In vivo myocardial electrical impedance during ischemia: phase shift as a marker of cellular...
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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
Canadian Cardiovascular Congress, Halifax NS
October 22, 2001
PlanPlan
• Motivation and objectives • Introduction• Measurement system• Experimental protocol• Results• Discussion et conclusions
Canadian Cardiovascular Congress, Halifax NS
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
Canadian Cardiovascular Congress, Halifax NS
October 22, 2001
IntroductionIntroduction
ImpedanceImpedance
Impedance amplitude
Impedance phase )/(
22
RXarctg
XRZ
Z = V / I = R + jX
I V
time
Canadian Cardiovascular Congress, Halifax NS
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++
Canadian Cardiovascular Congress, Halifax NS
October 22, 2001
Measurement systemMeasurement system
Impedance measurementImpedance measurement
i ac.
e
-+
f
gh
The four-electrode technique
Canadian Cardiovascular Congress, Halifax NS
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
Canadian Cardiovascular Congress, Halifax NS
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)
Canadian Cardiovascular Congress, Halifax NS
October 22, 2001
ResultsResults
Impedance (Impedance (nn=1)=1)
Fibrillation
Canadian Cardiovascular Congress, Halifax NS
October 22, 2001
ResultsResults
Impedance (Impedance (nn=1)=1)
Fibrillation
Canadian Cardiovascular Congress, Halifax NS
October 22, 2001
ResultsResults
Bidomain parameters (Bidomain parameters (nn=1)=1)
Fibrillation
Canadian Cardiovascular Congress, Halifax NS
October 22, 2001
ResultsResults
Bidomain parameters (Bidomain parameters (nn=1)=1)
Fibrillation
Canadian Cardiovascular Congress, Halifax NS
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)
Canadian Cardiovascular Congress, Halifax NS
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
Canadian Cardiovascular Congress, Halifax NS
October 22, 2001
Thank YouThank You
Questions?Questions?
Canadian Cardiovascular Congress, Halifax NS
October 22, 2001
ResistivityResistivity
In a resistive environment:
R = V/I = l / A
= resistivity [m]
A l
Canadian Cardiovascular Congress, Halifax NS
October 22, 2001
Measurement systemMeasurement system
Impedance measurementImpedance measurementThe acquisition system
Canadian Cardiovascular Congress, Halifax NS
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
Canadian Cardiovascular Congress, Halifax NS
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
Canadian Cardiovascular Congress, Halifax NS
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)
Canadian Cardiovascular Congress, Halifax NS
October 22, 2001
ResultsResults
Parameters (Parameters (nn=1)=1)
Fibrillation
Canadian Cardiovascular Congress, Halifax NS
October 22, 2001
RésultatsRésultats
Conductivités (Conductivités (nn=5)=5)
Canadian Cardiovascular Congress, Halifax NS
October 22, 2001
RésultatsRésultats
Conductivités (Conductivités (nn=5)=5)
Canadian Cardiovascular Congress, Halifax NS
October 22, 2001
Discussion and conclusionDiscussion and conclusion
Canadian Cardiovascular Congress, Halifax NS
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?