Components of Pacemaker and ICDs - understanding the hardware

Pacemaker and ICDs - structure and hardware

1. Components of cardiac pacing and ICD- Understand the hardware Dr Raghu Kishore Galla

2. History: 1700 ’ s Cardiac electrostimulation began in the mid-18 th century with the use of currents from the Leyden jar or Voltaic Pile ( Allessandra Volta, 1799) to stimulate cardiac nerves and muscles in animals and to attempt resuscitation of intact dead animals.

3. History: 1800 ’ s Dr.DeSanctis used “ Re-animation Chair. ” as described by Richmond Reece in his The Medical Guide (1820). It had 3 pertinent features: a bellows to give forced ventilation, a metallic tube to be inserted into the esophagus and a voltaic pile attached at one pole to the esophageal tube and at the other to an electrode. The electrode was to be successively touched to “ the regions of the heart, the diaphragm and the stomach….

4. History: 1900 ’ s In 1899, Prevost and Battelli demonstrated that electrical currents could cause ventricular fibrillation that often could be reversed by another powerful stimulus of either alternating or direct current. Robinvitch in a series of reports from 1907 through 1909 confirmed this work and designed the first portable electrical resuscitative apparatus for ambulances.

5. 1905 – Einthoven Published first human AV block using string galvanometer

6. History: 1930 ’ s In 1932, Albert Hyman developed a machine for controlled repetitive electrostimulation of heart and named his device the “ artificial cardiac pacemaker”

7. 1950 - John Hopps - Canadian electrical engineer paired with Dr. Wilfred Bigelow to create a pacemaker that could be used for long periods and treat many of the new dysarhythmias that had been discovered. The device that sat on a tabletop was large and heavy.

8. 1951 - Dr. Paul Zoll a cardiologist from Boston created pacemaker using modern transistors but still was large, heavy and relied on AC power. Despite these shortfalls the Zoll pacemaker remained a standard for pacing patients for several years.

9. History: 1950’s The first clinical implantation into a human of a fully implantable pacemaker was in 1958 at the Karolinska Institute in Solna , Sweden, using a pacemaker designed by Rune Elmqvist and surgeon Åke Senning . It connected to electrodes attached to the myocardium of the heart by thoracotomy . The device failed after three hours. A second device was then implanted which lasted for two days.

10. The world's first implantable pacemaker patient, Arne Larsson , went on to receive 5 different lead systems and 22 pulse generators of 11 different models of pacemakers during his lifetime. He died in 2001 with cancer, at the age of 86, outliving the inventor as well as the surgeon

11. 1960 – First atrial triggered pacemaker 1964 – First on demand pacemaker (DVI) 1977 – First atrial and ventricular demand pacing (DDD) 1980 – Griffin published first successful pacemaker intervention for supraventricular tachycardias

12. 1981 – Rate responsive pacing by QT interval, respiration, and movement 1994 – Cardiac resynchronization pacing 1998 – Automatic capture detection 2016 - Leadless pacemaker Now Approximately 3 million with pacemakers Approximately 1 million with ICD device

13. Introduction Modern day pacemakers serve the primary function of either maintaining a minimum heart rate to avoid symptomatic or potentially life-threatening brady or tachyarrhythmias or offering resynchronization between the left and right ventricles in the setting of heart failure. Multiple advances in device design, programming, sensor technology, and materials science have afforded the ability to offer an ever-widening range of devices with a variety of specialized features.

14. Pacemaker 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

15. Basic Concepts of Pacing Cardiac myocytes may be “activated” by the delivery of an electrical pacing stimulus. This stimulus creates an electrical field that allows for the generation of a self-propagating wave front of action potentials that may then advance from the stimulation site. The minimum amplitude and duration required to generate the self-propagating wave front that results in cardiac activation is referred to as the threshold .

16. In order to provide for consistent myocardial stimulation, there needs to be a constant source of energy for pulse delivery, which is provided by the pulse generator , a conductor that will deliver the stimulus from the source, which is the lead itself, an electrode at the end of the conductor that delivers the pulse, and underlying myocardium that is excitable. Failure at any of these points (e.g. due to fracture in the lead or loss of contact between the electrode and the underlying myocardium) will result in failure of myocardial stimulation. Currently available pacing systems comprise a pulse generator and one or more pacemaker leads with lead tips positioned in the cardiac chamber of interest. Basic Concepts of Pacing

17. Basic Concepts of Pacing Sensing of local electrograms (EGMs) is essential to the proper function of permanent pacemakers. Whether sensing takes place in a unipolar or bipolar system and despite the differences between the two, the principles of sensing remain the same. Two electrodes, a cathode and an anode, are required to complete the electrical circuit between the body and the pacemaker. In a bipolar system, both anode and cathode are located in the heart, whereas in a unipolar system only the cathode is located in the heart and the pacemaker generator can serve as the anode.

18. Basic Concepts of Pacing As a wavefront of depolarization travels toward an endocardial electrode in contact with resting myocardium, the electrode becomes positively charged relative to the depolarized region. This is manifest in the intracardiac EGM as a positive deflection. As the wave front of depolarization passes under the recording electrode, the outside of the cell suddenly becomes negatively charged relative to resting myocardium, and a brisk negative deflection is seen in the intracardiac EGM. The positive and negative deflections that precede and follow the intrinsic deflection represent activation in neighboring regions of myocardium relative to the recording electrode.

19. Basic Concepts of Pacing A typical bipolar ventricular electrogram (EGM) in a normal individual. The sharp downward deflection in the EGM represents the intrinsic deflection and indicates the moment of activation under the recording electrode. The slope of the intrinsic deflection ( dV / dt ) is expressed in volts per second and is referred to as the slew rate. For an EGM to be sensed by a sensing amplifier, the amplitude and slew rate must exceed the sensing thresholds .

20. Bipolar Versus Unipolar Stimulation Modern lead design has largely eliminated any significant clinical difference between bipolar and unipolar stimulation, but some inherent differences remain. Historically, the unipolar threshold was lower than the bipolar threshold in the same system due to a markedly larger anode and resulting reduced impedance in the unipolar system. With the contemporary lead tip design, this difference is attenuated as impedance is mainly determined by the lead tip properties.

21. Bipolar Versus Unipolar Stimulation The clinically important implication of unipolar pacing is that the pacemaker generator may cause pectoral muscle stimulation (muscle twitching) if implanted adjacent to the pectoral muscle. Because the distance between the cathode and anode is so much greater during unipolar pacing, the pacing stimulus on the surface ECG is also much larger than during bipolar pacing. The increased size of the “pacer spike” may be visually helpful to determine proper pacemaker function when interpreting cardiac telemetry recordings or trans-telephonic ECG tracings during remote pacemaker monitoring.

22. Bipolar Versus Unipolar Stimulation The larger amplitude signal from unipolar pacing is far more likely to interfere with appropriate sensing of the cardiac rhythm by an ICD in the rare instance that a patient has a separate pacemaker and ICD implanted. Specifically, a sensed large-amplitude unipolar pacing stimulus will result in subsequent under-detection of low-amplitude intracardiac signals, such as those that occur during ventricular fibrillation. It is for this reason that the use of bipolar pacing is critical when a separate pacemaker is present in an ICD patient. Bipolar pacing leads are also necessary for some rate-adaptive sensors , such as the minute-ventilation sensor, as well as for some types of automatic threshold algorithms, where the ring electrode is used to sense myocardial capture.

23. Bipolar Versus Unipolar Stimulation Due to the much smaller field of view, bipolar electrodes tend to be minimally influenced by electrical signals that originate outside the heart , while unipolar leads may detect electrical signals that originate near the pulse generator pocket. Thus, unipolar sensing is more susceptible to interference from electrical signals originating in skeletal muscle (myopotentials), which can result in inappropriate inhibition of pacing (if sensed in the ventricular channel) or triggering of pacing output (if sensed in the atrial channel). Thus, bipolar sensing is less prone to oversensing myopotentials, far-field cardiac signals, or electromagnetic interference from environmental sources. Shielding of the device and signal processing in the pacemaker circuitry, such as rectification and filtering of lower or higher frequency components, also help to attenuate recording of unwanted sign

24. Single-Chamber System : The pacing lead is implanted in the atrium or ventricle, depending on the chamber to be paced and sensed Advantages : Implantation of a single lead. Disadvantages : Single ventricular lead does not provide AV synchrony. Single atrial lead does not provide ventricular backup if A-to-V conduction is lost

25. Dual-Chamber System : Have Two Leads One lead implanted in the atrium One lead implanted in the ventricle

26. Benefits of Dual Chamber Pacing : Provides AV synchrony Lower incidence of atrial fibrillation Lower risk of systemic embolism and stroke Lower incidence of new congestive heart failure Lower mortality and higher survival rates

27. Pacemaker Components 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

28. Schematic of the typical circuits found in modern pacemakers

29. The Pulse Generator Contains a battery that provides the energy for sending electrical impulses to the heart Houses the circuitry that controls pacemaker operations

30. Battery A battery converts chemical energy into electrical energy. The source of this energy is the electrochemical reactions that occur within the battery. During a spontaneous chemical reaction, substances react to form more stable products. Redox reactions: types of reactions in which oxidation and reduction occur. They are called  redox reactions  because electrons are transferred from one reactant to another. 2Li + I 2  2LiI

31. Battery The major parts of a battery are the anode, the cathode, and the electrolyte. The anode and cathode must be physically separated and both must be in contact with the electrolyte

32. Battery In a spontaneous galvanic cell such as a battery, the anode is electrically negative and the cathode positive. In nonspontaneous electrochemical reactions, such as those that occur at pacing electrodes, electrochemical reactions are driven by an externally applied voltage. In this case  oxidation (loss of electrons) will occur at the positive electrode and  reduction  (gain of electrons) at the negative electrode. Thus for pacing electrodes, the anode is positive and the cathode is negative. The polarities are reversed, but the underlying electrochemical processes defining anode and cathode, namely, oxidation and reduction, respectively, are the same

33. Electrolyte The anode and the cathode must be separated from each other so they cannot directly react with one another, but they also need to be connected by an ionically conducting medium called the  electrolyte . As the battery discharges, it furnishes electrons at one terminal, pushes them through an external circuit, and receives them back at a second terminal. The electrolyte allows electrical charge, as ions, to flow within the battery, completing the circuit. The electrolyte must conduct ions but not electrons.

34. Separator The  separator  is a structural member of the battery that keeps the anode and cathode materials physically apart, thus preventing shorting of the battery. In batteries with liquid electrolytes, the separator is usually a porous polymer film that is immersed in and permeated by the electrolyte. In the case of lithium/iodine batteries, traditionally used for pacemakers, the separator and electrolyte are one and the same, namely, the growing layer of solid, ionically conductive lithium iodide discharge product.

35. Current Collector The  current collector  makes the connection between the positive or negative terminal of the battery and its respective active electrode material inside the cell. It is usually a wire connected to a screen, or grid, which is embedded in the anode or cathode material. The current collector may also serve as a structural member of the battery to provide physical integrity and strength to that electrode.

36. Sealing of Batteries Batteries are well sealed, most often in hermetically welded containers with glass electrical feedthroughs to make the electrical connections between the inside and the outside of the battery. Sealing is necessary to prevent any interchanges of materials between the battery and its surroundings. Medical batteries are typically considered hermetically sealed if the leak rate out of the battery for a test gas, usually helium, is less than 1 × 10 −7  cm 3 /sec at one atmosphere pressure difference between the inside and the outside of the battery.

37. Types of Batteries Primary Batteries can only be used once. not designed to be recharged Most batteries used to power modern implantable medical devices are primary batteries that use lithium anodes because such batteries have very high energy densities. Secondary Batteries Designed to be repetitively discharged and recharged. Eg : Lithium-ion batteries – use in LVADs, and implantable neurologic stimulators for control of chronic pain. Although they are not currently in development for pacemakers and ICDs, features such as more frequent telemetry could cause manufacturers to reconsider lithium-ion battery use in cardiac applications in the futu re.

38. Implantable Battery Design Requirements The most important requirement in battery selection for implantable devices is high reliability . Other significant factors include the desired longevity of the device (directly related to battery energy density, circuit design, and overall device size) and an appropriate indication of impending battery depletion ( end-of-service warning) . The basic considerations when designing a battery for an implantable medical device include the current variations that can be expected from the circuit as the device provides its service for individual patients. Once the range of these application requirements are defined, the current, voltage, and capacity requirements of the battery can be determined.

39. Elective Replacement Indicator(ERI) All modern implantable pulse generators have an ERI that alerts the clinician to impending battery depletion and allows adequate time for replacement of the device. Typically, this indicator is designed to occur at least 3 months before the battery voltage drops to a level that would result in erratic pacing, loss of capture, or loss of other critical features. Many newer devices conform to CENELEC standards (European Committee for Electrotechnical Standardization). For pacemakers, the standard requires a recommended replacement time (RRT) such that at least 95% of the devices will have a prolonged service period (PSP) of at least 180 days. For ICD and CRT devices, the requirement is that at least 95% of the devices have a PSP of at least 90 days

40. Battery Chemistries Used in Pacemakers The Lithium/Iodine Battery In general, lithium/iodine batteries have a single, central lithium anode that is surrounded by cathode material which is at least 96% iodine and has been thermally reacted with a polymer material to render a conductive mixture.  Central anode with an embedded current collector wire and the iodine cathode that fills much of the volume inside the battery . 

41. The Lithium/Carbon Monofluoride Battery: CF x is a cathode material with high capacity and moderate power capability. The CF x material is a powder that is mixed with carbon as a conductivity enhancer plus a polymer binder and then pressed into a porous pellet. The battery is composed of a lithium anode, a porous polymer separator material, and the porous pressed-powder cathode pellet that are all inserted into a case which is welded closed. In contrast to the lithium/iodine battery, the lithium/ CF x battery uses a liquid electrolyte that consists of a lithium salt dissolved in an organic solvent Voltage decline near end of battery life tends to be fairly abrupt, making it challenging for device manufacturers to engineer means of maintaining adequate replacement time warning.

42. The Lithium/Hybrid Cathode Battery: A new lithium battery chemistry with a cathode comprised of silver vanadium oxide (SVO), plus CF x , has been developed to meet the needs of implantable devices with higher rate therapies and features. SVO has high power capability and is the same cathode material used to power ICDs. The blend of the two cathode materials, called a hybrid cathode , yields a primary battery that has an energy density equal to that of a lithium/iodine battery with approximately 100 times more power capability.

43. The Lithium/Manganese Dioxide Battery Lithium/manganese dioxide batteries are being used in a new generation of pacemakers commercialized by one manufacturer. Manganese dioxide possesses good energy and power density characteristics and shows low self-discharge. As lithium/manganese dioxide batteries demonstrate greater power capability in comparison to lithium/iodine batteries, devices that require higher power, such as wireless telemetry capable of communicating over longer distances, can be successfully powered

44. Miniature Batteries for Leadless Devices Leadless pacemakers are powered by a cylindrical, pin-style, lithium metal based primary battery that typically contains a monolithic, thick cathode with adequate electrode area. Provide sufficient power for background electronics, stimulation, and low-power telemetry, while maintaining high energy density to achieve longevity on par with traditional pacemakers. Another distinguishing feature of the miniature batteries used in leadless pacemakers is that the battery may not be fully enclosed in a titanium (device) case as in traditional pacemakers; Instead, the battery may be welded to the end of the container housing the electronics and the fixation mechanism, such that the battery enclosure may be in direct contact with the body fluids.

45. Microprocessors Microprocessors have become the standard control circuits of implantable pacemakers and ICDs. Microprocessors have several advantages over older integrated circuits, including a far greater circuit density and greatly reduced current drain. Microprocessors also allow very sophisticated algorithms, requiring multiple calculations, to be incorporated into implantable devices, and have vastly increased data storage. The microprocessor can respond to changes in programming instructions that allow functions to be added or changed after implantation. The integrated circuit of pulse generators may contain both read-only memory (ROM) and random access memory (RAM).

46. Microprocessors ROM (typically 256 KB to 1 MB) is used to guide the sensing and output circuits. In addition, RAM is used to store diagnostic information regarding pacing rate, intrinsic heart rates, and sensor output. The amount of RAM (1–16 MB) included in the pulse generator varies between models and manufacturers, but has rapidly increased in modern pulse generators, allowing for a far greater amount of diagnostic information to be stored. The rapidly expanding diagnostic capabilities of pacemakers has allowed for improved assessment of the physiological condition of the patient, including stored information about heart rate variability, respiration, intracardiac pressure, patient activity, lung water, and arrhythmia logs .

47. Output circuit The output circuit contains the output section and voltage multipliers. Pacing outputs of greater than the specified voltage of a cell are achieved by a variety of methods. One approach is to use capacitors located on the output circuits. These capacitors are charged by the battery in parallel, but then discharged in series. Multiple capacitors can be used to achieve the desired output voltages. An alternative approach to capacitor-based voltage multipliers is to use the electromagnetic principle of inductance.

48. Sensing circuit The intracardiac EGM is conducted from the electrodes to the sensing circuit of the PG, where it is amplified and filtered. The intracardiac EGM is filtered to remove unwanted frequencies, a process that markedly affects the amplitude of the processed signal. Following filtering of the intracardiac signal, the processed signal is compared with a reference voltage to determine if the signal exceeds a threshold detection level (programmed sensitivity). Signals with amplitudes greater than the sensitivity threshold level are sensed as intracardiac events, whereas signals of lower amplitude are discarded as noise . Signals that exceed the threshold level are sent to the timing circuit and logic circuits.

49. Sensing circuit Most permanent pacemakers also contain noise reversion circuits that change the pulse generator to an asynchronous pacing mode when the sensing threshold level is exceeded at a rate faster than the noise reversion rate. The noise reversion mode prevents inhibition of pacing in the presence of electro magnetic interference. The sensing amplifier must prevent the detection of unwanted intracardiac signals, such as far-field R waves in the atrial EGM, afterpotentials, T waves, and retrogradely conducted P waves.

50. Timing circuit The pacing cycle length, sensing refractory and alert periods, pulse duration and AV interval are precisely regulated by the timing circuit of the pulse generator. The timing circuit of a pulse generator is a crystal oscillator that generates a very accurate signal with a frequency in the kilo Hertz range. The output of the crystal oscillator is sent to a digital timing and logic control circuit that operates internally generated clocks at divisions of the oscillator frequency. The output of the logic control circuit is a logic pulse that triggers the output pacing pulse, the blanking and refractory intervals, and the AV delay.

51. Timing circuit The timing circuit also receives input from the sense amplifier to reset the escape intervals of an inhibited pacing system or trigger initiation of an AV delay for triggered pacing modes. The pulse generator also contains a rate limiting circuit that prevents the pacing rate from exceeding an upper limit in the case of a random component failure. This runaway protection rate is typically in the range of 180–200 ppm .

52. Magnet mode Pacemakers and some ICDs have a reed switch which normally is open until a magnet or magnetic field [e.g. a magnetic resonance imaging (MRI) scanner] comes into close contact with the device. The magnet will close the reed switch and the device will be switched to the “magnet mode.” The magnet mode typically causes asynchronous pacing for a pacemaker (e.g. VOO, DOO, AOO) and deactivation of tachycardia therapy for most defibrillators, but bradycardia pacing and sensing functions are typically not affected. The magnet may be unable to close the reed switch if it is not powerful enough or the magnet function is programmed “off.” In contemporary devices (some pacemakers and most ICDs), other technology, such as the Hall effect sensor, integrated solid-state detection, or GMR sensor, is used in place of the reed switch to optimize response to the magnetic

53. Rate Responsive Pacing Sensors: When the need for oxygenated blood increases, the pacemaker ensures that the heart rate increases to provide additional cardiac output There are several different types of sensors that may be employed in pacemakers. Most commonly, sensors work to augment heart rate in response to physical activity, whether by detecting patient movement or changes in respiratory rate. Those most accepted in the market place are: Activity sensors that detect physical movement and increase the rate according to the level of activity Minute ventilation sensors that measure the change in respiration rate and tidal volume via transthoracic impedance readings

54. Types of sensors Using technology that detects changes in vibration, acceleration, or minute ventilation, pacemakers may be pre-programmed to induce concomitant changes in the paced rate if the physiological heart rate does not meet those parameters. Other sensors may use sensitivity to temperature, QT interval, or local myocardial contractility to respond to conditions under which increases in heart rate are desired, but for which sensors that detect only changes in physical activity would be inadequate.

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

56. During Pacing, the Impulse: Begins in the pulse generator Flows through the lead and the cathode (–) Stimulates the heart Returns to the anode (+)

57. Components of pacemakers leads Electrodes Conductors Insulation Connector pin Fixation mechanism

58. 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)

59. Unipolar leads Simplest lead design of all the leads have only one conductor surrounded by insulation. Tip of the lead is the cathode and the PG is the anode. Largely replaced by bipolar lead designs for most of the endocardial applications. Still commonly used in CS branches for CRT Demonstated impressive longevity and many are still in service today

60. 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

61. Bipolar lead PG is not the part of pace/sense circuit. Both the ring electrode(anode) and the tip electrode(cathode) are in contact with the myocardium Can be used for endocardial, CS and epicardial applications. Two main bipolar lead designs – Co-axial Co-radial

62. Types of lead design A) Coaxial lead body design consists of two nested coil conductors to the tip and ring electrodes, each wrapped in a separate layer of insulation. The inner coil connects to the tip cathode and contains a central lumen for stylet passage; the outer coil connects to the ring anode.can be attached to endocardium via active/passive fixing mechanisms but limited by large diameters B) In coradial design, a single coil contains the parallel conductor strands to the tip and ring electrodes, with each strand covered by a fluoropolymer (ETFE) insulator. A surrounding layer of outer insulation by polyurethane covers the lead body.Design can allow significantly smaller (<6F) diameters but limits the fixation mechanism.

63. ICD leads Defibrillator leads have greater complexity, with two, three, or four conductors that connect to the pacing/sensing electrodes as well as to the high-voltage shocking coil(s), depending on the specific type of lead. Because of the prohibitive bulk that would result from a coaxial design with more than two conductors, ICD leads generally have a different type of structure, known as a multilumen design . This type of ICD lead consists of a long cylinder of insulating material, with separate internal channels running down its length. Each conductor runs down an individual channel, usually with its own additional covering tube of insulation.

64. ICD leads Multilumen ICD lead design consists of a single body of insulation with several internal channels that contain the conductor elements (central pace/sense coil and outer high-voltage cables), each covered by its own layer of fluoropolymer insulation. A surrounding layer of outer polyurethane-based insulation is present. HP, High-performance.

65. ICD lead - Structural Overview Right ventricular (RV) defibrillation leads comprise a distal tip electrode with a fixation mechanism that anchors the lead to the heart, proximal terminals that connect to the generator, and a lead body that connects the two. The lead body consists of a flexible insulating cylinder with 3 to 6 parallel longitudinal lumens through which conductors run from the proximal terminals to small pace-sense electrodes and larger shock coil electrodes. This multilumen design permits more conductors in smaller-diameter leads than older coaxial designs. The subcutaneous ICD uses a parasternal electrode in which the larger shock coil is straddled by 2 small sensing electrodes. ICD leads differ in number of shock coils, number of sensing electrodes, and type of connector terminals.

66. Dual-Coil Versus Single-Coil Leads All transvenous leads have a distal shock coil in the RV. Dual coil leads have an additional proximal shock coil, which usually lies in the superior vena cava. Dual-coil leads were required for the first transvenous ICD systems, which preceded those in which the housing (can) of the generator served as a defibrillation electrode (active can). With contemporary biphasic waveforms and active cans, differences in defibrillation efficacy between dual-coil and single-coil shock pathways are rarely clinically significant for left-pectoral implants.

67. Dual-Coil Versus Single-Coil Leads The principal disadvantage of dual-coil leads is greater risk of extraction because of fibrotic tissue ingrowth into the proximal coil. An additional disadvantage is the possibility of a short between high-voltage elements of opposite polarity. However, dual-coil leads retain advantages, including more reliable atrial cardioversion , coil-coil electrograms for morphology algorithms that discriminate VT from SVT, and proximal coil-can EGMs that display atrial signals to improve interpretation of single-chamber EGMs .

68. Integrated Versus True Bipolar Sensing Sensing can either be true bipolar between the tip electrode and a small ring electrode or integrated bipolar between the tip electrode and RV coil. Modern integrated bipolar and true bipolar leads have similar performance for sensing ventricular fibrillation (VF) but differ in susceptibility to oversensing . The larger integrated bipolar antenna is more susceptible to external electromagnetic interference, R-wave double counting, and diaphragmatic myopotentials. True bipolar leads are more susceptible to T-wave oversensing , probably because of greater variations in R-wave amplitude. There is no consensus regarding which is preferred.

69. Multipolar leads The complex challenges of CRT system have resulted in development of multipolar leads. A central coil conductor extends to the tip, allowing the stylet or guidewire insertion. Conductors for the more proximal electrodes are cables arranged in parallel that terminate at their respective electodes . Unlike ICD leads the individual elements may be smaller in diameter as they need not conduct high voltages needed for defibrillation.

70. Multipolar leads Overall diameter of the leads can be small allowing stable positioning in the branches of CS. Since multiple pacing vectors are available, it may be possible to overcome phrenic nerve stimulation, pace from electrically more advantageous sites or pace from sites with better acing thresholds.

71. CRT leads Leads used in CRT deserve special consideration with respect to fixation and shape. CS branch anatomy is highly variable. Manufacturers offer a range of CS leads and it is up to the implanting physician to decide which lead is appropriate for a given patient. The implanter has to balance the frequently competing objectives of lead stability, electrical performance, avoidance of phrenic nerve capture, and resynchronization performance. Familiarity with a range of sizes, shapes, and fixation mechanisms of available leads is necessary for successful implantation. Lead diameters vary from 4 to 6 Fr, some leads do not have isodiametric lead bodies. Most leads use friction and tension to maintain their position within the CS vasculature.

72. CRT leads Most CS leads that are transvenously placed do not have a fixation helix or screw that embeds the lead to the myocardium. Most leads use friction and tension to maintain their position within the CS vasculature. Most leads are bipolar, but some of the smaller diameter leads are unipolar. Some leads (Boston Scientific Easy Trak2®) are straight with tines that allow them to be wedged into a distal target vessel and help provide additional stability through frictional force. Other leads have multiple cants or curves that apply pressure to the vessel wall, again providing stability by frictional force.

73. CRT leads (A)Bipolar lead with tines; (B) helical biased bipolar pacing lead; (C) bipolar pacing lead with can fixation; (D) helical biased, unipolar pacing lead; (E) bipolar pacing lead with curve fixation; (F) S-biased bipolar pacing lead. (Sources: (A, B, D, E) Boston Scientific Corporation. (C) Medtronic, Inc.. (F) St.Jude Medical,

74. CRT leads Alternatives to canted leads are leads with sigmoidal biasing in two dimensions (S shaped) or helical biasing in three dimensions (spiral). These leads also rely on the friction created both from wedging the distal tip in a branch and from the multiple contact points on the vessel walls. Despite the variety of available passive fixation CS leads , current passive leads often do not remain stable in the proximalportion of the CS tributaries. If a distal branch cannot be engaged or is prohibited due to phrenic nerve or extracardiac stimulation, a proximal position can be targeted with a lead such as the Medtronic Attain 4195 StarFix ® lead.

75. CRT leads The Medtronic StarFixR lead with its fixation lobes deployed (top) and retracted (bottom). This has a unipolar design with three lobes that are deployed by advancing the push tubing around the lead.

76. CRT leads Modern CRT devices allow for separate pacing circuits for the RV and LV leads, and allow LV leads with unipolar, bipolar, and multipolar configurations. The ability to separately assess the RV and LV leads allows the clinician to program parameters separately, and simplifies lead assessment while simultaneously reducing current drain on the battery. separate programming of the LV and RV channels allows pacing with multiple LV configurations and with optional different timing between the two channels. Multiple LV configurations allow non-invasive programming options to avoid phrenic nerve capture or minimize current drain during LV pacing.

77. Quadripolar leads

78. Fixation mechanisms The chronic performance of permanent pacing leads is critically dependent on stable positioning of the electrode(s). Proper fixation to the endocardial surface is essential to lead performance. two types of fixation mechanisms: Passive Active

79. Passive fixation leads Passive fixation leads have tines (fins) near their tip, which are made of the same material as the insulation. The number (two, three or four), length, and stiffness of the tines are variable. Passive fixation leads become entrapped within the trabeculae of the RA appendage or RV apex immediately upon correct positioning of the lead. Effective fixation of the lead can be confirmed at the time of implantation by its gentle traction or rotation. Tines generally add minimal technical difficulty to the implantation procedure, although they may occasionally become entrapped in the tricuspid valve apparatus.

80. Passive fixation leads These leads are not suitable for placement in non-traditional locations such as the high RV septum or RV outflow tract. The passive fixation leads are rapidly covered by fibrous tissue, making removal of the lead by simple traction difficult or impossible in as short a time as 6 months. In general, passive fixation leads are more difficult to extract than active fixation leads.

81. Active fixation leads In the present generation of active fixation, endocardial leads have a fixed helix or extendable–retractable helix that in most cases also serves as a pacing electrode. In leads with a fixed helix design, the helix is coated with mannitol or polyethylene to facilitate introduction of the lead through the vasculature into the desired chamber. The coating dissolves within a few minutes, allowing the lead to be positioned with a stylet. Fixation is performed by rotation of the entire lead body and transmission of the torque to the distal tip. Repositioning is accomplished by reverse (counterclockwise) rotation of the lead.

82. Active fixation leads The extendable–retractable design has become the most widely used active fixation mechanism because of its ease of implantation and because the fixation mechanism allows retraction long after implantation, thereby facilitating repositioning or extraction. Active fixation leads allow for stable positioning of the lead at many sites in either the atrium or the ventricle. Although active fixation leads are easier to extract than passive fixation leads, the risk of myocardial perforation during and after implantation is higher. Historically, the chronic pacing thresholds of active fixation leads were higher than those of passive fixation leads. This difference has largely been eliminated with the routine use of corticosteroids in active fixation leads.

83. Types of fixation

84. Epimyocardial leads Permanent epicardial pacing leads are used when tricuspid valve anormalités, central venous obstruction, congenital heart disease, or technical issues preclude transvenous lead placement. Epicardial leads may also be used when recurrent bloodstream infection is a concern, or when there is a need for lead implantation co-incident with another intrathoracic surgical procedure. Epicardial pacing leads are either sutured to the epicardial surface or screwed into the epimyocardium of the atrium or ventricle. Fixation mechanisms include a fishhook-shaped electrode that is stabbed into the atrial myocardium or a large screw helix that is rotated into the ventricular myocardium.

85. Epimyocardial leads These are typically unipolar and are frequently non-steroid eluting, with higher stimulation thresholds than modern endocardial electrodes. A newer epicardial lead design has a steroid-eluting electrode, rests against the epicardium , and is sutured in place available in unipolar and bipolar models with lower chronic pacing thresholds and better long-term performance. In the era of CRT, epicardial leads are also being used when a functional LV lead cannot be placed transvenously due to limitations imposed by the coronary venous anatomy From top to bottom: fish hook type, screw- inhelix type; and sew-on button type.

86. Conductors The primary conductors used in most pacing and ICD leads are MP35N and silver . MP35N is a superalloy that is double melted to remove impurities. It is composed of cobalt, nickel, chromium, and molybdenum . It is characterized by biocompatibility, high tensile strength, and resistance to corrosion. Because of its relatively high electrical resistivity (1033 μΩ ), MP35N is combined with efficient conductors such as silver. Single conducting filaments (wires) are made in two designs: a drawn brazed strand (DBS) and a drawn filled tube (DFT).

87. Conductors Cross-sections of the two types of conducting filaments (wires) used in pacemaker and ICD leads: Drawn brazed strand (DBS, left) and drawn filled tube (DFT, right).

88. Conductors The DBS design consists of the MP35N® alloy stranded around a core of softer, highly conductive silver. The resulting wire combines increased fatigue life, high conductivity, and solderability with the ability to withstand greater mechanical stresses. The DFT design is coated with platinum or platinum–iridium. Extreme compressive forces are applied in order to form a sound mechanical bond between surfaces. Single wires are combined together into strands and then wound into cables for use as cable conductors. Larger cables used for high voltage applications and smaller cables for pacing applications.

89. The number of filaments and their arrangement within a given cable is variable from manufacturer to manufacturer, even for similar applications. Compared individually, a 7 × 7 (49 wire) cable has relatively greater flexibility but relatively lower torquability than a 1 × 19 (19 wire) design. Neither design has been shown to be clinically superior.

90. Insulation The materials used in pacemaker leads for insulation play a critical role in their longevity and reliability, as well as in handling and implant characteristics. The ideal insulation material should be biologically inert, and exhibit no surface erosions, no molecular chain disruptions, no uptake of low-molecular-weight biological materials, and no tendency to calcifications, while retaining stable mechanical properties. There is no single ideal insulation and some leads are constructed using multiple materials. Pacemaker leads are generally made of one insulation type. ICD leads are more complex, utilizing combinations of insulation material.

91. Insulation Fluoropolymers are fluorocarbon-based polymers characterized by high resistance to solvents, acids, and bases. They have maximum biocompatibility and tensile strength, but their stiffness limits their use to thin coating (<0.076 mm) applications. Eg : PTFE (polytetrafluoroethylene, i.e. Teflon®, DuPont) ETFE (ethylene tetrafluoroethylene). Silicone rubber is a polymer both biostable and biocompatible, also has high resistance to extreme temperatures but has a low tensile strength, making it prone to tearing and abrasion wear. Polyurethanes are characterized by high tear strength, high elasticity, and a low co-efficient of friction. These qualities allow for smaller lead diameters.

92. Insulation

93. Electrodes The pacing electrode is the final interface between the lead and myocardium. Its design and composition greatly influence the overall electrical performance of the pacing system. In a bipolar pacing lead the tip electrode is the cathode and the ring electrode is the anode. The stimulation threshold is a function of the radius of the electrode. A smaller radius is associated with a higher current density, lower pacing threshold, and higher resistance at the electrode–myocardium interface. In contrast, smaller radius electrodes result in high sensing impedance and electrode polarization impairing myocardial EGM sensing.

94. Electrodes The materials currently used for electrodes of permanent pacing leads include platinum–iridium, Elgiloy (cobalt–chromium–nickel), platinum coated with platinized titanium, vitreous or pyrolytic carbon coating a titanium or graphite core, platinum, iridium oxide, or titanium–nitride. The use of corticosteroid-eluting electrodes has been a major advance in pacing lead technology. Dexamethasone sodium phosphate and/or dexamethasone acetate is impregnated on a silicone core or collar that surrounds the tip electrode. Corticosteriods have dramatically reduced the risk of exit block for pacing leads, ICD leads, and epimyocardial leads.

95. Steroid Eluting Leads Steroid eluting leads reduce the inflammatory process and thus exhibit little to no acute stimulation threshold peaking and low chronic thresholds Porous, platinized tip for steroid elution Silicone rubber plug containing steroid Tines for stable fixation

96. Connector pins Connector pins are made of stainless steel or titanium. The current standard is IS -1 (Industry Standard) for pacing leads. The lead diameter at the head block is 3.2 mm and sealing rings are integrated to the lead. With this industry standard, all current bipolar pacing leads are compatible with all current manufacturer header designs. It is important to visualize the connector pin extending beyond the distal set screw in the header block. If the connector pin is not properly seated in the header block, sensing artifact or failure to pace may result. Lead impedance measurements alone are not enough to detect this problem.

97. Connector pins Adapter for leads terminated with 5/6-mm pins that need to be connected to a pacemaker with an IS-1 header block. Photograph and schematic of an IS-1 pin terminated lead. Sealing rings are integrated into the lead Radiograph demonstrating proper extension of the connector pin beyond the set-screw (top; arrow indicates fluoroscopic image of a pacemaker header with properly implanted lead pin) and inadequate extension beyond the set-screw (bottom; circle indicates improper lead pin position).

98. Connector pins Multipolar pacing leads such as those used in the CS will not be IS-1 compatible. They are connected to specialized header blocks using an IS-4 LLLL type pin similar to the pin assembly found on a DF-4 ICD lead. Currently, there are two ISO standards for the ICD yoke (connector pin assembly): IS-1/DF-1 yokes and DF-4 (or IS-4) pin assembly. Until recently, the IS-1/DF-1 yoke design was the industry standard. The pace/ sense portion of the lead is terminated with an IS-1 pin and the high voltage coils are terminated with their respective DF-1 (ISO-11318) pins.

99. Connector pins The DF-4 design eliminates the possibility of lead connection errors (i.e. interchanging the proximal and distal coils) due to a uniquely compatible port at the header. This design also has advantage with respect to pocket bulk as well as for lead-to-lead and lead to- can interactions. A potential disadvantage is the possibility of multiple component fracture from one critically located stress point in the pocket. Comparison of the current DF-1 connector (bottom) and the proposed DF-4 connector (top).

100. Lead anchoring sleeve The anchoring sleeve allows the lead to be secured to the fascia or muscle, and its proper use can help reduce the risk of lead damage. Currently, most sleeves are made of a biocompatible, peroxide catalyzed (MDX) silicon rubber and may contain a radiographically dense material to allow visualization under fluoroscopy. These sleeves have one, two, or three circumferential grooves to which non-absorbable sutures are secured. Inadequate tie down force or an inadequate number of sutures is especially a problem with lead bodies coated with a lubricious material such as polyvinyl pyrrolidone (PVP). Balancing the risk of lead damage with lead dislodgement requires the implanter’s familiarity with the specific lead and sleeve.

101. MRI compatible lead system

102. Micra Transcatheter Pacing System The miniaturized  Micra ™ transcatheter pacing system (TPS) is the world’s smallest pacemaker, delivered percutaneously via a minimally invasive approach, directly into the right ventricle and does not require the use of leads. 99% implant success rate in 726-patient global trial 48% fewer major complications than traditional pacemakers 93% smaller than conventional pacemakers 5 Ultra low-power circuit design delivers an estimated average 12-year battery longevity. MRI SureScan ™ technology allows the patient to be safely scanned using either a 1.5T or 3T full body MRI.

103. Linear one-step deployment facilitates consistent capsule placement, no torque required.

104. THANK YOU