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In vivo myocardial electrical
impedance during ischemia: phase
shift as a marker of cellular
uncoupling 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
Plan
•
•
•
•
•
•
Motivation and objectives
Introduction
Measurement system
Experimental protocol
Results
Discussion et conclusions
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
Motivation 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
Canadian Cardiovascular
Congress, Halifax NS
Introduction
Impedance
Z = V / I = R + jX
Impedance amplitude
Z 
R X
2
2
  arctg ( X / R )
Impedance phase

I
V
time
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
Introduction
Cellular uncoupling
Healthy region
K+
Ca++
Na+
Na+
K+
Ca++
Na+ K+
Ca++
K+
Ca++
Na+
Ischemic region
K+
Ca++
Na+
Na+
K+
Ca++
Gap junction
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
Measurement system
Impedance measurement
The four-electrode technique
f
h
g
e
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
Measurement system
Resistivities determination
• From impedance to intracellular and
extracellular resistivities : The bidomain
anisotropic model
re extracellular
Rm
Cm
rc
intracellular
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
rgap
rj
Experimental 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
Canadian Cardiovascular
Congress, Halifax NS
Results
Impedance (n=1)
Fibrillation
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
Results
Impedance (n=1)
Fibrillation
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
Results
Bidomain parameters (n=1)
Fibrillation
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
Results
Bidomain parameters (n=1)
Fibrillation
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
Discussion 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
Canadian Cardiovascular
Congress, Halifax NS
Acknowledgments
• 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
Canadian Cardiovascular
Congress, Halifax NS
Thank You
Questions?
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
Resistivity
In a resistive environment:
R = V/I = l / A
 = resistivity [m]
 l A
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
Measurement system
Impedance measurement
The acquisition system
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
Système de mesure
La sonde: courant alternatif
Courant direct
Idc
g e -1
Rm
Courant alternatif
g i -1
g e -1
Rm
g i -1
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
Idc
Signal treatment software
Tension
Bruit
+ 
Signal filtré
Détecteu
r RMS
Z=V/I
Phase
+
-
Signal filtré
Détecteu
r RMS
Courant
Bruit
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
Source: Pierre
LeGuyader
Measurement system
Resistivities determination
Measures
Simulations
V/I
V/I
+  Error
f
f
• longitudinal + transverse
• frequencies (12Hz-10kHz)
Parameters
October 22, 2001
Minimisation of
the error
Canadian Cardiovascular
Congress, Halifax NS
Results
Parameters (n=1)
Fibrillation
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
Résultats
Conductivités (n=5)
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
Résultats
Conductivités (n=5)
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
Discussion and conclusion
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS
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?
October 22, 2001
Canadian Cardiovascular
Congress, Halifax NS