PACEMAKER BASIC AND TIMING CYCLE .pptx

PACEMAKER BASIC AND TIMING CYCLE .pptx

1. PACEMAKER BASICS AND TIMING CYCLE DR Awadhesh sharma Professor Cardiology LPS Institute of cardiology,Kanpur

2. PACEMAKER CIRCUIT Implantable pulse generator (IPG): Battery Circuitry Connector(s) Leads or wires Cathode (negative electrode) Anode (positive electrode) Body tissue IPG Lead Anode Cathode

3. Stuart Allen 06 Contains a battery that provides the energy for sending electrical impulses to the heart Houses the circuitry that controls pacemaker operations Circuitry Battery The Pulse Generator

4. The Pulse Generator Casing (can) Titanium (biocompatible, lightweight, stronger than steel) Connector (header) Leads plug into ports in the clear epoxy header Components Diodes, resistors, oscillator, microchips Battery The largest single component inside the pulse generator Lithium iodide

5. THE PULSE GENERATOR…… Common battery compositions include: Lithium-Iodine Lithium silver vanadium oxide with carbon monoflouride Starting battery voltage will vary depending on composition Longevity Dependent on impedance and output Commonly ranges from 6-12 years

6. LEADS

7. Leads are Insulated Wires Deliver electrical impulses from the pulse generator to the heart Sense cardiac depolarization Lead

8. Conductor Tip Electrode Insulation Connector Pin Pacing Lead Components Conductor Connector Pin Insulation Electrode

9. Lead Characterization Position within the heart Endocardial or transvenous leads Epicardial leads Fixation mechanism Active/Screw-in Passive/Tined Shape Straight J-shaped used in the atrium Polarity Unipolar Bipolar Insulator Silicone Polyurethane

10. Passive fixation The tines become lodged in the trabeculae

11. ACTIVE FIXATION The helix (or screw) extends into the endocardial tissue Allows for lead positioning anywhere in the heart’s chamber

12. Transvenous Leads - Fixation Mechanisms

13. CONDUCTORS - MP-35N – Alloy of nickel , cobalt, chromium, molybdenum advantage – high strength and resistance to corrosion disadvantage – high electrical resistance This is overcome by incorporating low resistance metals – silver ,titanium , platinum . These alloy can be constructed in two ways -

14. DFT vs DBS

15. COAXIAL LEAD VS CORADIAL LEADS SYSTEM

16. LEAD INSULATION - POLYURETHANE – High tensile strength resistance to mechanical abrasion has excellent lubricity with low frictional coefficient Thin layer of insulation can be used so reducing overall lead dimension Main disadvantage – in vivo polymer degradation

17. Two mechanism – ESC (environmental stress cracking ) at point of mechanical stress , at anchoring sleevs , venous entry point Metal ion oxidation (MIO)- at conductor insulator interface

18. SILICON INSULATION Completely inert and biostable More flexible – less risk of cardiac perforation Main disadvantage – low tensile strength susceptibility to abrasion and tear So thicker layer of insulation needed which lead to bulky design Cold flow phenomenon

19. 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

20. Epicardial Leads Leads applied directly to the surface of the heart Utilized in pediatric patients and patients contraindicated for transvenous leads Fixation mechanisms include: Epicardial stab-in Myocardial screw-in Suture-on Applied via sternotomy, thoroscopy, or limited thoracotomy

21. Flows through the tip electrode (cathode) Stimulates the heart Returns through body fluid and tissue to the PG (anode) A UNIPOLAR PACING SYSTEM CONTAINS A LEAD WITH AN ELECTRODE IN THE HEART Cathode Anode - +

22. Anode 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 A BIPOLAR PACING SYSTEM CONTAINS A LEAD WITH 2 ELECTRODES IN THE HEART Cathode

23. Unipolar leads Unipolar leads have a smaller diameter than bipolar leads Unipolar leads exhibit larger pacing artifacts on the surface ECG One electrode on the tip & one conductor coil Conductor coil may consist of multiple strands - ( multifilar leads)

24. Bipolar leads Bipolar leads are less susceptible to oversensing noncardiac signals (myopotentials and EMI) Coaxial Lead Design Circuit is tip electrode to ring electrode Two conductor coils (one inside the other) Inner layer of insulation Bipolar leads are typically thicker than unipolar leads

25. Unipolar Bipolar Advantages Smaller diameter Easier to implant Large spike No pocket stimulation Less susceptible to EMI Programming flexibility Disadvantages Pocket stimulation Far-field oversensing No programming flexibility Larger diameter Stiffer lead body Smal l spike Higher impedance Voltage threshold is 30% higher

26. CHARACTERISTICS OF AN PACEMAKER CIRCUIT: Voltage Current Impedance 33

27. VOLTAGE Voltage is the force, or “push,” that causes electrons to move through a circuit In a pacing system, voltage is: Measured in volts (V) Represented by the letter “V” Provided by the pacemaker battery Often referred to as amplitude or pulse amplitude

28. CURRENT The flow of electrons in a completed circuit In a pacing system, current is: Measured in milliamps (mA) Represented by the letter “I” Determined by the amount of electrons that move through a circuit

29. IMPEDANCE The opposition to current flow In a pacing system, impedance is: Measured in ohms ( W) Represented by the letter “R” The measurement of the sum of all resistance to the flow of current Impedance is a function of the characteristics of the conductor (wire), the electrode (tip), and the myocardium

30. Impedance is the sum of all resistance to the flow of current. The resistive factors to a pacing system include: Lead conductor resistance The resistance to current flow from the electrode to the myocardium POLARIZATION IMPEDANCE, which is the accumulation of charges of opposite polarity in the myocardium at the electrode-tissue interface.

31. Impedance Pacing lead impedance typically stated in broad ranges, i.e. 300 to 1500 Ω Factors that can influence impedance Resistance of the conductor coils Tissue between anode and cathode The electrode/myocardial interface Size of the electrode’s surface area Size and shape of the tip electrode

32. Voltage, Current, and Impedance are Interdependent The interrelationship of the three components is analogous to the flow of water through a hose Voltage represents the force with which . . . Current (water) is delivered through . . . A hose, where each component represents the total impedance: The nozzle, representing the electrode The tubing, representing the lead wire

33. Voltage and Current Flow Electrical Analogies Spigot (voltage) turned up, lots of water flows (high current drain) Spigot (voltage) turned low, little flow (low current drain) Water pressure in system is analogous to voltage – providing the force to move the current

34. Resistance and Current Flow Electrical Analogies Normal resistance – friction caused by the hose and nozzle More water discharges, but is all of it going to the nozzle? High resistance – a knot results in low total current flow Low resistance – leaks in the hose reduce the resistance

35. POLARIZATION After an output pulse, positively charged particles gather near the electrode. The amount of positive charge is Directly proportional to pulse duration Inversely proportional to the functional electrode size (i.e. smaller electrodes offer higher polarization) Polarization effect can represent 30–40% of the total pacing impedance As high as 70% for smooth surface, small surface area electrodes

36. Within the electrode, current flow is due to movement of electrons (e−). At the electrode–tissue interface, the current flow becomes ionic & (-) vely charged ions ( Cl −, OH−) flow into the tissues toward the anode leaving behind oppositely charged particles attracted by the emerging electrons. It is this capacitance effect at the electrode tissue interface, that is the basis of polarization

37. Lead wire fracture Increased resistance 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 Other reason for high impedance: Lead not seated properly in pacemaker header (usually an acute problem).

38. Low Impedance Conditions An Insulation Break Insulation breaks can cause impedance values to fall Current drain is high and can lead to more rapid battery depletion Current can drain through the insulation break into the body or other lead wire, not through myocardium Impedance values may be less than 300 W

39. Ohm’s Law Describes the relationship between voltage, current, and resistance V = I X R I = V / R R = V / I V I R V R I V R I R V I = = = X

40. Ohm’s law tells us: If the impedance remains constant, and the voltage decreases, the current decreases. If the voltage is constant, and the impedance decreases, the current increases.

41. Stimulation Threshold Pacing Voltage Threshold The minimum pacing voltage at any given pulse width required to consistently stimulate the heart outside the myocardial refractory period causing it to contract

42. E = Energy delivered by Pulse to the Pacing Circuit and Cardiac Tissue - V . I . t I 2 Rt V 2 t/R

43. Rheobase - ( the lowest point on the curve) by definition is the lowest voltage that results in myocardial depolarization at infinitely long pulse duration Chronaxie ( pulse duration time ) by definition, the chronaxie is the threshold pulse duration at twice the rheobase voltage

44. Strength interval curve

45. 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

46. STEROID ELUTING LEADS Steroid eluting leads reduce the inflammatory process Exhibit little to no acute stimulation threshold peaking Leads maintain low chronic thresholds

47. Effect of steroid on stimulation thresholds

48. Evolution of Pacing Threshold Voltage Threshold (V) Observation Time (weeks) Acute Phase Chronic Phase Safety Margin 6 s 4 3 2 1 4 8 12 16

49. INJURY CURRENT……. Due to pressure exerted by electrode on myocardium Seen in both active and passive leads(less pronounced) Lack of injury current – denotes poor contact / scarred myocardium Disappears over minutes to hours this may leads to high threshold soon after lead placement which subside at end of procedure

50. Magnet mode Activates magnetic reed switch Model dependent behavior with magnet Asynchronous pacing – most common No apparent rate or rhythm change Brief asynchronous pacing and then return to programmed value Continuous or transient loss of pacing Magnets will cause most DDDs to convert to DOO at about 85 with a BOL (beginning of life) battery, and to VOO at a rate of about 65 at ERI (effective replacement interval) is reached to conserve power.

51. The Pacing Pulse t Pacing Pulse Pulse Duration (Width) Output Voltage V = Pulse Amplitude in Volts (V) (say 2.5 V) t = Pulse Duration or Width in milliseconds ( ms ) (say 0.5 ms ) R = Impedance of Pacing Circuit (ohms) (say 500 ohms) I = V/R = Current through pacing circuit (mA) = 2.5 V/ 500 ohms = 0.005 A = 5 mA V t

52. Why measure stimulation threshold? To enable programming stimulus voltage amplitude and pulse width such that Consistent capture & Patient Safety is ensured Battery drain minimized, Pacemaker longevity maximized Good thresholds Ventricle - <1V @ 0.5ms Atrium - <1.5V @ 0.5ms

53. SENSING OF INTRINSIC HEARTBEATS Sensing is the ability of the pacemaker to “see” when an intrinsic depolarization is occurring Pacemakers record the Intracardiac Electrogram (EGM) by constantly recording the potential difference between the cathode and anode Depolarization Wave Processed by Device

54. Sensitivity Setting Sensitivity settings less than 2.5 mv – High sensitivity – can lead to oversensing Sensitivity settings greater than 2.5 mV – Low sensitivity – can lead to undersensing Amplitude (mV) Amplitude (mV) Time Time 5.0 2.5 1.25 5.0 2.5 1.25

55. Undersensing . . . Pacemaker does not “see” the intrinsic beat, and therefore does not respond appropriately Intrinsic beat not sensed Scheduled pace delivered VVI / 60

56. Oversensing An electrical signal other than the intended P or R wave is detected Pacing is inhibited Marker channel shows intrinsic activity... ...though no activity is present

57. FUSION AND PSEUDOFUSION COMPLEX

58. TIMING CYCLE

59. VVI/60(1000msec) ? Last paced event occur later than expected

60. HYSTERESIS…… Goal is to encourage own intrinsic activity . One of the cause of rate variation in paced ECG Hysteresis work best in patient with intrinsic rate near the programmed base rate.

61. V VP VP VP VOO TIMING VP VP

62. V VP VP VP VP VS VVI TIMING

63. PACEMAKER MEDIATED TACHYCARDIA Main trigger are – PVC loss of atrial capture

64. ECG- pacing at MTR no evidence of atrial capture retrograde P wave in inferior leads