Effects of Heart Position on
the Body-Surface ECG
Rob MacLeod, Quan Ni, Bonnie Punske,
Phil Ershler, Bulent Yilmaz,
Bruno Taccardi
Cardiovascular Research and Training Institute
University of Utah
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An Old Question
• Sigler (1938)
– body position
• Olbrich & WoodwardWilliams (1953)
– body position
• Dougherty (1970)
• Sutherland et al.:
(1983)
– body position and
respiration
• Green et al.: (1985)
– body habtitus
• MacLeod et al.: (1997)
• Shapiro, Berson, and • Hoekema (1999)
– heart/torso geometry
Pipberger (1976)
– heart position
– body position
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Sources of Variation
• Geometry variation:
– anatomic differences
– body position
– respiration
– electrode placement
• Physiologic variation:
– pathology
– beat to beat changes
– rate effects
– central control (ANS)
– …..
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Relevant Questions for ECG?
•
•
•
•
How much variation is there?
Where does it come from?
How can we isolate the sources?
Is compensation possible?
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Some New Approaches
• Clinical
– BSPM
– medical imaging
• Simulations
– forward/inverse solutions
• Experimental
– isolated heart
– electrolytic torso tank
– three-dimensional digitizer
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Technical
Apparatus
•
•
•
•
•
“Andy III”
370 electrodes
R = 500 W cm
Homogeneous
1024 channel
acquisition
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Isolated Heart Preparation
Electrolytic
Torso Tank
Flow Regulators
Heat Exchange
C
J
Support
Dog
Epicardial Sock
Electrodes
TorsoTank
Electrodes
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Shifting Heart Location
Z
X
Y
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Pacing Protocols
Atrial
Post
Anterior
LV
RV
Apex
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Parameter Extraction
QRS
STT
Shift (x, y, z)
STT
QRS
QRS
Ref. 1 cm
2 cm
3 cm
4 cm
5 cm
6 cm
Pacing
ATDR
RV
Ant.
LV
Post.
Apex
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X-shift; QRS; RV Pacing
Z
Y
X
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Z-Shift; QRS; Atrial Pacing
Z
Y
X
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Peak Amplitudes: Y-shift
Peak QRS-max
Peak ST-max
5
atrial
RV
anterior
left lat.
posterior
apex
ST-max on the tank [abs. mV]
QRS-max on the tank [abs. mV]
5
6
4
3
2
1
01
2
3
Shift in cm
4
5
4
atrial
RV
anterior
left lat.
posterior
apex
3
2
1
01
2
3
4
5
Shift in cm
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Peak Amplitudes: Z-shift
Peak QRS-max
Peak ST-max
5
4
atrial
RV
anterior
left lat.
posterior
apex
ST-max on the tank [abs. mV]
QRS-max on the tank [abs. mV]
5
3
2
1
01
2
3
Shift in cm
4
5
4
atrial
RV
anterior
left lat.
posterior
apex
3
2
1
01
2
3
4
5
Shift in cm
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Variability Index: X shift
QRS
3
2.5
Variability [mV]
atrial
RV
anterior
left lat.
posterior
apex
3
Variability [mV]
Var = RMS(Fi - Fref)
2
1.5
1
atrial
RV
anterior
left lat.
posterior
apex
2.5
2
1.5
1
0.5
0.5
0
STT
1
2
3
4
5
0
1
Shift in cm
2
3
4
5
Shift in cm
Sutherland et al.
QRS: 2.2--6.8
STT: 1.5--3.5
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Variability Index: Y shift
QRS
atrial
RV
anterior
left lat.
posterior
apex
2
1.5
1
0.5
0
atrial
RV
anterior
left lat.
posterior
apex
2.5
Variability [mV]
2.5
Variability [mV]
STT
2
1.5
1
0.5
1
2
3
Shift in cm
QRS: 2.2--6.8
4
5
0
1
Sutherland et al.
2
3
4
5
Shift in cm
STT: 1.5--3.5
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Relative Variability
Stnd. Dev.
RelVar =
RMSref
Isolated Heart
Pacing Site Rel. Var.
Atrial
0.224
RV
0.209
Anterior
0.419
LV
0.111
Post.
0.112
Apex
0.113
Hoekema (1999)
Source
Physiol.
Geomtry
Total
Rel. Var.
0.33
0.40
0.52
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What Did We Learn?
• Experiments replicated clinical results
– Sutherland: patterns, amplitudes, variability
– Hoekema: relative variation index
• The role of geometry is complex
• Geometry errors could affect diagnosis
• Future:
– mimic changes in body position
– compare with electrode placement errors
– recognize and compensate for geometry errors
– simulations
• Bicycling is essential for good research
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