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Basic Pacing Concepts Part I

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1 Basic Pacing Concepts Part I
Welcome to Basic Pacing Concepts, a course module in CorePace. The Basic Pacing module addresses concepts such as pacing system components, stimulation, sensing, EMI, and rate response.

2 Objectives Identify the components of pacing systems and their respective functions Define basic electrical terminology Describe the relationship of amplitude and pulse width defined in the strength duration curve Explain the importance of sensing Discuss sources of electromagnetic interference (EMI) and patient/clinician guidelines related to these sources Understand the need for and types of sensors used in rate responsive pacing

3 Pacing Systems

4 The Heart Has an Intrinsic Pacemaker
The heart generates electrical impulses that travel along a specialized conduction pathway This conduction process makes it possible for the heart to pump blood efficiently

5 Atrioventricular (AV) Node
During Conduction, an Impulse Begins in the Sinoatrial (SA) Node and Causes the Atria to Contract Atria Sinoatrial (SA) Node Ventricles Initiation of the cardiac cycle normally begins with at the SA node. A resulting wave of depolarization passes through the right and left atria, which stimulates atrial contraction. Atrioventricular (AV) Node

6 Then, the Impulse Moves to the Atrioventricular (AV) Node and Down the Bundle Branches, Which Causes the Ventricles to Contract Atria SA node Ventricles Following contraction of the atria, the impulse proceeds to the AV node. The impulse slows at the AV node, which allows time for contraction of the atria. Just below the AV node, the impulse passes quickly through the bundle of His, the right and left bundle branches and the Purkinje fibers and lead to contraction of the ventricles. AV node Bundle branches

7 Diseased Heart Tissue May:
Prevent impulse generation in the SA node Inhibit impulse conduction SA node AV node Impulses in a patient with diseased heart tissue may be: Intermittent Irregular Not generated at all At an inappropriate rate for the patient’s metabolic demand. Block can occur at any point–within the SA node, AV node, His bundle or distal conduction system.

8 Implantable Pacemaker Systems Contain the Following Components:
Lead wire(s) Implantable pulse generator (IPG) A basic pacing system is made up of: Implantable pulse generator that contains: A power source—the battery within the pulse generator that generates the impulse Circuitry—controls pacemaker operations Leads—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 heart.

9 Pacemaker Components Combine with Body Tissue to Form a Complete Circuit
Pulse generator: power source or battery Leads or wires Cathode (negative electrode) Anode (positive electrode) Body tissue Lead IPG In a bipolar system, body tissue is part of the circuit only in the sense that it affects impedance (at the electrode-tissue interface). In a unipolar system, contact with body tissue is essential to ground the IPG and allow pacing to occur. Anode Cathode

10 The Pulse Generator: Contains a battery that provides the energy for sending electrical impulses to the heart Houses the circuitry that controls pacemaker operations Circuitry Lithium-iodine is the most commonly used power source for today’s pacemakers. Microprocessors (both ROM and RAM) control sensing, output, telemetry, and diagnostic circuits. Battery

11 Leads Are Insulated Wires That:
Deliver electrical impulses from the pulse generator to the heart Sense cardiac depolarization Lead

12 Types of Leads Endocardial or transvenous leads
Myocardial/Epicardial leads

13 Transvenous Leads Have Different “Fixation” Mechanisms
Passive fixation The tines become lodged in the trabeculae (fibrous meshwork) of the heart

14 Transvenous Leads Active Fixation
The helix (or screw) extends into the endocardial tissue Allows for lead positioning anywhere in the heart’s chamber For smooth-walled hearts or those that lack trabeculation, or in patients that have had a previous CABG procedure, active fixation leads may be a better choice to prevent lead dislodgment. The lead pictured on top is a fixed screw design. Those pictured at the bottom have an extendable/retractable helix.

15 Myocardial and Epicardial Leads
Leads applied directly to the heart Fixation mechanisms include: Epicardial stab-in Myocardial screw-in Suture-on Epicardial 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.

16 Cathode An electrode that is in contact with the heart tissue
Negatively charged when electrical current is flowing Presenter Note: Explain that the system presented here is a bipolar system: the anode for a unipolar system is actually the IPG itself. Note that this topic will be covered in more detail within the next few minutes. Cathode

17 Anode An electrode that receives the electrical impulse after depolarization of cardiac tissue Positively charged when electrical current is flowing On this slide, the anode is labeled for a a bipolar system. Anode

18 Conduction Pathways Body tissues and fluids are part of the conduction pathway between the anode and cathode Anode Tissue Cathode

19 During Pacing, the Impulse:
Impulse onset Begins in the pulse generator Flows through the lead and the cathode (–) Stimulates the heart Returns to the anode (+) * During pacing, the electrical impulse: Begins in the pulse generator Flows through the cathode (negative electrode) Stimulates the heart tissue Returns through the body tissue to the anode (positive electrode) This pathway forms a complete pacing circuit.

20 + - Flows through the tip electrode (cathode) Stimulates the heart
A Unipolar Pacing System Contains a Lead with Only One Electrode Within the Heart; In This System, the Impulse: Flows through the tip electrode (cathode) Stimulates the heart Returns through body fluid and tissue to the IPG (anode) + Anode In 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 fluids The flow of the impulse makes a complete circuit. - Cathode

21 Flows through the tip electrode located at the end of the lead wire
A Bipolar Pacing System Contains a Lead with Two Electrodes Within the Heart. In This System, the Impulse: Flows through the tip electrode located at the end of the lead wire Stimulates the heart Returns to the ring electrode above the lead tip 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 tip Returns to the pulse generator by way of the lead wire Anode Cathode

22 Unipolar and Bipolar Leads

23 Unipolar leads Unipolar leads may have a smaller diameter lead body than bipolar leads Unipolar leads usually exhibit larger pacing artifacts on the surface ECG Lead technology is advancing such that unipolar and bipolar leads will have smaller French sizes than those currently available. Depending on the monitoring equipment, unipolar pacing usually exhibits a larger pacing spike on some surface ECGs.1 1Ellenbogen KA, et al. Clinical Cardiac Pacing. London: WB Sanders Company; Page 71.

24 Bipolar leads Bipolar leads are less susceptible to oversensing noncardiac signals (myopotentials and EMI) While unipolar and bipolar leads look similar (both have the appearance of one wire), most bipolar leads have a coaxial design, meaning an inner wire is insulated and wrapped with an outer wire, giving the lead the appearance of having only one wire. Bipolar leads are less susceptible to oversensing noncardiac signals as the spacing of the two electrodes (located in close proximity to one another) accounts for a much lower incidence of sensing extra-cardiac signals. Coaxial Lead Design

25 Lead Insulation May Be Silicone or Polyurethane

26 Advantages of Silicone-Insulated Leads
Inert Biocompatible Biostable Repairable with medical adhesive Historically very reliable Silicone 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 easily. Therefore, the silicone layer must be relatively thick to resist nicks at implant. Silicone also has a high coefficient of friction and the moving of two leads through a single vein may be difficult. Platinum-cured silicone rubber, characterized by improved mechanical strength, has partially alleviated the issues of low tear strength and friction (Silicure). From Cardiac Pacing, K. Ellenbogen, ed., 2nd edition, PP

27 Advantages of Polyurethane-Insulated Leads
Biocompatible High tear strength Low friction coefficient Smaller lead diameter Current polyurethane lead performance is excellent. Historically, polyurethane leads have not performed as well as silicone due to lead degradation, the causes of which fall into two categories: Environmental Stress Cracking (ESC) Metal-induced Oxidation (also referred to as metal ion oxidation) Environmental stress cracking is the result of the lead being exposed to a “hostile” biological environment (both at and after implant). This exposure leads to eventual breakdown of the insulation to the conductor. Metal-induced oxidation is an oxidative degradation of the polyurethane introduced by the bodies own defense mechanisms responding to the foreign body (lead). From Clinical Cardiac Pacing, K. Ellenbogen et al PP

28 A Brief History of Pacemakers
The first implantable pacemakers, developed in 1960, were asynchronous pacemakers, i.e., pacing without regard to the heart’s intrinsic action (VOO). Single-chamber “demand” pacemakers were introduced in the late 1960s. In 1979, the first dual chamber pacemaker (DVI) was introduced, followed closely by the 1981 release of the first DDD pacemaker, the Versatrax. The first single chamber, rate responsive pacemaker, Activitrax, was released in 1985. Today, dual-chamber pacemakers use rate responsive pacing to mimic the heart’s rate response to provide/meet metabolic needs, most recently using a combination of sensors to best accomplish this task… Pictured above: (upper left) One of the first implantable devices. The device is coated with epoxy. (upper right) Chardack Greatbatch device, late 1960’s. (lower left) Model 5943, a VVI device with titanium case (1974). (Middle) One of the first DDD devices, model number 7004. (lower right) Early 1998: Kappa 400!

29 Single-Chamber and Dual-Chamber Pacing Systems

30 Single-Chamber System
The pacing lead is implanted in the atrium or ventricle, depending on the chamber to be paced and sensed

31 Paced Rhythm Recognition
AAI / 60

32 Paced Rhythm Recognition
VVI / 60

33 Advantages and Disadvantages of Single-Chamber Pacing Systems
Implantation of a single lead Single ventricular lead does not provide AV synchrony Single atrial lead does not provide ventricular backup if A-to-V conduction is lost 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.

34 Dual-Chamber Systems Have Two Leads:
One lead implanted in the atrium One lead implanted in the ventricle

35 Paced Rhythm Recognition
The notation at the top refers to mode, lower rate, and upper rate parameters. This mode of operation can be described as atrial synchronous pacing or atrial tracking. DDD / 60 / 120

36 Paced Rhythm Recognition
DDD / 60 / 120

37 Paced Rhythm Recognition
Pacing in the atrium and ventricle is often described as AV sequential pacing. DDD / 60 / 120

38 Paced Rhythm Recognition
DDD / 60 / 120

39 Most Pacemakers Perform Four Functions:
Stimulate cardiac depolarization Sense intrinsic cardiac function Respond to increased metabolic demand by providing rate responsive pacing Provide diagnostic information stored by the pacemaker The modern pacemaker supports heart function in the following ways: Provides effective and consistent cardiac depolarization Prevents unnecessary pacing by sensing cardiac activity Increases rate to meet increased metabolic demand Provides information about how the patient’s heart and the implanted pacemaker are functioning

40 General Medtronic Pacemaker Disclaimer
INDICATIONS Medtronic pacemakers are indicated for rate adaptive pacing in patients who may benefit from increased pacing rates concurrent with increases in activity (Thera, Thera-i, Prodigy, Preva and Medtronic.Kappa 700 Series) or increases in activity and/or minute ventilation (Medtronic.Kappa 400 Series). Medtronic 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. 9790 Programmer The Medtronic 9790 Programmers are portable, microprocessor based instruments used to program Medtronic implantable devices. 9462 The Model 9462 Remote Assistant™ is intended for use in combination with a Medtronic implantable pacemaker with Remote Assistant diagnostic capabilities. CONTRAINDICATIONS Medtronic pacemakers are contraindicated for the following applications: ·       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. ·       Medtronic.Kappa 400 Series pacemakers are contraindicated for use with epicardial leads and with abdominal implantation. WARNINGS/PRECAUTIONS Pacemaker patients should avoid sources of magnetic resonance imaging, diathermy, high sources of radiation, electrosurgical cautery, external defibrillation, lithotripsy, and radiofrequency ablation to avoid electrical reset of the device, inappropriate sensing and/or therapy. Operation of the Model 9462 Remote Assistant™ Cardiac Monitor near sources of electromagnetic interference, such as cellular phones, computer monitors, etc. may adversely affect the performance of this device. See the appropriate technical manual for detailed information regarding indications, contraindications, warnings, and precautions.  Caution: Federal law (U.S.A.) restricts this device to sale by or on the order of a physician.

41 Medtronic Leads For Indications, Contraindications, Warnings, and Precautions for Medtronic Leads, please refer to the appropriate Leads Technical Manual or call your local Medtronic Representative. Caution: Federal law restricts this device to sale by or on the order of a Physician. Note: 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.

42 Continued in Basic Pacing Concepts Parts II and III

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