Applying Electrical Concepts to Pacemakers Module 4

Applying Electrical Concepts to Pacemakers Module 4
Student Notes This 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 Notes This module should take approximately 1.5 hours to complete. To deliver this module, the following materials are recommended: Printed participant guides for each participant Overhead projector and screen Optional: Whiteboard or flip chart While 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 Headquarters Medtronic, Inc. 710 Medtronic Parkway Minneapolis, MN USA Internet: Tel: (763) Europe Medtronic International Trading Sàrl Route du Molliau Ch Tolochenaz Switzerland Tel: (41 21) Asia-Pacific Medtronic International, Ltd. 16/F Manulife Plaza The Lee Gardens, 33 Hysan Avenue Causeway Bay Hong Kong Tel: (852) Canada Medtronic of Canada Ltd. 6733 Kitimat Road Mississauga, Ontario L5N 1W3 Tel: (905) Toll-free: 1 (800) Medtronic USA, Inc. Toll-free: 1 (800) (24-hour technical support for physicians and medical professionals) Latin America Medtronic USA, Inc. Doral Corporate Center II 3750 NW 87th Avenue Suite 700 Miami, FL 33178 USA Tel: (305) UC d EN Medtronic, Inc. Minneapolis, MN December 2007

Upon completion you will be able to:
Objectives Upon completion you will be able to: Recognize a high impedance condition Recognize a low impedance condition Recognize capture threshold Determine which sensitivity value is more (or less) sensitive Student Notes Meeting these objectives is imperative so you will have the ability to manage the electric interface between the cardiac device and the patient. Instructor Notes

Electrical Information
Why is this electrical information relevant? A pacemaker is implanted to: Provide a heart rate to meet metabolic needs In order to pace the heart, it must capture the myocardium In order to pace the heart, it must know when to pace, i.e., it must be able to sense A pacemaker requires an intact electrical circuit Student Notes As 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 paces Know when (and when not) to pace This requires an electrical circuit. In order to make informed decisions regarding device evaluation and programming, this basic knowledge is necessary. Instructor Notes

Ohm’s Law Relevance to Pacemaker Patients
High impedance conditions reduce battery current drain Can increase pacemaker battery longevity Why? R = V/I If “R” increases and “V” remains the same, then “I” must decrease Low impedance conditions increase battery current drain Can decrease pacemaker battery longevity R = V/I If “R” decreases and “V” remains the same, then “I” must increase Student Notes A 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 Notes Ask: So, are all high-impedance conditions a good thing? No, there are conditions that are issues. These will be discussed on upcoming slides.

The Effect of Lead Performance on Myocardial Capture
What would you expect to happen if a lead was partially fractured? Impedance (or Resistance) would rise Current 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 Notes Are 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

High Impedance Conditions A Fractured Conductor
A fractured wire can cause Impedance values to rise Current flow from the battery may be too low to be effective Impedance values may exceed 3,000 W Lead wire fracture Increased resistance Student Notes An 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 flow Impedance number will be “infinite,” or 9999 Ohms When 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 Notes Other reason for high impedance: Lead not seated properly in pacemaker header.

Lead Impedance Values Change as a Result of:
Wire fractures Insulation breaks Typically, normal impedance reading values range from 300 to 1,000 W Some leads are high impedance by design. These leads will normally show impedance reading values greater than 1,000 ohms Medtronic High Impedance leads are: CapSure® Z CapSure® Z Novus Student Notes Insulation failures also have other consequences for patient safety and the pacing system, which we’ll discuss a little later on. Instructor Notes Ask: If an insulation break occurs, but the conductor remains intact, what do you think will happen to the Impedance? The impedance will drop Ask: 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

Low Impedance Conditions
Insulation breaks expose the lead wire to the following Body fluids, which have a low resistance, or Another lead wire (in a bipolar lead) Insulation break that exposes a conductor causes the following Impedance values to fall Current to drain through the insulation break into the body, or into the other wire Potential for loss of capture More rapid battery depletion Student Notes Insulation 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 Notes Current will follow the path of LEAST resistance

Ventricular pacemaker 60 ppm
Capture Threshold The minimum electrical stimulus needed to consistently capture the heart outside of the heart’s own refractory period Ventricular pacemaker 60 ppm Capture Non-Capture Student Notes Let’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 Notes Ask: 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 origin This may by also normal sinus rhythm with a bundle branch block Ask: 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 rate If it is normal sinus rhythm with a bundle branch block, then it is normal AV conduction

Effect of Lead Design on Capture
Lead maturation Fibrotic “capsule” develops around the electrode following lead implantation May gradually raise threshold Usually no measurable effect on impedance Student Notes Once 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 low The 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 threshold1 The 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 Notes Ask: What fixation mechanism is shown in the graphic? Passive fixation

Steroid Eluting Leads Steroid eluting leads reduce the inflammatory process Exhibit little to no acute stimulation threshold peaking Leads maintain low chronic thresholds Silicone rubber plug containing steroid Tines for stable fixation Porous, platinized tip for steroid elution Student Notes Steroid 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

Effect of Steroid on Stimulation Thresholds
Pulse Width = 0.5 msec 3 6 Implant Time (Weeks) Textured Metal Electrode Smooth Metal Electrode 1 2 4 5 Steroid-Eluting Electrode 7 8 9 10 11 12 Volts Student Notes This 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 electrode Traditionally, 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. Ellenbogen Instructor Notes Ask: So, why is this clinically relevant? During the first several weeks after implant, a pacing safety margin is applied than for a chronic lead References: Pacing Reference Guide, Bakken Education Center, 1995, UC aEN. Cardiac Pacing, 2nd Edition, Edited by Kenneth A. Ellenbogen

Myocardial Capture Capture is a function of:
Amplitude—the strength of the impulse expressed in volts The 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 margin Pulse width—the duration of the current flow expressed in milliseconds The pulse width must be long enough for depolarization to disperse to the surrounding tissue Student Notes Voltage 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

Comparison 5.0 Volt Amplitude at Different Pulse Widths
Amplitude5.0 V 0.25 ms 1.0 ms 0.5 ms Student Notes The 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). BUT The 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

The Strength-Duration Curve
The strength-duration curve illustrates the relationship of amplitude and pulse width Any combination of pulse width and voltage, on or above the curve, will result in capture .50 1.0 1.5 2.0 .25 Chronaxie Capture Volts Rheobase Student Notes The 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 Notes No Capture 0.5 1.0 1.5 Pulse Width

Clinical 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 systems Thresholds fluctuate slightly daily Thresholds can change due to metabolic conditions or medications 2.0 X Programmed Output 1.5 Stimulation Threshold (Volts) 1.0 .50 Student Notes There 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 .25 0.5 1.0 1.5 Duration Pulse Width (ms)

Programming Outputs Primary goal: Ensure patient safety and appropriate device performance Secondary goal: Extend the service life of the battery Typically program amplitude to < 2.5 V, but always maintain adequate safety margins A common output value might be 2.0 V at 0.4 ms Amplitude values greater than the cell capacity of the pacemaker battery (usually about 2.8 V) require a voltage multiplier, resulting in markedly decreased battery longevity Student Notes In 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

Pacemaker Sensing Refers to the ability of the pacemaker to “see” signals Expressed in millivolts (mV) The millivolts (mV) refers to the size of the signal the pacemaker is able to “see” 0.5 mV signal 2.0 mV signal Student Notes Intrinsic 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

Sensitivity The Value Programmed into the IPG
5.0 mV 2.5 mV 1.25 mV Student Notes The 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 Notes Time

Time 5.0 mV 2.5 mV 1.25 mV 5 mV sensitivity Student Notes A 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 Notes At this value the pacemaker will not see the 3.0 mV signal

1.25 mV Sensitivity Time 5.0 mV 2.5 mV 1.25 mV But what about this? Student Notes In 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 Notes Ask: If the pacemaker is oversensing, do you increase or decrease the sensitivity? Decrease the sensitivity by programming a higher value At 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?

Sensing Amplifiers/Filters
Accurate sensing requires that extraneous signals are filtered out Because whatever a pacemaker senses is by definition a P- or an R-wave Sensing amplifiers use filters that allow appropriate sensing of P- and R-waves, and reject inappropriate signals Unwanted 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 Notes The 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 Notes In 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.

Sensing Accuracy Affected by: Pacemaker circuit (lead) integrity
Insulation break Wire fracture The characteristics of the electrode Electrode placement within the heart The sensing amplifiers of the pacemaker Lead polarity (unipolar vs. bipolar) The electrophysiological properties of the myocardium EMI – Electromagnetic Interference Student Notes A 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

Lead Conductor Coil Integrity Affect on Sensing
Undersensing occurs when the cardiac signal is unable to get back to the pacemaker Intrinsic signals cannot cross the wire fracture Oversensing occurs when the severed ends of the wire intermittently make contact Creates signals interpreted by the pacemaker as P- or R-waves Student Notes Lead 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

Lead Insulation Integrity Affect on Sensing
Undersensing occurs when inner and outer conductor coils are in continuous contact Signals from intrinsic beats are reduced at the sense amplifier, and amplitude no longer meets the programmed sensing value Oversensing occurs when inner and outer conductor coils make intermittent contact Signals are incorrectly interpreted as P- or R-waves Student Notes Lead 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

Where is the sensing circuit?
Unipolar Pacemaker Where is the sensing circuit? Anode Click for Answer Student Notes Another 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 Notes Lead tip to can This can produce a large potential difference (signal) because the cathode and anode are far apart _ Cathode

Bipolar Pacemaker Where is the sensing circuit? Click for Answer
Lead tip to ring on the lead This usually produces a smaller potential difference due to the short inter-electrode distance But, electrical signals from outside the heart (such as myopotentials) are less likely to be sensed Student Notes In 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) Afterpotentials Far-field intracardiac signals Noise EMI Instructor Notes We’ll discuss more details on uni-and bi-polar systems in more detail later Anode and Cathode

Cardiac 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 Notes Instructor Notes Auto-animated slide

Vectors and Gradients Sense Click for More
2.5 mV Click for More Student Notes A 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 Notes Auto-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.

Changing the Vector Sense Click for More
2.5 mV Click for More Student Notes The 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 Notes Auto-animated slide A 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.

Putting It All Together
Appropriate output programming can improve device longevity But, do not compromise patient safety! Lead design can improve device longevity via Steroid eluting leads Can help keep chronic pacing thresholds low by reducing inflammation and scarring High Impedance leads Medtronic CapSure Z and Medtronic CapSure Z Novus Designed so electrode W is high, but V low so current (I) is low as well, reducing battery drain Control of manufacturing Batteries, circuit boards, capacitors, etc., specific to needs, can lead to improved efficiencies and lowered static current drain Highly reliable lead design Student Notes Instructor Notes

Putting It All Together
Pacemaker Longevity is: A function of programmed parameters (rate, output, % time pacing) A function of useful battery capacity A function of Static current drain Circuit efficiency Output Impedance The lower the programmed sensitivity the MORE sensitive the device Lead integrity also affects sensing Student Notes Instructor Notes We’ll discuss optimum device programming later Physiologic pacing Safety margins

Status Check Determine the threshold amplitude Click for Answer
0.75 V 0.05 V 1.25 V 1.00 V Click for Answer Student Notes Instructor Notes Now let’s practice what you have learned. Capture threshold = lowest value with consist capture This is at 1.25 V

Status Check Which of these pacemakers is more sensitive? OR
Pacemaker A Pacemaker B OR Programmed Sensitivity 2.5 mV Programmed Sensitivity 0.5 mV Student Notes Instructor Notes Click for Answer Pacemaker A is able to “see” signals as small as 0.5 mV. Thus, it is more sensitive.

Status Check A pacemaker lead must flex and move as the heart beats. On average, how many times does a heart beat in 1 year? Click for Answer 35 MILLION times. It is not a simple task to design a lead that is small, reliable, and lasts a lifetime. Student Notes Instructor Notes

Status Check Do you notice anything on this x-ray? Lead Fracture:
Click for Answer Lead Fracture: High Impedance Possible failure to capture myocardium Student Notes Instructor Notes

Status Check What would you expect?
Which value is out of range? What could have caused this? Pacemaker Interrogation Report Mode: DDDR Lower: Rate 60 ppm UTR: 130 ppm USR: 130 ppm Atrial Lead Impedance: 475 Ohms Ventricular Lead Impedance: 195 Ohms Click for Answer Insulation failure Student Notes Instructor Notes

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. Contraindications IPGs 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.

Brief Statements (continued)
Warnings/Precautions Changes 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 complications Potential 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 at Caution: Federal law (USA) restricts these devices to sale by or on the order of a physician.

Brief Statement: Medtronic Leads
Indications Medtronic 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 indicated Contraindications Medtronic 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.

Brief Statement: Medtronic Leads (continued)
Warnings/Precautions People 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 Complications Potential 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 at Caution: Federal law (USA) restricts this device to sale by or on the order of a physician.

Disclosure 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.

Applying Electrical Concepts to Pacemakers Module 4

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Applying Electrical Concepts to Pacemakers Module 4

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