Principles and Applications of Electrical Circuits and Signal Theories in EP

Transcription

1 Principles and Applications of Electrical Circuits and Signal Theories in EP Graydon Beatty, VP Therapy Development Atrial Fibrillation Division, St. Jude Medical, Inc. CardioRhythm 2009

2 Background Biophysics of cardiac electrogram is complex 2

3 Background Biophysics of cardiac electrogram is complex Theories in electrical l circuits it and signals facilitate t understanding of electrogram and its measurement 3

4 Objectives Summarize electrical concepts of: resistance Ohm s Law capacitance volume conductor (resistivity) 4

5 Objectives Summarize electrical concepts of: resistance Ohm s Law capacitance volume conductor (resistivity) Apply concepts, together with physical geometry on: cellular resting and action potentials unipolar electrogram electrode sensing amplifier measurement 5

6 Resistance Resistance impedes the flow of electric current similar to the way a facet-valve impedes the flow of water 6

7 Resistance Resistance impedes the flow of electric current similar to the way a facet-valve impedes the flow of water Resistors in series add 7

8 Resistance Resistance impedes the flow of electric current similar to the way a facet-valve impedes the flow of water Resistors in series add Resistors in parallel divide 8

9 Ohm s Law When a current (I) is applied through a resistor (R), a voltage (V) appears across its terminals with a value that is proportional to both the current and the resistance: V = I x R I + V The voltage is positive at the terminal the current enters (positive with respect to the opposite terminal) 9

10 Capacitance Capacitance stores charge, similar to a battery, and impedes the flow of electric current with a dependence on frequency (low frequency = higher impedance) (high frequency = lower impedance) 10

11 Capacitance Capacitance stores charge, similar to a battery, and impedes the flow of electric current with a dependence on frequency (low frequency = higher impedance) (high frequency = lower impedance) Capacitors in series divide 11

12 Capacitance Capacitance stores charge, similar to a battery, and impedes the flow of electric current with a dependence on frequency (low frequency = higher impedance) (high frequency = lower impedance) Capacitors in series divide Capacitors in parallel add 12

13 Volume Conductor The thorax is a distributed volume of conductive material. Each type of tissue has its own net-total of series and parallel resistance 13

14 Volume Conductor The thorax is a distributed volume of conductive material. Each type of tissue has its own net-total of series and parallel resistance Volume conductors are characterized in terms of resistivity, which is scaled by both a unit area and a unit length 14

15 Cellular Resting and Action Potentials Advance needle electrode needle electrode across the cell membrane. membrane + - 0mV reference electrode outside of cell 15

16 Cellular Resting and Action Potentials Advance needle electrode across the cell membrane. + -.a resting potential of -90 mv is observed inside the cell with respect to outside the cell 0mV 16

17 Cellular Resting and Action Potentials Na + Na + K + Na + K + + The resting potential is maintained by an ATP powered sodium-potassium pump within the membrane that transports Na + ions outward and K + ions inward (3 Na + per 2 K + ). The gradient of ion-concentration separates charge across the membrane with an equal and opposite electrical gradient of -90 mv

18 Cellular Resting and Action Potentials + - The phospholipid bilayer membrane insulator creates a membrane capacitance that stores charge associated with the resting potential 18

19 Cellular Resting and Action Potentials Stimulate the cell. + -.a transmembrane AP is observed with 5 characteristic phases (Φ) 0mV 19

20 Cellular Resting and Action Potentials + - 0mV Φ1 Initial Recovery Φ0 Upstroke Φ2 Plateau (absolute refractory) Φ3 Recovery (relative refractory) Φ4 Resting 20

21 AP and Unipolar Electrogram While an AP is recorded across the membrane of a single active cell..an extracellular unipolar electrogram is recorded from the whole population of active cells surrounding the electrode, relative to a distant reference AP unipolar 21

22 AP and Unipolar Electrogram The influence of any active cell upon the unipolar recording is proportional to the projected angle between the cell s ion channels and the line-of-sight to the electrode and is inversely proportional to the distance between the ion channel and the electrode AP unipolar 22

23 AP and Unipolar Electrogram Because activation propagates from cell-to-cell, active cells are organized along a wave front unipolar 23

24 AP and Unipolar Electrogram Because activation propagates from cell-to-cell, active cells are organized along a wave front. and the unipolar electrogram is a summation-effect from all of the membrane currents along the wavefront line projected angle θ r distance along line-of-sight unipolar 24

25 AP and Unipolar Electrogram As the wavefront arrives at the electrode s location, the unipolar electrogram crosses zero along the descent of a rapid downstroke unipolar zero-crossing 25

26 AP and Unipolar Electrogram Consequently, each phase of the action potential, as defined in time, also occupies specific regions of substrate space, relative to the wavefront line <<Φ3 Φ2 Φ4 unipolar Φ1 Φ0 zero-crossing 26

27 AP and Unipolar Electrogram As the wavefront continues beyond the electrode, the surrounding myocardium is depolarized (Φ2), and a negative phase is displayed on the corresponding electrogram << Φ3 Φ2 Φ4 Φ1 Φ0 unipolar 27

28 AP and Unipolar Electrogram A simplified model can be applied on a single channel to characterize unipolar morphology, based on the dynamics of membrane currents - + << Φ3 Φ2 Φ4 Φ1 Φ0 unipolar 28

29 AP and Unipolar Electrogram A simplified model can be applied on a single channel to characterize unipolar morphology, based on the dynamics of membrane currents Actual unipolar electrograms have a composite morphology resulting from the sum of all active channels << Φ3 Φ2 - + Φ4 Φ1 Φ0 unipolar 29

30 Simple, Generalized Channel Model fast, early, net-inward membrane current slow, late, net-outward membrane current 30

31 Simple, Generalized Channel Model fast, early, net-inward membrane current 31

32 Simple, Generalized Channel Model slow, late, net-outward membrane current 32

33 Influence of Single, Dipolar Channel Net Positive 33

34 Influence of Single, Dipolar Channel Zero Crossing 34

35 Influence of Single, Dipolar Channel Net Negative 35

36 Influence of Single, Dipolar Channel Net Positive Zero Crossing Net Negative 36

37 37 Unipolar Analogy: Perspective View

38 38 Unipolar Analogy: Perspective View

39 Unipolar Analogy: Perspective View (Actual Area) x (Projected angle) 39

40 Unipolar Analogy: Perspective View (Actual Area) x (Projected angle) (Vertical Depth-of-Field) x (Horizontal Depth-of-Field) 40

41 Unipolar Analogy: Perspective View cosine(θ) (Actual Area) x (Projected angle) (Vertical Depth-of-Field) x (Horizontal Depth-of-Field) r r 41

42 Unipolar Analogy: Perspective View A cos(θ) r 2 42

43 Unipolar Analogy: Perspective View V m cos(θ) r 2 43

44 44 Unipolar Voltage in Space

45 Unipolar Voltage in Space (Top View) S41 S39 S37 S35 S33 S31 S29 S27 S25 S23 S21 S19 S17 S15 S13 S11 S9 S7 S5 S S1 Regional Distribution of Dipolar Voltage

46 Unipolar Voltage in Space (Top View) S41 S39 S37 S35 S33 S31 S29 S27 S25 S23 S21 S19 S17 S15 S13 S11 S9 S7 S5 S S1 Regional Distribution of Dipolar Voltage

47 Electrode Sensing An electrode acts as a transducer of ion current (in the tissue) to electron current (in the wire) 47

48 Electrode Sensing Electrode impedance varies with size and shape, which has an important impact on the quality of the electrogram recording 48

49 Amplifier Measurement + - Symmetry and balance is the key to high quality recording: 49

50 Amplifier Measurement + - Symmetry and balance is the key to high quality recording: Size and shape of the electrodes 50

51 Amplifier Measurement + - Symmetry and balance is the key to high quality recording: Size and shape of the electrodes Length, impedance, and juxtaposition of catheter wires, connecting cables, junction boxes, and circuit-board traces and components, and location of multiple systems in the laboratory 51

52 Amplifier Measurement + - Symmetry and balance is the key to high quality recording: Size and shape of the electrodes this is why: 52

53 Amplifier Measurement + - Symmetry and balance is the key to high quality recording: Size and shape of the electrodes this is why: Pairs of 1 mm electrodes on circular catheters deliver clean signals 53

54 Amplifier Measurement + - Symmetry and balance is the key to high quality recording: Size and shape of the electrodes this is why: Pairs of 1 mm electrodes on circular catheters deliver clean signals 4 mm tip ablation catheter (paired with 2 mm ring) is a compromise 54

55 Amplifier Measurement + - Symmetry and balance is the key to high quality recording: Size and shape of the electrodes this is why: Pairs of 1 mm electrodes on circular catheters deliver clean signals 4 mm tip ablation catheter (paired with 2 mm ring) is a compromise 8 mm tip ablation catheter (paired with 2 mm ring) is virtually unacceptable 55

56 56 Thank You!