PISA Evaluation of Mitral Regurgitation Raymond Graber, MD Cardiac Anesthesia Group University Hospitals Case Medical Center 4/07/2011
Introduction Evaluation of MR. What is PISA? Physiologic basis Issues How to do it with GE Vivid 7.
Zoghbi WA, et al. Recommendations for Evaluation of the Severity of Native Valvular Regurgitation with Two-dimensional and Doppler Echocardiography. J Am Soc Echocardiogr 2003;16:777-802. In the OR, typical methods for MR evaluation include qualitative measures such as color jet area, chamber size, and pulmonary vein flow. Quantitative measures include vena contracta and measures of EROA and regurgitant volume.
Regurgitant Color Doppler Flow Pattern: Distal jet. Vena contracta Proximal flow convergence
Jet Area Issues Evaluating color jet area would seem to be an easy thing to do, but there are multiple caveats: Assumes that regurgitant velocities correlates with regurgitant volumes. Is one point in time, whereas volume includes duration of flow. Behavior of jet depends on receiving chamber can be constrained by side of atrium Jets can course outside of ultrasound plane. Depend on machine settings. Depends on driving pressure across the mitral valve.
Phenylephrine used to elevate BPsys by 40-50 mm Hg in group A. Gain settings changed.
Fehske W et al: Am J Cardiol 73:268-274, 1994 Note the overlap between groups!
What is PISA? PISA = Proximal Isovelocity Surface Area A concept that can be used to help determine size of a regurgitant or stenotic orifice. Based on flow dynamics, use of aliasing and continuity principle.
Flow Dynamics 1 When fluid is forced from a chamber thru an orifice, the fluid accelerates towards the orifice, and velocity is greatest at the narrowest point of the orifice.
Flow Dynamics 2 Conceptually, this results in a series of concentric hemispheres of increasing velocity as the orifice is approached. These are the proximal isovelocity hemispheric shells that we will calculate the surface area of.
With color Doppler, as flow accelerates towards orifice at some point, velocity may exceed the aliasing velocity, and color will reverse from red to blue. At this hemisphere, the velocity is thus known (it equals the aliasing velocity). Use of Aliasing
Continuity Principle Because of the conservation of mass principle, flow rate must remain constant along the length of a conduit (assuming the absence of any leaks or additional input) A 1 x V 1 = A 2 x V 2
Applying this to MR: Regurgitant Orifice Flow = Flow at hemisphere of color change EROA x V orifice = A hemisphere V hemisphere V orifice =V max (by CWD) A hemisphere = 2πr 2 V hemisphere = V Aliasing EROA x V max = 2 πr 2 x V Aliasing
The end result: EROA = 2 πr 2 (V Aliasing / V max ) RV mr = EROA x TVI mr
Assumptions: Assumes accurate Doppler measurement of regurgitant velocity. Assumes regurgitant orifice is circular. Assumes that the orifice is on a planar surface, and that the incoming flow forms a complete hemisphere. Assumes single orifice. Depends on accurate measurement of radius. Assumes that regurgitant orifice is constant in size.
Can we measure regurgitant velocity accurately with Doppler?
Central jet: good CWD curve.
Eccentric jet: suboptimal CWD curve.
Are Regurgitant Orifices Circular? This 3D TEE shows a regurgitant orifice that is elongated.
Rifkin and Sharma. Alternative Isovelocity Surface Model. J A C C : Cardiovascular Imaging 2010 Other mathematical models being developed for PISA in non-hemispherical orifices.
Is the orifice on a planar surface? Eccentric jets frequently don t have a planar surface. A correction factor (a/180) can be used. (Multiply this times the calculated EROA and RV)
Is There A Single Orifice? Frequently not!
Getting an Accurate Measurement of Radius: Adjusting the aliasing velocity by shifting the color Doppler baseline towards the direction of flow increases the measured radius and improves accuracy.
Is the Regurgitant Orifice Constant In Size? Orifices can change in size over time, especially with prolapse. It is recommended to use the PISA radius that corresponds to the time of peak regurgitant velocity.
(J Am Coll Cardiol Img 2010; 3:235 43) How good are these measurements? Can we agree upon them?
In the ideal situation clinicians would look at a measure, and all would agree that the MR was severe, or agree that it was not. Yet in this study, was not the case. For example, looking at Jet size in patient 1, 39% rated it as severe, and 61% rated it as not severe!
Cardiologist Agreement The authors defined substantial agreement as >80% of cardiologists were in agreement with a finding for a specific patient. In what % of images was there substantial agreement? : Jet Area: 44% Vena Contracta: 44% EROA: 38%
Reasons for Variability of Assessments > 30% variation of PISA radius during the course of the MR jet: 44% > 30% variation of VC width during the course of the MR jet : 44% Effective MR orifice identifiable: 44% Eccentric were much harder to evaluate quantitativly then central jets
Their Conclusions: The VC and PISA measurements for distinction of severe versus non-severe MR are only modestly reliable and associated with suboptimal interobserver agreement. The presence of an identifiable effective regurgitant orifice improves reproducibility of VC and a central regurgitant jet predicts substantial agreement among multiple observers of PISA assessment.
Example: PISA Step By STEP
Use MELAX view, obtain image of MR jet that includes PISA shell, flow convergence and vena contracta. Also obtain image of CWD thru mitral valve, lining up with the regurgitant jet. Note the timing of the peak velocity of MR jet.
Bring up the MELAX view, and scroll to image that shows PISA shell. Ideally, this should correspond to the time of peak MR velocity.
Zoom to magnify the image, adjust the color Doppler baseline towards jet direction to achieve an aliasing velocity of.30-.40 m/sec.
In the Measurement menu find PISA MR under the PISA folder.
Turn color off to visualize ventricular side of orifice center.
Place cursor at this location to start radius measurement.
Turn color back on, and draw radius to PISA shell.
Bring up CWD of mitral regurg jet. Find PISA MR under the PISA folder.
Trace MR curve. ERO and RV are calculated by the machine.
EROA = 2 πr 2 (V Aliasing / V max ) EROA = 2 (3.14)(.8 cm) 2 (.29 m/sec)/(4.35 m/sec) EROA =.269 cm 2 RV = EROA x TVI mr =.269 cm 2 x 137.9 cm RV = 37.09 cm 3 Note rounding by the machine!
Putting it All Together: Jet Area: 7 cm 2 Vena Contracta:.3 cm EROA:.269 cm 2 RV: 37 ml
Jet Area: 7 cm 2 Vena Contracta:.3 cm EROA:.269 cm 2 RV: 37 ml Moderate MR (low end)
Notes: If you are doing calculations by hand, make sure you convert units as needed. Some machines use cm/sec, others use m/sec. GE Vivid 7: m/sec
Notes: Use angle correction factor as needed: Generally don t need to correct central jets, but becomes an issue with eccentric jets and also when used in mitral stenosis. Multiply machine calculated EROA and RV by (a/180) to get corrected numbers. If doing your own calculations, use this factor only in the EROA calculation. Then this corrected EROA x TVI mr = corrected RV.
Modifications: Derivation of Angle Correction: If hemisphere is not complete because of impingement by wall or leaflet (leading to a funnel constraining flow), area of hemisphere is modified: A hemisphere = 2πr 2 (a/180) Where a is the proximal flow convergence angle Thus: EROA = 2 πr 2 (V Aliasing / V max ) (a/180)
Modifications: No CWD Measures If you can t get a good CWD waveform, here is a method to estimate EROA. Set aliasing velocity to 40 cm/sec. Assume Vmax = 500 cm/sec (This works when LV systolic pressure is greater than left atrial pressure by about 100 mm Hg) EROA x V max = 2 πr 2 x V Aliasing EROA = 2(3.14)r 2 (40)/(500) EROA = r 2 /2
Conclusions: We discussed basis of PISA calculations. Discussed pitfalls of PISA. Showed an example how to do PISA measurements with the GE Vivid 7.
In the end, one must integrate all the qualitative and quantitative measures to come up with a good MR severity assessment. It seems that we have a lot of room for improvement, and that current echocardiographic grading of MR severity is more art than science. Paul A. Grayburn, MD, Paul Bhella, MD 2010
References: Zoghbi WA, et al. Recommendations for Evaluation of the Severity of Native Valvular Regurgitation with Two-dimensional and Doppler Echocardiography. J Am Soc Echocardiogr 2003;16:777-802. Lambert S. Proximal Isovelocity Surface Area Should Be Routinely Measured in Evaluating Mitral Regurgitation: A Core Review. Anesth Analg 2007;105:940 3 Shanewise JS. PRO: Proximal Isovelocity Surface Area Should Be Routinely Measured in Evaluating Mitral Regurgitation. Anesth Analg 2007;105:947-8 Savage RM, Konstadt S. CON: Proximal Isovelocity Surface Area Should Not Be Measured Routinely in All Patients with Mitral Regurgitation Anesth Analg 2007;105:944-6 Paul A. Grayburn, MD, Paul Bhella, MD Grading Severity of Mitral Regurgitation byechocardiography: Science or Art? JACC: Cardiovascular Imaging 2010. 3: 244-246 Biner S, Rafique A, Rafii F, et al. Reproducibility of proximal isovelocity surface area, vena contracta, and regurgitant jet area for assessment of mitral regurgitation severity. J Am Coll Cardiol Img 2010;3:235 43.