Determinants of functional tricuspid regurgitation in incomplete tricuspid valve closure: Doppler color flow study of 109 patients

OBJECTIVES

The aim of this study was to investigate the association between the pattern of incomplete tricuspid valve closure and the presence of tricuspid regurgitation and to identify factors that determine the severity of regurgitation associated with this pattern.

BACKGROUND

The incomplete tricuspid valve closure pattern (defined as apical displacement of the leaflets) has been described by two-dimensional echocardiography. However, whether this pattern is universally associated with tricuspid regurgitation and the determinants of severity of regurgitation in its presence have not been studied by Doppler color flow mapping.

METHODS

We identified 109 consecutive patients (mean age 62 +/- 17 years) with incomplete tricuspid valve closure who were studied by Doppler color flow mapping. We measured the linear apical displacement of the coaptation point from the tricuspid annulus and the area of displacement between the leaflets and annulus. Right atrial, ventricular and annular dimensions were measured and compared with those in a group of normal subjects.

RESULTS

Tricuspid regurgitation was present in all patients with the incomplete closure pattern; it was mild in 14%, moderate in 19% and severe in 67%. Apical displacement was significantly greater (p < 0.02) in those with severe regurgitation than in those with mild regurgitation or in normal subjects. Tricuspid annulus dilation was the only independent predictor of severity of regurgitation. The right ventricle was not significantly dilated in 32% of patients, and right ventricular systolic pressure was not correlated with the severity of regurgitation and was < 30 mm Hg in 11% of patients.

CONCLUSIONS

Tricuspid regurgitation was associated with incomplete tricuspid valve closure in all patients studied and was moderate to severe in 86%. Impaired coaptation is best reflected by the displacement area between the leaflets and the annulus. High pulmonary pressure and significant right ventricular dilation are not prerequisites for functional tricuspid regurgitation. Annular dilation is the most consistent and important determinant of this lesion.

Quantification of pericardial effusions by three-dimensional echocardiography

OBJECTIVES

The purpose of this study was to examine the accuracy of three-dimensional echocardiography for the quantification of asymmetric pericardial effusion volume and to compare this new technique with two-dimensional echocardiography.

BACKGROUND

Quantification of pericardial effusion by two-dimensional echocardiography relies on a symmetric distribution of the fluid. Three-dimensional echocardiography can quantitate volume without these limitations, but its accuracy for pericardial effusion volume has not yet been assessed.

METHODS

In six open chest dogs, 41 different asymmetrically distributed pericardial effusions of known volume were created by serial infusions of fluid through a pericardial catheter. The hearts were imaged using an automated echocardiographic method that integrates three-dimensional spatial and imaging data. The surfaces of the pericardial sac and heart were then reconstructed, and the volumes of pericardial effusions were calculated. Two-dimensional echocardiography was performed simultaneously, and volumes were calculated using the prolate ellipsoid method. Asymmetric distribution of the fluid was obtained by applying localized hydrostatic pressure to the pericardium.

RESULTS

The volumes of pericardial effusion quantified using three-dimensional echocardiography correlated well with actual volumes (y = 1.0x - 1.4, SEE = 7.7 ml, r = 0.98). Two-dimensional echocardiography had an acceptable correlation (y = 1.0x + 2.3, SEE = 23 ml, r = 0.84), but a marked degree of variation from the true value was observed for any individual measurement.

CONCLUSIONS

Three-dimensional echocardiography accurately quantifies pericardial effusion volume in vivo, even when the fluid is distributed asymmetrically, whereas two-dimensional echocardiography is less reliable. This new technique may be of clinical value in quantitating pericardial effusion, especially in the serial evaluation of asymmetric or loculated effusions.

Effect of static pressure on the disappearance rate of specific echocardiographic contrast agents

Contrast echocardiography has been applied to identify cardiac structures, shunts, and perfusion territories. Most recently, quantification of flow has been proposed based on disappearance of contrast intensity. This requires that contrast agents are stable and produce a predictable effect. To assess the possible effect of pressure on their stability, the rates of backscatter decay of four echocardiographic contrast agents (Albunex, Levovist, agitated Angiovist, and agitated saline solution) exposed to constant pressures (0, 50, 100, 150, and 200 mm Hg) were quantitated. Contrast was recorded by echocardiography and measured to construct time-intensity curves. The peak decay rate for each agent at each pressure was determined. For all four agents, contrast intensity (I) decreased over time and could be described by the sigmoid function: I = a [e-lambda(t-ts)/1 + e-lambda(t-ts)] + C. Peak decay rate was significantly affected by pressure (p < 0.005) in a proportionate fashion. At pressures of 0, 100, and 200 mm Hg, the rates increased for each agent in the following fashion: Albunex, 0.144 +/- 0.109 to 0.410 +/- 0.142 to 1.442 +/- 0.309; Levovist, 0.060 +/- 0.023 to 0.162 +/- 0.049 to 0.495 +/- 0.142; Angiovist, 0.089 +/- 0.028 to 0.166 +/- 0.057 to 0.224 +/- 0.027; and saline solution, 0.068 +/- 0.039 to 0.110 +/- 0.036 to 0.154 +/- 0.057. The effect of pressure on the peak rate of contrast disappearance (lambda) was significantly different among agents (p < 0.001). Thus attempts to quantitate blood flow with contrast agents must take into account the influence of pressure.

Three-dimensional echocardiography: in vivo validation for right ventricular free wall mass as an index of hypertrophy

OBJECTIVES

This study tested the ability of three-dimensional echocardiography to reconstruct the right ventricular free wall and determine its mass in vivo using a system that automatically combines two-dimensional images with their spatial locations.

BACKGROUND

Right ventricular free wall thickness is limited as an index of right ventricular hypertrophy because right ventricular mass may increase by dilation without increased thickness and because trabeculations and oblique views can exaggerate thickness in individual M-mode and two-dimensional scans. Three-dimensional echocardiography may have potential advantages because it can integrate the entire free wall mass, uninfluenced by oblique views or geometric assumptions.

METHODS

The three-dimensional system was applied to 12 beating canine hearts to reconstruct the right ventricular free wall in intersecting views. The corresponding mass was compared with actual weights of the excised right ventricular free wall (15.5 to 78 g). For comparison, right ventricular sinus and outflow tract thickness were also measured by two-dimensional echocardiography, and the ability to predict mass from these values was determined.

RESULTS

The three-dimensional algorithm successfully reproduced right ventricular free wall mass, which agreed well with actual values: y = 1.04x + 0.02, r = 0.985, SEE = 2.7 g (5.7% of the mean value). The two-dimensional predictions showed increased scatter: The variance of mass estimation, based on thickness, was 9.5 to 12.5 (average 11) times higher than the three-dimensional method (p < 0.02).

CONCLUSIONS

Despite the irregular crescentic shape of the right ventricle, its free wall mass can be accurately measured by three-dimensional echocardiography in vivo, providing closer agreement with actual mass than predictions based on wall thickness. This method, with the increased efficiency of the three-dimensional system, can potentially improve our ability to evaluate the presence and progression of right ventricular hypertrophy.

Three-dimensional echocardiography. In vivo validation for right ventricular volume and function

BACKGROUND

Current two-dimensional echocardiographic measures of right ventricular volume are limited by the asymmetrical and crescentic shape of the ventricle and by difficulty in obtaining standardized views. Three-dimensional echocardiographic reconstruction, which does not require geometric assumptions or standardized views, may therefore have potential advantages for determining right ventricular volume. Three-dimensional techniques, however, have not been applied to the right ventricle in vivo, where cardiac motion and contraction could affect accuracy. The purpose of this study was to determine the feasibility and accuracy of three-dimensional echocardiographic reconstruction for quantifying right ventricular volume and function in vivo. In particular, it was designed to test the accuracy of a newly developed system that provides rapid, efficient, and automated three-dimensional data collection (minimizing motion effects) and takes advantage of the full three-dimensional data set to obtain volume.

METHODS AND RESULTS

The three-dimensional system was applied to reconstruct the right ventricle and measure its volume and function during 20 hemodynamic stages created in five dogs. Actual instantaneous volumes were measured continuously by an intracavitary balloon connected to an external column. Hemodynamics were varied by volume loading and induction of ischemia. Three-dimensional reconstruction successfully reproduced right ventricular volume compared with actual values at end diastole (y = 1.0 chi-3.4, r = .99, SEE = 1.8 mL) and end systole (y = 1.0 chi+ 2.0, 4 = .98, SEE = 2.5 mL). The mean difference between calculated and actual volumes throughout the cycle was 2.1 mL, or 4.9% of the mean. Ejection fraction also correlated well with actual values (y = 0.96 chi-0.3, r = .98, SEE = 3.3%).

CONCLUSIONS

Despite the irregular crescentic shape of the right ventricle, this newly developed three-dimensional system and surfacing algorithm can accurately reconstruct its shape and quantitate its volume and function in vivo without geometric assumptions. The increased efficiency of the system should increase applicability to issues of clinical and research interest.

Quantification of tricuspid regurgitation by means of the proximal flow convergence method: a clinical study

Quantitation of valvular regurgitation remains an important goal in clinical cardiology. It has been described previously that with the use of color Doppler flow mapping, simple measurements of apparent jet size do not correlate closely with quantitative regurgitant indices. 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. Assuming hemispherical convergence, flow rate Q can be calculated as Q = 2 pi r2va, where va is the aliasing velocity at a distance r from the orifice. For maximal accuracy, previously validated correction factors must be used to account for the flattening effect of the isovelocity contours close to the orifice and for the actual sector angle subtended by the valve leaflets (alpha), to yield a flow rate formula Q = 2 pi r2va.(vp/vp - va).(alpha/180), where vp is the orifice velocity obtained by continuous wave Doppler. In 45 patients (35 in sinus rhythm, 10 with atrial fibrillation) with tricuspid regurgitation, regurgitant stroke volume, regurgitant flow rate, and regurgitant fraction were calculated using the proximal flow convergence method and were compared with values obtained by the Doppler two-dimensional echocardiographic method. Regurgitant stroke volumes (SV) calculated by the proximal flow convergence method correlated very closely with values obtained by the Doppler two-dimensional method with r = 0.95 (y = 0.94x + 0.99) and delta SV = -0.3 +/- 5.2 cm3. Regurgitant flow rates (Q) calculated by both methods showed a similar correlation: r = 0.96 (y = 0.97x + 45) and delta Q = 1.6 +/- 429 cm3/min.(ABSTRACT TRUNCATED AT 250 WORDS)

Spatial and temporal variability in the pattern of recovery of ventricular geometry and function after acute occlusion and reperfusion

Myocardial ischemia and infarction are known to cause changes in both ventricular shape and function. Little is known about the recovery of ventricular geometry after transient myocardial ischemia and its relationship to recovery of function. To examine the pattern of recovery of ventricular geometry following transient coronary artery occlusion and to assess the relationship of this to the return of systolic function, we used echocardiography to study 13 dogs following 15-minute occlusion of the left anterior descending coronary artery. During ischemia, total endocardial surface area (ESA) increased from 32.55 +/- 1.77 to 45.36 +/- 3.18 cm2 (p = 0.001). The most striking increase was at the apex, where circumference increased from 5.04 +/- 0.24 at baseline to 7.86 +/- 0.43 cm at the end of occlusion (p = 0.0001), an increase of 58%. During reperfusion, ventricular geometry rapidly returned toward normal (baseline), with recovery of 80% of the increase in ESA evident by 15 minutes of reperfusion. Recovery of systolic function was substantially slower (p < 0.005 for all periods of observation during the 2 hours of reperfusion). During reperfusion, recovery of ventricular geometry and function was not uniform throughout the ischemic bed. The apex recovered most slowly, with the centroid of the area of abnormal contraction progressively moving along the long axis of the left ventricle toward the apex. There was also a progressive decrease in the radius of the area of dysfunction, from 2.0 +/- 0.15 at end occlusion to 0.13 +/- 0.07 cm at 120 minutes of reperfusion (p = 0.0001). There was no difference in blood flow between the apical and anterior segments during ischemia or reperfusion. Reperfusion favorably reduced the ischemic zone dilation before recovery of active systolic function and geometric recovery thus may be important in determining ultimate functional recovery. In addition, recovery of function proceeded inward towards the center of the ischemic territory and in a wavefront from the base to apex. This heterogeneous and asymmetric recovery suggests that sampling at one point within the ischemic zone may not reflect the true temporal pattern of recovery.

Continuous wave Doppler echocardiography for noninvasive assessment of left ventricular dP/dt and relaxation time constant from mitral regurgitant spectra in patients

OBJECTIVES

We previously demonstrated experimentally that the mitral regurgitant velocity spectrum can be used to estimate left ventricular pressure throughout systole and may provide a new noninvasive method for estimating maximal dP/dt and the relaxation time constant. This study was designed to test this method in patients.

BACKGROUND

The maximal first derivative of left ventricular pressure (dP/dt) and the time constant of left ventricular isovolumetric relaxation (tau) are important variables of left ventricular function, but the need for invasive measurement with high fidelity catheters has limited their use in clinical cardiology.

METHODS

Twelve patients with mitral regurgitation were studied. The Doppler mitral regurgitant velocity spectrum was recorded simultaneously with micromanometer left ventricular pressure tracings in all patients. The regurgitant velocity profiles were digitized and converted to ventriculoatrial (VA) pressure gradient curves using the simplified Bernoulli equation and differentiated into instantaneous dP/dt. The relaxation time constant (tau) was calculated assuming a zero pressure asymptote from catheter left ventricular pressure decay (tau c) and from the Doppler-derived VA gradient curve with corrections. Two methods were used to correct the Doppler gradient curve to better approximate the left ventricular pressure decay before calculating the relaxation time constant: 1) adding an arbitrary 10 mm Hg (tau 10), and 2) adding the actual mean pulmonary capillary pressure (tau LA).

RESULTS

The Doppler-derived maximal positive dP/dt (1,394 +/- 302 mm Hg/s [mean +/- SD]) correlated well (r = 0.91) with the catheter-derived maximal dP/dt (1,449 +/- 307 mm Hg/s). Although the Doppler-derived negative maximal dP/dt differed slightly from catheter measurement (1,014 +/- 289 vs. 1,195 +/- 354 mm Hg/s, p < 0.01), the correlation between Doppler and catheter measurements was similarly good (r = 0.89, p < 0.0001). The correlation between tau 10 and tau c was excellent (r = 0.93, p < 0.01), but the Doppler-derived tau 10 (50.0 +/- 11.0 ms) slightly underestimated the catheter-derived tau c (55.5 +/- 12.8 ms, p < 0.01). This slight underestimation could be corrected by adding the actual pulmonary capillary wedge pressure to the Doppler gradient curve.

CONCLUSIONS

Doppler echocardiography provides an accurate and reliable method for estimating left ventricular maximal positive dP/dt, maximal negative dP/dt and the relaxation time constant (tau) in patients with mitral regurgitation.

[A description of a new method of quantifying the regurgitant flow in patients with an incompetent mitral valve]

BACKGROUND

It has been shown previously that using color Doppler flow mapping, 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 r2va where va is the aliasing velocity at a distance r from the orifice.

PATIENTS AND METHODS

In 54 patients (43 in sinus rhythm, 11 with atrial fibrillation) with at least mild mitral regurgitation by semi-quantitative assessment, regurgitant stroke volume, regurgitant flow rate, and regurgitant fraction were calculated using the proximal flow convergence method and compared with values obtained by the Doppler/two-dimensional echocardiographic method.

RESULTS

Regurgitant stroke volumes (VL) calculated by the proximal flow convergence method correlated very closely with values obtained by the Doppler-2D method with r = 0.93 (y = 0.95x + 0.55) and delta VL = -0.3 +/- 4.0 cm3. Regurgitant flow rates (Q) 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) 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 in sinus rhythm compared with the study group in atrial fibrillation.

CONCLUSION

This study demonstrates that the proximal flow convergence method is an accurate and reproducible technique to quantify mitral regurgitation. This approach is easy and less time-consuming than the Doppler-echocardiographic method. While future improvements of this method are to be expected, flow calculations based on the assumption of simple hemispheric symmetry of the proximal flow field appear suitable for clinical application at the present time.

Automated assessment of ventricular volume and function by echocardiography: validation of automated border detection

To determine the utility of a new on-line echocardiographic automated border detection (ABD) algorithm in assessing ventricular volume and ejection fraction, an optimal model was studied. This open-chest canine model allowed continuous measurement of actual left ventricular volume. In four dogs, true end-systolic and end-diastolic volume and ejection fraction were compared with those obtained by two-dimensional echocardiography with an automated method calculated from a border detection algorithm to define left ventricular endocardium and the single-plane Simpson method to calculate volume. Left ventricular volumes that used manual, off-line tracings of the left ventricle by two-dimensional echocardiograms and the single-plane Simpson method were compared. The automated echocardiographic volumes correlated with true volumes (y = 0.7x + 8.9; standard error of the estimate = 13.5 cc; r = 0.81). A significant mean underestimation of 11 +/- 15 cc was noted (p < 0.0001). Volumes obtained from the manual tracings of left ventricular endocardial contours also correlated well with true volumes (y = 0.89x + 4; standard error of the estimate = 6.7 cc; r = 0.96). However, the 3 +/- 7 underestimation was significantly lower than the error of the ABD method (p = 0.00005). Both on-line ABD and off-line ejection fractions correlated well with true ejection fractions (r = 0.94 and 0.96, respectively). There was no statistically significant difference between the mean errors of the ABD or manually derived ejection fractions. In the setting of optimal left ventricular imaging, the on-line and rapid features of this automated method make it potentially useful for quickly obtaining left ventricular volumes and ejection fraction.

Three-dimensional echocardiographic reconstruction of right ventricular volume: in vitro comparison with two-dimensional methods

Two-dimensional echocardiographic measures of right ventricular volume are limited by the asymmetric and crescentic shape of that ventricle and the difficulty in obtaining standardized views. We have developed a three-dimensional echocardiographic system that automatically integrates images and positional data and calculates right ventricular volume without the need for geometric assumptions or standardized views and a surfacing algorithm that takes advantage of the full three-dimensional data set. The accuracy of this system was studied and compared with two-dimensional methods in 12 gel-filled excised human right ventricles (18 to 74 ml). Volumes calculated by three-dimensional echocardiography correlated well with actual values (r = 0.99) and agreed more closely with them than did those obtained by two-dimensional methods (p < 0.02).

Three-dimensional reconstruction of ventricular septal defects: validation studies and in vivo feasibility

OBJECTIVES

The purpose of this study was to demonstrate the feasibility of in vivo three-dimensional reconstruction of ventricular septal defects and to validate its quantitative accuracy for defect localization in excised hearts (used to permit comparison of three-dimensional and direct measurements without cardiac contraction).

BACKGROUND

Appreciating the three-dimensional spatial relations of ventricular septal defects could be useful in planning surgical and catheter approaches. Currently, however, echocardiography provides only two-dimensional views, requiring mental integration. A recently developed system automatically combines two-dimensional echocardiographic images with their spatial locations to produce a three-dimensional construct.

METHODS

Surgically created ventricular septal defects of varying size and location were imaged and reconstructed, along with the left and right ventricles, in the beating heart of six dogs to demonstrate the in vivo feasibility of producing a coherent image of the defect that portrays its relation to surrounding structures. Two additional gel-filled excised hearts with defects were completely reconstructed. Quantitative localization of the defects relative to other structures (ventricular apexes and valve insertions) was then validated for seven defects in excised hearts. The right septal margins of the exposed defects were also traced and compared with their reconstructed areas and circumferences.

RESULTS

The three-dimensional images provided coherent images and correct spatial appreciation of the defects (two inlet, two trabecular, one outlet and one membranous Gerbode in vivo; one inlet and one apical in excised hearts). The distances between defects and other structures in the excised hearts agreed well with direct measures (y = 1.05x-0.18, r = 0.98, SEE = 0.30 cm), as did reconstructed areas (y = 1.0x-0.23, r = 0.98, SEE = 0.21 cm2) and circumferences (y = 0.97x + 0.13, r = 0.97, SEE = 0.3 cm).

CONCLUSIONS

Three-dimensional reconstruction of ventricular septal defects can be achieved in the beating heart and provides an accurate appreciation of defect size and location that could be of value in planning interventions.

Three-dimensional echocardiography. In vivo validation for left ventricular volume and function

BACKGROUND

Current two-dimensional quantitative echocardiographic methods of volume assessment require image acquisition from standardized scanning planes. Left ventricular volume and ejection fraction are then calculated by assuming ventricular symmetry and geometry. These assumptions may not be valid in distorted ventricles. Three-dimensional echocardiography can quantify left ventricular volume without the limitations imposed by the assumptions of two-dimensional methods. We have developed a three-dimensional system that automatically integrates two-dimensional echocardiographic images and their positions in real time and calculates left ventricular volume directly from traced endocardial contours without geometric assumptions.

METHODS AND RESULTS

To study the accuracy of this method in quantifying left ventricular volume and performance in vivo, a canine model was developed in which instantaneous left ventricular volume can be measured directly with an intracavitary balloon connected to an external column. Ten dogs were studied at 84 different cavity volumes (4 to 85 cm3) and in conditions of altered left ventricular shape produced by either coronary occlusion or right ventricular volume overload. To demonstrate clinical feasibility, 19 adult human subjects were then studied by this method for quantification of stroke volume. Left ventricular volume, stroke volume, and ejection fraction calculated by three-dimensional echocardiography correlated well with directly measured values (r = .98, .96, .96 for volume, stroke volume, and ejection fraction, respectively) and agreed closely with them (mean difference, -0.78 cm3, -0.60 cm3, -0.32%). In humans, there was a good correlation (r = .94, SEE = 4.29 cm3) and agreement (mean difference, -0.98 +/- 4.2 cm3) between three-dimensional echocardiography and Doppler-derived stroke volumes.

CONCLUSIONS

Three-dimensional echocardiography allows accurate assessment of left ventricular volume and systolic function.

Application of color Doppler flow mapping to calculate effective regurgitant orifice area. An in vitro study and initial clinical observations

BACKGROUND

Analogous to stenotic valve area in the assessment of valvular stenosis, regurgitant orifice area (ROA) represents a fundamental parameter to assess valvular insufficiency. However, this parameter has not been routinely available up to now. In this study, we introduce the concept and provide the methodology to calculate regurgitant orifice area noninvasively, based on the analysis of the proximal flow convergence zone.

METHODS AND RESULTS

In an in vitro study, we showed the feasibility and the accuracy of calculating effective ROA by the proximal flow convergence method throughout a range of driving pressures. The calculated and true ROA showed an excellent correlation with r = .992, delta ROA = -1.4 +/- 2.9 mm2. We then applied this concept clinically in 77 patients with mitral regurgitation and showed a very good correlation between effective ROA calculated by the proximal flow convergence method and calculated by the Doppler echocardiographic method: r = .95, delta ROA = -0.2 +/- 3.9 mm2. The ROA also correlated very well with Doppler echocardiographic-derived regurgitant stroke volume (r = .93) and regurgitant fraction (r = .82). In a subgroup of 20 patients who underwent invasive evaluation, the calculated effective ROA also correlated well with the angiographic grade of mitral regurgitation (rho = .81).

CONCLUSIONS

We conclude that effective ROA represents unique information on the severity of a regurgitant lesion and can easily be calculated by the proximal flow convergence method. This new parameter should enhance our understanding and improve the serial assessment of valvular regurgitation.

Validation of the proximal flow convergence method. Calculation of orifice area in patients with mitral stenosis

BACKGROUND

It has been proposed recently that measuring the flow convergence region proximal to an orifice by Doppler flow mapping can provide a means of calculating regurgitant flow rate. Although verified in experimental models, this approach is difficult to validate clinically because there is no ideal gold standard for regurgitant flows in patients. However, this method also can be used to derive cardiac output or flow rate proximal to stenotic orifices and therefore to calculate their areas by the continuity equation (area = flow rate/velocity). Applying this method in mitral stenosis would provide a unique way of validating the underlying concept because the predicted areas could be compared with those measured directly by planimetry.

METHODS AND RESULTS

We studied 40 patients with mitral stenosis using imaging and Doppler echocardiography. Doppler color flow recordings of mitral inflow were obtained from the apex, and the radius of the proximal flow convergence region was measured at its peak diastolic value from the orifice to the first color alias along the axis of flow. Flow rate was calculated assuming uniform radial flow convergence toward the orifice, modified by a factor that accounted for the inflow funnel angle formed by the mitral leaflets. Mitral valve area was then calculated as peak flow rate divided by peak velocity by continuous-wave Doppler. The calculated areas agreed well with those from three comparative techniques over a range of 0.5 to 2.2 cm2: 1) cross-sectional area by planimetry (y = 1.08x-0.13, r = .91, SEE = 0.21 cm2); 2) area derived from the Doppler pressure half-time (y = 1.02x-0.14, r = .89, SEE = 0.24 cm2); and 3) area calculated by the Gorlin equation in the 26 patients who underwent catheterization (y = 0.89x + 0.08, r = .86, SEE = 0.24 cm2). Agreement with planimetry was similar for 22 patients with mitral regurgitation and 18 without it (P > .6), as well as for 6 in atrial fibrillation (P > .2).

CONCLUSIONS

These results validate the proximal flow convergence concept in the clinical setting and also demonstrate that it can be extended to orifice area calculation using the continuity equation.

Automated flow rate calculations based on digital analysis of flow convergence proximal to regurgitant orifices

OBJECTIVES

The purpose of the study was to develop and validate an automated method for calculating regurgitant flow rate using color Doppler echocardiography.

BACKGROUND

The proximal flow convergence method is a promising approach to quantitate valvular regurgitation noninvasively because it allows one to calculate regurgitant flow rate and regurgitant orifice area; however, defining the location of the regurgitant orifice is often difficult and can lead to significant error in the calculated flow rates. To overcome this problem we developed an automated algorithm to locate the orifice and calculate flow rate based on the digital Doppler velocity map.

METHODS

This algorithm compares the observed velocities with the anticipated relative velocities, cos psi/2 pi r2. The orifice is localized as the point with maximal correlation between predicted and observed velocity, whereas flow rate is specified as the slope of the regression line. We validated this algorithm in an in vitro model for flow through circular orifices with planar surroundings and a porcine bioprosthesis.

RESULTS

For flow through circular orifices, flow rates calculated on individual Doppler maps and on an average of eight velocity maps showed excellent agreement with true flow, with r = 0.977 and delta Q = -3.7 +/- 15.8 cm3/s and r = 0.991 and delta Q = -4.3 +/- 8.5 cm3/s, respectively. Calculated flow rates through the bioprosthesis correlated well but underestimated true flow, with r = 0.97, delta Q = -10.9 +/- 12.5 cm3/s, suggesting flow convergence over an angle > 2 pi. This systematic underestimation was corrected by assuming an effective convergence angle of 212 degrees.

CONCLUSIONS

This algorithm accurately locates the regurgitant orifice and calculates regurgitant flow rate for circular orifices with planar surroundings. Automated analysis of the proximal flow field is also applicable to more physiologic surfaces surrounding the regurgitant orifice; however, the convergence angle should be adjusted. This automated algorithm should make quantification of regurgitant flow rate and regurgitant orifice area more reproducible and readily available in clinical cardiology practice.

Analysis of mitral inertance: a factor critical for early transmitral filling

The upslope of the transmitral E wave depends on the combined influence of the rate of change of the atrioventricular gradient and the inertial mass of blood within the mitral apparatus (inertance). To use observed transmitral velocity to predict the atrioventricular pressure (delta p) difference requires knowledge of the magnitude of mitral inertance (M, inertial mass divided by effective orifice area), closely related to the length over which blood accelerates and decelerates on passing through the valve. To define the magnitude and determining factors for mitral inertance in typical valvular geometries, we used an in vitro model in which a known atrioventricular gradient (delta p, range 3.8 to 39 mm Hg) was applied instantaneously to orifices (areas of 0.5, 1, 1.5, 2, and 2.5 cm2) and conduits (volume 2.5 to 24 ml). Continuous wave Doppler spectra were recorded and the slope (dv/dt) of the tangent to the upslope was measured manually. From slope and pressure difference, inertance was calculated as delta p/(dv/dt). In 103 combinations of pressure gradients and orifices or conduits, inertance ranged between 1.9 and 12.7 gm/cm2. Linear regression showed that inertance M was highly correlated with orifice diameter D (M = 3.17 D; r = 0.84; p < 0.0001) and, in the conduits, with diameter and length L (M = 4.1 D + 0.7 L-1.8; r = 0.87; p < 0.0001). Inertance was not significantly related to the pressure gradient. In conclusion, inertance depends mainly on the mitral apparatus geometry and most strongly on orifice diameter. Knowledge of mitral inertance should help to extract quantitative data on atrioventricular pressure difference from the upslope of the transmitral E wave.

Long-term effects of acute thrombolytic therapy on ventricular size and function

To investigate the influence of thrombolytic therapy on the natural history of left ventricular size and regional function after myocardial infarction, 32 patients treated with acute thrombolytic therapy (treatment group) were studied by echocardiography on admission to the hospital and at 1 week, 3 months, and 1 year after myocardial infarction; they were compared with 40 patients who did not receive acute intervention (control group). The endocardial surface area index (cm2/m2) and the area of abnormal wall motion (cm2) were calculated from left ventricular dimensions and measurements of abnormal wall motion. Although no differences in the endocardial surface area index were noted over the year for the groups as a whole, a significant difference was noted in treated anterior infarctions with early functional infarct expansion compared with untreated infarct expansion (treatment group: 85.8 +/- 2.0 cm2/m2 [entry] to 77.4 +/- 2.7 cm2/m2 [1 week] to 69.9 +/- 4.2 cm2/m2 [3 months] to 67.2 +/- 6.4 cm2/m2 [1 year] versus control group: 84.0 +/- 6.4 cm2/m2 [entry] to 83.7 +/- 8.5 cm2/m2 [1 week] to 96.3 +/- 8.6 cm2/m2 [3 months] to 81.5 +/- 4.2 cm2/m2 [1 year]; p < 0.01). When early expansion was present, those receiving thrombolysis exhibited a consistent decrease in the initially enlarged endocardial surface area in contrast to control subjects, who demonstrated continued increases in endocardial surface area during the first 3 months. In all groups a decrease in the area of abnormal wall motion was observed during the year of follow-up. However, the magnitude and timing of the improvement was accelerated in the treatment group. Thus acute thrombolytic therapy alters the natural history of left ventricular size and function with a more rapid recovery of abnormal endocardial segments and reversal of functional infarct expansion.

Benefit of late coronary reperfusion on ventricular morphology and function after myocardial infarction

OBJECTIVES

This study was designed to examine the relation between the timing and adequacy of perfusion of the infarct bed and changes in ventricular size and the extent of abnormal wall motion after acute myocardial infarction.

METHODS

A validated echocardiographic mapping technique was used to measure the left ventricular endocardial surface area index and the extent of abnormal wall motion over a 3-month period in 91 patients who had either 1) no anterograde or collateral flow to the infarct bed (n = 14), 2) only collateral flow to the infarct bed (n = 18), 3) restoration of anterograde flow to the infarct bed within hours of chest pain (early [n = 43]), or 4) restoration of anterograde flow to the infarct bed within a mean of 5 days after acute myocardial infarction (late [n = 16]).

RESULTS

Over the follow-up period, a progressive and significant increase in endocardial surface area index was observed only in the group of patients without anterograde or collateral flow to the infarct bed (entry 64 +/- 3.4 cm2/m2 vs. 3 months 75.9 +/- 6.4 cm2/m2, p < 0.005). In contrast, a progressive reduction in the extent of abnormal wall motion was evident in the group of patients in whom anterograde flow to the infarct bed was restored within hours (entry 26.7 +/- 2.5 cm2 vs. 3 months 11.8 +/- 2.9 cm2, p < 0.001) or days (entry 22.1 +/- 3.6 cm2 vs. 3 months 11.8 +/- 3.3 cm2, p < 0.001) of coronary occlusion. Multiple stepwise linear regression analysis confirmed that by 3 months, 1) ventricular size was independently related to endocardial surface area index and abnormal wall motion at entry (p < 0.0001) and to the change in abnormal wall motion over the follow-up period (p < 0.0001), and 2) the change in abnormal wall motion was related to the presence of anterograde flow to the infarct bed (p < 0.0001) independent of the timing of reperfusion, infarct site or the extent of abnormal wall motion on admission.

CONCLUSIONS

After myocardial infarction, the process of ventricular remodeling is influenced by changes in the extent of abnormal wall motion, which in turn are related to the adequacy rather than the timing of perfusion of the infarct bed.

A new integrated system for three-dimensional echocardiographic reconstruction: development and validation for ventricular volume with application in human subjects

OBJECTIVES

The purpose of this study was to improve three-dimensional echocardiographic reconstruction by developing an automated mechanism for integrating spark gap locating data with corresponding images in real time and to validate use of this mechanism for the measurement of left ventricular volume.

BACKGROUND

Initial approaches to three-dimensional echocardiographic reconstruction were often limited by inefficient reconstructive processes requiring manual coordination of two-dimensional images and corresponding spatial locating data.

METHODS

In this system, a single computer overlays the binary-encoded positional data on the two-dimensional echocardiographic image, which is then recorded on videotape. The same system allows images to be digitized, traced, analyzed and displayed in three dimensions. This system was validated by using it to reconstruct 11 ventricular phantoms (19 to 271 ml) and 11 gel-filled excised ventricles (21 to 236 ml) imaged in intersecting long- and short-axis views and by apical rotation. To measure cavity volume, a surface was generated by an algorithm that takes advantage of the full three-dimensional data set.

RESULTS

Reconstructed cavity volumes agreed well with actual values: y = 0.96x + 2.2 for the ventricular phantoms in long- and short-axis views (r = 0.99, SEE = 2.7 ml); y = 0.95x + 2.9 for the phantoms, reconstructed by apical rotation (r = 0.99, SEE = 2.7 ml); and y = 0.99x + 0.11 ml for the excised ventricles (reconstructed in long- and short-axis views; r = 0.99, SEE = 5.9 ml). The mean difference between three-dimensional and actual volumes was 3% of the mean (3.0 ml) for the phantoms and 6% (4.6 ml) for the excised ventricles. Observer variability was 2.3% for the phantoms and 5.6% for the excised ventricles. Application to 14 normal subjects demonstrated feasibility of left ventricular reconstruction, which provided values for stroke volume that agreed well with an independent Doppler measure (y = 0.97x + 0.94; r = 0.95, SEE = 3.2 ml), with an observer variability of 4.9% (2.4 ml).

CONCLUSIONS

A system has therefore been developed that automatically integrates locating and imaging data in no more time than the component two-dimensional echocardiographic scans. This system can accurately reconstruct ventricular volumes in vitro over a wide range and is feasible in vivo, thus laying the foundation for further applications. It has increased the efficiency of three-dimensional reconstruction and enhanced our ability to address clinical and research questions with this technique.

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.

Effects of dobutamine on Gorlin and continuity equation valve areas and valve resistance in valvular aortic stenosis

Previous studies demonstrated changes in aortic valve area calculated by the Gorlin equation under conditions of varying transvalvular flow in patients with valvular aortic stenosis (AS). To distinguish between flow-dependence of the Gorlin formula and changes in actual orifice area, the Gorlin valve area and 2 other measures of severity of AS, continuity equation valve area and valve resistance, were calculated under 2 flow conditions in 12 patients with AS. Transvalvular flow rate was varied by administration of dobutamine. During dobutamine infusion, right atrial and left ventricular end-diastolic pressures decreased, left ventricular peak systolic pressure and stroke volume increased, and systolic arterial pressure did not change. Heart rate increased by 19%, cardiac output by 38% and mean aortic valve gradient by 25%. The Gorlin valve area increased in all 12 patients by 0.03 to 0.30 cm2. The average Gorlin valve area increased from 0.67 +/- 0.05 to 0.79 +/- 0.06 cm2 (p < 0.001). In contrast, the continuity equation valve area (calculated in a subset of 6 patients) and valve resistance did not change with dobutamine. The data support the conclusion that flow-dependence of the Gorlin aortic valve area, rather than an increase in actual orifice area, is responsible for the finding that greater valve areas are calculated at greater transvalvular flow rates. Valve resistance is a less flow-dependent means of assessing severity of AS.