Basic Pacing Concepts Part I
Basic Pacing Concepts Part I 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 Pacing Systems 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 During Conduction, an Impulse Begins in the Sinoatrial (SA) Node and Causes the Atria to Contract Atria Sinoatrial (SA) Node Ventricles Atrioventricular (AV) Node Then, the Impulse Moves to the Atrioventricular (AV) Node and Down the Bundle Branches, Which Causes the Ventricles to Contract Atria SA node Ventricles AV node Bundle branches Diseased Heart Tissue May: Prevent impulse generation in the SA node SA node Inhibit impulse conduction AV node Implantable Pacemaker Systems Contain the Following Components: Lead wire(s) Implantable pulse generator (IPG) Pacemaker Components Combine with Body Tissue to Form a Complete Circuit Pulse generator: power source or battery Lead Leads or wires Cathode (negative electrode) Anode (positive electrode) Body tissue IPG Anode Cathode 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 Battery Leads Are Insulated Wires That: Deliver electrical impulses from the pulse generator to the heart Sense cardiac depolarization Lead Types of Leads Endocardial or transvenous leads Myocardial/Epicardial leads Transvenous Leads Have Different “Fixation” Mechanisms Passive fixation – The tines become lodged in the trabeculae (fibrous meshwork) of the heart Transvenous Leads Active Fixation – The helix (or screw) extends into the endocardial tissue – Allows for lead positioning anywhere in the heart’s chamber Myocardial and Epicardial Leads Leads applied directly to the heart – Fixation mechanisms include: Epicardial stab-in Myocardial screw-in Suture-on Cathode An electrode that is in contact with the heart tissue Negatively charged when electrical current is flowing Cathode Anode An electrode that receives the electrical impulse after depolarization of cardiac tissue Positively charged when electrical current is flowing Anode Conduction Pathways Body tissues and fluids are part of the conduction pathway between the anode and cathode Anode Tissue Cathode During Pacing, the Impulse: Begins in the pulse generator Flows through the lead and the cathode (–) Stimulates the heart Returns to the anode (+) Impulse onset * 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 Cathode 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 Anode Cathode Unipolar and Bipolar Leads 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 Bipolar leads Bipolar leads are less susceptible to oversensing noncardiac signals (myopotentials and EMI) Coaxial Lead Design Lead Insulation May Be Silicone or Polyurethane Advantages of Silicone-Insulated Leads Inert Biocompatible Biostable Repairable with medical adhesive Historically very reliable Advantages of Polyurethane-Insulated Leads Biocompatible High tear strength Low friction coefficient Smaller lead diameter A Brief History of Pacemakers Single-Chamber and Dual-Chamber Pacing Systems Single-Chamber System The pacing lead is implanted in the atrium or ventricle, depending on the chamber to be paced and sensed Paced Rhythm Recognition AAI / 60 Paced Rhythm Recognition VVI / 60 Advantages and Disadvantages of Single-Chamber Pacing Systems Advantages Disadvantages 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 Dual-Chamber Systems Have Two Leads: One lead implanted in the atrium One lead implanted in the ventricle Paced Rhythm Recognition DDD / 60 / 120 Paced Rhythm Recognition DDD / 60 / 120 Paced Rhythm Recognition DDD / 60 / 120 Paced Rhythm Recognition DDD / 60 / 120 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 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. 9462 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. 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. Continued in Basic Pacing Concepts Parts II and III
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