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Basic Pacing Concepts Part II. Electrical Concepts.

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Presentation on theme: "Basic Pacing Concepts Part II. Electrical Concepts."— Presentation transcript:

1 Basic Pacing Concepts Part II

2 Electrical Concepts

3 zVoltage zCurrent zImpedance Every Electrical Pacing Circuit Has the Following Characteristics:

4 Voltage zVoltage is the force or “push” that causes electrons to move through a circuit zIn a pacing system, voltage is: –Measured in volts –Represented by the letter “V” –Provided by the pacemaker battery –Often referred to as amplitude

5 Current zThe flow of electrons in a completed circuit zIn a pacing system, current is: –Measured in mA (milliamps) –Represented by the letter “I” –Determined by the amount of electrons that move through a circuit

6 Impedance zThe opposition to current flow zIn a pacing system, impedance is: –Measured in ohms –Represented by the letter “R” (  for numerical values) –The measurement of the sum of all resistance to the flow of current

7 Voltage, Current, and Impedance Are Interdependent zThe interrelationship of the three components can be likened to the flow of water through a hose –Voltage represents the force with which... –Current (water) is delivered through... –A hose, or lead, where each component represents the total impedance: yThe nozzle, representing the electrode yThe tubing, representing the lead wire

8 Voltage and Current Flow Spigot (voltage) turned up (high current drain) Spigot (voltage) turned low (low current drain)

9 Resistance and Current Flow “Normal” resistance “Low” resistance “High” resistance Low current flow High current flow

10 Ohm’s Law is a Fundamental Principle of Pacing That: VI R V = I X R I = V / R R = V / I zDescribes the relationship between voltage, current, and resistance x

11 zIf you reduce the voltage by half, the current is also cut in half zIf you reduce the impedance by half, the current doubles zIf the impedance increases, the current decreases When Using Ohm’s Law You Will Find That:

12 Ohm’s Law Can Be Used to Find Amounts of Current Passing Through Pacemaker Circuitry If:Voltage = 5 V Impedance = 500  What will the current be? I = V/R I = 5 V ÷ 500  = Amperes x 1000 = 10 mA

13 In This Example, the Voltage is Halved If:Voltage = 2.5 V Impedance = 500  Current = ? I = V/R V = 2.5 V ÷ 500  = Amperes x 1000 = 5 mA

14 In This Example, the Impedance is Reduced By Half If:Voltage = 5 V Impedance = 250  Current = ? I = V/R I = 5 V ÷ 250  = Amperes x 1000 = 20 mA

15 Impedance Changes Affect Pacemaker Function and Battery Longevity zHigh impedance reading reduces battery current drain and increases longevity zLow impedance reading increases battery current drain and decreases longevity  Impedance reading values range from 300 to 1,000  –High impedance leads will show impedance reading values greater than 1,000 ohms

16 Lead Impedance Values Will Change Due to: zInsulation breaks zWire fractures

17 An Insulation Break Around the Lead Wire Can Cause Impedance Values to Fall zInsulation breaks expose the wire to body fluids which have a low resistance and cause impedance values to fall zCurrent drains through the insulation break into the body which depletes the battery  An insulation break can cause impedance values to fall below 300  Insulation break Decreased resistance

18 A Wire Fracture Within the Insulating Sheath May Cause Impedance Values to Rise zImpedance values across a break in the wire will increase zCurrent flow may be too low to be effective  Impedance values may exceed 3,000  Lead wire fracture Increased resistance

19 Stimulation

20 Stimulation Process Time (Milliseconds) Phase 2 Phase 1 Phase 3 Phase 4 Transmembrane Potential (Millivolts) Phase 0 Threshold

21 Stimulation Threshold zThe minimum electrical stimulus needed to consistently capture the heart outside of the heart’s refractory period VVI / 60 Capture Non-Capture

22 zAmplitude zPulse width Two Settings Are Used to Ensure Capture:

23 Amplitude is the Amount of Voltage Delivered to the Heart By the Pacemaker zAmplitude reflects the strength or height of the impulse: –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

24 Pulse Width Is the Time (Duration) of the Pacing Pulse zPulse width is expressed in milliseconds (ms) zThe pulse width must be long enough for depolarization to disperse to the surrounding tissue 5 V 0.5 ms0.25 ms 1.0 ms

25 The Strength-Duration Curve zThe strength-duration curve illustrates the relationship of amplitude and pulse width –Values on or above the curve will result in capture Duration Pulse Width (ms) Stimulation Threshold (Volts) Capture

26 Clinical Usefulness of the Strength-Duration Curve zAdequate safety margins must be achieved due to: –Acute or chronic pacing system –Daily fluctuations in threshold Capture Duration Pulse Width (ms) Stimulation Threshold (Volts)

27 After Patient Safety, the Second Most Important Goal in Programming is to Extend Battery Life zThe best way to extend the service life of a battery is to lower voltage settings while maintaining adequate safety margins –Amplitude values greater than the cell capacity of the pacemaker battery require a voltage multiplier, resulting in decreased battery longevity

28 zLead impedance zAmplitude and pulse width setting zPercentage paced vs. intrinsic events zRate responsive modes programmed “ON” Factors That Affect Battery Longevity Include:

29 Electrode Design May Also Impact Stimulation Thresholds zLead maturation process

30 Lead Maturation Process zFibrotic “capsule” develops around the electrode following lead implantation

31 Steroid Eluting Leads zSteroid 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

32 Lead Maturation Process zEffect of Steroid on Stimulation Thresholds Pulse Width = 0.5 msec 0 36 Implant Time (Weeks) Textured Metal Electrode Smooth Metal Electrode Steroid-Eluting Electrode Volts

33 General Medtronic Pacemaker Disclaimer INDICATIONS Medtronic pacemakers are indicated for rate adaptive pacing in patients who may benefit from increased pacing rates concurrent with increases in activity (Thera, Thera-i, Prodigy, Preva and Medtronic.Kappa 700 Series) or increases in activity and/or minute ventilation (Medtronic.Kappa 400 Series). Medtronic pacemakers are also indicated for dual chamber and atrial tracking modes in patients who may benefit from maintenance of AV synchrony. Dual chamber modes are specifically indicated for treatment of conduction disorders that require restoration of both rate and AV synchrony, which include various degrees of AV block to maintain the atrial contribution to cardiac output and VVI intolerance (e.g., pacemaker syndrome) in the presence of persistent sinus rhythm Programmer The Medtronic 9790 Programmers are portable, microprocessor based instruments used to program Medtronic implantable devices The Model 9462 Remote Assistant™ is intended for use in combination with a Medtronic implantable pacemaker with Remote Assistant diagnostic capabilities. CONTRAINDICATIONS Medtronic pacemakers are contraindicated for the following applications:  Dual chamber atrial pacing in patients with chronic refractory atrial tachyarrhythmias.  Asynchronous pacing in the presence (or likelihood) of competitive paced and intrinsic rhythms.  Unipolar pacing for patients with an implanted cardioverter-defibrillator because it may cause unwanted delivery or inhibition of ICD therapy.  Medtronic.Kappa 400 Series pacemakers are contraindicated for use with epicardial leads and with abdominal implantation. WARNINGS/PRECAUTIONS Pacemaker patients should avoid sources of magnetic resonance imaging, diathermy, high sources of radiation, electrosurgical cautery, external defibrillation, lithotripsy, and radiofrequency ablation to avoid electrical reset of the device, inappropriate sensing and/or therapy Operation of the Model 9462 Remote Assistant™ Cardiac Monitor near sources of electromagnetic interference, such as cellular phones, computer monitors, etc. may adversely affect the performance of this device. See the appropriate technical manual for detailed information regarding indications, contraindications, warnings, and precautions. Caution: Federal law (U.S.A.) restricts this device to sale by or on the order of a physician.

34 Medtronic Leads For Indications, Contraindications, Warnings, and Precautions for Medtronic Leads, please refer to the appropriate Leads Technical Manual or call your local Medtronic Representative. Caution: Federal law restricts this device to sale by or on the order of a Physician. Note: This presentation is provided for general educational purposes only and should not be considered the exclusive source for this type of information. At all times, it is the professional responsibility of the practitioner to exercise independent clinical judgment in a particular situation.

35 Continued in Basic Pacing Concepts Part III

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