Adjacent solid boundaries alter the size of regurgitant jets on Doppler color flow maps

Pitfalls in the color Doppler diagnosis of valvular regurgitation

Color Doppler flow mapping of the regurgitant jet is frequently used as a means of assessing the severity of valvular regurgitation. Although convenient, this method of assessing valvular regurgitation is subject to a number of hemodynamic and technical factors that may limit its accuracy. Variations in hemodynamic and structural factors such as orifice size, jet geometry, receiving chamber constraints, afterload, fluid viscosity, heart rate, and cardiac output may have profound effects on the measured regurgitant jet area. Variations in scanning and machine factors, such as scanning direction, Doppler angle, frame rate, color display algorithms, pulse repetition frequency (PRF), system gain, packet size, carrier frequency, wall filter, and transmit power have been shown to alter the measured regurgitant jet area significantly. Despite these limitations, color flow Doppler provides a relatively reliable noninvasive method for semiquantitative assessment of valvular regurgitation. Obviously, standardization of the design and application of the various available color mapping algorithms, as well as other machine and hemodynamic factors, would help provide more reliable and reproducible quantitative information about the degree of valvular insufficiency.

Influence of jet impingement on color Doppler parameters of aortic regurgitation

In vitro studies have demonstrated that the characteristics of a color Doppler jet are influenced by a number of factors including jet eccentricity and jet impingement. To explore the relationship of a jet impingement and aortic regurgitant color Doppler jet parameters, jet area, width, and length were measured from apical echocardiographic views of 84 patients 4 +/- 11 days prior to catheterization and compared to angiographic grade. An impinging color jet contacted the interventricular septum or mitral valve beneath the aortic valve in the imaging plane and a nonimpinging jet did not contact the septum or mitral valve in the imaging plane. As expected, the percentage of patients with impinging jets increased with aortic regurgitation angiographic grade. Neither left ventricular chamber dimensions nor the presence of an aortic prosthesis significantly influenced the color Doppler variables. For a given angiographic grade of aortic regurgitation, impinging jets were associated with larger color Doppler jet widths (P less than 0.05) and areas (P = 0.001) than nonimpinging jets. The color Doppler area and length increased significantly with angiographic grade for nonimpinging jets (P less than 0.05) but not for impinging jets. Impinging jets are associated with larger color Doppler widths and areas than nonimpinging jets for a given grade of aortic regurgitation, possibly because of the effect of jet deflection toward an adjacent wall. Jet impinging should be considered when using color Doppler techniques to evaluate aortic regurgitation.

Quantitative Doppler assessment of valvular regurgitation

BACKGROUND

Quantitation of valvular regurgitation remains a challenge. The accuracy of quantitative Doppler is controversial, and its ability to measure regurgitant volume is unknown; therefore, it is not widely used.

METHODS AND RESULTS

In 120 patients (20 without regurgitation, 19 with aortic regurgitation, and 81 with mitral regurgitation), the stroke volume through the mitral annulus and left ventricular outflow tract were measured using pulsed-wave Doppler concurrently with left ventricular stroke volume calculated using left ventricular volumes measured by two-dimensional echocardiography Simpson's biapical method. Regurgitant volume and fraction were thus computed using Doppler or ventricular methods. In normal patients there were good correlations between Doppler and left ventricular measurements of stroke volume. Doppler regurgitant volume and fraction were 4.4 +/- 4.4 mL and 5.3 +/- 4.5%, respectively. In patients with aortic regurgitation, there were good correlations between Doppler and left ventricular measurements of stroke volume, regurgitant volume, and regurgitant fraction (r = 0.97, r = 0.95, and r = 0.93, respectively; p < 0.0001). In patients with mitral regurgitation, despite good correlations between Doppler and ventricular methods for stroke volume, regurgitant volume, and regurgitant fraction (r = 0.94, r = 0.93, and r = 0.94, respectively; p < 0.001), these variables were overestimated by Doppler. However, in the last 54 patients compared with the first 27, overestimation decreased significantly for regurgitant volume (5 +/- 10 mL versus 18 +/- 27 mL, p < 0.05) and regurgitant fraction (3.3 +/- 6.7% versus 6.2 +/- 6.8%, p = 0.05).

CONCLUSIONS

Quantitative Doppler can be performed in large numbers of patients in a clinical laboratory. Its potential limitation was identified as overestimation of mitral regurgitation, which is overcome with increased experience. Its achieved accuracy in mitral and aortic regurgitation allows measurement not only of regurgitant fraction but most importantly of regurgitant volume.

Doppler color flow mapping of epicardial coronary arteries: initial observations

OBJECTIVES

We addressed the hypothesis that blood flow could be imaged by Doppler color flow mapping of the coronary arteries and characteristic patterns described in normal and diseased vessels.

BACKGROUND

Echocardiographic imaging of the epicardial coronary arteries has been suggested as a useful adjunct to their intraoperative evaluation. Addition of Doppler color flow mapping could potentially enhance this evaluation by displaying the flow disturbance produced by anatomic lesions whose physiologic significance may otherwise be uncertain. In experimental models, such displays could also potentially provide insights into the pathophysiology of coronary blood flow and stenosis.

METHODS

Epicardial coronary arteries were examined with a high resolution 7-MHz linear phased-array transducer both in vivo and in vitro. 1) The coronary arteries were studied in the beating hearts of 10 open chest dogs in which experimental stenoses were also created; the maximal extent of the arterial tree in which flow could be seen in the most ideal setting was also examined in four additional excised perfused canine hearts. 2) Six excised human coronary arteries were perfused in a pulsatile manner to determine whether abnormal flow patterns could be prospectively identified and subsequently correlated with pathologic evidence of stenosis.

RESULTS

All normal coronary artery segments studied showed homogeneous flow without evidence of flow disturbance. In the excised heart, flow could be visualized to the distal extent of the epicardial vessels; in the open chest model, visualization of the proximal 5 to 6 cm was comparable, although surrounding structures limited access to the terminal portions of the vessels. The stenotic lesions created in the canine hearts (n = 9) showed recognizable alterations in the flow pattern: localized aliasing, proximal blood flow acceleration, distal flow disturbance and recirculatory flow. In the excised human arteries, these features identified 12 lesions, all of which corresponded to areas of > or = 50% lumen narrowing by pathologic examination.

CONCLUSION

Blood flow in the epicardial coronary arteries can be imaged by Doppler color flow mapping and characteristic flow patterns described in normal and diseased vessels.

Accuracy of flow convergence estimates of mitral regurgitant flow rates obtained by use of multiple color flow Doppler M-mode aliasing boundaries: an experimental animal study

The proximal flow convergence method of multiplying color Doppler aliasing velocity by flow convergence surface area has yielded a new means of quantifying flow rate by noninvasively derived measurements. Unlike previous methods of visualizing the turbulent jet of mitral regurgitation on color flow Doppler mapping, flow convergence methods are less influenced by machine factors because of the systematic structure of the laminar flow convergence region. However, recent studies have demonstrated that the flow rate calculated from the first aliasing boundary of color flow Doppler imaging is dependent on orifice size, flow rate, aliasing velocity and therefore on the distance from the orifice chosen for measurement. In this study we calculated the regurgitant flow rates acquired by use of multiple proximal aliasing boundaries on color Doppler M-mode traces and assessed the effect of distances of measurement and aliasing velocities on the calculated regurgitant flow rate. Six sheep with surgically induced mitral regurgitation were studied. The distances from the mitral valve leaflet M-mode line to the first, second, and third sequential aliasing boundaries on color Doppler M-mode traces were measured and converted to the regurgitant flow rates calculated by applying the hemispheric flow equation and averaging instantaneous flow rates throughout systole. The flow rates that were calculated from the first, second, and third aliasing boundaries correlated well with the actual regurgitant flow rates (r = 0.91 to 0.96). The mean percentage error from the actual flow rates were 151% for the first aliasing boundary, 7% for the second aliasing boundary, and -43% for the third aliasing boundary; and the association between aliasing velocities and calculated flow rates indicates an inverse relationship, which suggests that in this model, there were limited velocity-distance combinations that fit with a hemispheric assumption for flow convergence geometry. The second aliasing boundary with an aliasing velocity, of 102 cm/sec, (which was achieved by use of a 4 kHz pulse repetition frequency, a 3.75 MHz transducer, and no color baseline shift), provided the closest fit to the actual regurgitant flow rates (r = 0.99; y = 0.95x + 0.07). The averaged calculated flow rates from all aliasing velocities also resulted in excellent correlation (r = 0.97; y = 0.99x + 0.5). A hemispheric flow convergence method that is based on color Doppler M-mode echocardiography is a feasible and automatable method for quantifying mitral regurgitant rate.(ABSTRACT TRUNCATED AT 400 WORDS)

Quantification of regurgitant flow through bileaflet heart valve prostheses: theoretical and in vitro studies

A theoretical treatment using turbulent jet theory has yielded a new equation for predicting regurgitant flow through bileaflet heart valve prostheses, the most commonly implanted mechanical valve design. Previously reported techniques assuming an axisymmetric jet are not applicable to the slot-like orifices presented in these valves. The equations were therefore rederived in the context of the prosthetic valve geometry. The purpose of this study was to develop such a method and demonstrate its applicability in principle by using in vitro models. The method was validated under both steady and pulsatile flow conditions. Having derived a method geometrically specific to the orifices presented in bileaflet mechanical heart valves, it should be applicable from patient to patient due to the rigid nature of the valve. These idealized in vitro studies, along with the accompanying theoretical derivation, will guide implementation in the clinical setting.

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

Accurate quantitation of valvular incompetence remains an important goal in clinical cardiology. It has been shown previously that when color flow Doppler mapping is used, simple measurements of apparent jet size do not correlate closely with regurgitant flow rate and regurgitant fraction. Recently the proximal flow convergence method has been proposed to quantify valvular regurgitation by analysis of the converging flow field proximal to a regurgitant lesion. Flow rate Q can be calculated as Q = 2 pi r2v(a), where v(a) is the aliasing velocity at a distance r from the orifice. In 54 patients (43 with sinus rhythm and 11 with atrial fibrillation) who had at least mild mitral regurgitation according to semiquantitative assessment, regurgitant stroke volume, regurgitant flow rate, and regurgitant fraction were calculated with the proximal flow convergence method and compared with values that were obtained by the Doppler two-dimensional echocardiographic method. Regurgitant stroke volumes (Vr) as calculated by the proximal flow convergence method correlated very closely with values that were obtained by the Doppler two-dimensional method, with r = 0.93 (y = 0.95x + 0.55) and delta Vr = -0.3 +/- 4.0 cm3. Regurgitant flow rates (Q) as calculated by both methods showed a similar correlation: r = 0.93 (y = 0.95x + 54) and delta Q = -34 +/- 284 cm3/min. The correlation for regurgitant fraction (RF) as calculated by both techniques showed r = 0.89 (y = 0.98x + 0.006) and delta RF = -0.005 +/- 0.06. All correlations were slightly better for the group of patients with sinus rhythm than for the study group of patients with atrial fibrillation.(ABSTRACT TRUNCATED AT 250 WORDS)

Relation between Doppler color flow variables and invasively determined jet variables in patients with aortic regurgitation

OBJECTIVES

The purpose of this study was to test the hypothesis that invasively derived jet variables including regurgitant orifice area and momentum determine the characteristics of Doppler color flow jets in patients with aortic regurgitation.

BACKGROUND

In vitro studies have demonstrated that the velocity distribution of a regurgitant jet is best characterized by the momentum of the jet, which incorporates orifice area and velocity of flow through the orifice.

METHODS

Peak jet momentum, peak flow rate and regurgitant orifice area were determined with intraaortic Doppler catheter and cardiac catheterization techniques in 22 patients with chronic aortic regurgitation. These invasively derived variables were compared with apical and parasternal long-axis Doppler color echocardiographic variables obtained in the catheterization laboratory.

RESULTS

Jet momentum increased significantly with the angiographic grade of regurgitation. The apical color jet area of aortic regurgitation increased linearly with jet momentum and regurgitant orifice area in vivo, but the correlations were only moderately good (r = 0.63 and 0.65, respectively). Color jet length also increased linearly with jet momentum and with regurgitant orifice area. There was only a trend for Doppler color jet width to increase with all invasively derived jet variables.

CONCLUSIONS

Whereas jet area by Doppler color flow imaging is directly related to both orifice area and jet momentum in vivo, Doppler color variables measured in planes normal to the orifice do not correlate well enough with either jet momentum or regurgitant orifice area to predict jet flow variables in patients with aortic regurgitation. It is likely that the important influence of adjacent boundaries will limit the use of the velocity distribution of aortic regurgitant jets for determining the severity of disease.

Intraoperative evaluation of mitral valve regurgitation and repair by transesophageal echocardiography: incidence and significance of systolic anterior motion

OBJECTIVE

This study was designed to delineate the utility and results of intraoperative transesophageal echocardiography in the evaluation of patients undergoing mitral valve repair for mitral regurgitation.

BACKGROUND

Mitral valve reconstruction offers many advantages over prosthetic valve replacement. Intraoperative assessment of valve competence after repair is vital to the effectiveness of this procedure.

METHODS

Intraoperative transesophageal echocardiography was performed in 143 patients undergoing mitral valve repair over a period of 23 months. Before and after repair, the functional morphology of the mitral apparatus was defined by two-dimensional echocardiography; Doppler color flow imaging was used to clarify the mechanism of mitral regurgitation and to semiquantitate its severity.

RESULTS

There was significant improvement in the mean mitral regurgitation grade by composite intraoperative transesophageal echocardiography after valve repair (3.6 +/- 0.8 to 0.7 +/- 0.7; p less than 0.00001). Excellent results from initial repair with grade less than or equal to 1 residual mitral regurgitation were observed in 88.1% of patients. Significant residual mitral regurgitation (grade greater than or equal to 3) was identified in 11 patients (7.7%); 5 underwent prosthetic valve replacement, 5 had revision of the initial repair and 1 patient had observation only. Of the 100 patients with a myxomatous mitral valve, the risk of grade greater than or equal to 3 mitral regurgitation after initial repair was 1.7% in patients with isolated posterior leaflet disease compared with 22.5% in patients with anterior or bileaflet disease. Severe systolic anterior motion of the mitral apparatus causing grade 2 to 4 mitral regurgitation was present in 13 patients (9.1%) after cardiopulmonary bypass. In 8 patients (5.6%), systolic anterior motion resolved immediately with correction of hyperdynamic hemodynamic status, resulting in grade less than or equal to 1 residual mitral regurgitation without further operative intervention. Transthoracic echocardiography before hospital discharge demonstrated grade less than or equal to 1 residual mitral regurgitation in 86.4% of 132 patients studied. A significant discrepancy (greater than 1 grade) in residual mitral regurgitation by predischarge transthoracic versus intraoperative transesophageal echocardiography was noted in 17 patients (12.9%).

CONCLUSIONS

Transesophageal echocardiography is a valuable adjunct in the intraoperative assessment of mitral valve repair.

Variability in the quantitation of mitral regurgitation by Doppler color flow mapping: comparison of transthoracic and transesophageal studies

OBJECTIVES

This study was designed to assess the most accurate and reproducible methods to quantitate mitral regurgitation by color flow transthoracic and transesophageal echocardiography.

BACKGROUND

Quantitative measurements of mitral regurgitant jets have resulted in an intraobserver and interobserver variability of up to 20%. Few data are available evaluating the various techniques by which mitral regurgitant jets are quantitated.

METHODS

Forty patients who underwent cardiac catheterization and both transesophageal and transthoracic echocardiography within 1 week were studied. Two boundaries of the color regurgitant jet area were identified and quantitated: 1) the central aliased core of the regurgitant jet with the mosaic pattern excluding any swirling low velocity flow; and 2) the largest definable area of the regurgitant flow, including low velocity flow considered to be part of the regurgitant jet.

RESULTS

The total regurgitant areas obtained by transthoracic and transesophageal studies did not differ (5.7 +/- 4.6 vs. 5.7 +/- 3.7 cm2; p = NS). However, the transesophageal mosaics were significantly larger than those obtained by transthoracic echocardiography (3.6 +/- 3.1 vs. 2.8 +/- 3.4 cm2; p less than 0.01). In transthoracic studies observer variability was higher when the mosaic aspect of the regurgitant jet rather than the total regurgitant area was measured (24 +/- 20 vs. 16 +/- 11%; p less than 0.05). In contrast, in transesophageal studies variability was lower when the mosaic area rather than the total regurgitant area was measured (11 +/- 12% vs. 18 +/- 18%; p less than 0.05). The best correlations with left ventriculography were obtained by using the absolute total regurgitant area (r = 0.72) for transthoracic studies and the mosaic area of the jets (r = 0.87) for transesophageal studies.

CONCLUSIONS

Doppler color flow jet areas correlate closely with angiographic results in the evaluation of mitral regurgitation. The total regurgitant area (including the surrounding swirling flow) in transthoracic studies and the aliased core of the regurgitant jet (mosaic) in transesophageal studies appear to be the most accurate and reproducible measurements for evaluating mitral regurgitation.

Three-dimensional echocardiography: techniques and applications

Current echocardiographic devices provide only 2-dimensional views of the heart. To appreciate 3-dimensional structural relations, therefore, requires mental reconstruction of 2-dimensional views by an experienced observer. Our ability to answer new questions about the heart could be increased if 2-dimensional images could be combined to display 3-dimensional relations. Such 3-dimensional reconstruction would permit analysis of structures of unknown or complex shape and the noninvasive quantification of cardiac chamber size and function without making geometric assumptions. To overcome previous limitations, mechanisms have been developed for automated integration of images and positional data during routine echocardiographic scanning, thereby greatly enhancing the efficiency and application of image reconstruction. Refining the diagnosis of mitral valve prolapse has presented a uniquely 3-dimensional problem requiring information previously unavailable from the 2-dimensional technique. To date, 3-dimensional studies have demonstrated that the mitral valve is saddle-shaped in systole, so that apparent superior leaflet displacement in the mediolateral 4-chamber view, often seen in otherwise normal individuals, lies entirely within the bounds defined by the mitral annulus and occurs without leaflet distortion or actual displacement above the entire mitral valve. Other applications of 3-dimensional image reconstruction include calculation of ventricular volume and ejection fraction by transthoracic or transesophageal scanning without geometric assumptions; improving the standardization and accuracy of 2-dimensional measurements by improving spatial appreciation; and 3-dimensional reconstruction of vascular walls to guide interventions. In the future, systems for acquiring multiple views more rapidly by parallel processing and improving endocardial border extraction should allow more routine application of 3-dimensional methods as the next stage in the evolution of cardiac ultrasound, thereby expanding the range of questions that can be answered. Achieving these goals will depend, in large measure, on persistence in developing the necessary technology.

Influence of the Coanda effect on color Doppler jet area and color encoding. In vitro studies using color Doppler flow mapping

We studied surface adherence and its effects on color Doppler jet areas and color encoding in an in vitro model with a noncompliant receiving chamber into which a steady flow jet was directed parallel to either a straight or a curved surface adjacent to and 4 mm away from the inflow orifice (1.50 mm2) with the control condition being a free jet matched for flow rates and driving pressures. Jets were imaged perpendicular to the plane of the surface, the plane in which most clinical images of jet-surface interactions are obtained. Ten different flow rates ranging from 0.13 to 0.30 l/min were used. Surface-adherent jet areas were smaller than control jets for every driving pressure-volume combination (paired t test, p less than 0.01). Computer analysis of color Doppler images showed more green and blue (reverse flow) pixels on the surface side of the adherent jets than the control jets (p less than 0.05), suggesting that viscous energy loss and flow deceleration and reversal play a role in the jet-surface interaction. Analysis of variance demonstrated that linear regression slopes of flow rate versus jet area for surface jets were lower (slopes, 11-21 cm2/l/min; r = 0.95-0.97) than those for the control (slope, 33 cm2/l/min; r = 0.97) (p less than 0.0001). Surface adherence (Coanda effect) influences jet size and color encoding, causing smaller color Doppler jet areas and greater variance and reverse velocity encoding.

Evaluation of mitral regurgitation by Doppler echocardiography

The diagnosis and assessment of mitral regurgitation has been one of the main challenges for cardiac ultrasound. Imaging techniques (M-mode and two-dimensional echocardiography) provide direct morphologic and etiologic information of the evaluation of patients with suspected mitral regurgitation. The advent of cardiac Doppler increased tremendously the ability to evaluate mitral regurgitation noninvasively. Continuous-wave and pulsed Doppler have been found to be sensitive and specific in the detection of mitral regurgitation. The introduction of color flow Doppler simplified enormously the assessment of patients with suspected mitral regurgitation. The maximal regurgitant area and maximal regurgitant area corrected for left atrial size have become the most commonly used parameters to evaluate mitral regurgitation by color flow Doppler in the clinical setting. However, the color regurgitant jet area is highly dependent on anatomical, hemodynamic, and equipment factors. A new method, based on the proximal isovelocity surface area, is being evaluated and appears to be relatively independent of equipment factors. Transesophageal echocardiography has been shown to be exquisitely sensitive in the detection of mitral regurgitation. Quantitation of mitral regurgitation by transesophageal echocardiography is currently based on the maximal regurgitant area and this parameter appears to correlate closely with the angiographic degree of mitral regurgitation. Pulmonary venous flow analysis had been used in conjunction with color flow mapping for the evaluation of mitral regurgitation by transesophageal echocardiography. The presence of reversed systolic flow has been shown to be sensitive and specific for the diagnosis of severe mitral regurgitation. Patients with clinically difficult surface studies, flail mitral valve leaflets, and prosthetic mitral valve are best evaluated by the transesophageal approach with interrogation of pulmonary venous flow.

Impact of impinging wall jet on color Doppler quantification of mitral regurgitation

BACKGROUND

In clinical color Doppler examinations, mitral regurgitant jets are often observed to impinge on the left atrial wall immediately beyond the mitral valve. In accordance with fluid dynamics theory, we hypothesized that a jet impinging on a wall would lose momentum more rapidly, undergo spatial distortion, and thus have a different observed jet area from that of a free jet with an identical flow rate.

METHODS AND RESULTS

To test this hypothesis in vivo, we studied 44 patients with mitral regurgitation--30 with centrally directed free jets and 14 with eccentrically directed impinging wall jets. Maximal color jet areas (cm2) (with and without correction for left atrial size) were correlated with mitral regurgitant volumes, flow rates, and fractions derived from pulsed Doppler mitral and aortic forward flows. The groups were compared by analysis of covariance. Mean +/- SD mitral regurgitant fraction, regurgitant volume, and mean flow rate averaged 37 +/- 17%, 3.06 +/- 2.65 l/min, and 147 +/- 118 ml/sec, respectively. The maximal jet area from color Doppler imaging correlated relatively well with the mitral regurgitant fraction in the patients with free mitral regurgitant jets (r = 0.74, p less than 0.0001) but poorly in the patients with impinging wall jets (r = 0.42, p = NS). Although the mitral regurgitant fraction was larger (p less than 0.05) in patients with wall jets (44 +/- 20%) than in those with free jets (33 +/- 15%), the maximal jet area was significantly smaller (4.78 +/- 2.87 cm2 for wall jets versus 9.17 +/- 6.45 cm2 for free jets, p less than 0.01). For the same regurgitant fraction, wall jets were only approximately 40% of the size of a corresponding free jet, a difference confirmed by analysis of covariance (p less than 0.0001).

CONCLUSIONS

Patients with mitral regurgitation frequently have jets that impinge on the left atrial wall close to the mitral valve. Such impinging wall jets are less predictable and usually have much smaller color Doppler areas in conventional echocardiographic views than do free jets of similar regurgitant severity. Jet morphology should be considered in the semiquantitative interpretation of mitral regurgitation by Doppler color flow mapping. Future studies of the three-dimensional morphology of wall jets may aid in their assessment.