A new control volume method for calculating valvular regurgitation

BACKGROUND

The purpose of the present study was to develop a new method of measuring heart valvular regurgitation based on control volume theory and to verify its accuracy in vitro and in vivo. Current methods of quantifying valvular regurgitation rely too much on assumptions about the flow field and therefore are difficult to apply in vivo. In particular, the proximal isovelocity surface area (PISA) method oversimplifies the proximal velocity field by assuming hemispherical isovelocity contours proximal to the orifice. This severely limits the applicability of the PISA method. Use of the basic control volume theory, however, removes the need to assume the manner in which the proximal flow accelerates toward the regurgitant orifice, the shape and size of the orifice, the shape of the orifice plate, and the non-newtonian behavior of the fluid. Apart from a correction that is necessary if the orifice plate is moving, the control volume method assumes only the incompressibility of the fluid and therefore is a potentially more accurate approach. In addition, the use of magnetic resonance imaging (MRI) precludes the need for an acoustic window.

METHODS AND RESULTS

MRI has been used to measure the three-dimensional velocity field proximal to regurgitant orifices, including single and multiple orifices and a cone-shaped orifice plate. Both steady (0 to 7.5 L/min) and pulsatile (2 and 3 L/min) flows were used. By intergrating this velocity over a control volume surrounding the orifice, we calculated the flow rate through the orifice. As a validation, the cardiac output of a 50-kg pig also was measured and was compared with thermodilution measurements. It was found that MRI could be used to measure the three-dimensional flow proximal to regurgitant orifices. This enabled the calculation of the flow rate through the orifice by integrating the velocity over the surface of a control volume covering the orifice. This flow rate correlated well with the actual rate (0.992; correlation line slope, 1.01). Care had to be taken, however, to exclude from the integration regions of aliased velocity. The cardiac output of the pig measured using MRI was in close agreement with the themodilution measurements.

CONCLUSIONS

Our new method of measuring valvular regurgitation has been shown to be very accurate in vitro and in vivo and therefore is a potentially accurate way to quantify valvular regurgitation.

Adenine nucleotide depletion in cryopreserved human cardiac valves: the "stunned" leaflet interstitial cell population

Preparation protocols for human cardiac valves are intended to minimize cytotoxicity because it has been thought that viable leaflet interstitial cells may enhance homograft durability. Preimplantation factors influencing the status of these cells at the time of transplantation include ischemia, disinfection, and cryopreservation freezing programs. In these experiments, adenine nucleotide quantitation was undertaken to assess metabolic consequences of preparation; preharvest ischemia served as an independent variable to examine the relationship between time of procurement (postmortem) and high-energy phosphate status of the cryopreserved leaflets at thaw. Nucleotides were measured using high-performance liquid chromatography performed on extracts of semilunar cusps from 25 cryopreserved human valves with documented ischemic times. Results indicate total adenine nucleotides (TAN; [ATP] + [ADP] + [AMP], in nmol TAN/mg leaflet protein) are higher (P < 0.05) after < 2 h of harvest ischemia (1.16 +/- 0.36) than with ischemic times of 3-6 h (undetected), 7-12 h (0.18 +/- 0.07), and 13-20 h (0.06 +/- 0.06). Depletion of ATP was similar, with many leaflets devoid of detectable levels. Net utilization of leaflet energy stores demonstrates time dependency when assayed after completed processing. However, relatively elevated catabolites, even with brief ischemia, and infrequently identified ATP, ADP, and AMP, suggest a consumption so accelerated that the following cryopreservation it is virtually independent of procurement-associated ischemia. We conclude resumption of a functional cell population obligates significant de novo phosphoanhydride boned reformation or a repopulation of dead/dying interstitial cells from a subset surviving the apparently severe rigors of valve preparation.

Surgical repair and reconstruction of valvular lesions

Thirty-six years have passed since the inception of mitral valve repair by Lillehei and McGoon. In the period presently under review it is apparent that mitral valve repair and the late results have become more predictable. Previously, repair was not attempted because of concern that valve replacement, with its attendant problems, might be necessary. This attitude appears to be slowly changing. The current issue is whether patients who have severe mitral regurgitation but are relatively asymptomatic should be referred for repair before ventricular function deteriorates or atrial fibrillation develops. Current evidence suggests that approximately 10% of asymptomatic patients will progress sufficiently each year to require surgical intervention. Systolic anterior motion of the mitral valve causing left ventricular outflow tract obstruction, has, since the era of routine intraoperative transesophageal echocardiography, become a well-recognized occasional consequence of mitral valve repair. Numerous theories have been suggested as to its cause: the most plausible suggest that risk factors include the presence of excess valvular tissue, a bulging septum, a nondilated hyperdynamic left ventricle, and a narrow mitral-aortic angle. The fact that numerous annuloplasty techniques exist, each having its own proponent(s), suggests that different techniques or types of annuloplasty are equally effective. Reparative techniques for the aortic valve have lagged behind those for the mitral valve because of limited previous success. The type of valve pathology was recently classified in terms of repair and new techniques, which are briefly documented, have been tried.(ABSTRACT TRUNCATED AT 250 WORDS)

Advances in noninvasive assessment of valvular heart disease

Echocardiography continues to be the noninvasive method of choice in the evaluation of valvular heart disease. Important recent developments include clinical validation of approaches used to quantify valvular regurgitation, in particular the proximal flow convergence zone method; use of transesophageal imaging to monitor and evaluate surgical or percutaneous interventions in valvular heart disease, in particular mitral valve repair; insight into flow-related stretch of the orifice area in aortic stenosis; and validation of nuclear magnetic resonance imaging in small series for quantification of left-sided valvular stenotic and regurgitant lesions.

Transesophageal echocardiography and adult cardiac operations

Transesophageal echocardiography (TEE) now is used widely as a monitoring technique during and after cardiac operations. Widespread adoption of the technique has provided a wealth of new information. This review analyzes the influence of TEE on the routine conduct of cardiac operations and on surgical decision making in specific areas. Its use in routine hemodynamic monitoring and problem solving, both intraoperatively and postoperatively, is discussed. Transesophageal echocardiography has a particular role in valve operations, in guiding and assessing the immediate results of mitral valve repair. It also has found application in the grading and operative management of the severely atheromatous aorta, the diagnosis and management of aortic dissection, and other aspects of surgery of the thoracic aorta. In addition, management in specialized areas, such as cardiopulmonary transplantation and the insertion and monitoring of ventricular assist devices, have also been helped by the information provided by TEE.

[The contribution and usefulness of routine intraoperative transesophageal echocardiography in cardiac surgery. An analysis of 130 consecutive cases]

PURPOSE

To assess the value of routine intraoperative transesophageal echocardiography (TEE) in unselected patients (P) undergoing cardiac surgery.

DESIGN

Routine intraoperative TEE in unselected patients undergoing cardiac surgery and evaluation of its usefulness and contribute to a successful surgery.

PATIENTS

In-hospital patients from cardiology, cardiac surgery and intensive care departments of a general hospital classified as a reference medical centre in cardiovascular pathology.

MATERIAL AND METHODS

From February 1994 to May 1994 an intraoperative TEE was routinely performed in patients undergoing cardiac surgery. A total of 130 TEE studies were made corresponding to 128 patients, 69 males and 61 females, with a mean age of 49.4 +/- 12.1 years. Indications for surgery were as following: a) Coronary artery bypass grafting (C.A.B.G.)-39; b) Valvular surgery-76; c) C.A.B.G. and valvular surgery-5; d) Thoracic aorta pathology associated or not to aortic valve surgery and/or coronary arteries re-implantation-6; e) Other-4. TEE performed using either a monoplane, biplane or multiplane probe and the images acquisition was made before thoracotomy and cardiopulmonary bypass (CPB) and after CPB with hemodynamic stabilization.

RESULTS

Pre CPB imaging yielded unsuspected findings in 11 P (8.5%) that changed the planned surgery in 7 cases (5.4%). Post CPB echo study, which was performed after hemodynamic stabilization, modified the surgical strategy in 13 cases (10.9%) avoiding 1 predetermined surgical procedure (tricuspid ring annuloplasty) and a new surgery in another case, leading to a 3 non-predetermined surgical procedures (by showing significative tricuspid regurgitation), to a further surgery in the same valve in 6 patients (mitral paravalvular leak with significative regurgitation in 1P, another mitral prosthesis dysfunction in 1P, residual mitral valve insufficiency after mitral valve repair in 3 P and aortic prosthesis dysfunction in 1 P), to a intraaortic counterpulsation balloon device in 1 P and to new CPB due to an insufficient extraction of calcified pericardium in one case of constrictive pericarditis. In 23 cases (17.7%) TEE has modified the anesthetic procedure by demonstrating signs of hemodynamic changes before Swan-Ganz catheter, thus prompting changes in the administrations of fluids and either in inotropic or vasodilator agents. In total, intraoperative TEE has changed the surgical and/or anesthetic plan in 43 cases (33.0%). There was no difficulties or complications related to the procedure.

CONCLUSION

These data indicate that intraoperative TEE is useful in formulating the surgical plan and assessing immediate operative results as well as a guide to anesthetic procedures. Its high rentabillity in modifying the surgical and/or anesthetic plans lead us to believe that it must be used as a routine procedure in patients undergoing cardiac surgery.

A model based on dimensional analysis for noninvasive quantification of valvular regurgitation under confined and impinging conditions: in vitro pulsatile flow validation

A technique is proposed for the noninvasive quantification of regurgitant flows under confined and impinging conditions. Its use requires only the knowledge of the jet orifice velocity, receiving chamber diameter, orifice-to-end wall distance and any downstream jet centerline velocity at a known distance from the orifice. The technique is based on dimensional analysis and provides a prediction of peak regurgitant flow rates. To validate the technique, known physiologic pulsatile flows were pumped through 2- and 4-mm circular orifices at 70 to 150 beats/min, into two different receiving chambers of 51 and 88 mm in diameter. At each heart rate, the peak orifice velocity was varied from 2 to 5 m/s, and the orifice-to-end wall distance was varied from 30 to 93 mm. Centerline velocities were recorded by pulsed Doppler ultrasound and averaged over multiple beats. A dimensional analysis of the parameters of the study provided an equation relating normalized centerline velocity to orifice-to-end wall distance, chamber diameter and downstream location. Statistical modeling of the experimental data was performed to compute the constants involved in this equation. The estimated (i.e., predicted by the technique) peak regurgitant flow rates were found to fall within 10% of the actual values, when centerline velocities were measured over a range of centerline distances from six orifice diameters to 85% of the chamber length. Therefore, the proposed technique provides, for the first time, a quantitative method for calculating valvular regurgitant flow rates under confined and impinging conditions.

A numerical and experimental investigation of the flow acceleration region proximal to an orifice

Attempts to quantify valvular regurgitation have recently been focused on the proximal orifice flow field. A complete description of the proximal orifice flow field is provided in this investigation. A steady state in vitro model accessible by both color Doppler ultrasound (CDU) and laser Doppler velocimetry (LDV) was utilized. Velocities for varying flow rates and orifices were calculated by finite element modeling (FEM), by LDV and by CDU. The steady flow model was composed of circular orifices of 3, 5 and 10 mm diameters at flow rates from 0.7 to 10 L/min. Regurgitant flow rates were calculated from the proximal CDU data by two separate methods. The first approach utilized angle corrected velocities while the second approach utilized only velocities which did not require angle correction (centerline velocities). Both methods correlated well with known flow rates (y = 0.97x -0.09, r = 0.98, SEE = 0.45, p < 0.0001; and y = 1.0x + 0.07, r = 0.99, SEE = 0.27, p < 0.0001, respectively) and were superior to results obtained by assuming a hemispherical geometry as is done in the aliasing technique. The methodology provides a complete analysis of the proximal flow field and involves fewer geometric assumptions than the aliasing approach. This may prove to be an advantage when analyzing in vivo flow fields with complex, uncertain geometry.

Limitations of Doppler echocardiography in the assessment of prosthetic valve hemodynamics

The purpose of this study was to determine the relationship between effective orifice areas of mechanical valves in the aortic position assessed by Doppler echocardiography, and published data from in vitro studies. Eighty-six patients with a normally functioning Standard St. Jude Medical (n = 56) or Björk-Shiley (n = 30) prosthesis in the aortic position were studied. Valve sizes varied between 19 and 27 mm. Pressure gradient was calculated by the Bernoulli, and effective orifice area by the continuity equation. Published data on prosthetic orifice areas from in vitro pulsatile flow experiments using the Gorlin formula were used for comparison. A weak correlation was present between Doppler derived pressure gradient and in vitro estimated effective orifice area, which significantly decreased with increasing valve size (R = -0.61; p < 0.0001). There was only a moderate correlation between Doppler derived and in vitro estimated effective orifice areas whether sewing ring diameter or left ventricular outflow tract diameter was used in the Doppler studies (R = 0.75 and R = 0.71, p < 0.0001, respectively). The difference between in vitro measured and Doppler derived areas was greater with Standard St. Jude Medical than with Björk-Shiley valves, both using the sewing ring diameter (1.04 +/- 0.61 cm2 vs. 0.53 +/- 0.39 cm2, p < 0.0003) and the outflow tract diameter (1.20 +/- 0.68 vs. 0.68 +/- 0.46 cm2, p < 0.006). The presence of atrial fibrillation, concomitant mitral valve replacement, small prosthesis size (19 to 23 mm) or a postoperative interval of less than one year did not change the uniform underestimation of prosthetic orifice areas by Doppler echocardiography. These findings are attributable to pressure recovery and localized transprosthetic velocities, and should be taken into account in the case of a suspected prosthesis malfunction.

Left and right heart Doppler stress echo in congestive heart failure

Doppler echocardiographic assessment of the left and right ventricular function at rest, during and 6 minutes after submaximal exercise was performed in 60 patients with a mean age of 43 +/- 11 years suffering from heart failure classified stage I-III according to the NYHA-criteria and 10 volunteers with a mean age of 36 +/- 9 years who served as a control group. At mitral (m) and tricuspid (t) valve early diastolic peak-flow velocity (VEm, VEt), atrial peak-flow velocity (VAm, VAt), speed-time integrals (Em, Et, Am, At) and the ratios (VE/VAm, VE/VAt, E/Am, E/At) were determined. The left ventricular end-diastolic diameter (LVEDD) and the right ventricular outflow tract (RVOT) were measured in addition. The left ventricular ejection fraction (LVEF) was decreased to < 36% in 9 patients (group 1). In 51 individuals LVEF was found to be > 35% but < 50% or LVEF was shown to be > 50% but VE/VAm-ratio was found to be < 1 (group 2). Out of all the determined parameters, VE/VAt, VEt and VAm during exercise were found to be the most sensitive parameters for the detection of early to advanced grade left heart failure.

Estimation of regurgitant flow volume based on centerline velocity/distance profiles using digital color M-Q Doppler: application to orifices of different shapes

OBJECTIVES

In this study we investigated the centerline velocity profile method for flow computation as applied to noncircular, as well as circular, orifices using digital color flow data.

BACKGROUND

Recently it has been suggested that flow volume through an orifice can be estimated more accurately by computing the axial "centerline" flow velocity/distance profile proximal to the orifice.

METHODS

A total of seven different orifices were mounted in a constant-flow model: four circular orifices, two rectangular orifices with a major/minor axis ratio of 4:1 and 8:1 and an ovoid orifice having a major/minor axis ratio of 2:1. Three different flow rates were examined (1.68, 3.48 and 6.48 liters/min). Digital measurements of flow velocity at discrete positions along the centerline progressing toward the orifice were analyzed to yield complete flow velocity profiles for each orifice at each flow rate.

RESULTS

A clear separation of the flow profiles for the three different flow rates was observed independent of orifice size for all of the circular orifices. The velocity/distance acceleration curves showed highly significant correlations using multiplicative regression fits (y = ax-b, r = 0.94 to 0.99, all p < 0.0001). An equation for quantitatively correlating the a and b coefficients from the multiplicative regression fits with flow rates was derived from stepwise regression analysis: Flow rate = 23a + 3.3b - 1.5 (r = 0.97, p < 0.0001, SEE 0.46 liter/min).

CONCLUSIONS

In view of the various sizes and shapes encountered clinically for regurgitant orifices, the simplicity of this method for the estimation of the severity of regurgitant lesions might be of importance for clinical applications of this method.

The echocardiographic assessment of the human fetal foramen ovale

The foramen ovale size and interatrial flow patterns were studied by combined real-time and Doppler echocardiography in 100 normal human fetuses between 20 and 38 weeks gestation. The foramen ovale, atrioventricular, and semilunar valve diameters increased linearly with gestational age. The foramen flap motion and interatrial flow patterns showed biphasic flow patterns with interatrial flow reversal with atrial systole. Color flow mapping of the diameter of the interatrial flow profile showed good correlation with the foramen ovale size as measured by two-dimensional echocardiography. These data represent the first large study of the normal human foramen ovale correlated with gestational age, thus expanding the reference base for ultrasound assessment of fetal heart.

Ultrasonic dynamic three-dimensional visualization of the heart with a multiplane transesophageal imaging transducer

Dynamic three-dimensional echocardiography enables objective analysis of structures and pathologic conditions of complex geometry. In addition, it may provide more accurate quantitative analysis of cardiac function. This study presents the first results obtained with multiplane transesophageal diagnostic imaging system that is connected to a dedicated software configuration allowing three-dimensional tissue reconstruction and its dynamic display at 25 frames/sec. In addition, it permits "computer slicing" through the beating heart along arbitrary orientations and the display of synthetic cross sections along these orientations with excellent resolution and grey values (dynamic anyplane echocardiography). The advantage of a multiplane transesophageal imaging transducer is that the acquisition of cross sections for three-dimensional reconstruction becomes an integral part of a routine diagnostic transesophageal study and only requires an additional 7 to 10 minutes of examination time. This approach will help to develop three-dimensional echocardiography and synthetic anyplane echocardiography into a practical clinical tool offering diagnostic information similar to magnetic resonance imaging.

Current status of valvular surgery

Surgical treatment of valvular heart disease is a field of constant clinical and experimental research. Recently, much attention has been devoted to the improvement of valve repair techniques. The physiopathology of the left ventricular outflow tract obstruction following mitral valve repair has become better understood. Surgical techniques to correct this infrequent complication have been developed. Conservative valvular surgery or homograft use are among the surgical treatments for infective endocarditis; innovative experimental and clinical studies on mitral and tricuspid homografts have provided interesting results. New biological valves have come into use; intraoperative creation of a cardiac bioprosthesis using glutaraldehyde-treated autologous pericardium is an attractive surgical innovation. Stentless bioprostheses are also under investigation, to evaluate their hemodynamic and clinical characteristics. The biology of bioprosthesis deterioration progresses at the cellular level, with the implication of phagocytosis as a contributing factor.

Dependence of Gorlin formula and continuity equation valve areas on transvalvular volume flow rate in valvular aortic stenosis

BACKGROUND

Valve areas derived by the Gorlin formula have been observed to vary with transvalvular volume flow rate. Continuity equation valve areas calculated from Doppler-echo data have become a widely used alternate index of stenosis severity, but it is unclear whether continuity equation valve areas also vary with volume flow rate. This study was designed to investigate the effects of changing transvalvular volume flow rate on aortic valve areas calculated using both the Gorlin formula and the continuity equation in a model of chronic valvular aortic stenosis.

METHODS AND RESULTS

Using a canine model of chronic valvular aortic stenosis in which anatomy and hemodynamics are similar to those of degenerative aortic stenosis, each subject (n = 8) underwent three studies at 2-week intervals. In each study, transvalvular volume flow rates were altered with saline or dobutamine infusion (mean, 10.3 +/- 5.1 flow rates per study). Simultaneous measurements were made of hemodynamics using micromanometer-tipped catheters, of ascending aortic instantaneous volume flow rate using a transit-time flowmeter, and of left ventricular outflow and aortic jet velocity curves using Doppler echocardiography. Valve areas were calculated from the invasive data by the Gorlin equation and from the Doppler-echo data by the continuity equation. In the 24 studies, mean transit-time transvalvular volume flow rate ranged from 80 +/- 33 to 153 +/- 49 mL/min (P < .0001). Comparing minimum to maximum mean volume flow rates, the Gorlin valve area changed from 0.54 +/- 0.22 cm2 to 0.68 +/- 0.21 cm2 (P < .0001), and the continuity equation valve area changed from 0.57 +/- 0.18 cm2 to 0.70 +/- 0.20 cm2 (P < .0001). A strong linear relation was observed between Gorlin valve area and mean transit-time volume flow rate for each study (median, r = .88), but the slope of this relation varied between studies. The Doppler-echo continuity equation valve area had a weaker linear relation with transit-time volume flow rate for each study (median, r = .51).

CONCLUSIONS

In this model of chronic valvular aortic stenosis, both Gorlin and continuity equation valve areas were flow-dependent indices of stenosis severity and demonstrated linear relations with transvalvular volume flow rate. The changes in calculated valve area that occur with changes in transvalvular volume flow should be considered when measures of valve area are used to assess the hemodynamic severity of valvular aortic stenosis.

[Value of transesophageal echocardiography in diagnosis of diseases of native heart valves]

In the clinical management of patients with valvular heart disease, transthoracic echocardiography (TTE) combined with Doppler has become the central diagnostic tool during the past decades. The development of transesophageal echocardiography (TEE) has led to an improved image quality especially of structures distant to the chest wall. However, since TEE is a semi-invasive technique, its use has to be considered carefully. In aortic valve disease, TEE facilitates a detailed study of valve morphology and allows sufficiently reliable planimetry of aortic valve area, at least when the multiplane approach is used. This is particularly helpful in those patients where Doppler interrogation from precordial windows fails. Aortic regurgitation is diagnosed more frequently by TEE color-flow imaging than by TTE; however, both techniques allow only semiquantitative assessment of the severity of regurgitation. TEE is also superior to TTE in defining the exact origin site, number and configuration of regurgitant jets in patients with mitral insufficiency. In particular minimal and mild mitral regurgitation is more easily detected by TEE than by TTE. The same is true for flail mitral leaflets, chordal and papillary muscle rupture, and potentially also for discrete forms of mitral valve prolapse. During surgery, TEE can be considered as an ideal tool for immediate assessment of the results of mitral valve reconstruction. Calculation of pressure gradients and valve area by TEE Doppler analysis shows comparable results to precordial studies. When multiplane TEE is available, Doppler beam alignment may become even improved in selected cases with severely excentric flow jet orientation. In addition, TEE provides of course clinically important information concerning presence or absence of atrial and particularly atrial appendage thrombi as well as of spontaneous echo contrast in patients with stenotic mitral valve. This is not only helpful regarding the decision for anticoagulation but it may also be critical in the selection of candidates for percutaneous mitral balloon valvuloplasty. TEE does also allow the morphological and functional evaluation of tricuspid and pulmonic valves. In this context, the use of biplane or multiplane TEE probes is superior to that of monoplane devices. However, currently available data does not provide unequivocal evidence that the analysis of tricuspid and pulmonic valve disease by TEE is superior to the conventional transthoracic approach.

[Biplane transesophageal echocardiography. Diagnostic improvement over the mono-plane technique]

Monoplane transesophageal echocardiography (TEE) is a well established diagnostic tool of examination of great value in determining pathological changes in both atria, atrioventricular valves, the left-ventricular outflow tract, and in the thoracic aorta (Table 1). With the monoplane technique, however, it is never possible to obtain more than parallel, or oblique transverse views of the heart and surrounding vessels. The only means with which to examine anatomic structures in their cranio-caudal dimension by way of this method is to make a composite of a number of transverse sections. This makes three-dimensional interpretation of monoplane images difficult. The biplane transesophageal technique provides images of orthogonal sections to the transverse plane, allowing three-dimensional reconstruction and thus greatly improved insight into the cardial anatomy. By ante- or retroflection and lateral angulation of the probe, it becomes possible to see structures as a whole, the greatest dimension of which may not lie in the strictly sagittal section, but on a craniocaudal diagonal plane, e.g. the ascending aorta, or the aortic valve plane. The diagnostic gain of additional data through biplane TEE stems from its images of cardial structures, which remain either unsatisfactory or not attainable on monoplane examination (Table 2). Above all this pertains to the superior vena cava in its longitudinal extension (Figure 6), the right-ventricular outflow tract with pulmonary valve, the longitudinal two-chamber view (Figure 3), and the CW-Doppler analysis in presence of tricuspid valve regurgitation (Figure 13). Transversal visualization of the aortic arch is only feasible by using biplane imaging technique (Figure 12). Compared to the monoplane technique, it shows clearly more distinct views of the apex of the left ventricle (Figure 1), the atrial anatomy (Figures 5 and 6), and here in particular the pathology of interatrial septum (Figure 7), as well as the aortic valve and the ascending aorta (Figures 8, 10 and 11). By using the longitudinal imaging plane left atrial appendage can be seen without additional anteflection of the probe, thus, reducing stress to the patient during examination. The loss of an infinite range of planes available to the multiplane technique is a disadvantage, but this can usually be compensated by appropriate flecting of the probe and adequate simultaneous lateral angulation. The range of rotation of the probe in the multiplane method allows better three-dimensional imaging of anatomic structures and regurgitant jets than do the mono- and biplane techniques, and comparable data are often only attained under much longer examination with the biplane instrument.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Physiologic multivalvular regurgitation during pregnancy: a longitudinal Doppler echocardiographic study

Valvular function, assessed by Doppler technique, has not been extensively investigated during normal pregnancy. To prospectively study this feature, 18 normal pregnant women were followed during their pregnancies and puerperium, with serial clinical and pulsed-continuous Doppler echocardiographic examinations. In four gestational periods and the puerperium, we analysed: (a) ventricular and atrial dimensions, as well as valve annular diameters; (b) prevalence and characteristics of trivial valvular regurgitations. During pregnancy, slight but significant increases of the four cardiac chamber dimensions and valve annular diameters were observed, except for the aortic ring. The prevalence of physiologic valvular regurgitation in early pregnancy (mitral, 0%; tricuspid, 38.9%; pulmonary, 22.2%; aortic, 0%), was similar to a control group of 18 healthy non-pregnant women. As pregnancy evolved, there was a progressive and significant increase of multivalvular regurgitation, maximal at full-term (mitral, 27.8%; tricuspid, 94.4%; pulmonary, 94.4%, P < 0.05 vs. early pregnancy). Aortic regurgitation was not detected in any stage of pregnancy. In the puerperium, mitral regurgitation resolved, but tricuspid and pulmonary regurgitation were still significantly prevalent (83.3% and 66.7%, respectively, P < 0.05 vs. early pregnancy). It is concluded that physiologic multivalvular regurgitation is frequent in pregnancy, mainly involving right-sided valves in late gestational periods, occasionally persisting in the early puerperium. Chamber enlargement, valve annular dilatation, and increased prevalence of trivial valve regurgitation are time-related events during normal pregnancy, resulting from a reversible cardiac remodeling process induced by physiologic volume overload. These aspects should be considered for a correct interpretation of Doppler echocardiographic findings in pregnant women with suspected heart disease.

Calculation of volume flow rate by the proximal isovelocity surface area method: simplified approach using color Doppler zero baseline shift

OBJECTIVES

The goal of this study was to develop an accurate, simplified proximal isovelocity surface area (PISA) method for calculating volume flow rate using lower blue-red interface velocity produced by a color Doppler zero baseline shift technique.

BACKGROUND

The Doppler color proximal isovelocity surface area method has been shown to be accurate for calculating the volume flow rate (Q) across a narrowed orifice by the formula Q = PISA x Blue-red interface velocity. A hemispheric model is generally used to calculate proximal isovelocity surface area (PISA = 2 pi a2, where a = the radius corresponding to the blue-red interface velocity). Although a hemispheric model is simple, requiring measurement of one radius, it may underestimate the actual volume flow rate because, in the general case, the shape of a proximal isovelocity surface area is hemielliptic. Although a hemielliptic model is generally more accurate for calculating proximal isovelocity surface area, it is more complex, requiring measurement of two orthogonal radii.

METHODS

Sixteen in vitro constant flow model studies were performed using planar circular orifices (diameter range 6 to 16 mm). The blue-red interface velocity was changed from 3 to 54 cm/s using color Doppler zero baseline shift.

RESULTS

1) With decreasing blue-red interface velocity, the size of the proximal isovelocity surface area was increased, and its shape changed from hemielliptic to hemispheric. 2) With the blue-red interface velocity in the range 11 to 15 cm/s, the proximal isovelocity surface area became nearly hemispheric; however, it was difficult to determine the blue-red interface radius at a blue-red interface velocity < 10 cm/s because of interface fluctuations. 3) Calculated volume flow rate using the hemispheric proximal isovelocity surface area model with a single radius was relatively accurate at a blue-red interface velocity of 11 to 15 cm/s (mean percent difference from actual volume flow rate was -3.6%).

CONCLUSIONS

Because the shape of the proximal isovelocity surface area is nearly hemispheric at a blue-red interface velocity of 11 to 15 cm/s, volume flow rate can be accurately calculated in this proximal isovelocity surface area interface velocity range (produced by zero baseline shift) by measuring a single-interface radius. This approach should be clinically useful for calculating the volume flow rate across stenotic and regurgitant valves and across shunt defects.

Copper deficiency alters collagen types and covalent cross-linking in swine myocardium and cardiac valves

Dietary copper deficiency induces alterations of connective tissue metabolism that are associated with lesions in cardiovascular and other organ systems. To determine the impact of copper deficiency on characteristics of collagen in porcine myocardium and cardiac valves, weaned pigs were fed diets with adequate or deficient levels of copper. Although dietary copper did not affect the concentration of collagen in either myocardium or bicuspid valves, the degree of collagen cross-linking, as assessed by the level of hydroxylysylpyridinoline, was lower in both tissues of copper-deficient pigs. Proportions of type III collagen were increased in the left ventricle and bicuspid valves of copper-deficient pigs. Copper deficiency induced extensive remodeling, however, of the collagen fraction of cardiac interstitium. Reduction in left ventricular collagen cross-linking may provide the stimulus for the development of cardiac hypertrophy, which characterizes severe copper deficiency, by increasing the compliance of the ventricular wall. The shift in the phenotypic profile of collagen that is associated with this cardiac hypertrophy indicates synthesis of new collagen, which could affect collagen cross-linking irrespective of copper status.

Contrast echocardiography during cardiac catheterization in patients with congenital heart diseases

Contrast echocardiography performed during cardiac catheterization has mostly been limited to a few published case reports. We studied 37 patients with congenital heart disease to assess the capability of the method to diagnose cardiac shunts and valve regurgitation. Injections of 5% dextrose in water through an angiographic catheter were made to evaluate septal integrity and valve competence compared with conventional contrast angiography. An overall sensitivity of 93% and specificity of 78% were found. In four cases of atrial septal defect and seven of mitral regurgitation, the sensitivity was 100%. It was slightly lower for eleven cases of ventricular septal defect (91%) and four of patent ductus arteriosus (75%). When assessing aortic, tricuspid and pulmonary valve competence, the method proved to be more sensitive than conventional angiography to detect mild regurgitation. Contrast echocardiography is a sensitive and safe technique that may be used in association with conventional angiography reducing the need for radiographic contrast and ionizing radiation time.

Neurologic complications of infective endocarditis

The average overall incidence of neurologic complications in patients with infective endocarditis is 30%, with the vast majority of these complications in patients with left-sided valvular disease. The incidence of central nervous system manifestations, particularly of embolic events, tends to be higher in cases of endocarditis caused by more virulent organisms, such as S. aureus and the Enterobacteriaceae. The clinical presentation is dependent on the area of the central nervous system involved. CT and MRI scanning are useful radiologic imaging techniques for the diagnosis of central nervous system complications in patients with infective endocarditis; cerebral angiography should be used in patients with suspected intracranial mycotic aneurysm. The cornerstone of management is appropriate antimicrobial therapy. Neurosurgical intervention may be required for certain patients with intracranial mycotic aneurysms that do not disappear after antimicrobial therapy or for aneurysms that enlarge or bleed. Anticoagulants should be continued in patients with prosthetic valve endocarditis who do not have evidence of intracranial hemorrhage. Anticoagulants should be avoided (unless thromboembolic events are from a site other than the vegetation) in patients with native valve endocarditis owing to the risk of hemorrhagic central nervous system complications. Case fatality rates tend to be higher in patients with neurologic complications of infective endocarditis. Earlier diagnostic and therapeutic interventions for patients with central nervous system complications of infective endocarditis will, it is hoped, improve the outcome in patients with this disorder.