In vivo myocardial electrical impedance during ischemia: phase shift as a marker of cellular...

In vivoIn vivo myocardial electrical myocardial electrical impedance during ischemia: phase impedance during ischemia: phase

shift as a marker of cellular shift as a marker of cellular uncoupling and predictor of fibrillationuncoupling and predictor of fibrillation

Eric Plourde1, Pierre LeGuyader2, Pascal Daleau3 and Pierre Savard1

1Institut de génie biomédical and Hôpital du Sacré Cœur de Montréal, 2Institut de cardiologie de Montréal

and 3Institut de cardiologie de Québec

Canadian Cardiovascular Congress, Halifax NS

October 22, 2001


October 22, 2001

PlanPlan

• Motivation and objectives • Introduction• Measurement system• Experimental protocol• Results• Discussion et conclusions


October 22, 2001

Motivation and objectivesMotivation and objectives

• Motivation– Cellular uncoupling during ischemia is related to

cardiac arrhythmias1.

• Objectives– Impedance and resistivity measurements in order to

better understand the relation between ischemia, cellular uncoupling and arrhythmias :

• Are resistivity measurements or impedance phase measurements able to reflect cellular uncoupling?

• Is there a link between cellular uncoupling and fibrillation?

1Smith et al. Circulation 1995;92:3051-3060


October 22, 2001

IntroductionIntroduction

ImpedanceImpedance

Impedance amplitude

Impedance phase )/(

22

RXarctg

XRZ

Z = V / I = R + jX

I V

time


October 22, 2001

IntroductionIntroduction Cellular uncouplingCellular uncoupling

Healthy region Ischemic region

Gap junction

Na+ K+K+

Na+

K+Na+

Na+

K+

Ca++

Ca++

Ca++

Ca++ K+

Na+

K+Na+

Ca++

Ca++


October 22, 2001

Measurement systemMeasurement system

Impedance measurementImpedance measurement

i ac.

e

-+

f

gh

The four-electrode technique


October 22, 2001

Rm Cm

rc

rgap

rj

Measurement systemMeasurement system Resistivities determinationResistivities determination

• From impedance to intracellular and extracellular resistivities : The bidomain anisotropic model

re

intracellular

extracellular


October 22, 2001

Experimental protocolExperimental protocol

1. n = 13 pigs in vivo

2.Electrode fixation on the heart

• Orientation determination

3.LAD occlusion

4. Impedance

measurements during 3

hours (12 Hz - 10 kHz)


October 22, 2001

ResultsResults

Impedance (Impedance (nn=1)=1)

Fibrillation


October 22, 2001

ResultsResults

Bidomain parameters (Bidomain parameters (nn=1)=1)

Fibrillation


October 22, 2001

Discussion and conclusionDiscussion and conclusion• Are resistivity measurements or impedance phase

measurements able to reflect cellular uncoupling?– The phase doesn’t mark cellular uncoupling in all

experiments (2 / 4)– Cellular uncoupling was observed in all experiments with

the use of the bidomaine anisotropic model including an intracellular capacitance (4 / 4)

• Is there a link between cellular uncoupling and fibrillation?– Fibrillation follows cellular uncoupling in two experiments (2

/ 4)


October 22, 2001

AcknowledgmentsAcknowledgments• Pr. Pierre Savard

• Dr. Pierre Le Guyader

• Personnel of the Research Center at the Sacré-Cœur Hospital– Ms Caroline Bouchard– Mr Michel Vermeulen– Mr Bruno Dubé

• Supported in part by the Natural Science and Engineering Research Council of Canada (NSERC) and the Heart and Stroke Foundation of Canada


October 22, 2001

Thank YouThank You

Questions?Questions?


October 22, 2001

ResistivityResistivity

In a resistive environment:

R = V/I = l / A

= resistivity [m]

A l


October 22, 2001

Measurement systemMeasurement system

Impedance measurementImpedance measurementThe acquisition system


October 22, 2001

Courant direct

Courant alternatif

g -1

R m

e

g i-1

R m

g e-1

g i-1

IdcIdc

Système de mesure Système de mesure

La sonde: courant alternatifLa sonde: courant alternatif


October 22, 2001

Signal treatment softwareSignal treatment software

Phase

+ Détecteur RMS

Signal filtré-

BruitTension

Z=V/I

+ Détecteur RMSSignal filtré

Bruit

-Courant

Source: Pierre LeGuyader


October 22, 2001

Measurement systemMeasurement system Resistivities determinationResistivities determination

Minimisation of the error

V/I

f

V/I

f

+ -

Simulations Measures

Error

Parameters

• longitudinal + transverse

• frequencies (12Hz-10kHz)


October 22, 2001

ResultsResults

Parameters (Parameters (nn=1)=1)

Fibrillation


October 22, 2001

RésultatsRésultats

Conductivités (Conductivités (nn=5)=5)


October 22, 2001

Discussion and conclusionDiscussion and conclusion


October 22, 2001

Ce que je dit dans l ’abstract

• The most striking change was observed in the phase of the high frequency impedance, with a significant phase lag (4+/-1 degrees) that occurred rapidly (within about 5 minutes), 26 to 74 minutes after LAD occlusion, and was soon followed by fibrillation.

• Preconditioning (which resulted from defibrillation in some animals) seemed to eliminate this abrupt phase lag

• Questions:– Since a small inter-electrode distance was used (350 um),

the current flowed only in the extracellular domain at low frequencies... Pourquoi?

In vivo myocardial electrical impedance during ischemia: phase shift as a marker of cellular...

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