead) integrity Insulation breakWire fractureThe characteristics of the electrodeElectrode placement within the heartThe sensing amplifiers of the pacemakerLead polarity (unipolar vs. bipolar)The electrophysiological properties of the myocardiumEMI – Electromagnetic InterferenceStudent NotesA loss of circuit integrity, for example lead fracture or lead insulation break, can result in appropriate sensing and inappropriate pacemaker operation.Thus, we can see how the electrical concepts discussed earlier apply to sensing.Instructor Notes
24Lead Conductor Coil Integrity Affect on Sensing Undersensing occurs when the cardiac signal is unable to get back to the pacemakerIntrinsic signals cannot cross the wire fractureOversensing occurs when the severed ends of the wire intermittently make contactCreates signals interpreted by the pacemaker as P- or R-wavesStudent NotesLead fractures that are intermittent are also referred to as “make and break” fractures, due to the artifacts in the electrogram that are produced as the conductor wires make and break contact.Instructor Notes
25Lead Insulation Integrity Affect on Sensing Undersensing occurs when inner and outer conductor coils are in continuous contactSignals from intrinsic beats are reduced at the sense amplifier, and amplitude no longer meets the programmed sensing valueOversensing occurs when inner and outer conductor coils make intermittent contactSignals are incorrectly interpreted as P- or R-wavesStudent NotesLead insulation integrity has improved greatly over the years. Despite exhaustive testing, some earlier models of leads, particularly those using polyurethane insulators, were subject to insulation degradation over time. This situation has greatly improved; however, the body is a harsh environment, and the lead is subject to many inexorable mechanical forces.Instructor Notes
26Where is the sensing circuit? Unipolar PacemakerWhere is the sensing circuit?AnodeClick for AnswerStudent NotesAnother effect on sensing has to do with the position of the cathode and anode.Unipolar sensing, in which the anode is the pacemaker case, produces a large potential difference due to a cathode and anode that are farther apart than a bipolar system. Because both electrodes may contribute to the electrical signal that is sensed, the unipolar electrode configuration may detect electrical signals that occur near the pacemaker pocket, as well as those inside the heart.Unipolar sensing has improved over the years, but these devices are likely more prone to myopotential oversensing.Instructor NotesLead tip to canThis can produce a large potential difference (signal) because the cathode and anode are far apart_Cathode
27Bipolar Pacemaker Where is the sensing circuit? Click for Answer Lead tip to ring on the leadThis usually produces a smaller potential difference due to the short inter-electrode distanceBut, electrical signals from outside the heart (such as myopotentials) are less likely to be sensedStudent NotesIn a Bipolar system, the anode and cathode are close together, thus producing a small potential difference, and the intracardiac signal arrives at each electrode at almost the same time.Less likely to sense:Myopotentials: depolarization of muscles near the heart or the anode (the wave produced after the action potential wave passes along a nerve)AfterpotentialsFar-field intracardiac signalsNoiseEMIInstructor NotesWe’ll discuss more details on uni-and bi-polar systems in more detail laterAnode and Cathode
28Cardiac Conduction and Device Sensing By now we should be familiar with the surface ECG and its relationship to cardiac conduction. But, how does this relate to pacemaker sensing?Student NotesInstructor NotesAuto-animated slide
29Vectors and Gradients Sense Click for More 2.5 mVClick for MoreStudent NotesA gradient, or difference, is created as the cells around the cathode (and then anode) depolarize (become more negative), and then repolarize (return to baseline).The direction, or vector, of the current as it passes the cathode and anode, creates a differential, or gradient. A large gradient produces a large signal.Instructor NotesAuto-animated slide.The wave of depolarization produced by normal conduction creates a gradient across the cathode and anode. This changing polarity creates the signal.Once this signal exceeds the programmed sensitivity – it is sensed by the device.
30Changing the Vector Sense Click for More 2.5 mVClick for MoreStudent NotesThe variance we see in signal amplitude explains why we program at least a 2-times sensing safety margin. For example, sometimes an intrinsic R-wave might measure > 22 mV, but we will program a ventricular sensitivity of 2.5 mV. As long as there is no evidence of oversensing, this programming is acceptable.Sensing is evolving in pacing. Many modern pacemakers are using adaptive sensing algorithms, pioneered by Medtronic. These algorithms automatically change the programmed sensitivity in response to measured P- and R-waves.ICDs use a unique sensing algorithm called Auto-Adjusting Sensitivity (also a Medtronic innovation). These are also being used in some pacemakers. We’ll cover more on this in a later module.Instructor NotesAuto-animated slideA PVC occurs, which is conducted abnormally. Since the vector relative to the lead has changed, what effect might this have on sensing?In this case, the wave of depolarization strikes the anode and cathode almost simultaneously. This will create a smaller gradient and thus, a smaller signal.
31Putting It All Together Appropriate output programming can improve device longevityBut, do not compromise patient safety!Lead design can improve device longevity viaSteroid eluting leadsCan help keep chronic pacing thresholds low by reducing inflammation and scarringHigh Impedance leadsMedtronic CapSure Z and Medtronic CapSure Z NovusDesigned so electrode W is high, but V low so current (I) is low as well, reducing battery drainControl of manufacturingBatteries, circuit boards, capacitors, etc., specific to needs, can lead to improved efficiencies and lowered static current drainHighly reliable lead designStudent NotesInstructor Notes
32Putting It All Together Pacemaker Longevity is:A function of programmed parameters (rate, output, % time pacing)A function of useful battery capacityA function ofStatic current drainCircuit efficiencyOutput ImpedanceThe lower the programmed sensitivity the MORE sensitive the deviceLead integrity also affects sensingStudent NotesInstructor NotesWe’ll discuss optimum device programming laterPhysiologic pacingSafety margins
33Status Check Determine the threshold amplitude Click for Answer 0.75 V0.05 V1.25 V1.00 VClick for AnswerStudent NotesInstructor NotesNow let’s practice what you have learned.Capture threshold = lowest value with consist captureThis is at 1.25 V
34Status Check Which of these pacemakers is more sensitive? OR Pacemaker APacemaker BORProgrammed Sensitivity 2.5 mVProgrammed Sensitivity 0.5 mVStudent NotesInstructor NotesClick for AnswerPacemaker A is able to “see” signals as small as 0.5 mV. Thus, it is more sensitive.
35Status CheckA pacemaker lead must flex and move as the heart beats. On average, how many times does a heart beat in 1 year?Click for Answer35 MILLION times. It is not a simple task to design a lead that is small, reliable, and lasts a lifetime.Student NotesInstructor Notes
36Status Check Do you notice anything on this x-ray? Lead Fracture: Click for AnswerLead Fracture:High ImpedancePossible failure to capture myocardiumStudent NotesInstructor Notes
37Status Check What would you expect? Which value is out of range?What could have caused this?Pacemaker Interrogation ReportMode: DDDRLower: Rate 60 ppmUTR: 130 ppmUSR: 130 ppmAtrial Lead Impedance: 475 OhmsVentricular Lead Impedance: 195 OhmsClick for AnswerInsulation failureStudent NotesInstructor Notes
38Brief 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.
39Brief 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.
40Brief 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.
41Brief Statement: Medtronic Leads (continued) Warnings/PrecautionsPeople with metal implants such as pacemakers, implantable cardioverter defibrillators (ICDs), and accompanying leads should not receive diathermy treatment. The interaction between the implant and diathermy can cause tissue damage, fibrillation, or damage to the device components, which could result in serious injury, loss of therapy, or the need to reprogram or replace the device.For the SelectSecure Model 3830 lead, total patient exposure to beclomethasone 17,21-dipropionate should be considered when implanting multiple leads. No drug interactions with inhaled beclomethasone 17,21-dipropionate have been described. Drug interactions of beclomethasone 17,21-dipropionate with the Model 3830 lead have not been studied.Potential ComplicationsPotential complications include, but are not limited to, valve damage, fibrillation and other arrhythmias, thrombosis, thrombotic and air embolism, cardiac perforation, heart wall rupture, cardiac tamponade, muscle or nerve stimulation, pericardial rub, infection, myocardial irritability, and pneumothorax. Other potential complications related to the lead may include lead dislodgement, lead conductor fracture, insulation failure, threshold elevation or exit block.See specific 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 this device to sale by or on the order of a physician.
42DisclosureNOTE: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.