Editorial
CON: Proximal Isovelocity Surface
Area Should Not Be Measured
Routinely in All Patients with
Mitral Regurgitation
Robert M. Savage, MD, FACC*
Steven Konstadt, MD, FACC†
From the *Intraoperative Echocardiography, Cleveland Clinic Heart Center,
Cleveland, Ohio; and †Department of Anesthesiology, Maimonides Medical Center,
Brooklyn, New York.
Accepted for publication August 6, 2007.
Address correspondence and reprint requests to Robert M. Savage, MD, FACC,
Director, Intraoperative Echocardiography,
Cleveland Clinic Heart Center, Cleveland,
OH. Address e-mail to [email protected].
Copyright © 2007 International Anesthesia Research Society
DOI: 10.1213/01.ane.0000278524.33706.95
944
L
ong-standing moderate and severe mitral regurgitation (MR) lead to
remodeling of the left atrium, left ventricle, and, ultimately, the right ventricle.
These changes are associated with increased morbidity and mortality. Because
of the importance of the MR severity in a patient’s long-term outcome, the
American Society of Echocardiography has recommended that the evaluation
of MR severity take the time to “integrate multiple parameters of severity
assessment rather than rely on a single measurement (1).” In taking this
approach to severity assessment, the inherent theoretical, technical, or measurement errors associated with each method are minimized. Color flow
Doppler (CFD) measurements of maximal jet area (MJA) at an aliasing
velocity of 50 – 60 cm/s, the ratio of jet area/left atrial area, and the vena
contracta combined with pulsed wave Doppler interrogation of the pulmonary veins, in the absence of proximal isovelocity surface area (PISA), can
provide the required multiple techniques.
Just because one can do PISA measurements, it does not necessarily
follow that they should be done routinely. Though PISA is a recognized
means to assess the severity of MR, there are many reasons that its use
should not be universal. Even in the most simplified ways, PISA calculations may be time consuming for novices and require focus. Thus,
performance of these measurements may lead to distraction from patient
care. Another reason not to perform PISA calculations intraoperatively on
a routine basis is that in many, if not most, cases there are conditions that
invalidate the findings (Table 1). PISA measurements assume perfectly
symmetric spherical unconstrained flow acceleration. Unfortunately, in the
real world of pathologic mitral valves (MV), the geometry is often irregular
and not symmetric (Fig. 1). Another problem is that the measurements
vary throughout the cardiac cycle. Several studies evaluated continuous
PISA-regurgitant orifice area (ROA) using computational calculations of
the PISA-eROA (the effective size of the regurgitant orifice) through the
complete systolic period (2– 4). These instantaneous calculations were
computationally performed using instantaneous MR flow rates and the
corresponding simultaneous mitral regurgitant velocity in patients with
rheumatic, functional, and myxomatous MR. Patients with rheumatic MR
demonstrated parabolic MR flow rates and MR velocities which yielded a
relatively a fixed PISA-ROA. Patients with functional MR demonstrated a bifid
MR flow rate and parabolic MR velocity spectral envelope yielding a bifid
PISA-ROA curve that was largest in early and late systole. The ROA in MV
prolapse demonstrated a late peak as a result of a parabolic MR velocity
spectral envelope and a mid-to-late increase in the MR flow rate. This
study suggests that the maximal instantaneous PISA-ROA may not provide a reliable reflection of the ROA throughout systole or of the average
systolic ROA (4).
In patients with Carpentier Type I and III mechanisms of regurgitation,
there are often multiple regurgitant sites in addition to the dynamic nature
Vol. 105, No. 4, October 2007
Table 1. Assumptions Involved in Mitral Regurgitation (MR PISA Calculations) and Limitations
Theoretical assumptions
Single orifice
With one regurgitant orifice
area (ROA)
Circular orifice
Proximal flow isovelocity
zones are spherical
without contour
flattening approaching
orifice
Flow constraint by
proximal structures (e.g.,
LV wall)
Determination of proximal
orifice for PISA radius
measurement
Limiting circumstance
Potential impact
Correction
Multiple MR sites and
ROAs
Underestimate total ROA
Independent calculation
of multiple ROA
Non-hemispherical
Flow convergence (FC)
with flattening
Flattening of isovelocity FC
zones conicalization of
FC
Underestimates true ROA
Reduce aliasing velocity
to create true
hemisphere
Use aliasing velocity
that yields radius
near 10–15 mm
Hemisphere
Surface area 2␲r2
Eccentric MR jet FC
hemisphere impinges on
LV wall
Thickened orifice; eccentric
MR jet
Sphere pushed outward
leading to
overestimation
Radius error is squared
increasing exponentially
MR is pan-systolic
Less than pan-systolic MR
duration
Color flow doppler (CFD)
Maximal jet area (MJA)
overestimates severity
Temporal shape of
regurgitant orifice (RO)
is constant
Variable RO is not constant
in systole with functional
MR (early and late
systolic) or prolapse/flail
(late systole)
Dynamic ROA throughout
systole which is not fixed
May overestimate ROA
Vmax not simultaneous
with max PISA radius in
functional type III B or II
MR
Type IIIB and II
mechanisms impacted by
transmitral loading
conditions
Systolic LV-LA gradient is
variable-invalidates
Valiasing of 40 cm/s
Non-simultaneous events
lead to inaccuracy
Max ROA equivalent to
mean ROA in calculating
regurgitant volume
Maximal PISA radius is
simultaneous with MR
Vmax (Max MR velocity)
Loading conditions do not
effect ROA size or shape
Simplified PISA
assumption that systolic
LA-LV gradient is 100
mm Hg
Over estimates average
ROA
Changes in ROA and
shape
Invalidates simplified
equation
Impingement angle
correction of (X°/180) ⫻
(ROA)
Use vena contracta (VC)
automated orifice ID
and interaliasing
distance possible?
M-mode determination
of systolic % of MR
jet; if ⬍50% adjust
severity
Qualitative adjustment
using Color M-mode
Use simultaneous max
radius and Velocity
for calculations or
Use mean of ROA in
early, mid, late-mid,
and late systole
Correspond max radius
with V by ECG
timing
Always record MR
severity with MAP
and pre-load
pressures
Use aliasing velocity
according to Vmax;
ratio of 40/500 used
to determine correct
aliasing velocity
Valiasing ⫽ MR Vmax/12.5
FC ⫽ flow convergence; X ⫽ impingement angle; LA; left atrium. LV ⫽ left ventricle; MAP ⫽ Mean arterial pressure; PISA ⫽ proximal isovelocity surface area; ROA ⫽ regurgitant orifice area;
RO ⫽ regurgitant orifice.
of the ROA. Using PISA in these circumstances would
require an independent assessment of each regurgitant orifice. On the other hand, multiple jets do not
cause a problem when using CFD MJA color or
pulse-wave Doppler pulmonary vein assessment. Just
as one would not try to calculate mitral valve area by
the pressure half-time method in patients with significant aortic regurgitation; you should not rely on the
PISA measurement in all patients.
Another key point relates to patients scheduled for
MV surgery. The decision regarding the severity of
MR has already been made, and the most important
Vol. 105, No. 4, October 2007
role of the prepump transesophageal echocardiography examination is to determine the mechanism of the
MR not the severity. In MV repair surgery, the surgeon needs to know exactly why and where the valve
is leaking. This determination requires a careful twodimensional analysis of all views of the valve and then
CFD is used to confirm the location and mechanism.
Furthermore, as it has been shown in previous work
(5), due to variations in loading conditions under
anesthesia, intraoperative assessment may underestimate the severity of MR using CFD and pulmonary
venous flow analysis. The effects of changes in
© 2007 International Anesthesia Research Society
945
context of the patient’s presentation and 2) integrated
with other severity assessment methods in a manor that
is weighted by the quantitative ability of the specific
method, and the quality of the recorded data (1).
REFERENCES
Figure 1. Image of an ischemic Type IIIb restricted mitral
valve. Note the irregular shape of the deformity.
loading conditions on PISA measurements are not
well characterized.
In conclusion, PISA is not routinely indicated in all
intraoperative TEEs. However, in those circumstances
when MR severity is critical in guiding the intraoperative management of our patients, the PISA measurements should be performed. Most importantly,
however, PISA findings must be 1) considered in the
946
Editorial
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CD, Levine RA, Nihoyannopoulos P, Otto CM, Quinones MA,
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2. Schwammenthal E, Chen C, Benning F, Block M, Breithardt G,
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4. Schwammenthal E, Chunguang C, Benning F, Block M,
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5. Konstadt SN, Louie EK, Shore-Lesserson L, Black S, Scanlon P.
The effects of loading changes on intraoperative doppler assessment of mitral regurgitation. J Cardiothorac Vasc Anesth
1994;8:19 –23
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