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Biomedical subjects

W J Stewart

Publications and source records attributed to W J Stewart.

At least 19 recordsLinked to original sources
PubMed1996

Mechanisms of hemolysis with mitral prosthetic regurgitation. Study using transesophageal echocardiography and fluid dynamic simulation.

OBJECTIVES: The aims of this study were to define the hydrodynamic mechanisms involved in the occurrence of hemolysis in prosthetic mitral valve regurgitation and to reproduce them in a numeric simulation model in order to estimate peak shear stress. BACKGROUND: Although in vitro studies have demonstrated that shear stresses > 3,000 dynes/cm2 are associated with significant erythrocyte destruction, it is not known whether these values can occur in vivo in conditions of abnormal prosthetic regurgitant flow. METHODS: We studied 27 patients undergoing reoperation for significant mitral prosthetic regurgitation, 16 with and 11 without hemolysis. We classified the origin and geometry of the regurgitant jets by using transesophageal echocardiography. By using the physical and morphologic characteristics defined, several hydrodynamic patterns were simulated numerically to determine shear rates. RESULTS: Eight (50%) of the 16 patients with hemolysis had paravalvular leaks and the other 8 had a jet with central origin, in contrast to 2 (18%) and 9 (82%), respectively, of the 11 patients without hemolysis (p = 0.12, power 0.38). Patients with hemolysis had patterns of flow fragmentation (n = 2), collision (n = 11) or rapid acceleration (n = 3), whereas those without hemolysis had either free jets (n = 7) or slow deceleration (n = 4) (p < 0.001, power 0.99). Numeric simulation demonstrated peak shear rates of 6,000, 4,500, 4,500, 925 and 950 dynes/cm2 in these five models, respectively. CONCLUSIONS: The distinct patterns of regurgitant flow seen in these patients with mitral prosthetic hemolysis were associated with rapid acceleration and deceleration or high peak shear rates, or both. The nature of the flow disturbance produced by the prosthetic regurgitant lesion and the resultant increase in shear stress are more important than the site of origin of the flow disturbance in producing clinical hemolysis.

Aged↗
PubMed1996

Diagnosis of patent foramen ovale by contrast versus color Doppler by transesophageal echocardiography: relation to atrial size.

To ascertain the factors related to the transesophageal echocardiographic diagnosis of patent foramen ovale, the primary echocardiographic data were reviewed from 74 patients with that diagnosis. Similar detection rates were observed with contrast echocardiography (82%) and color flow mapping (78%), but contrast was more sensitive in patients with normal-sized atria (94%) and isolated right atrial enlargement (100%) than in those with enlarged left atria, all but three of whom had biatrial enlargement (52%) (p < 0.001 by chi-square test). Doppler flow mapping was less sensitive for normal-sized atria (66%) than for isolated enlarged right atria (81%) and left (bi-) atrial enlargement (96%) (p = 0.024). Patent foramen ovale was directly visualized by two-dimensional echocardiography in 80%, with close agreement to the size of the color flow jet (r = 0.90, delta = 0.1 +/- 0.4 mm); foramen ovale size was related to right atrial area (r = 0.31, p = 0.015). Thus both saline contrast and color flow imaging are necessary to exclude the diagnosis of patent foramen ovale.

Case-Control Studies↗
PubMed1996

Characterization of left atrial appendage Doppler flow in atrial fibrillation and flutter by Fourier analysis.

The aim of this study was to characterize left atrial appendage mechanical function in atrial fibrillation and flutter by Fourier analysis to analyze frequency and regularity of flow. Left atrial appendage function is central to a patient's risk for thromboembolism. Although the function of the appendage can be analyzed by Doppler echocardiography in sinus rhythm, its mechanical function in atrial fibrillation and flutter has not been well characterized. This lack of adequate definition is caused by the complexity and temporal variability of the Doppler flow profiles. We assessed left atrial appendage function in 21 cases of atrial fibrillation (n - 11) and flutter (n = 10) and five in sinus rhythm with transesophageal Doppler echocardiography. Doppler profiles were examined by Fourier analysis, and the power spectra compared and analyzed between patients with atrial fibrillation and flutter. Left atrial appendage Doppler flow in atrial fibrillation produced Fourier spectra over a narrow band of frequencies with a peak frequency of 6.2 +/- 1.0 Hz, significantly higher than in atrial flutter (3.9 +/- 0.6 Hz, p < 0.00001). Additionally, a significant difference in subharmonic modulation (spectral power below the peak frequency) was observed between atrial appendage flow in atrial fibrillation and flutter, because 37% +/- 16% of the total spectral power was achieved before the dominant frequency in atrial fibrillation compared with 20% +/- 14% in atrial flutter (p = 0.02). Conversely, patients in sinus rhythm exhibited broad-banded Fourier spectra with most of the power in discrete frequency spikes at harmonics above the fundamental frequency with very little subharmonic modulation (1% +/- 0.05%). Left atrial appendage function in atrial fibrillation and flutter can be well characterized by Fourier analysis of Doppler flow. Atrial fibrillation has higher dominant frequencies and greater subharmonic modulation compared with flutter. Moreover, atrial fibrillation demonstrated quasiperiodic contraction patterns typically found in chaotic systems. Fourier analysis of left atrial appendage contraction patterns may therefore have significant promise in providing insights into mechanisms of atrial fibrillation and thromboembolism.

Aged↗
PubMed1995

Influence of left ventricular hypertrophy on detection of coronary artery disease using exercise echocardiography.

OBJECTIVES: This study examined the influence of left ventricular hypertrophy on the accuracy of exercise electrocardiography and echocardiography for detection of coronary artery disease. BACKGROUND: Electrocardiographic repolarization abnormalities caused by left ventricular hypertrophy compromise the diagnostic accuracy of exercise electrocardiography but not of exercise echocardiography. The relative merits of these investigations are less well defined in patients with hypertrophy but without electrocardiographic (ECG) changes. METHODS: We prospectively evaluated 147 consecutive patients without prior myocardial infarction undergoing both exercise echocardiography and coronary arteriography. Coronary stenoses > 50% diameter were present in 62 patients (42%). Positive test results were defined by a new or worsening wall motion abnormality or > 0.1 mV of ST depression. Echocardiographic left ventricular hypertrophy (mass > 131 g/m2 in men, > 100 g/m2 in women) was identified in 68 patients. A subgroup with clinically suspected hypertrophy was defined according to the presence of ECG evidence of hypertrophy, hypertension or aortic stenosis. RESULTS: The overall sensitivity of exercise echocardiography exceeded that of exercise electrocardiography (71% vs. 54%, p = 0.06). Echocardiographic hypertrophy had no significant effect on the sensitivity of either test. The specificity of exercise echocardiography exceeded that of exercise electrocardiography (91 vs. 74%, p = 0.01). In patients with hypertrophy, the specificity of exercise echocardiography exceeded that of exercise electrocardiography (95% vs. 69%, p < 0.01), whereas among patients without hypertrophy, the specificities (respectively, 87% and 78%) were more comparable. The accuracy of exercise echocardiography exceeded that of the exercise ECG in the overall group (82% vs. 65%, p = 0.002) and in patients with hypertrophy (85% vs. 60%, p = 0.004), but this difference was less prominent in patients without hypertrophy (80% vs. 69%, p = NS). In patients with clinically suspected hypertrophy, exercise echocardiography demonstrated a higher sensitivity, specificity and accuracy than exercise electrocardiography. The cost incurred in the identification of coronary disease was least with a strategy involving use of the exercise echocardiogram instead of routine exercise testing in patients with known or clinically suspected left ventricular hypertrophy. CONCLUSIONS: Exercise echocardiography is more accurate than exercise electrocardiography for the detection of coronary artery disease in patients with known or clinically suspected left ventricular hypertrophy.

Adult↗
PubMed1995

Quantification of mitral regurgitation by the proximal convergence method using transesophageal echocardiography. Clinical validation of a geometric correction for proximal flow constraint.

BACKGROUND: Proximal flow convergence is a promising method to quantify mitral regurgitation but may overestimate flow when the flow field is constrained. This has not been investigated clinically, nor has a correction factor been validated. METHODS AND RESULTS: Eighty-five patients were studied intraoperatively with transesophageal echocardiography and divided into two groups: central convergence (no constraining wall) and eccentric convergence (at least one constraining wall). Regurgitant stroke volume (RSV) and orifice area (ROA) were calculated by ROA = 2 pi r2 Va/Vp and RSV = ROA x VTIcw, where r and va are the radius and velocity of the aliasing contour and vp and VTIcw are the peak and integral of regurgitant velocity. In eccentric convergence patients, convergence angle (alpha) was measured from two-dimensional Doppler color flow maps, and ROA and RSV were corrected by multiplying by alpha/180. For reference, RSV was the difference between thermodilution and pulsed Doppler stroke volumes. In central convergence patients (n = 45), RSV (r = .95, delta = 2.5 +/- 10.8 mL) and ROA (r = .96, delta = 0.02 +/- 0.08 cm2) were accurately calculated, but significant overestimation was noted in the eccentric convergence patients (n = 40, delta RSV = 63.9 +/- 38.0 mL, delta ROA = 0.54 +/- 0.31 cm2), 68% of whom had leaflet prolapse or flail. delta RSV was correlated with alpha (r = -.69, P < .001). After correction by alpha/180, overestimation was largely eliminated (delta RSV = 15.5 +/- 19.3 mL and delta ROA = 0.14 +/- 0.14 cm2) with excellent correlation for the whole group (RSV, r = .91; ROA, r = .95). CONCLUSIONS: A simple geometric correction factor largely eliminates overestimation caused by flow constraint with the proximal convergence method and should extend the clinical utility of this technique.

Case-Control Studies↗
PubMed1995

Anatomic explanation of mobile systolic clicks: implications for the clinical and echocardiographic diagnosis of mitral valve prolapse.

An echocardiogram (echo) is often ordered for suspected mitral valve prolapse (MVP). Using echo as the gold standard, we conducted a meticulous physical examination on 61 patients with this referral diagnosis. Ninety percent of patients with negative physical examination and echo results for MVP had physical examination findings likely to have been misinterpreted as MVP by the referring physician. Redundant portions of the mitral valve apparatus were found in 57% of patients with MVP on our physical examination but not on echo. A carefully performed physical examination (including dynamic auscultation) can exclude MVP. Not all mobile systolic clicks are associated with anatomic echo prolapse; they can be generated by redundant chordae tendineae and, in the absence of echo prolapse, probably by redundant leaflets. Patients with mobile systolic clicks should have an echo to determine the portion of the spectrum of echo prolapse present and to determine risk stratification and management.

Adult↗
PubMed1995

Initial experience with the Cosgrove-Edwards Annuloplasty System.

BACKGROUND: The mitral valve has a nonplanar shape and a sphincter action. Pathologic dilatation occurs along the posterior annulus. To preserve the physiologic function and correct annular dilatation, we developed an annuloplasty system that is universally flexible and produces a measured plication of the posterior annulus (Cosgrove-Edwards Annuloplasty System). METHODS: The results of 150 consecutive mitral valve repairs using this system were analyzed. Mean age was 58 +/- 13 years; 59% were men. The cause of the valve disease was degenerative in 75% of the patients, rheumatic in 13%, ischemic in 8%, and infectious in 4%. Associated procedures were performed in 61 patients (41%). RESULTS: Echocardiographic mitral regurgitation decreased from 3.7 +/- 0.6 before repair to 0.2 +/- 0.4 after repair (p < 0.0001). There were no hospital deaths and no cases of hemodynamically significant systolic anterior motion or other annuloplasty-related complications. Follow-up was 100% complete at a mean of 3.1 +/- 3.6 months. There were three late deaths, three transient ischemic attacks, and one episode of endocarditis. Five patients (3.3%) have undergone reoperation for recurrent mitral insufficiency; no reoperations were related to the annuloplasty system. At a mean of 9 months, three-dimensional reconstruction of the mitral annulus from multiple echocardiographic images confirmed the nonplanar shape and sphincter mechanism of the annulus. Annular orifice area decreased 19% during the cardiac cycle from a mean of 10.3 cm2 in diastole to 8.6 cm2 in systole. CONCLUSIONS: This annuloplasty system is effective for repair of insufficiency secondary to all causes, preserves physiologic annulus function, and is associated with a low incidence of valve-related complication.

Adult↗
PubMed1995

Progression of aortic stenosis in 394 patients: relation to changes in myocardial and mitral valve dysfunction.

OBJECTIVES: This study reports the results of echocardiographic follow-up in a large cohort of patients with aortic stenosis and correlates the progression of aortic stenosis with changes in the degree of mitral regurgitation and left ventricular hypertrophy and systolic dysfunction. BACKGROUND: Progressive aortic stenosis often causes left ventricular dysfunction and mitral regurgitation. Doppler echocardiography has greatly assisted in the noninvasive evaluation and follow-up of aortic stenosis. Nevertheless, the longitudinal follow-up of patients with Doppler echocardiography for the progression of aortic stenosis and the significance of progressive ventricular hypertrophy and mitral regurgitation have not been reported. METHODS: Serial Doppler echocardiography was performed in 394 consecutive patients with valvular aortic stenosis at baseline and after a mean follow-up period of 37 +/- 16 months. Mean and peak aortic gradients, aortic valve area, left ventricular systolic and diastolic diameters and percent area change (shortening fraction) were expressed as continuous variables, and systolic dysfunction, mitral regurgitation, ventricular hypertrophy and filling properties were tabulated as categoric variables using a semiquantitative grading system. RESULTS: Peak and mean gradients increased by an average of 8.3 and 6.3 mm Hg/year, respectively; end-systolic and end-diastolic diameters increased by 1.9 and 1.6 mm/year, respectively; and aortic valve area decreased by 0.14 cm2/year during the follow-up interval (p < 0.001 for all), indicating progression of aortic stenosis and ventricular dilation. Patients in the lowest quartile of aortic valve area and highest quartiles of mean and peak gradients had the least change compared with those in the highest quartile of aortic valve area and lowest quartile of mean and peak gradients (p < 0.01 for all). Patients with more mitral regurgitation at follow-up than at baseline had higher mean percent increase in mean and peak gradients as well as more progression of ventricular dilation and worsening systolic function compared with those with stable or improving mitral regurgitation (p < 0.05 for all). Similarly, subjects with worsening left ventricular hypertrophy had larger mean percent increase in mean and peak gradients than those with stable left ventricular hypertrophy (p < 0.01) but maintained stable ventricular volumes and systolic function. There was no correlation between the amount of change in mean or peak gradients and degree of deterioration in systolic function. CONCLUSIONS: Aortic stenosis progresses predictably over time; however, systolic dysfunction is an inconsistent marker of the hemodynamic consequences of severe aortic stenosis. As an adaptive response to pressure overload, progressive hypertrophy appears to prevent ventricular dilation and development or worsening of mitral regurgitation. Conversely, progressive mitral regurgitation may be seen as a maladaptive consequence of increasing aortic stenosis.

Aged↗
PubMed1995

Selection of patients for transesophageal echocardiography after stroke and systemic embolic events. Role of transthoracic echocardiography.

BACKGROUND AND PURPOSE: This study examined whether patients suffering from stroke and other systemic embolic events may be selected for transesophageal echocardiography on the basis of clinical and transthoracic echocardiographic findings. METHODS: We performed transthoracic and transesophageal echocardiography on 824 patients after stroke and other suspected embolic events. Patients were classified into group A if they were in sinus rhythm and had a normal transthoracic echocardiogram. Group B consisted of all other patients. Transesophageal echocardiographic findings of left atrial spontaneous contrast, left atrial thrombus, complex aortic atheroma, and interatrial septal anomalies were correlated with clinical and transthoracic echocardiographic results. RESULTS: Transesophageal echocardiography detected at least one potential source of embolism in 399 patients (49%): spontaneous contrast in 214 patients (26%), left atrial thrombus in 54 (7%), complex atheroma in 111 (13%), and interatrial septal anomalies in 126 (15%). In group A (n = 236), only 3 (1%) had spontaneous contrast, 11 (4.6%) had complex atheroma, and none had left atrial thrombus. In group B (n = 588), 211 patients (36%, P < .001) had spontaneous contrast, 54 (9.2%, P < .001) had atrial thrombus, and 100 (17%, P < .001) had complex atheroma. Interatrial septal anomalies were detected in similar proportions of patients (18% in group A versus 14% in group B). Left atrial spontaneous echo contrast, thrombus, and complex atheroma were significantly more prevalent in older patients, but interatrial septal anomalies were more prevalent in younger patients irrespective of transthoracic echocardiographic findings. Multivariate analysis identified both an abnormal transthoracic echocardiogram and patient age to be independent predictors of transesophageal echocardiographic findings of left atrial spontaneous echo contrast, left atrial thrombus, or complex atheroma. CONCLUSIONS: Transesophageal echocardiography has a low yield for left atrial spontaneous contrast, left atrial thrombus, or complex aortic atheroma in patients with normal transthoracic echocardiogram and sinus rhythm and in younger patients. Interatrial septal anomalies are more prevalent in younger patients. Transthoracic echocardiogram should be performed in patients after stroke or systemic embolic events as a noninvasive screening tool. We recommend transesophageal echocardiogram for patients with abnormal transthoracic echocardiogram and in younger patients when the finding of a patent foramen ovale may contribute to patient management.

Age Factors↗
PubMed1995

Multiplane transesophageal echocardiographic evaluation of mitral valve disease.

With the additional ability to rotate the image around the axis of the centerline of the sector, multiplane transesophageal echocardiography (TEE) improves over single or biplane TEE in ease of use and diagnostic accuracy. This article reviews the anatomic, physiological, and topographic considerations that affect the use of multiplane TEE in evaluation of patients with mitral valve disease. The optimum mitral valve examination includes a true "short-axis" view, obtained by a transverse (zero-degree angle) transgastric image orientation with the probe tip flexed anteriorly, and several "long-axis" views, obtained from various rotations of the basilar multiplane TEE image planes. This provides a useful and accurate means to determine the mechanism of mitral regurgitation, which is useful in planning and timing, determining the likelihood, and predicting the surgical techniques that will be required for mitral valve repair. The postcardiopulmonary bypass (postpump) TEE examination in a patient with mitral regurgitation is a second important component of the process of repair, to determine the presence and severity of residual mitral regurgitation, and identify any complications of surgery. Of 1,550 mitral repair operations studied with postpump echocardiography at our hospital since 1987, a total of 105 (7%) have had second pump runs. Multiplane TEE is also useful to pinpoint the exact site of periprosthetic regurgitation around a mitral prosthesis, enabling direct surgical closure in some cases. Understanding special technical features of multiplane TEE is an important component for optimum utilization of this powerful diagnostic modality.

Echocardiography, Transesophageal↗
PubMed1995

The diagnosis of prosthetic valve endocarditis by echocardiography.

Echocardiography, using the standard transthoracic and transesophageal (TEE) approaches, has been shown to be a useful tool in the diagnosis and management of patients with prosthetic valve endocarditis (PVE). The role of echocardiography involves (1) finding evidence for vegetations, (2) characterizing valvular dysfunction, (3) identifying periprosthetic spread of infection, and (4) determining preoperative prognostic data that impact on the need and timing of surgical intervention. Incorporation of echocardiography into the diagnostic criteria for endocarditis prevents delay in management and costly errors, particularly in patients with culture-negative infections and complications of the infection including jet lesions and deep tissue infections of the heart. TEE is particularly helpful in PVE, because shielding by the prosthesis may prevent adequate transthoracic imaging, which give false-negative results. With the aid of intraoperative TEE, the surgical mission should be to extirpate all the infection and reconstruct the heart with as little prosthetic material as possible. Transthoracic echocardiography is also useful in the follow-up management of patients with PVE.

Echocardiography↗
PubMed1994

Systolic anterior motion of mitral valve after the posterior leaflet sliding advancement procedure.

The posterior leaflet sliding advancement procedure was developed to prevent the occurrence of systolic anterior motion of mitral valve and consequently outflow obstruction after mitral annuloplasty. We present a patient with extremely redundant posterior mitral leaflet in whom outflow obstruction developed despite employment of this procedure. This case underscores the utility of preoperative and intraoperative echocardiography in surgical decision making. Systolic anterior motion can develop in some patients despite this new surgical technique.

Humans↗
PubMed1994

Should all patients undergo transesophageal echocardiography before electrical cardioversion of atrial fibrillation?

The management of anticoagulant therapy in patients with atrial fibrillation undergoing electrical cardioversion remains controversial, largely because of inadequate studies demonstrating risk or benefit, a relatively inconvenient anticoagulation management strategy and the increasing use of transesophageal echocardiography. Recent investigations into the potential mechanisms involved in the development of thrombus and systemic embolism in patients undergoing electrical cardioversion of atrial fibrillation may provide insight into underlying predisposing factors, with subsequent modification of management strategies. Conventional wisdom suggests that preexisting thrombus is responsible for thromboembolic events after cardioversion. However, development of a thrombogenic milieu after cardioversion, particularly in the left atrial appendage, may also be an important predisposing factor. To protect against both potential mechanisms of embolization, these data support therapeutic anticoagulation for all patients with atrial fibrillation of > 2 days in duration from the time of, as well as after cardioversion for a total of 4 weeks, undergoing cardioversion, even in the absence of thrombus on echocardiography. Therefore, the role of transesophageal echocardiography in this setting should be to enable early cardioversion if atrial thrombus is excluded and to identify high risk patients with atrial thrombi so as to postpone cardioversion and avoid the risk of embolization. Ultimately, however, a controlled, randomized and prospective clinical trial will be required to compare conventional management with a transesophageal echocardiography-guided strategy.

Anticoagulants↗
PubMed1994

Left ventricular to right atrial fistula after aortic homograft replacement for endocarditis.

The treatment is described of a patient who had severe bacterial endocarditis with aortic valve destruction and septal abscess complicated by left ventricular to right atrial fistula 3 months after aortic homograft root replacement and septal debridement and repair. The status of the aortic homograft and anatomy of the fistula were defined precisely by echocardiography, making successful repair through a right atriotomy possible without disturbing the aortic homograft and the implanted coronary arteries.

Abscess↗