CVRTICVRTI

Effects of Heart Position on the Body-Surface ECG

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 InstituteUniversity of Utah

CVRTICVRTI

An Old QuestionAn Old Question

• Sigler (1938)– body position

• Olbrich & Woodward-Williams (1953)– body position

• Dougherty (1970)– heart position

• Shapiro, Berson, and Pipberger (1976)– body position

• Sutherland et al.: (1983)– body position and

respiration• Green et al.: (1985)

– body habtitus• MacLeod et al.: (1997)• Hoekema (1999)

– heart/torso geometry

CVRTICVRTI

Sources of VariationSources of Variation

• Geometry variation: – anatomic differences– body position– respiration– electrode placement

• Physiologic variation: – pathology– beat to beat changes– rate effects– central control (ANS)– …..

CVRTICVRTI

Relevant Questions for ECG?Relevant Questions for ECG?

• How much variation is there?• Where does it come from?• How can we isolate the sources?• Is compensation possible?

CVRTICVRTI

Some New ApproachesSome New Approaches

• Clinical– BSPM– medical imaging

• Simulations– forward/inverse solutions

• Experimental– isolated heart– electrolytic torso tank– three-dimensional digitizer

CVRTICVRTI

Technical ApparatusTechnical Apparatus

• “Andy III”• 370 electrodes• R = 500 cm• Homogeneous• 1024 channel

acquisition

CVRTICVRTI

Isolated Heart PreparationIsolated Heart Preparation

TorsoTank Electrodes

Epicardial Sock Electrodes

Support Dog

Flow Regulators

Heat ExchangeC J

ElectrolyticTorso Tank

CVRTICVRTI

Shifting Heart LocationShifting Heart Location

YY

ZZ

XX

CVRTICVRTI

Pacing ProtocolsPacing Protocols

RV LV

Apex

Atrial Post

Anterior

CVRTICVRTI

Parameter ExtractionParameter ExtractionQRS STT

Shift (x, y, z)

Ref. 1 cm 5 cm4 cm3 cm2 cm 6 cm

ATDR

RV

Ant.

LV

Post.

Apex

Pac

ing

QRSQRS

STT

CVRTICVRTI

X-shift; QRS; RV Pacing X-shift; QRS; RV Pacing

YYZZ

XX

CVRTICVRTI

Z-Shift; QRS; Atrial PacingZ-Shift; QRS; Atrial Pacing

YYZZ

XX

CVRTICVRTI

Peak Amplitudes: Y-shiftPeak Amplitudes: Y-shift

1 2 3 4 50

1

2

3

4

5

6

Shift in cm

QR

S-m

ax o

n t

he

tan

k [a

bs.

mV

]

Peak QRS-max

atrialRVanteriorleft lat.posteriorapex

1 2 3 4 50

1

2

3

4

5

Shift in cm

ST

-max

on

th

e ta

nk

[ab

s. m

V]

Peak ST-max

atrialRVanteriorleft lat.posteriorapex

CVRTICVRTI

Peak Amplitudes: Z-shiftPeak Amplitudes: Z-shift

1 2 3 4 50

1

2

3

4

5

Shift in cm

QR

S-m

ax o

n t

he

tan

k [a

bs.

mV

]

Peak QRS-max

atrialRVanteriorleft lat.posteriorapex

Shift in cm

1 2 3 4 50

1

2

3

4

5

ST

-ma

x o

n t

he

ta

nk

[a

bs

. m

V]

Peak ST-max

atrialRVanteriorleft lat.posteriorapex

CVRTICVRTI

Variability Index: X shiftVariability Index: X shift

1 2 3 4 50

0.5

1

1.5

2

2.5

3

Shift in cm

Va

ria

bil

ity

[m

V]

QRS

atrialRVanteriorleft lat.posteriorapex

1 2 3 4 50

0.5

1

1.5

2

2.5

3

Shift in cm

Va

ria

bil

ity

[m

V]

STT

atrialRVanteriorleft lat.posteriorapex

Sutherland et al.

STT: 1.5--3.5QRS: 2.2--6.8

Var = RMS(iref)

CVRTICVRTI

Variability Index: Y shiftVariability Index: Y shift

1 2 3 4 5

Shift in cm

Va

ria

bil

ity

[m

V]

QRS

atrialRVanteriorleft lat.posteriorapex

0

0.5

1

1.5

2

2.5

0

0.5

1

1.5

2

2.5

1 2 3 4 5

Shift in cm

Va

ria

bil

ity

[m

V]

STT

atrialRVanteriorleft lat.posteriorapex

Sutherland et al.

STT: 1.5--3.5QRS: 2.2--6.8

CVRTICVRTI

Relative VariabilityRelative Variability

Pacing Site Rel. Var.Atrial 0.224RV 0.209Anterior 0.419LV 0.111Post. 0.112Apex 0.113

Isolated Heart Hoekema (1999)

Source Rel. Var.Physiol. 0.33Geomtry 0.40Total 0.52

RelVar = Stnd. Dev.

RMSref

CVRTICVRTI

What Did We Learn?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