Transcript Slide 1

Electrical Cardiometry for the measurement of
cardiac output in pregnancy
Tom Archer, MD, MBA
Clinical Professor and Director of Obstetric Anesthesia
University of California, San Diego
Modified June 19, 2013
Our Research Team
• Tom Archer, MD, MBA
• Jerry Ballas, MD, MPH
• Kristin Mantell, MD
• Kristen Buono, MD
• Thao Huyhn-Covey RDCS
Cardiac output in OB—why?
Post-partum hemorrhage?
Preeclampsia?
Cardiomyopathy?
Sepsis?
Valvular heart disease?
Anesthesia?
Aortocaval compression?
Obesity?
Uterotonic titration?
Study of normal events?
Cardiac output in OB—why not?
Predominantly awake and healthy patients
Happy, “normal” event (hopefully)
Reduced tolerance for discomfort during personal, happy, normal event
There has been no good technology to measure
cardiac output comfortably, cheaply and
continuously in awake patients!
But first, the bad news about
Electrical Cardiometry…
I am fascinated with this technology but it has
several possibly insurmountable barriers to its
being accepted…
“Problems” with electrical cardiometry (EC)
• EC is too easy to use, both for operator and patient.
• EC does not look impressive.
• EC does not require bulky and intimidating equipment.
• EC is not even slightly uncomfortable for the patient.
• EC does not require advanced training.
“Problems” with electrical cardiometry (EC)
• EC does not require assistants or technicians to obtain
measurements and to clean and maintain the equipment.
• EC does not required the placement of large tubes in
large blood vessels.
“Problems” with electrical cardiometry (EC)
• EC costs almost nothing on a per-use basis (four EKG
patches).
• EC does not require workshops in order to master it.
• There is no American Society of Electrical Cardiometry
(yet) for you to belong to and which will certify you so that
you can have more cool letters behind your name such as
“FASEC”.
• EC is not fashionable (yet).
“Problems” with electrical cardiometry (EC)
• But, the worst aspect of EC-- which probably makes it
totally unacceptable to the medical community– is that:
• EC involves mathematics and electricity.
All kidding aside…
• Electrical cardiometry is a very promising
technology which I believe may facilitate
patient management not just in obstetrics, but
in all of medicine…
Tolerated by
Pain-free in
Cardiac
awake OB
output method awake patient? patient?
Pulmonary
artery catheter
“Weird”?
Maybe
Yes
No
Yes
Somewhat
No
No
No
No
Yes
Yes
No
No
No
USCOM
(sternal notch
Doppler VTI)
Yes
Maybe
Electrical
cardiometry/
NICOM
Yes
Yes
No (arterial
line required)
Yes
Continuous,
hands-free
data?
No
Pulse contour
analysis
No
Easy to
apply?
No
(Flo-Trac, LiDCO)
Transesophageal
echocardiography
No
(TEE)
Transthoracic
echocardiography
No
No
Maybe
Maybe
No
Sort of
No
Yes
Yes
Yes
(TTE)
Cardio-Q
(esophageal
Doppler VTI)
Yes
Background and Review
Stroke volume from “formal” TTE– one easy and one hard measurement.
Easy (from LPSLAX view):
Left ventricular outflow tract
(LVOT) diameter, gives
LVOT Area.
Stroke volume is the volume
of a cylinder:
Base x Height =
LVOT Area x Stroke distance
Hard (from Apical view):
Stroke distance = Velocity-Time Integral (VTI_TTE)
VTI_TTE = Vmean_TTE x Envelope Time_TTE
Background
Echocardiography for Measuring Cardiac Output
Π x LVOT Diameter2
4
LVOT Area
Left parasternal long axis
(cm2)
Apical 5 chamber view with PW
Doppler aligned with LVOT
VTI = Distance
Traveled by Blood
through LVOT (cm)
SV = VTI x LVOT area
Tracing the envelope provides
the Velocity-Time Integral (VTI)
LVOT Diameter
CO = SV x HR
https://www.stanford.edu/group/ccm_echocardio/cgi-bin/mediawiki/index.php/Cardiac_output
Examples of high and low VTI. VTI– the “area under the curve”-- is the stroke distance.
Patient 13
2
Equivalent terms: stroke distance,
velocity-time integral, or VTI
SV_TTE = LVOT_Area * Vmean_TTE * Envelope_Time_TTE
Equation for stroke volume from TTE.
Summary of study results
Summary
• Non-invasive, painless, continuous and
inexpensive measurement of cardiac output
might be useful in some pregnant patients (as
well as in critical care in general).
• Electrical cardiometry, without further
modification, appears to identify trends in
cardiac output in pregnant patients.
Summary
• Electrical cardiometry, without further
modification, appears not to give acceptably
accurate absolute values of cardiac output in
pregnant patients.
• We propose modifications to electrical
cardiometry in order to deliver absolute
values of cardiac output with acceptable
accuracy.
Summary
• We propose two models for using left
ventricular outflow tract diameter together
with electrical cardiometry to acquire absolute
values for stroke volume:
• Model A
• Model B
Summary
• Model A uses left ventricular outflow tract
diameter to “calibrate” the existing “off the shelf”
measurement of stroke volume.
Stroke Volume
from Model A
A term involving the “off the
shelf” estimate of stroke
volume (SV_EC) by current
electrical cardiometry.
A term which
“calibrates” the
SV_EC to a specific
LVOT area.
SV_Model_A = (-17.4) + (0.356 x SV_EC) + (17.7 x LVOT_Area)
A constant
Summary
• Model B uses the fundamental electrophysiological
parameters underlying electrical cardiometry to construct a
“virtual velocity time integral”, which can be trended by
itself, or– if absolute values for stroke volume are required–
it can be multiplied by the LVOT area to acquire the
absolute value of stroke volume.
• Model B is attractive intellectually because it makes
electrical cardiometry understandable– and testable–
using the same mathematical model as “formal”
transthoracic echocardiography.
EC parameters can be used to predict TTE parameters!
Model B uses the underlying parameters of electrical cardiometry (height, weight, ICON and LVET_EC) to
construct a “Vmean_EC” which is a prediction as to Vmean_TTE , and the LVET_EC which is prediction
as to Envelope_Time_TTE.
SQRT_ICON correlates with Vmean_TTE only when it is corrected for BMI, as shown here.
(Vmean_EC)
SV_RM_B = K2
It works!
*
SQRT_ICON / (16.8 – 0.2 * BMI)
Hand-held
TTE needed
Yes!
*
LVET_EC
Yes!
SV_TTE = LVOT_Area * Vmean_TTE * Envelope_Time_TTE
Stroke volume equation from TTE.
Clinical examples:
Electrical cardiometry for
trending cardiac output,
ignoring absolute value.
We compare measurements
over time in a single patient
Each patient is “her own control.”
Ballas et al SOAP 2012
SBG painful labor, no epidural. Uterine contractions, in the presence of an open inferior
Ballas et al SOAP 2012
SBG painful labor: Increases in cardiac output are mostly due to increases in heart rate
Ballas et al SOAP 2012
Pt FEW. Pain free, epidural in place. “Autotransfusion waves” follow uterine
contractions by about 40 seconds. Similar to patient SBG, except…
Ballas et al SOAP 2012
Pt FEW. Pain free, epidural in place. “Autotransfusion waves” are mostly due to
increased stroke index (SI), not heart rate (HR).
Pt FEW. Epidural in place. Position change from right side down to left side down is associated with increased blood pressure and
cardiac index and appearance of “autotransfusion waves”, which were absent prior to position change, despite occurrence of
contractions. Also: position change is associated with increased contraction frequency. Does this denote improved uterine
Uterine contractions in the presence of an open inferior vena cava cause
“autotransfusion waves” of increased cardiac output, which follow the uterine
contractions by 20-40 seconds.
Blockage of the inferior vena cava by the gravid uterus causes the overall cardiac
output to decrease. Furthermore, autotransfused blood from uterine contractions
cannot easily and quickly return to the heart and autotransfusion waves do not occur,
or are decreased in amplitude.
Cesarean delivery and oxytocin administration usually cause increases in heart rate
and cardiac output, along with modest increases in stroke volume.
Archer TL, Conrad BE, Tarsa M, Suresh P. J Clin Anesth. 2012 Feb;24(1):79-82
Magnesium sulfate decreases systemic vascular resistance and increases cardiac output, but lowers blood pressure only slightly.
Labetalol furthers decreases SVR and BP, and further increases CO.
Archer TL, Conrad BE. Int J Obstet Anesth. 2011 Jan;20(1):91-2.
Hydralazine reduces systemic vascular resistance and blood pressure and increases cardiac output.
Magnesium sulfate augments these tendencies. A decrease in fetal heart rate is reversed by patient’s adopting
left side down position.
Archer TL, Conrad BE. Int J Obstet Anesth. 2011 Jan;20(1):91-2.
Maternal position affects cardiac index and stroke volume at 26+3 weeks gestation in an asymptomatic patient.
Could chronic aortocaval compression cause fetal problems during gestation?
Maternal
heart rate
Archer TL, Suresh PJ, Ballas J. Ultrasound in Obstetrics and Gynecology 2011 Aug 11 doi: 10.1002/uog.10065 (Epub ahead of print).
Pt R
28 yo G2P0 at 35 weeks 5 days presenting with type I diabetes (since age 9) and severe preeclampsia. Patient had Cesarean section for severe pre-eclampsia and non-reassuring fetal heart rate.
Patient had severe postpartum hemorrhage, but recovered after multiple blood transfusions and reexploration for bleeding. Note small ventricular size during PPH, with increase in dimensions after recovery.
During postpartum hemorrhage and hypotension, her heart rate never increased—possibly due to
autonomic neuropathy?
Archer et al SOAP 2013
Pt R– HR, SV and CO during post-partum hemorrhage and after recovery
120
20
18
100
16
14
80
12
60
10
8
40
6
4
20
2
July 8-----------------------------------------------
0
7:40:48
July 13
0
8:09:36
8:38:24
9:07:12
HR
Archer et al unpublished. Pt R from SOAP 2013 poster
9:36:00
SV
10:04:48
CO
10:33:36
11:02:24
Electrical cardiometry for
absolute value of cardiac output.
Except for two slides which are noted, all measurements are from 23
laboring and non-laboring patients with their left side down and with
time difference between TTE and EC measurements = or < 10 sec.
Patient 13
2
Single laboring patient 13
Percentage Error = 15.4 % in a single patient.
Bland Altman Plot
30% upper limit = 1.5 mL
Upper limit of agreement (Bias + 2 SD) = -8.8 mL
Bias = -19.2 mL
Limit of agreement (Bias - 2 SD) = -29.6 mL
30% lower limit = -39.9 mL
23 patients, 18 non-laboring and 5 laboring.
Percentage Error = 45.6 %, before Model A
Bland Altman Plot
Upper limit of agreement (Bias + 2 SD) = 12.2 mL
30% upper limit = -1.4 mL
Bias = -27.8 mL
30% lower limit = -54.2 mL
Lower limit of agreement (Bias - 2 SD) = -67.8 mL
Our theory: within a single patient,
SV_EC trends with SV_TTE. But
between patients agreement of
absolute values is poor.
Is this due to varying LVOT diameters?
Calibrating electrical cardiometry using measured LVOT diameter:
Model A
18 Non-laboring patients (91 data points)
Develop Model A:
SV_Model_A = -17.4 + 0.356*SV_EC + 17.7*LVOT_Area_cm2
Test SV_Model_A
on the 5 laboring patients (391 data points)
Developing Model A in 18 non-laboring patients, 91 data points
18 non-laboring patients, 91 data points.
Bland Altman analysis. Percentage error = 38.2 %
Upper limit of agreement (Bias + 2 SD) = 17.9 mL
30% upper limit = 10.8 mL
Bias = -15.3 mL
30% lower limit = -41.4 mL
Lower limit of agreement (Bias - 2 SD) = -48.5 mL
Model A, which calibrates stroke volume estimation by electrical cardiometry using
knowledge of the left ventricular outflow tract (LVOT) area– was developed from 18 nonlaboring patients using step-wise linear regression.
This term “scales”
the EC estimate to a
specific LVOT area.
SV_Model_A = -17.4 + 0.356*SV_EC + 17.7*LVOT_Area_cm2
Model_A applied to 5 laboring patients
Before applying Model_A
After applying Model_A
% error =
18.4 %
% error =
18.9 %
Model B
• Model B uses the fundamental electrophysiological
parameters underlying electrical cardiometry to
construct a “virtual velocity time integral”, which is
then multiplied by the LVOT area to acquire the
absolute value of stroke volume.
• Model B is attractive intellectually because it
makes electrical cardiometry understandable– and
testable– using the same mathematical model as
“formal” transthoracic echocardiography.
Stroke volume from “formal” TTE– one easy and one hard measurement.
Easy (from LPSLAX, TTE view):
Left ventricular outflow tract
(LVOT) diameter, gives
LVOT Area.
Stroke volume is the volume
of a cylinder:
Base x Height =
LVOT Area x Stroke distance
Hard (from Apical, TTE view):
Stroke distance = Velocity-Time Integral (VTI_TTE)
VTI_TTE = Vmean_TTE x Envelope Time_TTE
Stroke volume from hand-held TTE + EC-- two easy measurements.
Easy (from LPSLAX
view):
Left ventricular outflow
tract (LVOT) diameter
from hand-held device
(e.g. GE Vscan), gives
LVOT Area.
Stroke volume is the volume
of a cylinder:
Base x Height =
LVOT Area x Stroke distance
Easy (from EC):
“Virtual Velocity-Time Integral” (VTI_EC),
derived as follows:
LVET_EC x Vmean_EC =
LVET_EC x SQRT_ICON / (16.8 – 0.2 x BMI)
Calibrating electrical cardiometry using measured LVOT diameter:
Model B
18 Non-laboring patients (using 18 data
points-- one average value for each
patient).
Develop Model B on 18 non-laboring patients:
SV_Model_B = LVOT_Area x LVET_EC x SQRT_ICON / (16.8 – 0.2 * BMI)
Test SV_Model_B on the 5 laboring patients (391 data points)
EC parameters can be used to predict TTE parameters!
Model B uses the underlying parameters of electrical cardiometry (height, weight and ICON) to construct
a “Vmean_EC” which is a prediction as to Vmean_TTE , and the LVET_EC which is prediction as to
Envelope_Time_TTE. This “virtual VTI” (VTI_EC) is then multiplied by the LVOT area to get SV.
(VTI_EC)
(Vmean_EC)
SV_RM_B = K2
It works!
*
SQRT_ICON / (16.8 – 0.2 * BMI)
Hand-held
TTE needed
Yes!
*
LVET_EC
Yes!
SV_TTE = LVOT_Area * Vmean_TTE * Envelope_Time_TTE
Stroke volume equation from TTE.
LVET_EC = Envelope_Time_TTE, without adjustment!
Percentage error = 14.6%
Bland Altman Plot
30% upper limit = 83.7 msec
Upper limit of agreement (Bias + 2 SD) = 40.4 msec
Bias = - 0.6 msec
Lower limit of agreement (Bias - 2 SD) = - 41.6 msec
30% lower limit = - 84.9 msec
Envelope time by transthoracic
echocardiography agrees with
Left ventricular ejection time (LVET)
by electrical cardiometry
There is no obvious correlation between SQRT_ICON and Vmean_TTE. Does this
mean there is no relationship between the two variables? No.
There is a relationship if we correct SQRT_ICON for the patient’s BMI, as
shown in the next slides.
23 patients, 482 data points
All 25 patients, all positions (942 data points)
All 25 patients, all positions (942 data points)
18 non-laboring patients. One data point per patient.
This data and linear model shown below are used to derive Vmean_EC (our
prediction of Vmean_TTE) from ICON and BMI. Equation is: Vmean_EC =
SQRT_ICON / (16.8 – 0.2*BMI)
25 patients, one point per patient. Showing two more high BMI patients with a low ratio of
SQRT_ICON/Vmean. Further support for idea that high BMI suppresses the ICON for a
given Vmean.
Our data suggest that increasing BMI decreases the ICON for a given Vmean_TTE.
(Is this because thoracic fat (breast tissue?) acts as a capacitor or resistor?)
This is a key hypothesis which needs verification or refutation from future studies.
BMI 25?
ICON = 89.1
Vmean_TTE = 0.8 m/sec
BMI 35?
ICON = 61.5
Vmean_TTE = 0.8 m/sec
Our theory: EC parameters can be used to predict TTE parameters!
Model B uses the underlying parameters of electrical cardiometry (height, weight,
ICON and LVET_EC) as follows:
(Vmean_EC)
SV_RM_B = K2
It works!
*
SQRT_ICON / (16.8 – 0.2 * BMI)
Hand-held
TTE needed
Yes!
*
LVET_EC
Yes!
SV_TTE = LVOT_Area * Vmean_TTE * Envelope_Time_TTE
Vmean_EC agrees with Vmean_TTE with a
percentage error = 19.8%
Bland Altman Plot
30% upper limit = 0.22 m/sec
Upper limit of agreement (Bias + 2 SD) = 0.14 m/sec
Bias = -0.02 m/sec
Limit of agreement (Bias - 2 SD) = -0.18 m/sec
30% lower limit = -0.26 m/sec
VTI_EC (which is Vmean_EC x LVET_EC) agrees with
VTI_TTE (which is Vmean_TTE x Envelope Time)
with a percentage error = 20.5%
Bland Altman Plot
30% upper limit = 6.2 cm
Upper limit of agreement (Bias + 2 SD) = 4.15 cm
Bias = -0.65 cm
Limit of agreement (Bias - 2 SD) = -5.45 cm
30% lower limit = -7.52 cm
Model_B applied to 5 laboring patients
Before applying Model_B
After applying Model_B
% error =
20.8
% error =
21.4
Comparison
in 5 laboring
patients.
SV_TTE
vs.
SV_EC
SV_TTE
vs.
SV_Model_A
Vmean_TTE
vs.
Vmean_EC
Model B
Envelope
Time_TTE
vs.
LVET_EC
VTI_TTE
vs.
VTI_EC
Model B
SV_TTE
vs.
SV_
Model_B
Bias
(SD)
-27.8 mL
(20)
-3.4 mL
(7.0)
-0.02 m/sec
(0.08)
0.71 msec -0.65 cm -1.6 mL
(22.1 )
(2.4 cm) (7.6)
Average of
2 methods
87.7 mL
74.1 mL
0.81 m/sec
285 msec
22.9 cm
45.5%
18.4%
19.8%
15.5%
20.5%
20.8%
0.686
0.921
0.391
0.879
0.541
0.884
Yes
No
No
No
Percentage
error
(1.96*SD
of Bias)/
Average of 2
methods)
Pearson
Correlation
Coefficient
Requires
knowledge
of LVOT area
No
HR_TTE
vs
HR_EC
CO_TTE
vs.
CO_
Model_B
-0.14
-0.3 bpm L/min
(1.5)
(0.6)
73.2 mL 77.1 bpm 5.6
L/min
Yes
3.9%
21.4%
0.984
0.78
No
Yes
Possible future research
• Repeat what we have done in more patients to see if it is true.
• Can EC optimize maternal positioning in labor to prevent
aortocaval compression and decrease occurrence of
hypotension after epidural, “fetal distress” or CS itself?
• Can EC optimize maternal positioning during gestation in
selected patients at risk for chronic aortocaval compression?
Could this palliate complications such as chronic abruption or
some cases of IUGR, by improving placental hemodynamics?
Possible future research
• Can EC help to predict, diagnose or manage preeclampsia?
• Can EC aid in diagnosing post-partum hemorrhage
and sepsis?
• Can EC be useful in fluid management in patients
with heart disease?
Possible future research
• Can EC help us to understand autotransfusion and
other normal events of labor?
• Can EC be useful in general Critical Care (outside of
obstetrics)?
The End
Patient 13
2
Overview
• A one-time measurement of the left
ventricular outflow tract diameter-- as could
be obtained with relative ease from hand-held
transthoracic echocardiography– may allow
the “calibration” of electrical cardiometry to
give absolute values of cardiac output with
acceptable accuracy.
A question and a challenge:
• If you could effortlessly, continuously and noninvasively measure cardiac output after a 5
minute, pain free set up time– would this be
useful?
• We believe we can do this.
• I challenge you to prove us right or wrong.
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SBG, painful labor and pushing. Delivery occurs when HR decreases.
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60
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HR
SV
CO