Quantification of mitral regurgitation with the proximal flow convergence method: a clinical study

Assessment of the severity of native mitral valve regurgitation

Mitral regurgitation (MR) is a major cause of cardiovascular morbidity and mortality. MR is classified as primary (organic) if it is due to an intrinsic valve abnormality, or secondary (functional) if the etiology is because of remodeling of left ventricular geometry and/or valve annulus. Transthoracic echocardiography (TTE) is the initial modality for MR evaluation. Parameters used for the assessment of MR include valve structure, cardiac remodeling, and color and spectral Doppler. Quantitative measurements include effective regurgitant orifice area, regurgitant volume, and regurgitant fraction. Knowledge of advantages and limitations of echo-Doppler parameters is essential for accurate results. An integrative approach is recommended in overall grading of MR as mild, moderate, or severe since singular parameters may be affected by several factors. When the mechanism and/or grade of MR is unclear from the TTE or is discrepant with the clinical scenario, further evaluation with transesophageal echocardiography or cardiac magnetic resonance imaging is recommended, the latter emerging as a powerful MR quantitation tool.

Comparison of three-dimensional proximal isovelocity surface area to cardiac magnetic resonance imaging for quantifying mitral regurgitation

The aim of our study was to evaluate 3-dimensional (3D) color Doppler proximal isovelocity surface area (PISA) as a tool for quantitative assessment of mitral regurgitation (MR) against in vitro and in vivo reference methods. A customized 3D PISA software was validated in vitro against a flowmeter MR phantom. Sixty consecutive patients, with ≥mild MR of any cause, were recruited and the regurgitant volume (RVol) was measured by 2D PISA, 3D peak PISA, and 3D integrated PISA, using transthoracic (TTE) and transesophageal echocardiography (TEE). Cardiac magnetic resonance imaging (CMR) was used as reference method. Flowmeter RVol was associated with 3D integrated PISA as follows: y = 0.64x + 4.7, r(2) = 0.97, p <0.0001 for TEE and y = 0.88x + 4.07, r(2) = 0.96, p <0.0001 for TTE. The bias and limit of agreement in the Bland-Altman analysis were 6.8 ml [-3.5 to 17.1] for TEE and -0.059 ml [-6.2 to 6.1] for TTE. In vivo, TEE-derived 3D integrated PISA was the most accurate method for MR quantification compared to CMR: r(2) = 0.76, y = 0.95x - 3.95, p <0.0001; 5.1 ml (-14.7 to 26.5). It was superior to TEE 3D peak PISA (r(2) = 0.67, y = 1.00x + 6.20, p <0.0001; -6.3 ml [-33.4 to 21.0]), TEE 2D PISA (r(2) = 0.54, y = 0.76x + 0.18, p <0.0001; 8.4 ml [-20.4 to 37.2]), and TTE-derived measurements. It was also most accurate by receiver operating characteristic analysis (area under the curve 0.99) for the detection of severe MR, RVol cutoff = 48 ml, sensibility 100%, and specificity 96%. RVol and the cutoff to define severe MR were underestimated using the most accurate method. In conclusion, quantitative 3D color Doppler echocardiography of the PISA permits a more accurate MR assessment than conventional techniques and, consequently, should enable an optimized management of patients suffering from MR.

ASSESSMENT OF MITRAL REGURGITATION THROUGH DOPPLER ECHOCARDIOGRAPHY: FEASIBILITY, PITFALLS AND DIAGNOSTIC ADVANTAGES

Background: Echodoppler quantification of mitral regurgitation (MR) is still controversial, in particular little is known about correlation between quantitative and semi-quantitative methods. Methods and Results: 95 patients (pts) aged 58 +/- 13 years, 56% male, with at least moderate organic MR were enrolled in the period between Oct 2006 and Nov 2014. The etiology of MR was flail of MV leaflet. Regurgitant volume (RV) and effective regurgitant orifice (ERO) quantified by PISA (RV 56 ± 17 mL, ERO 0.32 ± 0.09 cm2), Doppler (RV 58 ± 17 mL, ERO 0.34 ± 0.12 cm2) and Volumetric (RV 48 ± 17 mL, ERO 0.27 ± 0.1 cm2) methods, were similar, particularly by quantitative Doppler and PISA (R2 0.89, p < 0.001). By semiquantitative methods jet area 4C was 9.1 ± 4.4 cm2, jet area/left atrium (LA) area 41 ± 20%, vena contracta (VC) was 5 ± 4.2 mm; pulmonary vein (PV) systolic flow reversal was present in 44% of patients. Only VC width among semiquantitative methods showed a sufficient correlation with RV (R2 0.52, p < 0.001), weaker with ERO (R2 0.46, p < 0.001). Conclusion: MR should be always evaluated by quantitative methods, particularly doppler and PISA RV and ERO, which showed the best correlation. Among semiquantitative methods only VC width represents a good option to RV or ERO evaluation by quantitative methods.

Surgical timing of degenerative mitral regurgitation: what to consider

Severe primary mitral regurgitation (MR) is a progressive condition which engenders significant mortality and morbidity if left untreated. The optimal timing of surgery in patients with MR of degenerative origin continues to be debated, especially for those who are asymptomatic. Apart from symptoms, current authoritative guidelines recommend intervention when there is incipient left ventricular dysfunction, pulmonary hypertension or new onset atrial fibrillation. This review focuses on the asymptomatic subject with severe MR, and examines contemporary clinical decision-making and management strategies, including the 2012 European guidelines on valvular heart disease. We discuss the rationale for risk stratifying the asymptomatic individual, and highlight current and novel diagnostic tools that may have a useful role, with an emphasis on echocardiographic imaging.

A three-dimensional insight into the complexity of flow convergence in mitral regurgitation: adjunctive benefit of anatomic regurgitant orifice area

Mitral effective regurgitant orifice area (EROA) using the flow convergence (FC) method is used to quantify the severity of mitral regurgitation (MR). However, it is challenging and prone to interobserver variability in complex valvular pathology. We hypothesized that real-time three-dimensional (3D) transesophageal echocardiography (RT3D TEE) derived anatomic regurgitant orifice area (AROA) can be a reasonable adjunct, irrespective of valvular geometry. Our goals were to 1) to determine the regurgitant orifice morphology and distance suitable for FC measurement using 3D computational flow dynamics and finite element analysis (FEA), and (2) to measure AROA from RT3D TEE and compare it with 2D FC derived EROA measurements. We studied 61 patients. EROA was calculated from 2D TEE images using the 2D-FC technique, and AROA was obtained from zoomed RT3DE TEE acquisitions using prototype software. 3D computational fluid dynamics by FEA were applied to 3D TEE images to determine the effects of mitral valve (MV) orifice geometry on FC pattern. 3D FEA analysis revealed that a central regurgitant orifice is suitable for FC measurements at an optimal distance from the orifice but complex MV orifice resulting in eccentric jets yielded nonaxisymmetric isovelocity contours close to the orifice where the assumptions underlying FC are problematic. EROA and AROA measurements correlated well (r = 0.81) with a nonsignificant bias. However, in patients with eccentric MR, the bias was larger than in central MR. Intermeasurement variability was higher for the 2D FC technique than for RT3DE-based measurements. With its superior reproducibility, 3D analysis of the AROA is a useful alternative to quantify MR when 2D FC measurements are challenging.

Direct measurement of proximal isovelocity surface area by real-time three-dimensional color Doppler for quantitation of aortic regurgitant volume: an in vitro validation

OBJECTIVE

The proximal isovelocity surface area (PISA) method is useful in the quantitation of aortic regurgitation (AR). We hypothesized that actual measurement of PISA provided with real-time 3-dimensional (3D) color Doppler yields more accurate regurgitant volumes than those estimated by 2-dimensional (2D) color Doppler PISA.

METHODS

We developed a pulsatile flow model for AR with an imaging chamber in which interchangeable regurgitant orifices with defined shapes and areas were incorporated. An ultrasonic flow meter was used to calculate the reference regurgitant volumes. A total of 29 different flow conditions for 5 orifices with different shapes were tested at a rate of 72 beats/min. 2D PISA was calculated as 2pi r(2), and 3D PISA was measured from 8 equidistant radial planes of the 3D PISA. Regurgitant volume was derived as PISA x aliasing velocity x time velocity integral of AR/peak AR velocity.

RESULTS

Regurgitant volumes by flow meter ranged between 12.6 and 30.6 mL/beat (mean 21.4 +/- 5.5 mL/beat). Regurgitant volumes estimated by 2D PISA correlated well with volumes measured by flow meter (r = 0.69); however, a significant underestimation was observed (y = 0.5x + 0.6). Correlation with flow meter volumes was stronger for 3D PISA-derived regurgitant volumes (r = 0.83); significantly less underestimation of regurgitant volumes was seen, with a regression line close to identity (y = 0.9x + 3.9).

CONCLUSION

Direct measurement of PISA is feasible, without geometric assumptions, using real-time 3D color Doppler. Calculation of aortic regurgitant volumes with 3D color Doppler using this methodology is more accurate than conventional 2D method with hemispheric PISA assumption.

Real-time 3-Dimensional Color Doppler Flow of Mitral and Tricuspid Regurgitation: Feasibility and Initial Quantitative Comparison with 2-Dimensional Methods

BACKGROUND

Visualization of valvular regurgitation using 3-dimensional (3D) echocardiography has been attempted but not routinely performed to date because of technical limitations. With the recent development of a fully sampled matrix-array probe, real-time color flow imaging allows display and analysis of regurgitant jets. Accordingly, the aim of this study was 2-fold. We: (1) investigated the feasibility of transthoracic, real-time visualization of 3D color flow jets; and (2) compared conventional 2-dimensional (2D) Doppler/color flow methods of quantitation (ie, 2D jet/left atrial [LA] area, flow convergence, and vena contracta [VC]) to 3D-derived measurements (3D jet/LA volume, flow convergence, and VC).

METHOD

In all, 56 patients with good acoustic windows and varying degrees of mitral regurgitation (MR) (n = 32) and tricuspid regurgitation (TR) (n = 24) scheduled for a routine echocardiogram were studied. Using a broadband transducer, 2D color Doppler imaging of TR and MR jets was performed to obtain jet/atrial area ratio, effective regurgitant orifice area, and VC measurements. Subsequently, real-time 3D echocardiography imaging of these jets was performed and analyzed offline using software, resulting in jet/atrial volume ratio, effective regurgitant orifice area, and VC (major and minor axes).

RESULTS

Of the 56 patients recruited into the study, 86% had sufficient data quality for analysis (87.5% in patients with MR and 83% in patients with TR). Both LA and right atrium were adequately visualized in all patients. Manually traced 3D MR and TR volumes had good agreement when compared with proximal isovelocity surface area-derived volumes (r = 0.7, y = 0.4x + 6.4; and r = 0.8, y = 1.1x + 5.1; respectively) with minimal underestimation and overestimation of volumes for MR and TR (8 and 7 mL, respectively), but with relatively wide limits of agreement for MR (28 mL) versus TR (12 mL). When comparing 3D MR jet/LA volume ratios and TR jet/right atrial volume ratios to 2D MR jet/LA area and 2D TR jet/right atrial area ratios, the former were significantly smaller. The 3D minimum and maximum VC diameter for MR were significantly different compared with those measured with 2D (minimum diameter = 0.7 +/- 0.1 cm, P < .01; maximum diameter = 1.1 +/- 0.5 cm, P < .02 vs 2D = 0.8 +/- 0.3 cm). Conversely, the TR VC minimum diameter was similar but maximum diameter measurements were larger in 3D compared with 2D (3D = 1.3 +/- 0.6 cm vs 2D = 0.7 +/- 0.2 cm, P < .001).

CONCLUSION

Three-dimensional echocardiography of color flow Doppler of MR and TR jets was feasible. Quantitative methods using 3D echocardiography such as MR and TR volumes correlated well with 2D flow convergence methods. TR VC has more of an elliptic shape, whereas MR is more circular or oval when visualized in 3D. Regurgitant/atrial volume ratios provide a new method of assessing the severity of regurgitant lesions; however, 3D volume-derived ratios were comparatively smaller than those measured with 2D echocardiography.

Quantification of mitral regurgitation by the proximal flow convergence method--comparison of transthoracic and transesophageal echocardiography

BACKGROUND

No dataexist to indicate whether transthoracic (TTE) and transesophageal echocardiography (TEE) are of comparable value for the detection and quantification of mitral regurgitation using the proximal flow convergence method.

HYPOTHESIS

The study was performed to compare the value of TTE and TEE for the detection and quantification of mitral regurgitation using this method.

METHODS

The study included 57 patients with and 11 patients without mitral regurgitation. In all patients, the proximal flow convergence region was imaged by transthoracic and transesophageal color Doppler echocardiography, and proximal isovelocity surface area radii were determined. In 19 patients, monoplane TEE and in 49 patients multiplane TEE was performed. Thirty-one patients with mitral regurgitation underwent cardiac catheterization.

RESULTS

Both methods had a comparable sensitivity for the detection of mitral regurgitation. Proximal isovelocity surface area radii derived from TTE and TEE agreed moderately (mean difference -0.5 +/- 1.3 mm). TTE and TEE correlated significantly with the angiographic grade (rank correlation coefficients 0.83 and 0.81), and both differentiated mild to moderate from severe mitral regurgitation with an accuracy of 90%. Regurgitant volumes derived from both echocardiographic techniques and cardiac catheterization correlated moderately (correlation coefficients between 0.67 and 0.81).

CONCLUSIONS

TTE and TEE were of comparable value for the detection and quantification of mitral regurgitation using the proximal flow convergence method.

Estimación de la severidad de la insuficiencia mitral según un método simplificado basado en el flujo de convergencia proximal

INTRODUCTION AND OBJECTIVES

Calculation of the effective regurgitant orifice (ERO) is regarded as the most accurate way of assessing the severity of mitral regurgitation (MR), but the technique's complexity limits its use. Our objective was to modify and validate a previously published semiquantitative method of assessment based on measurement of the proximal isovelocity surface area (PISA) in order to adapt it to recent recommendations from American and European cardiology societies.

METHODS

In the PISA method, maximum regurgitant flow (MRF) is a function of the radius and aliasing velocity (AV). Using this relationship, it is possible to construct a nomogram formed by lines of different MRF value, which can be easily derived by looking for radius values on the graph and observing where they cross with AV values. The MR severity limits on the nomogram were set to reflect the different severity grades and limits recommended for use with ERO measurements by American and European cardiology societies.

RESULTS

We studied 76 patients with MR using Doppler echocardiography. There was an excellent correlation between MRF and ERO (r=0.98, P< .001). Estimates of MR severity made using the new nomogram were in good agreement with those derived from the ERO: for a scale with three severity grades, kappa was 0.951 and the standard error was 0.11; for four grades, kappa was 0.969 and the standard error, 0.11.

CONCLUSIONS

Estimates of MR severity derived semiquantitatively from MRF using the nomogram proposed here were in excellent agreement with quantitative estimates obtained using the ERO, and the method was faster and easier to use.

Value of the proximal flow convergence method for quantification of the regurgitant volume in mitral regurgitation Influence of the mechanism of regurgitation, the imaging of the flow convergence region, and different calculation modalities

The purpose of this study was to evaluate whether the underlying mechanism of mitral regurgitation influences the reliability of the proximal flow con- vergence method to assess the regurgitant volume. Furthermore, the mode of imaging the flow convergence region and different correction algorithms for calculation of the regurgitant volume were compared.

METHODS

Regurgitant volume was assessed in 45 patients (age 61+/-13 years) with organic (n=19) and functional (n=26) mitral regurgitation by the proximal flow convergence method for aliasing velocities between 14 and 64 cm/s using two-dimensional color Doppler imaging. Different correction and calculation algorithms were compared. In addition, regurgitant volume was determined using color Doppler M-mode for an aliasing velocity of 28 cm/s. The quantitative Doppler method was used as reference.

RESULTS

In organic mitral regurgitation correlation coefficients (mean differences) between the proximal flow convergence method and the reference method were 0.25-0.43/ 0.58-0.67 (46-111 ml/15-17 ml) before/after geometric correction of the regurgitant volume for the aliasing velocities investigated. The correlation coefficient (mean difference) using color Doppler M-mode imaging was 0.68 (85 ml). The corresponding values in functional mitral regurgitation were 0.74-0.88/0.74-0.88 (-5-8 ml/-7-5 ml) for two-dimensional color Doppler and 0.88 (-1 ml) for M-mode imaging.

CONCLUSIONS

The regurgitant volume was overestimated by the proximal flow convergence method in organic mitral regurgitation irrespective of the application of different correction algorithms or the use of color Doppler M-mode. A sufficiently reliable determination of the regurgitant volume by the proximal flow convergence method was possible in functional mitral regurgitation. In that case a simplified calculation of the regurgitant volume based on the proximal flow convergence method was feasible.

Reproducibility of the proximal flow convergence method in mitral and tricuspid regurgitation

BACKGROUND

The follow-up of patients with mitral and tricuspid regurgitation is important for their clinical treatment. We aimed to evaluate the reproducibility of the flow convergence method in mitral and tricuspid regurgitation.

METHODS

The proximal flow convergence region was imaged with color Doppler ultrasound scanning echocardiography in 83 patients with mitral regurgitation, tricuspid regurgitation, or both. Proximal isovelocity surface area radii for aliasing velocities of 27 to 29 cm/s and 41 to 43 cm/s were repeatedly measured by the same experienced investigator on different days and by experienced and less experienced investigators at 1 day.

RESULTS

In mitral regurgitation, the intraobserver variability rate was 0.2% +/- 13.5% (2.8% +/- 13.3%) and the interobserver variability was 0.1% +/- 13.8% (1.7% +/- 18.0%) for an aliasing velocity of 27 to 29 cm/s (41-43 cm/s). For the aliasing velocity of 27 to 29 cm/s (41-43 cm/s), the 95% ranges for change of the proximal isovelocity surface area radii were +/- 2.7 mm (+/- 1.8 mm) for measurements repeated by the same investigator and +/- 2.7 mm ( +/- 2.4 mm) for different investigators. Interobserver variability was independent of the investigators' experience. Similar data were achieved in tricuspid regurgitation.

CONCLUSIONS

The proximal flow convergence method is acceptably reproducible in mitral and tricuspid regurgitation independent of the investigators experience. For the aliasing velocity of 27 to 29 cm/s (41-43 cm/s), the proximal isovelocity surface area radius has to change for >2.7 (2.4) mm before an altered severity of mitral or tricuspid regurgitation in a single patient can be assumed.

Use of tissue Doppler echocardiography in early detection of left ventricular systolic dysfunction in patients with mitral regurgitation

OBJECTIVE

Left ventricular ejection fraction (EF) and left ventricular (LV) end-systolic diameter measurements are the most widely accepted and utilized methods to demonstrate LV dysfunction in patients with mitral regurgitation (MR). However, these parameters still have many drawbacks in predicting early LV dysfunction. This study investigates the clinical usefulness of tissue Doppler echocardiography technique in detecting early disturbance of myocardial contractility in asymptomatic patients with chronic, severe MR and normal LV ejection fraction values.

METHODS AND RESULTS

Regional systolic peak velocities of mitral annular motion during the ejection phase of systole (SW2) were obtained at the mitral annuli of the ventricular septal, lateral, anteroseptal, posterior, anterior and inferior wall sites in the long axis in 31 asymptomatic patients with severe MR (with a regurgitant volume of more than 50 ml) and with EFs more than 60%. The patients were grouped according to their dP/dt values (more or less than 1300 mmHg/s) estimated non-invasively by using continuous Doppler wave of MR SW2 measurements of Group I were higher than Group II in all of the analyzed segments. The difference was statistically significant for all of the segments. SW2 values of the whole study group was moderately correlated with dP/dt measurements in all of the analyzed segments other than the interventricular septum.

CONCLUSION

SW2 measurements in the long axis, which are considered to be relatively independent from afterload conditions may be helpful in early detection (while EF is still in normal range) of LV systolic dysfunction during the follow-up of patients with chronic MR.

Real-time three-dimensional color doppler evaluation of the flow convergence zone for quantification of mitral regurgitation: Validation experimental animal study and initial clinical experience

BACKGROUND

Pitfalls of the flow convergence (FC) method, including 2-dimensional imaging of the 3-dimensional (3D) geometry of the FC surface, can lead to erroneous quantification of mitral regurgitation (MR). This limitation may be mitigated by the use of real-time 3D color Doppler echocardiography (CE). Our objective was to validate a real-time 3D navigation method for MR quantification.

METHODS

In 12 sheep with surgically induced chronic MR, 37 different hemodynamic conditions were studied with real-time 3DCE. Using real-time 3D navigation, the radius of the largest hemispherical FC zone was located and measured. MR volume was quantified according to the FC method after observing the shape of FC in 3D space. Aortic and mitral electromagnetic flow probes and meters were balanced against each other to determine reference MR volume. As an initial clinical application study, 22 patients with chronic MR were also studied with this real-time 3DCE-FC method. Left ventricular (LV) outflow tract automated cardiac flow measurement (Toshiba Corp, Tokyo, Japan) and real-time 3D LV stroke volume were used to quantify the reference MR volume (MR volume = 3DLV stroke volume - automated cardiac flow measurement).

RESULTS

In the sheep model, a good correlation and agreement was seen between MR volume by real-time 3DCE and electromagnetic (y = 0.77x + 1.48, r = 0.87, P <.001, delta = -0.91 +/- 2.65 mL). In patients, real-time 3DCE-derived MR volume also showed a good correlation and agreement with the reference method (y = 0.89x - 0.38, r = 0.93, P <.001, delta = -4.8 +/- 7.6 mL).

CONCLUSIONS

real-time 3DCE can capture the entire FC image, permitting geometrical recognition of the FC zone geometry and reliable MR quantification.

Quantitative assessment of regurgitant flow with total digital three-dimensional reconstruction of color Doppler flow in the convergent region: in vitro validation

BACKGROUND

This study was designed to develop and test a total digital 3-dimensional (3D) color flow map reconstruction for proximal isovelocity surface area (PISA) measurement in the convergent region.

METHODS

Asymmetric flow convergent velocity field was created in an in vitro pulsatile model of mitral regurgitation. Image files stored in the echocardiographic scanner memory were digitally transferred to a computer workstation, and custom software decoded the file format, extracted velocity information, and generated 3D flow images automatically. PISA and volume flow rate were calculated without geometric assumption. For comparison, regurgitant volume was also calculated, using continuous wave Doppler, 2-dimensional (2D), and M-mode color flow Doppler with the hemispheric approach.

RESULTS

Flows from 3D digital velocity profiles showed a closed, excellent relation with actual flow rates, especially for instantaneous flow rate. Regurgitant volume calculated with the 3D method underestimated the actual flow rate by 2.6%, whereas 2D and the M-mode method show greater underestimation (44.2% and 32.1%, respectively).

CONCLUSION

Our 3D reconstruction of color flow Doppler images gives more exact information of the flow convergent zone, especially in complex geometric flow fields. Its total digital velocity process allows accurate measurement of convergent surface area and improves quantitation of valvular regurgitation.

Interaliasing distance of the flow convergence surface for determining mitral regurgitant volume: a validation study in a chronic animal model

OBJECTIVES

We aimed to validate a new flow convergence (FC) method that eliminated the need to locate the regurgitant orifice and that could be performed semiautomatedly.

BACKGROUND

Complex and time-consuming features of previously validated color Doppler methods for determining mitral regurgitant volume (MRV) have prevented their widespread clinical use.

METHODS

Thirty-nine different hemodynamic conditions in 12 sheep with surgically created flail leaflets inducing chronic mitral regurgitation were studied with two-dimensional (2D) echocardiography. Color Doppler M-mode images along the centerline of the accelerating flow towards the mitral regurgitation orifice were obtained. The distance between the two first aliasing boundaries (interaliasing distance [IAD]) was measured and the FC radius was mathematically derived according to the continuity equation (R(calc) = IAD/(1 - radicalv(1)/v(2)), v(1) and v(2) being the aliasing velocities). The conventional 2D FC radius was also measured (R(meas)). Mitral regurgitant volume was then calculated according to the FC method using both R(calc) and R(meas). Aortic and mitral electromagnetic (EM) flow probes and meters were balanced against each other to determine the reference standard MRV.

RESULTS

Mitral regurgitant volume calculated from R(calc) and R(meas) correlated well with EM-MRV (y = 0.83x + 5.17, r = 0.90 and y = 1.04x + 0.91, r = 0.91, respectively, p < 0.001 for both). However, both methods resulted in slight overestimation of EM-MRV (Delta was 3.3 +/- 2.1 ml for R(calc) and 1.3 +/- 2.3 ml for R(meas)).

CONCLUSIONS

Good correlation was observed between MRV derived from R(calc) (IAD method) and EM-MRV, similar to that observed with R(meas) (conventional FC method) and EM-MRV. The R(calc) using the IAD method has an advantage over conventional R(meas) in that it does not require spatial localization of the regurgitant orifice and can be performed semiautomatedly.

A semiautomated objective technique for applying the proximal isovelocity surface area method to quantitate mitral regurgitation: Clinical studies with the digital flow map

BACKGROUND

Clinical application of the color Doppler proximal isovelocity surface area (PISA) method to quantify mitral regurgitation (MR) has been limited by the often inaccurate assumption that isovelocity surfaces are hemispheric. This study applied an objective method for selecting the region where the hemispheric geometry holds best on the basis of mathematic analysis of results at different distances from the orifice. We aimed to demonstrate this approach can be applied accurately in the clinical setting and can be semiautomated to promote routine use by extracting velocities from the digital Doppler output and then performing all the calculations automatically.

METHODS

In 75 patients with isolated MR, centerline velocities (V(r)) at each distance (r) from the orifice in the proximal flow field were extracted digitally. The automated analysis calculated peak MR flow rates as 2pir(2)V(r) and plotted these against their respective velocities. The optimal value for peak flow rate was obtained mathematically at the site where the slope of this curve was minimal (least inaccuracy). This value was combined with continuous wave Doppler data to provide regurgitant stroke volume (RSV) and orifice area (ROA), which were compared with quantitative Doppler in 75 patients and angiography in 42.

RESULTS

RSV and ROA by this optimized, semiautomated PISA method correlated and agreed well with values from quantitative Doppler (y = 0.9x + 1.9, r = 0.90, standard error of the estimate [SEE] = 8.1 mL, mean difference = -0.7 +/- 8.5 mL for RSV; y = 0.9x + 0.02, r = 0.90, SEE = 0.048 cm(2), mean difference = -0.005 +/- 0.1 cm(2) for ROA) and correlated well with angiography (rho = 0.90 for both RSV and ROA).

CONCLUSIONS

This objective PISA method for quantifying MR is accurate in the clinical setting and has been semiautomated by use of analysis of digital velocity data to provide a rapid and practical technique suitable to facilitate more extensive application in routine practice.

Simple method for estimating regurgitant volume with use of a single radius for measuring proximal isovelocity surface area: an in vitro study of simulated mitral regurgitation

The proximal isovelocity surface area (PISA) color Doppler method with use of a hemielliptic formula is reported to be accurate for quantitating regurgitant volume (RV). However, this formula ideally requires the measurement of 2 or 3 radii and therefore is not widely used clinically. The purpose of this in vitro study was to derive a simple PISA formula for estimating RV with use of a single radius axial to the valve orifice and to compare it with the clinically used single-radius hemispherical formula (2 x pi R(2) x AV x TVI/Vp), where AV is the apparent color Doppler aliasing velocity, R is the PISA color Doppler aliasing radius, TVI is time-velocity integral of the jet by continuous wave Doppler, and Vp is the peak velocity of the jet by continuous wave Doppler. Pulsatile flow studies were performed across a convex curvilinear surface, which more closely approximates the shape of the mitral valve than does a planar surface. Pulse rates (60 to 80 bpm), peak flow velocities (4.0 to 6.0 m/s), and regurgitant orifice areas (0.2 to 1.0 cm(2)) were varied to simulate mitral regurgitation. The AVs were varied from 11 to 39 cm/s, and a single PISA aliasing radius was measured at each AV. Excellent linear correlations were obtained between the PISA radius and the actual RV measured with use of a beaker (r = 0.94 to 0.97, P <.0001). A series of simplified formulas was derived from the regression line of the PISA radius versus the RV. For example, with an AV of 21 cm/s, RV was estimated by a simplified PISA formula (where RV[mL] = 10 x R [mm] - 30) with an accuracy of 3.3 +/- 6.3 mL versus -20.3 +/- 8.7 mL for the standard single-radius PISA method (P <.0001). By using the standard single-radius hemispherical PISA formula, RV was underestimated if the radius was <20 mm. By using simplified regression equations, the PISA radius accurately estimated RV at a PISA radius <20 mm. Clinical studies are necessary to validate this concept.

Three-dimensional echocardiographic reconstruction of mitral valve color Doppler flow events

In vitro studies have suggested superior accuracy of 3-dimensional echocardiography over conventional methods for the characterization and quantitation of color Doppler flow events. Little in vivo work has been reported in this area; this study demonstrates the feasibility of 3-dimensional reconstruction of mitral valve flow events in an unselected group of adult patients and discusses optimal instrument settings for the acquisition of 3-dimensional datasets.

Quantitation of Doppler color flow jet areas for mitral regurgitation in children: angiographic correlation

Eighteen patients with chronic isolated rheumatic mitral regurgitation aged between 7 and 19 years (mean age +/-SD, 12.69+/-3.47 years) were analyzed with color Doppler imaging. Sixteen patients were performed cardiac catheterization within 24 h. Jets were classified as eccentric and central. Regurgitant jet area and its ratio to left atrial area and body surface area were measured by Doppler color flow imaging. Regurgitant volume and regurgitant fractions were calculated with angiography. There was a good correlation between regurgitant jet area and angiographic grade of mitral regurgitation (P<0.01). The correlation between regurgitant jet area/left atrial area ratios and angiographic grade of mitral regurgitation was limited (P<0.01). There was excellent correlation between regurgitant jet area/body surface area and angiographic regurgitant fraction (r = 0.85; P<0.001). There was also a good correlation between regurgitant jet area and regurgitant fraction (r = 0.82; P<0.001). However, the relation of regurgitant jet area/left atrial area to regurgitant fraction was weak (r = 0.72; P<0.01). In conclusion, the measurement of regurgitant fraction and its ratios to left atrial area and body surface area by color Doppler flow imaging can predict the angiographic severity in children who have even eccentric regurgitant jets.

Clinical value of parameters derived by the application of the proximal isovelocity surface area method in the assessment of mitral regurgitation

To determine the clinical value of several parameters derived by application of the proximal isovelocity surface area method in the assessment of mitral regurgitation (MR), 28 consecutive patients with angiographic diagnosis of MR underwent color Doppler echocardiography within 48 h of cardiac catheterization. Aliasing velocities (V(N)) were baseline-shifted to 25 cm/s and the maximal radius (R) was measured from the first aliasing boundary to the tips of the mitral valve. By continuity, the regurgitant orifice area (ROA) and regurgitant stroke volume (RSV(PISA)) were obtained. We have related them to the angiographic grade, and with determination of the regurgitant stroke volume (RSV(DE)) and the regurgitant fraction (RF), we calculated the volume of the transmitral flow according to Fisher's method.

RESULTS

RSV(DE) correlated well with RSV(PISA) (r = 0.98). A clear relation existed between the isovelocity radius and the RSV(DE) and RF (r = 0.95 and 0.88, respectively). A radius of 8 mm or more was identified well with an RSV(DE) of 40 cm3 or more (sensitivity: 100%, specificity: 95%) and an RF of 35% or more (sensitivity: 88%, specificity: 94%). The ROA was closely related to the RSV(DE) and RF, with r = 0.92 and 0.88, respectively. An ROA of 20 mm2 or more identified well patients with RSV(DE) values of 40 cm3 or more and RF values of 35% or more. The radius, RSV(PISA) and ROA were closely related to the angiographic grade of MR (r = 0.91, 0.83 and 0.92, respectively). A radius of 7 mm or more identified patients with grade III or IV of regurgitation (sensitivity: 82%, specificity: 94%), while an ROA of 15 mm2 or more discriminated well significant regurgitation (sensitivity: 91%, specificity: 94%).

CONCLUSIONS

Parameters derived by application of the proximal isovelocity surface area method provide quantitative information that can be helpful in predicting the severity of mitral regurgitation noninvasively.

Quantification of mitral and tricuspid regurgitation by the proximal flow convergence method using two-dimensional colour Doppler and colour Doppler M-mode: influence of the mechanism of regurgitation

In patients with mitral (n=77: organic=49, functional=28) and tricuspid regurgitation (n=55: functional=54) quantified by angiography, the temporal variation of the proximal flow convergence region throughout systole was assessed by colour Doppler M-Mode, and peak and mean radius of the proximal isovelocity surface area for 28 cm/s blood flow velocity were measured. Additionally, the peak radius derived from two-dimensional colour Doppler was obtained. About 50% of the patients with mitral and tricuspid regurgitation showed a typical temporal variation of the flow convergence region related to the mechanism of regurgitation. The different proximal isovelocity surface area radii were similarly correlated to the angiographic grade in mitral and tricuspid regurgitation (rank correlation coefficients 0.55-0.89) and they differentiated mild to moderate (grade < or =II) from severe (grade > or =III) mitral and tricuspid regurgitation with comparable accuracy (82-96%). However, moderate mitral regurgitation due to leaflet prolapse in two patients was correctly classified by the mean M-mode radius and overestimated by both peak radii. Only half of the patients showed a typical variation of the flow convergence region related to the mechanism of regurgitation. The different proximal isovelocity surface area radii were suitable to quantify mitral and tricuspid regurgitation in most patients. However, in mitral regurgitation due to leaflet prolapse the use of the mean M-mode radius may avoid overestimation.

Evaluation of mitral valve disease using transesophageal echocardiography

In the past 10 years, clinical application of transesophageal echocardiography (TE) has grown explosively. Intraoperative TE offers a powerful diagnostic and monitoring tool for the physicians in the cardiac operating room. The use of TE revolutionizes the assessment of patients with mitral valve disease. Surgical decisions are often altered based on the information obtained from TE. This review describes the basic features of TE as well as its uses in the intraoperative setting for evaluation of the mitral valve.

Application of color Doppler flow mapping to calculate orifice area of St Jude mitral valve

BACKGROUND

The effective orifice area (EOA) of a prosthetic valve is superior to transvalvular gradients as a measure of valve function, but measurement of mitral prosthesis EOA has not been reliable.

METHODS AND RESULTS

In vitro flow across St Jude valves was calculated by hemispheric proximal isovelocity surface area (PISA) and segment-of-spheroid (SOS) methods. For steady and pulsatile conditions, PISA and SOS flows correlated with true flow, but SOS and not PISA underestimated flow. These principles were then used intraoperatively to calculate cardiac output and EOA of newly implanted St Jude mitral valves in 36 patients. Cardiac output by PISA agreed closely with thermodilution (r=0.91, Delta=-0.05+/-0.55 L/min), but SOS underestimated it (r=0.82, Delta=-1.33+/-0.73 L/min). Doppler EOAs correlated with Gorlin equation estimates (r=0.75 for PISA and r=0.68 for SOS, P<0.001) but were smaller than corresponding in vitro EOA estimates.

CONCLUSIONS

Proximal flow convergence methods can calculate forward flow and estimate EOA of St Jude mitral valves, which may improve noninvasive assessment of prosthetic mitral valve obstruction.

Progressive tricuspid valve disease in patients with congenitally corrected transposition of the great arteries

BACKGROUND

The outcome of patients with corrected transposition of the great arteries (CTGA) is variably affected by associated intracardiac defects, tricuspid valve competence, and systemic right ventricular (RV) function. The relative importance of these factors in long-term outcome has not been evaluated.

METHODS AND RESULTS

Since 1958, 40 patients with CTGA were studied to determine risk factors for poor outcome, including age, open heart surgery, tricuspid insufficiency (TI), cardiac rhythm, pulmonary overcirculation, and RV dysfunction. Follow-up ranged from 7 to 36 years (mean 20 years). Intracardiac repair was performed in 21 patients; 19 were unoperated or had closed heart procedures. For the purposes of this study the designation TI(S) refers to at least moderately severe TI as delineated by echocardiogram and/or angiography. TI(s) was the only independently significant factor for death (P=0.01), and in turn, only the presence of a morphologically abnormal TV predicted TI(s)(P=0.03). Twenty-year survival without TI(S)was 93%, but only 49% with TI(S). Poor long-term postoperative outcome was due to TI(S) in all but 1 patient; 20-year survival rates for operated patients with and without TI(s)were 34% and 90%, respectively (P=0.002). Similarly, 20-year survival rates for unoperated patients with and without TI(s)were 60% and 100%, respectively, whether or not attempts to repair the TI were made (P=0.08).

CONCLUSIONS

TI(S)represents the major risk factor for CTGA patients; RV dysfunction appears to be almost always secondary to long-standing TI. Decisions related to surgical interventions with or without associated lesions must be strongly influenced by the status of the tricuspid valve.

Evaluating isovelocity surface area flow convergence method with finite element modeling

Through numerical experimentation we investigated the isovelocity surface area flow convergence method used in estimating regurgitant valve flow rates. Recent advances in three-dimensional color Doppler flow imaging have created renewed interest in this method. Experimentation was based on the use of depth-averaged finite element models of the left heart. The heart models studied varied from "synthetic" representations to a model of a left heart traced from an actual echocardiographic image of a patient with a prolapsed mitral valve. The isovelocity surface area flow convergence method overestimated regurgitant flow rates throughout the Nyquist limits considered with a critical Nyquist limit in which this overestimation is minimized. The angle dependence of Doppler color flow imaging partially corrects for this overestimation. The isovelocity surface area flow convergence method is a viable alternative to methods currently in use. Through numerical experimentation, we have begun to shed light on the inaccuracies inherent in this flow convergence method.

The role of intraoperative echocardiography in valve surgery

The widespread use and popularity of intraoperative echocardiography (IOE) has resulted from advances in cardiac surgery, reparative procedures for valvular heart disease and, most specifically, mitral valve repair. IOE has grown exponentially and is becoming an integral part of the planning and evaluation of many types of surgical procedures such that it is now considered standard of care especially for the perioperative management of patients undergoing mitral and aortic valve repair. This article discusses the application of intraoperative echocardiography and focus specifically on valvular heart disease as this represents the most widely accepted indication for the procedure in current clinical practice.

Rapid estimation of regurgitant volume by the proximal isovelocity surface area method in mitral regurgitation: Can continuous-wave Doppler echocardiography be omitted?

The proximal isovelocity surface area (PISA) method is accurate for quantitating mitral regurgitation but requires recording both mitral maximal and integrated jet velocities using the same continuous-wave Doppler jet signal. In 272 consecutive patients with isolated mitral regurgitation, the mean ratio of maximal to integral of velocity had a narrow range of variation (mean +/- SD, 3.25 +/- 0.47). The estimated regurgitant volume, calculated as regurgitant flow/3.25, showed an excellent correlation with reference regurgitant volumes (r = 0.96 and r = 0.97; standard error of the estimate, 11 ml; both p < 0.0001), with limited overestimation and high sensitivity and specificity for severe mitral regurgitation. The estimated regurgitant volume is a useful measurement in patients in whom the continuous-wave Doppler signal of mitral regurgitation cannot be obtained.

Determinants of functional capacity in chronic mitral regurgitation unassociated with coronary artery disease or left ventricular dysfunction

Impaired functional capacity is common in patients with mitral regurgitation (MR), but the determinants of functional capacity in patients with normal left ventricular (LV) function are unclear. Forty patients with chronic, isolated, nonrheumatic MR with no coronary artery disease underwent exercise echocardiography with continuous expired gas analysis. Cardiac output and regurgitant stroke volume were measured at rest and immediately after exercise by pulsed-wave Doppler echocardiography. For controls, 17 healthy volunteers without MR were also studied. Patients achieved a significantly lower VO2max compared with controls (25.6 +/- 7.7 vs 31.7 +/- 7.7 ml/kg/min, p = 0.008). VO2max showed better correlations with exercise cardiac output than with cardiac output at rest in both patients and controls. Multiple linear regression identified exercise cardiac output (partial r = 0.65), patient age (partial r = -0.56), and gender as independent determinants of VO2max (multiple R = 0.85, p <0.001). Cardiac output at rest, LV ejection fraction, regurgitant stroke volume, and fraction were not significant determinants. With exercise, the regurgitant stroke volume increased in 13 patients and decreased in 27 patients. The former 13 patients had a significantly lower exercise cardiac output (7.4 +/- 2.5 vs 9.4 +/- 2.6 L/min, p = 0.026). Patients who stopped exercise due to dyspnea (n = 7) had a significantly lower exercise cardiac output and VO2max compared with those who stopped due to fatigue (n = 33), with no differences in resting or exercise regurgitant volume. Patients with an increase in LV end-systolic volume with exercise (n = 8) also had a significantly lower exercise cardiac output (6.9 +/- 1.9 vs 9.2 +/- 2.7 L/min, p = 0.037) and showed a trend toward a lower VO2max (21 +/- 7.5 vs 26 +/- 6.4 ml/kg/min, p = 0.07). In patients with chronic MR, exercise cardiac output is the major determinant of VO2max. Regurgitant volume and fraction are not related to functional capacity. Limitations in functional capacity in these patients may be more related to a diminished cardiac reserve than to a large regurgitant volume.

Usefulness of color Doppler proximal isovelocity surface area method in quantitating valvular regurgitation

To define the clinical utility of the color Doppler proximal isovelocity surface area (PISA) method for estimating regurgitant stroke volume (SV), 160 regurgitant lesions were evaluated in 104 patients with mitral (MR), aortic (AR), and tricuspid (TR) regurgitation. Regurgitant SV by PISA was calculated as 2 pi R2 x V x (time-velocity integral/peak flow velocity), where R is the radius corresponding to the first blue-red interface velocity of the maximal PISA during the cardiac cycle. The time-velocity integral and peak flow velocity from the continuous-wave Doppler recording of the regurgitant jet were used to correct PISA for phasic variations in regurgitant flow. Fifteen lesions were excluded because of difficulty in tracing the continuous-wave Doppler regurgitant curve. Among 145 remaining regurgitant lesions, PISA was measurable in 50 (78%) of 64 cases of MR and 24 (69%) of 35 cases of TR but in only 12 (26%) of 46 cases of AR (p < 0.001). Regurgitant SV by PISA correlated modestly well with jet area/atrial area in all atrioventricular valve lesions (MR: r = 0.55; TR: r = 0.65; p < 0.001). However, the correlation improved if only central jets were considered (MR: r = 0.70; TR; r = 0.75; p < 0.001). These findings are not unexpected because jet area/atrial area underestimates the true severity of regurgitation in cases of eccentric (wall-impinging) jets. PISA was detected in all severe cases of regurgitation but in only 64% of cases of mild MR, 45% of cases of mild TR, and 6% of cases of mild AR (p < 0.01). The color Doppler PISA method is clinically useful in estimating regurgitant SV in MR and TR, including mild cases, but is less useful in AR.

Digital storage and analysis of color Doppler echocardiograms

Color Doppler flow mapping has played an important role in clinical echocardiography. Most of the clinical work, however, has been primarily qualitative. Although qualitative information is very valuable, there is considerable quantitative information stored within the velocity map that has not been extensively exploited so far. Recently, many researchers have shown interest in using the encoded velocities to address the clinical problems such as quantification of valvular regurgitation, calculation of cardiac output, and characterization of ventricular filling. In this article, we review some basic physics and engineering aspects of color Doppler echocardiography, as well as drawbacks of trying to retrieve velocities from video tape data. Digital storage, which plays a critical role in performing quantitative analysis, is discussed in some detail with special attention to velocity encoding in DICOM 3.0 (medical image storage standard) and the use of digital compression. Lossy compression can considerably reduce file size with minimal loss of information (mostly redundant); this is critical for digital storage because of the enormous amount of data generated (a 10 minute study could require 18 Gigabytes of storage capacity). Lossy JPEG compression and its impact on quantitative analysis has been studied, showing that images compressed at 27:1 using the JPEG algorithm compares favorably with directly digitized video images, the current goldstandard. Some potential applications of these velocities in analyzing the proximal convergence zones, mitral inflow, and some areas of future development are also discussed in the article.

Requirement for accurate measurement of regurgitant stroke volume by the combined continuous-wave Doppler and color Doppler flow convergence method

The examination conditions necessary for accurate measurement of regurgitant volume by the proximal flow convergence method applying a simple hemispheric equation remain uncertain. This study investigated the requirement for measuring regurgitant stroke volume from the combined continuous-wave and color Doppler proximal flow convergence approach. Twenty-five pulsatile flow rates were produced by driving five regurgitant stroke volumes ranging from 30 to 70 ml/beat through planar orifices with cross-sectional areas ranging from 0.10 to 1.0 cm2. Four different shaped orifices (circular, rectangular with a major/minor axis ratio 2:1, slitlike with a major/minor axis ratio of 8:1, and square) having identical orifice areas (0.5 cm2) were examined. Regurgitant volume (RV) was estimated from the combined continuous-wave and color Doppler approach according to the previously described equation RV = 2 pi x (r max)2 x AV x (TVI/Vmax), where r max is maximal radial distance, AV is aliasing velocity, TVI is time velocity integral of regurgitant jet, and Vmax is peak velocity of regurgitant jet. Plotting the difference between actual and calculated RV versus radial distance of the proximal convergence shell for each flow rate from circular to rectangular orifices yielded curves conforming to a curvilinear function that crossed the point of zero difference at 1.0 cm. However, in the slitilke orifice, a more remote distance (1.6 cm) is required for the best agreement. Actual regurgitant stroke volume can be estimated well by the combined continuous-wave Doppler and proximal flow convergence method applying a simple hemispheric equation if an aliasing velocity is used that results in a radial distance of at least 1.0 cm.

Transesophageal echocardiography

This article presents an overview of the benefits and efficacy of transesophageal echocardiography (TEE) in the critically ill patient. The echocardiographic evaluation of ventricular function both regional and global, is discussed with special emphasis on ischemic heart disease; assessment of preload, interrogation of valvular heart disease (prosthetic and native) and its complications; endocarditis and its complications; intracardiac and extracardiac masses, including pulmonary embolism; aortic diseases (e.g., aneurysan, dissection, and traumatic tears); evaluation of patent foramen ovale and its association with central and peripheral embolic events; advancements in computer technology; and finally, the effect of TEE on critical care.