Presentation on theme: "Pacemaker Basics Module 5"— Presentation transcript:
1 Pacemaker Basics Module 5 Student NotesThis module is the final introductory module, discussing the basic pacing system components and their operation.This module will instruct you on 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 or provide more practice. 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 hour to cover.To deliver this module, the following materials are recommended:Printed participant guides for each participantOverhead projector and screenOptional: Whiteboard or flip chartDemo leads (passive and active fixation)Demo pacemakers (single and dual chamber)Heart path modelWhile delivering this module, engage the learners by asking questions and encouraging them to discuss what they already know about the topic.Evaluate the learners by delivering the knowledge check at the end of this module. An acceptable score is 80%.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
2 Objectives Identify the components of a pacemaker circuit Identify how pacemaker leads and systems are characterizedPerform basic pacemaker rhythm recognitionStudent NotesMeeting these objectives is imperative for you to achieve the ability to talk knowledgably about different types of pacemaker systems. In addition, achieving these objectives provides the foundation necessary for more advanced understanding of pacemaker operation.Instructor Notes
3 Intrinsic PacemakerThe heart generates electrical impulses that travel along a specialized conduction pathwayTypically, the sinus node (SA node) generates the impulsesConduction paths include:Bachman’s BundleAV nodeBundle of HISBundle BranchesPurkinje NetworkThis pattern of conduction makes it possible for the heart to pump blood efficientlyStudent NotesTo begin, let’s briefly review the cardiac conduction system. Keep in mind that it is by utilizing this specialized cardiac conduction system that mechanical contraction is most efficient, and cardiac output maximized.Instructor Notes
4 Cardiac Conduction Review SA nodeAtriaVentriclesAV nodeStudent NotesInitiation of the cardiac cycle normally begins with the SA node. A resulting wave of depolarization passes through the right and to the left atria, via Bachman’s Bundle, that stimulates atrial contraction.Following contraction of the atria, the impulse proceeds to the AV node. Impulse conduction through the AV node is slightly delayed (compared to the rest of the conduction system). This allows time for atrial contraction to complete, before ventricular contraction begins. Just below the AV node, the impulse then passes quickly through the bundle of His, the right and left bundle branches, and the Purkinje fibers, leading to contraction of the ventricles.Instructor NotesPoint out the locations mentioned on this slide on the heart path model.Bundle branches
5 The Diseased Heart May: Prevent, or delay, impulse generation in the SA nodePrevent, or delay, impulse conduction via the AV nodeInhibit impulse conduction via the bundle branchesSA nodeAV nodeStudent NotesImpulses in a patient with diseased heart tissue may be:IntermittentIrregularNot generated at allAt an inappropriate rate for the patient’s metabolic demandBlock can occur at any point:SA nodeAV nodeHis bundleDistal conduction systemInstructor Notes
6 Implantable Pacemaker System Lead wire(s)Implantable pulse generator (IPG)Myocardial tissueStudent NotesA basic pacing system is made up of:Implantable pulse generator that contains:A power source—the battery within the pulse generator that generates the impulseCircuitry—controls pacemaker operationsLeads—insulated wires that deliver electrical impulses from the pulse generator to the heart. Leads also transmit electrical signals from the heart to the pulse generator.Electrode—a conductor located at the end of the lead; delivers the impulse to the heartMyocardial tissueReceives electrical implulse from the lead and stimulates the heartProduces an electrical signal that the lead senses, or “sees”Instructor NotesDistribute the demo pacemakers to the class.
7 Implantable Pacemaker Circuit Implantable pulse generator (IPG):BatteryCircuitryConnector(s)Leads or wiresCathode (negative electrode)Anode (positive electrode)Body tissueLeadIPGStudent NotesIn a pacing system, body tissue is part of the circuit in the sense that it transmits the electrical impulse cell-to-cell (at the electrode-tissue interface). When the lead impedance is measured it includes this portion of the circuit as well.Instructor NotesAnodeCathode
8 The Pulse GeneratorContains a battery to provide energy for sending electrical impulses to the heartHouses the circuitry that controls pacemaker operationsIncludes a connector to join the pulse generator to the lead(s)Connector BlockCircuitryStudent NotesLithium-iodine is the most commonly used power source for today’s pacemakers. Microprocessors (both ROM and RAM) control sensing, output, telemetry, and diagnostic circuits.Instructor NotesBattery
9 Leads are Insulated Wires Deliver electrical impulses from the pulse generator to the heartSense cardiac depolarizationLeadStudent NotesThe average heart beats about 35 million times in a year, and a pacemaker lead must be able to survive this harsh environment. The lead is subject to mechanical torque, flexing, bending, and the body’s natural defenses and bio-chemicals produced in response to inflammation.Instructor Notes
10 Lead Characterization Position within the heartEndocardial or transvenous leadsEpicardial leadsFixation mechanismActive/Screw-inPassive/TinedShapeStraightJ-shaped used in the atriumPolarityUnipolarBipolarInsulatorSiliconePolyurethaneStudent NotesWe characterize and describe leads based on their:PositionFixation mechanismPolarityInsulatorShapeInstructor Notes
11 Endocardial Passive Fixation Leads The tines become lodged in the trabeculae, a fibrous meshwork, of the heartInserted via a cut-down or transvenous sheathStudent NotesPassive fixation leads are very popular. The tines are made of soft silicone. Eventually the tines become enmeshed in the fibrous tissue, which slowly grows after implantation. This fixation mechanism is very reliable.Instructor NotesDistribute the passive fixation leads to the class.Tines
12 Transvenous Active Fixation Leads The helix, or screw, extends into the endocardial tissueAllows for lead positioning anywhere in the heart’s chamberThe helix is extended using an included toolInserted via a cut-down or transvenous sheathStudent NotesFor smooth-walled hearts, or those that lack trabeculation (e.g., dilated hearts), or in patients that have had a previous CABG procedure, active fixation leads may be a better choice to prevent lead dislodgment.Some feel that these leads are somewhat easier to remove, should it become necessary, since the fixation mechanism is active, i.e., has to be secured into the heart muscle. Initial models did not offer steroid elution, but Medtronic introduced steroid eluting, active fix leads in the mid-1990’s. Since then active-fixation leads have continued to grow in popularity.Instructor NotesDemonstrate how the active fixation works with the demo leadDistribute the active fixation leads to the classEncourage the participants to extend and retract the helix of the pacing lead
13 Epicardial Leads Leads applied directly to the surface of the heart Fixation mechanisms include:Epicardial stab-inMyocardial screw-inSuture-onApplied via sternotomy or laproscopyStudent NotesEpicardial or myocardial leads are implanted to the outside of the heart. These implants represent less than 5% of leads implanted, and are used primarily in pediatric cases, or for patients in whom transvenous lead implant is contraindicated.Instructor Notes
14 Lead Polarity Unipolar leads Bipolar leads May have a smaller diameter lead body than bipolar leadsUsually exhibit larger pacing artifacts on the surface ECGBipolar leadsUsually less susceptible to oversensing of non-cardiac signals (i.e., myopotentials, EMI, etc.)Unipolar leadTo tip (cathode)Bipolar coaxial leadStudent NotesUnipolar leads consist of a single conductor coil extending to the tip electrode. Bipolar leads include 2 coils—one to the tip, the other to the ring-anode. The coils are separated by an insulating layer. Bipolar leads are slightly larger in diameter (measured in French-sizes). However, lead technology is advancing such that unipolar and bipolar leads will soon have smaller French sizes available.Depending on the monitoring equipment, unipolar pacing usually exhibits a larger pacing spike on some surface ECGs.11Ellenbogen KA, et al. Clinical Cardiac Pacing. London: WB Sanders Company; Page 71.Instructor Notes
15 Unipolar Pacing System The lead has only one electrode – the cathode – at the tipThe pacemaker can is the anodeWhen pacing, the impulse:Flows through the tip electrode (cathode)Stimulates the heartReturns through body fluid and tissue to the IPG can (anode)Anode +Student NotesIn the unipolar system, the impulse:Travels down the lead wire to stimulate the heart at the tip electrode, also referred to as the cathode (–)Returns to the metal casing of the impulse generator, or the anode (+), by way of body fluidsThe flow of the impulse makes a complete circuit.Instructor NotesCathode -
16 Bipolar Pacing System The lead has both an anode and cathode The pacing impulse:Flows through the tip electrode located at the end of the lead wireStimulates the heartReturns to the ring electrode, the anode, above the lead tipAnode +Student NotesIn the bipolar system, the impulse:Travels down the lead wire to stimulate the heart at the tip electrode, which is the cathode (–)Travels to the ring electrode, which is the anode (+), located several inches above the lead tipReturns to the pulse generator, by way of the lead wireInstructor NotesCathode -AnodeCathode
17 Newer bipolar lead insulation Lead InsulatorsSilicone insulated leadsInertBiocompatibleBiostableRepairable with medical adhesiveHistorically very reliablePolyurethane insulated leadsHigh tear strengthLow friction coefficientSmaller lead diameterPolyurethaneSiliconeNewer bipolar lead insulationStudent NotesSilicone has proven to be a reliable insulating material for more than three decades of clinical experience. However, silicone is a relatively fragile material, which can tear more easily than urethane. Therefore, the silicone layer must be relatively thick to resist tears, or shearing at implant.Silicone also has a higher coefficient of friction, and the moving of two leads through a single vein may be difficult.Medtronic’s platinum-cured silicone rubber, characterized by improved mechanical strength, has partially alleviated the issues of low tear strength and friction (Silicure).Polyurethane is a more lubricious material and slightly more durable, allowing thinner applications when compared to silicone. However, early types of urethane were subject to chemical reactions secondary to the inflammatory response leading to insulation breakdown over time.From Cardiac Pacing, K. Ellenbogen, ed., 2nd edition, PPInstructor Notes
18 Single Chamber and Dual Chamber Pacing Systems Student NotesLet’s discuss pacing systems in a bit more detail.Instructor Notes
19 Single Chamber SystemThe pacing lead is implanted in the atrium or ventricle, depending on the chamber to be paced and sensedHow else can you describe this system?Student NotesPacing systems are also generally described by the number of chambers paced by the device. A single chamber system paces EITHER the atrium or ventricle.Instructor NotesClick for answerVentricular pacemaker with a bipolar lead
20 Paced Rhythm Recognition Student NotesOn this slide we see an atrial pacemaker in operation. Note that at the beginning of the EKG strip we see pacing at 1000 ms, or 60 bpm. Each pacing spike is closely followed by a P-wave, indicating atrial capture. Towards the second half of the strip, the patient's intrinsic heart rate exceeds 60 bpm. The pacemaker is “inhibited” by the intrinsic rate. This is also called “demand” pacing.KeyP = pacedS = sensedV = ventricularA = atriumVP = ventricular paceVS = ventricular senseAP = atrial paceAS = atrial senseInstructor NotesAtrial pacing at a rate of 60 ppm
21 Paced Rhythm Recognition Student NotesOn this slide we see a ventricular single chamber system regularly pacing, unless it is inhibited by intrinsic activity.Instructor NotesVentricular pacing at a rate of 60 ppmThe “spike” is an artifact created by the pacemaker’s output
22 Paced Rhythm Recognition On the ECG, note the difference between the paced and intrinsic beats. Why do you think this is?Student NotesGenerally, a wide QRS indicates that the right and left ventricles are not working in concert, (dyssynchrony). This may or may not have clinical implications for the patient. In the case of a pacemaker, we may have to accept ventricular pacing, (and a wide QRS), because the patient has a heart block, for example.Instructor NotesAsk: Why do the paced and intrinsic beats differ in morphology so much?Because they are conducted differently through the heartAsk: Does this change in the conduction pattern affect the efficiency of contraction?AbsolutelyAsk: If the patient has an intrinsically wide QRS, and evidence of HF (low EF), what might the MD prescribe?CRT pacingClick for answerBecause the paced beat originates and is conducted differently than the intrinsic beat.
23 Advantages/Disadvantages of Single Chamber Pacing Systems Implant only one leadPacemaker itself usually smallerDisadvantagesSingle ventricular lead does not provide AV synchronyVentricular based pacing linked to AF and HF hospitalizationsSingle atrial lead does not provide ventricular backup if A-V conduction is lostStudent NotesThere are advantages and disadvantages to either system. However, clinical need dictates the indication for pacing, and drives the choice for which system is implanted.Pacing in the VVI/R mode, and loss of AV synchrony, can lead to pacemaker syndrome. Pacemaker syndrome can be defined as “an assortment of symptoms related to the adverse hemodynamic impact from the loss of AV synchrony.”Atrial pacemakers should only be used with patients who have proven AV conduction, and regular follow-up testing available.The most common system implanted today is a dual chamber. VVI systems are typically used for chronic AF patient’s with a slow ventricular response, although there are other indications.Instructor Notes
24 Dual Chamber System Two leads These systems can be unipolar or bipolar One lead implanted in the atriumOne lead implanted in the ventricleThese systems can be unipolar or bipolarAre these leads in the picture active or passive fixation?Student NotesDual chamber systems, as the name implies, consist of 2 leads, one in the atrium the other in the ventricle. Dual chamber systems may be used in cases of sinus node disease even without AV block. Many physicians recognize there is some risk to the patient later developing block, and would rather implant a dual chamber system to begin with.Going back and revising a single chamber system into a dual chamber is not easy, and involves some increased operative risks to patients, and there is always the risk of damaging the previously implanted lead.Instructor NotesClick for answerPassive fixation. Note, the tines look like small grappling hooks, but are actually soft silicone.
25 Paced Rhythm Recognition Student NotesPacing in the atrium and ventricle is often described as AV sequential pacing. We’ll discuss how the pacemaker decides when to pace - the timing - in a later module.Instructor NotesDual chamber pacing at a rate of 60 ppmThe “spike” followed closely by the P- or R-wave is how we tell if the pacemaker has “captured” the myocardium
26 Why a Pacemaker is Implanted 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 senseToday’s pacemakers also:Provide diagnostic informationAbout the pacing systemAbout the patientStudent NotesAs we covered in Module 2, cardiac devices are implanted to perform one main function – 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 paceInstructor NotesAsk: What diagnostic information about the device do you think the pacemaker obtains and reports?Battery voltageLead impedanceAsk: What diagnostic information about the patient do you think the pacemaker obtains and reports?Percent pacingAF burdenWe’ll discuss how a pacemaker performs these functions in upcoming CorePace modules.
27 Status Check Which beats are paced? 1 2 3 4 5 6 7 Click for answer Student NotesInstructor NotesAnimated slide. Click for answerClick for answerBeats 3 and 6 are intrinsic
28 Status Check Is this a unipolar or bipolar lead? Click for answer Student NotesInstructor NotesAnimated slide. Click for answer.Ask: Is this lead active or passive fixation?ActiveBipolar. The tip (screw) is the cathode, the ring is the anode. For simplicity’s sake we often refer to these as the “tip” and “ring.”
29 Status CheckIn this unipolar system, the lead tip is negatively charged (cathode). What acts as the positive electrode (anode)?Cathode -Anode +Click for answerStudent NotesInstructor NotesAnimated slide. Click for answer.The pacemaker case.
30 ? Status Check Click for answer Provide an explanation for why the pacemaker did not “capture” (think of the electrical concepts)?Click for answerStudent NotesInstructor NotesAnimated slide. Click for answer.Lead fracture, failing battery, improper programming, insulation failure any or all might explain this. We’ll discuss how to determine the cause in “Evaluation and Troubleshooting.”
31 Status CheckIdentify the most likely pacemaker that resulted in this stripClick for answerStudent NotesInstructor NotesAnimated slide. Click for answer.Answers:There are only one channel of markers – atrial – so, it is an atrial pacemakerAnother option is that it could be a dual chamber pacemaker programmed AAIThis cannot be a pacemaker with MVP™, because when MVP operates in AAI there are still ventricular markersAtrial pacemakerVentricular pacemakerDual chamber pacemaker
32 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.
33 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.
34 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.
35 Brief 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.
36 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.Student NotesInstructor Notes