Martin Giesler

New Method for Accurate Calculation of Regurgitant Flow Rate Based on Analysis of Doppler Color Flow Maps of the Proximal Flow Field Validation in a Canine Model of Mitral Regurgitation With Initial Application in Patients

OBJECTIVES The purpose of this study was to develop a rational and objective method for selecting a region in the proximal flow field where the hemispheric formula for calculating regurgitant flow rates by the flow convergence technique is most accurate. BACKGROUND A major obstacle to clinical implementation of the proximal flow convergence method is that it assumes hemispheric isovelocity contours throughout the Doppler color flow map, whereas contour shape depends critically on location in the flow field. METHODS Twenty mitral regurgitant flow rate stages were produced in six dogs by implanting grommet orifices into the anterior mitral leaflet and varying driving pressures so that actual peak flow rate could be determined from the known effective regurgitant orifice times the orifice velocity. Because plotting flow rate calculated by using a hemispheric formula versus alias velocities produces underestimation near the orifice and overestimation far from it, this plot was fitted to a polynomial function to allow identification of an inflection point within a relatively flat intermediate zone, where factors causing overestimation and underestimation are expected to be unimportant or balanced. The accuracy of flow rate calculation by the inflection point was compared with unselective and selective averaging techniques. Clinical relevance, initial feasibility and correlation with an independent measure were tested in 13 consecutive patients with mitral regurgitation who underwent cardiac catheterization. RESULTS 1) The accuracy of single-point calculations was improved by selecting points in the flat portion of the curve (y = 1.15x - 3.34, r = 0.87, SEE = 22.1 ml/s vs. y = 1.34x - 1.99, r = 0.71, SEE = 45.6 ml/s, p < 0.01). 2) Selective averaging of points in the flat portion of the curve further improved accuracy and decreased scatter compared with unselective averaging (y = 1.08x + 4.8, r = 0.96, SEE = 11.6 ml/s vs. y = 1.30x + 0.6, r = 0.90, SEE = 20.9 ml/s, p < 0.01). 3) The proposed algorithm for mathematically identifying the inflection point provided the best results (y = 0.96x + 4.5, r = 0.96, SEE = 9.9 ml/s), with a mean error of 1.6 +/- 9.7 ml/s vs. 11.4 +/- 11.7 ml/s for selective averaging (p < 0.01). In patients, the proposed algorithm identified an inflection point at which calculated regurgitant volume agreed best with invasive measurements (y = 1.1x - 0.61, r = 0.93, SEE = 17 ml). CONCLUSIONS The accuracy of the proximal flow convergence method can be significantly improved by analyzing the flow field mathematically to identify the optimal isovelocity zone before using the hemispheric formula to calculate regurgitant flow rates. Because the proposed algorithm is objective, operator independent and, thus, suitable for automatization, it could provide the clinician with a powerful quantitative tool to assess valvular regurgitation.

Color Doppler echocardiographic determination of mitral regurgitant flow from the proximal velocity profile of the flow convergence region

Flow rate across an orifice can be determined from color Doppler echocardiographic maps of the flow convergence region proximal to the orifice. Different methods have been developed in vitro. The proximal velocity profile method was prospectively evaluated in patients with mitral regurgitation. Color Doppler echocardiography was performed in 74 patients before cardiac catheterization. The increasing velocities within the flow convergence region were determined in an apical plane on the straight line from the transducer to the leak; thus the proximal velocity profile was established and plotted on a nomogram. Instantaneous regurgitant flow rate was derived from the position of the resulting curve in relation to the nomograms reference curves, which were derived from in vitro measurements. Regurgitant stroke volume was calculated as regurgitant flow rate.regurgitant velocity-time integral/regurgitant peak velocity, using additional continuous-wave Doppler. The 55 patients with angiographic regurgitation had a close association between regurgitant flow rate (0 to 600 ml/s) and angiographic grade (Spearmans rank correlation coefficient = 0.91; p < 0.0001). Regurgitant flow rate did not overlap between grades < or = 2+, 3+ and 4+. In 16 patients, regurgitant stroke volume by echocardiography correlated well with that by the angiography/Fick method (r = 0.88; SEE = 17.1 ml), with a regression line close to identity (y = 0.89x + 12.7 ml). The proximal velocity profile method enables determination of mitral regurgitant flow and estimation of regurgitant volume.

Color Doppler Determination of Regurgitant Flow: From Proximal Isovelocity Surface Areas to Proximal Velocity Profiles: An In Vitro Study

There is not yet a completely satisfactory Doppler method for determining the severity of valvular regurgitation. Recently, interest has focused on the so‐called “flow convergence region”. Color Doppler provides a longitudinal velocity profile of the flow convergence region proximal to restrictive orifices. With respect to determination of regurgitant flow rate, we studied the influence of orifice flow rate and orifice size on the proximal velocity profile. In a phantom model, flow across circular orifices was studied. The distance r(v) of discrete velocities detected proximal to the orifice was measured along the flow center line. Velocity profiles were established. (1) Proximal isovelocity surfaces: The radius r(v) also represented the central radius of the proximal isovelocity surfaces. Increases in flow resulted in larger central radii r(v). Application of the continuity equation and analysis of the resulting values yielded a radius and an orifice size dependence of the geometric isovelocity surface shape. Therefore, their surface area and flow rate could not be calculated from these axial measurements alone. (2) Proximal velocity profiles: The resulting hyperbolic velocity profile curves (x axis = velocity [v], y axis = distance [r(v)]) are shifted rightward by increases in flow. In contrast, increases in orifice size make the curve steeper, but large r(v) are not affected. This differential influence of flow rate and orifice size allows orifice size independent determination of flow rate. A nomogram is presented as one possible method for flow determination.

Doppler echocardiographic evaluation of left ventricular diastolic function in acute hypothyroidism

OBJECTIVE Left ventricular diastolic dysfunction Is an important cause of symptomatic heart failure. Previous studies suggest that thyroid dysfunction affects left ventricular diastolic function but the underlying mechanisms remain controversial. The study was undertaken to assess the influence of acute hypothyroidism on left ventricular diastolic function and to elucidate possible underlying mechanisms by means of Doppler echocardiography in a group of athyreotic patients, whose thyroid state depended only on external thyroid hormone supply and could therefore easily be controlled.

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.

Influence of the orifice inlet angle on the velocity profile across a flow convergence region by color Doppler in vitro.

The converging flow field proximal to a leaking valve is determined among other things by the orifice inlet angle formed by the leaflets. Thus, the inlet angle affects the determination of regurgitant flow rate by the flow convergence method. Based on the hypothesis of spheric isovelocity surfaces, others had postulated that a local velocity within the flow convergence should change inversely proportional to changes in the three‐dimensional inlet angle. This concept would allow correction of the determination of regurgitant flow for nonplanar orifice inlet angles. We tested this concept in vitro. In a flow model, the flow convergence region proximal to different orifice plates was imaged by color Doppler: funnel‐shaped, planar and tip‐shaped (inverted funnels) orifice plates, with circular orifices of 2‐ and 7‐mm diameter. Velocity profiles across the flow convergence along the flow centerline were read from the color maps. As predicted, the local velocities were inversely related to the inlet angle, but only at the 2‐mm funnel orifices, this effect was inversely proportional to the three‐dimensional inlet angle (i.e., in agreement with the mentioned concept). However, for any 7‐mm orifice and/or inlet angle of > 180°, the effect of the inlet angle was considerably less than predicted by the aforementioned concept. With increasing orifice diameter and with decreasing distance to the orifice, the effect of the orifice inlet angle was reduced. The effect of the orifice inlet angle on the flow convergence region is modulated by orifice size and the distance to the orifice. Therefore, correction of flow estimates in proportion to the three‐dimensional inlet angle will lead to considerable errors in most situations of clinical relevance, namely to massive overcorrection when analyzing velocities located close to wide orifices.

Aortic regurgitant flow by color Doppler measurement of the local velocity 7 mm above the leak orifice - Part 2: comparison with cardiac catheterization

Eine In-vitro-Studie zur Flußkonvergenz-Methode bei Aorteninsuffizienz hatte gezeigt, daß der Regurgitationsfluß aus der lokalen Geschwindigkeit v(7 mm) 7 mm oberhalb des Leckostiums abgeleitet werden kann. In dieser klinischen Studie wurde dieser Zusammenhang an Patienten erprobt. Bei 67 Patienten mit Aorteninsuffizienz wurde die Flußkonvergenz-Region mit dem Farbdoppler dargestellt. Analog zu der o. g. In-vitro-Studie wurden Geschwindigkeitsprofile der Beschleunigung durch die Flußkonvergenz aus den Farbkarten extrahiert. Die Profile wurden mit einer multiplikativen Regression gefittet. Auf der Regressionskurve wurde die v(7 mm) abgelesen und daraus der Regurgitationsfluß Q errechnet gemäß dem in vitro gefundenen Zusammenhang (Q = v(7 mm)· cm2/0,28). Es fand sich ein enger Zusammenhang zum angiographischen Schweregrad. Das aus Q errechnete Regurgitationsvolumen pro Schlag korrelierte signifikant mit den Werten der Angio-Fick-Methode (r = 0,897, SEE = 19,9 ml, y = 0,88x + 5,9 ml). Somit läßt sich auch bei Patienten aus der lokalen Geschwindigkeit 7 mm oberhalb des Leckostiums direkt der Aorten-Regurgitationsfluß bestimmen. Aims: An in vitro study of the flow convergence region in aortic regurgitation has shown that regurgitant flow rate can be derived from the local velocity v(7 mm) at 7 mm distance above the leak orifice. This clinical study was performed to test this method in patients. Methods and results: In 67 patients with aortic regurgitation, the flow convergence region was imaged by color Doppler. By analogy with the afore mentioned in vitro study, velocity profiles of the acceleration across the flow convergence region were read from the color maps. The profiles were fitted by using a multiplicative regression model. The v(7 mm) was read from the regression curve, and instantaneous regurgitant flow Q was derived from the v(7 mm) with the equation developed in vitro (Q = v(7 mm)· cm2/0,28). Q showed a close association with the angiographic grade. Q-derived regurgitant stroke volume correlated significantly with invasive measurements by the angio-Fick method (r = 0,897, SEE = 19,9 ml, y = 0,88x + 5,9 ml). Conclusions: Within the color Doppler flow convergence region of aortic regurgitation, the local velocity at 7 mm distance to the leak reflects regurgitant flow rate.

Influence of pulse repetition frequency and high pass filter on color Doppler maps of converging flow in vitro

Assessment of regurgitant flow by the flow convergence method is based on reading absolute velocities from color Doppler maps. Velocity overestimation by high pass filtering above 100 Hz has been reported. An extremely low filter, however, is inpracticable in patients. A ratio of pulse repetition frequency (PRF)/filter of 10/1 usually results in good quality color maps as judged visually. We studied in vitro the influence of PRF and filter on the absolute velocities within color maps of the flow convergence, keeping PRF/filter at 10/1. The color maps were also compared with computerized flow simulations.Flow across different orifice plates was scanned using two different setups for each flow condition: low velocity setup (PRF 600–2500 Hz, filter 50–300 Hz) and high (PRF 1500–6000 Hz, filter 200–600 Hz). From the color maps, velocity profile curves were read along the flow center line across the flow convergence.The high velocity setup provided artefact-free color maps at a distanced=2–4 through 8–11 mm to the orifice, the low setup atd=6–8 through 18 mm. Within the overlapping range (d=6–8 through 8–11 mm), the resulting curves showed no significant differences in local velocity, with a slight trend towards higher velocities with the high velocity setup (2.2–2.9%). The simulations agreed well with color Doppler except for slightly lower values at d>10–12 mm.Changes in PRF and filter have no significant influence on the absolute velocities displayed within color maps as long as PRF/filter is kept close to 10/1.

Quantification of mitral regurgitation by colour flow Doppler imaging--value of the 'proximal isovelocity surface area' method.

In this study 97 patients with mitral regurgitation (age 62 +/- 11 years, 55 men, 42 women) quantified by angiography were studied using colour flow Doppler imaging of isovelocity surface areas in the flow convergence region proximal to the regurgitant orifice. The radii of the proximal isovelocity surface areas for the flow velocities of 28 and 41 cm/s were measured. A flow convergence region was imaged in 100% (96%) of the patients with Grade I/II or more and in 92% (64%) of the patients with Grade I mitral regurgitation for a flow velocity of 28 (41) cm/s. The radii of the proximal isovelocity surface areas correlated significantly with the angiographic grade in patients with sinus rhythm as well as atrial fibrillation. A correct differentiation of Grade I to II from Grade III to IV mitral regurgitation was provided in more than 90% of all patients for both flow velocities investigated. Assuming hemispheric proximal isovelocity surface areas, in 11 patients the regurgitant volumes from echocardiography (range: 2.6-241 (0.9-198) ml for a flow velocity = 28 (41) cm/s) correlated with, but considerably overestimated the values from cardiac catheterization (range: 1.4-72.5 ml) with r = 0.79 (0.82) (P < 0.01) and SEE = 57.9 (42.4) ml for a flow velocity of 28 (41) cm/s. It was concluded that colour flow Doppler imaging of the flow convergence region enables the diagnosis of mitral regurgitation and the differentiation between Grade I to II and Grade III to IV mitral regurgitation, but may be of little value in estimating the regurgitant volume, assuming a hemispheric symmetry of the proximal flow convergence region.

Aortic regurgitant flow by color Doppler measurement of the local velocity 7 mm above the leak orifice –¶Part 1: in vitro measurements

Die Flußkonvergenz-Methode dient der Bestimmung des Flusses durch Ostien unbekannter Größe. Sie wurde validiert für plane Lochblenden und AV-Klappen. Ihre Anwendung bei Aorteninsuffizienz wird jedoch erschwert durch die komplexe Anatomie der Klappe sowie des Bulbus und die dadurch bedingte Deformierung des konvergierenden Flusses: Der offene Winkel, den die Klappenränder bilden, bewirkt relativ niedrigere Geschwindigkeiten in der Nähe des Leckostiums, was zur Unterschätzung des Flusses führt. Die seitliche Begrenzung der Flußkonvergenzregion durch die Wand der Aorta ascendens bewirkt relativ erhöhte Geschwindigkeiten in größerer Entfernung zum Leck und kann dadurch zur Überschätzung des Flusses führen. Diese Untersuchung prüfte unsere Hypothese, daß es dazwischen, nämlich in mittlerem Abstand zum Leck, eine Region gibt, in der diese beiden Einflüsse auf das Flußmuster minimal sind, so daß dort die lokale Geschwindigkeit nur eine Funktion des Flusses ist. In einem Strömungsmodell zur Simulation einer Aorteninsuffizienz wurde die Flußkonvergenzregion mit dem Farbdoppler unter verschiedenen Anlotrichtungen dargestellt (in der Mittellinie analog zum apikalen und von 60° lateral analog dem parasternalen Zugang). Geschwindigkeitsprofile durch die Flußkonvergenz-Region wurden erstellt entlang der Linie vom Schallkopf zum Leck. Im 7 mm Abstand zum Leck fand sich ein einheitlicher Wert für den Quotienten aus der lokalen Geschwindigkeit v(7 mm) durch Fluß (v(7 mm)/Q=0,28cm−2). Änderungen der Lochgröße (3,5 vs. 7 mm), seiner Lokalisation (zentrales vs. randständiges Loch), des Öffnungswinkels (planare Lochblende vs. inverser Trichter) oder der Anlotrichtung hatten nur minimalen Einfluß auf v(7 mm)/Q. Somit weist die Flußkonvergenz-Region der Aorteninsuffizienz einen uniformen Wert auf für v(7 mm)/Q. Innerhalb der hier untersuchten Grenzen spiegelt daher die v(7 mm) direkt den Regurgitationsfluß wider, unabhängig von Variationen der Klappenanatomie oder der Anlotrichtung. Aims: The flow convergence method enables the determination of flow across restrictive orifices. It was validated for planar orifice plates and atrioventricular valves. However, its quantitative application to aortic regurgitation is complicated due to the complex valve anatomy which distorts the converging flow field. An open angle formed by the leaflets causes relatively lower velocities in the region near the orifice, resulting in underestimation of flow. Confinement of the flow convergence region by the ascending aorta relatively increases the velocities at greater distance to the orifice and can cause overestimation of flow. We hypothesized that there is a region at intermediate distance to the orifice, where both these effects on the flow field are minimal, so that the local velocity there is only a function of flow. Methods and results: In a flow model, aortic regurgitation was simulated. The flow convergence was imaged by color Doppler. Different scanning directions were used (analogue to apical and parasternal approach). Velocity profiles across the flow convergence were read along the line from the scanhead to the orifice. At a distance of 7 mm to the orifice, a uniform value was found for the ratio of local velocity v(7 mm)/flow (=0.28cm−2). Variations in size (3.5 to 7 mm), site (central versus lateral) and leaflet angle (planar versus inverted funnel) of the orifice and in the scanning approach had only a minimal effect on this value. Conclusion: The aortic regurgitant flow convergence is characterized by a relatively uniform V (7 mm)/Q. Independent of variations in the anatomy and the scanning approach, this value directly reflects flow.