Doppler evaluation of aortic valve area in children with aortic stenosis

Echocardiographic Follow-Up of Congenital Aortic Valvular Stenosis II

We evaluated the natural course of congenital aortic valvular stenosis (AVS) and factors affecting AVS progression during long-term follow-up with echocardiography. Medical records of 388 patients with AVS were reviewed; patients with concomitant lesions other than aortic regurgitation (AR) were excluded. Trivial AVS was defined as a transvalvular Doppler peak systolic instantaneous gradient of < 25 mmHg; mild stenosis, 25-49 mmHg; moderate stenosis, 50-75 mmHg; and severe stenosis, > 75 mmHg. Median age of the patients was 3 years (range 0 day to 21 years), and 287 (74%) were male. A total of 355 patients were followed with medical treatment alone for a median of 4.6 years (range 1 month to 20.6 years), and the degree of AVS increased in 75 (21%) patients. The risk of AVS progression was higher when AVS was diagnosed in neonates (OR 4.29, CI 1.81-10.18, p = 0.001) and infants (OR 3.79, CI 2.21-6.49, p = 0.001). After the infancy period, bicuspid valve morphology increased AVS progression risk (OR 2.4, CI 1.2-4.6, p = 0.034). Patients with moderate AVS were more likely to have AVS progression (OR 2.59, CI 1.3-5.1, p = 0.006). Bicuspid valve morphology increased risk of AR development/progression (OR 1.77, CI 1.1-2.7, p = 0.017). The patients with mild and moderate AVS were more likely to have AR development/progression (p = 0.001). The risk of AR development/progression was higher in patients with AVS progression (OR 2.25, CI 1.33-3.81, p = 0.002). Newborn babies and infants should be followed more frequently than older patients according to disease severity. Bicuspid aortic valve morphology and moderate stenosis are risk factors for the progression of AVS and AR.

In Vitro Simulation and Validation of the Circulation with Congenital Heart Defects

Despite the recent advances in computational modeling, experimental simulation of the circulation with congenital heart defect using mock flow circuits remains an important tool for device testing, and for detailing the probable flow consequences resulting from surgical and interventional corrections. Validated mock circuits can be applied to qualify the results from novel computational models. New mathematical tools, coupled with advanced clinical imaging methods, allow for improved assessment of experimental circuit performance relative to human function, as well as the potential for patient-specific adaptation. In this review, we address the development of three in vitro mock circuits specific for studies of congenital heart defects. Performance of an in vitro right heart circulation circuit through a series of verification and validation exercises is described, including correlations with animal studies, and quantifying the effects of circuit inertiance on test results. We present our experience in the design of mock circuits suitable for investigations of the characteristics of the Fontan circulation. We use one such mock circuit to evaluate the accuracy of Doppler predictions in the presence of aortic coarctation.

Non-invasive estimation of pressure gradients in regurgitant jets: an overdue consideration

AIMS

This investigation sought to discern the relative accuracy of Doppler predictions of pressure drops in regurgitant jets across a broad spectrum of conditions, using an in vitro pulsatile flow model.

METHODS AND RESULTS

We studied the accuracy of Doppler pressure gradients derived from regurgitant jet peak velocities using the simplified Bernoulli equation (SBE) using an in vitro flow model of atrio-ventricular valve regurgitation. We observed overall a good correlation (r = 0.89, P < 0.0001) with actual pressure gradient, when there is normal fluid viscosity and the jet is free of wall interaction. However, we observed various degrees of underestimation of pressure gradient by Doppler when regurgitant chamber size was reduced (P = 0.0003), when fluid viscosity was increased (P < 0.0001), or in the presence of wall interaction (P < 0.0001). Chamber compliance had no effect on the accuracy of pressure gradient prediction (P = 0.36). Significant underestimation error in pressure gradient prediction by Doppler of up to 43.2% was observed.

CONCLUSION

When jet impingement or wall interaction are present, or when viscosity is increased, caution should be used in applying the SBE to a regurgitant jet, as significant underestimation in pressure gradient prediction may occur.

Comparison of simultaneous invasive and noninvasive measurements of pressure gradients in congenital aortic valve stenosis

PURPOSE

Congenital aortic valve stenosis is a common problem in pediatric cardiology. The catheter peak to peak systolic gradient is the accepted standard used for prognosis and intervention, but noninvasive correlation in pediatric patients is frequently associated with underestimation or overestimation of this gradient. The purpose of this study was to compare different noninvasive measurements with simultaneous catheter gradients to identify which best predicts the catheter peak to peak gradient.

METHODS

Twenty-five simultaneous Doppler and catheter measurements of aortic stenosis gradient were performed in 14 children (all 14 before valvuloplasty and 11 after valvuloplasty). Noninvasive estimates of pressure gradient were compared with catheter measurements with linear regression and Bland-Altman analysis.

RESULTS

The Doppler peak instantaneous pressure gradient overestimated the catheter peak to peak gradient but correlated well with the catheter peak instantaneous gradient. The Doppler mean systolic gradient correlated well with the catheter peak to peak gradient at low gradients and underestimated higher catheter gradients but agreed well at all levels with the catheter mean gradient. The modification of a catheter-derived correlation equation produced good correlation with the catheter peak to peak gradient (slope, 1.14; intercept, -1.8; R, 0.92), as did the use of estimated pressure recovery (slope, 1.04; intercept, 5.0; R, 0.94), calculated from a defined fluid mechanic equation.

CONCLUSION

The catheter peak to peak gradient can be accurately estimated noninvasively using estimated pressure recovery or correlation equations incorporating Doppler measurements.

Jet eccentricity: a misleading source of agreement between Doppler/catheter pressure gradients in aortic stenosis

Characterization of the severity of aortic stenosis relies on accurate measurement of the pressure gradient across the valve and the valve area. Pressure gradients measured by Doppler ultrasound based on the clinical form of the Bernoulli equation often overestimate pressure gradients by catheter as the result of pressure recovery. Doppler techniques measure the velocity of the vena contracta of the stenotic jet. This corresponds to the maximal pressure gradient and the minimal effective valve area. Pressure recovery can be characterized by analysis of the spread of the stenotic jet downstream of the valve as it fills the aorta and should be influenced by the shape of the velocity profile of the decaying jet. In this study, we addressed the hypothesis that the site of complete pressure recovery (the point at which the jet fully expands to the size of the aorta), the effective valve area, and the maximal pressure gradient are affected by jet eccentricity. To accomplish this, we developed a computational model of aortic stenosis that provides detailed velocity and pressure information in the vicinity of the valve. The results show that the width of the eccentric wall jet decreased and maximal velocity increased with greater jet eccentricity. Furthermore, for a constant anatomic area, the effective valve area decreased, the distance to complete pressure recovery increased, and the maximal pressure gradient increased with the degree of eccentricity. Failure to take this into account could fortuitously drive Doppler and catheter measurements toward agreement because the distal pressure sensor will not record the fully recovered pressure. Therefore the pressure gradient across a stenotic valve depends on jet eccentricity. The spread of the wall jet after attachment must be characterized to develop a robust method for the prediction of pressure recovery.

Insights into catheter/Doppler discrepancies in congenital aortic stenosis

Despite inherent discrepancies between Doppler and catheter gradients in aortic stenosis, the simplified Bernoulli equation is still the accepted noninvasive technique to quantitate severity. The Reynolds number is a dimensionless parameter that characterizes the nature of flow as being viscous, turbulent, or transitional. Recently, in vivo and animal studies have successfully used a Reynolds number-based approach to reconcile Doppler-estimated and catheter-measured discrepancies. At the midrange of Reynolds number, pressure recovery effects are most evident, resulting in "overestimation" of catheter gradients by Doppler. At the lower range of the Reynolds number viscous effects are important, whereas at a higher range, turbulent factors are dominant; both result in a tendency toward agreement. We recorded 18 peak instantaneous gradients from dual left ventricular catheters (15 to 95 mm Hg), while simultaneously recording Doppler velocities before and after intervention in 11 pediatric patients (ages 0.5 to 16 years, mean 4.5). Doppler correlated but overestimated catheter-measured peak instantaneous gradients (y = 0.84x + 18.4, r = 0.8, SEE +/- 15.2 mm Hg, mean percent difference 29.9 +/- 36) over the range of catheter gradients measured. Accounting for the Reynolds number successfully collapsed data onto a single curve. Our study confirms in a clinical setting the importance of applying fluid dynamic principles such as the Reynolds number to explain apparent discrepancies between catheter and Doppler gradients. These principles provide a foundation for developing clinically appropriate correction factors.

[Clinical and echocardiographic impact of neonatal aortic valvuloplasty]

OBJECTIVES

The selection of patients for balloon aortic valvuloplasty is a vital clinical challenge in neonatal aortic stenosis. The present study was designed to establish possible predicting factors for poor results after balloon therapy.

PATIENTS AND METHODS

2D echocardiographic, Doppler color and clinical variables (grade of cardiac failure, aortic "anulus", mitral anulus, left ventricular diameter, ascending aorta, instantaneous Doppler gradient, and grade of aortic regurgitation) were analyzed in 32 neonates submitted to balloon dilation at 22 +/- 18 days of life. The evaluations were conducted during three periods in respect to balloon therapy (A: before; B: immediately after, and C: mid-term follow-up). The outcome in both, B and C periods was defined as favorable (all survivors with Doppler gradient < or = 70 mmHg and no other intervention on the valve) and unfavorable (death, first stage of univentricularization, valvular replacement or survivors with Doppler gradient > 70 mmHg). Mean values between subgroups were compared by Wilcoxon test; unconditional logistic regression was used to analyze the impact of cardiac failure and anatomic variables (continuous, categorized or Z) on the outcome.

RESULTS

The Doppler gradient decreased from 70 +/- 28 to 34 +/- 14 mmHg after the valvuloplasty, and no changes were detected in the follow-up period (36 +/- 8 mmHg). An immediate favorable result was obtained in 72% of the patients; its consisted of 50% in period C. Nine neonates had an immediate unfavorable outcome (6 deaths and 3 with Norwood operation). In the follow-up, three patients had valvular replacement, one patient Doppler gradient > 70 mmHg and one patient with left ventricular endomyocardial abnormalities died. The severe cardiac failure (odds ratio: 33; CL 2.4-443; p = 0.008) and all categorized anatomic variables (aortic "anulus" < or = 6 mm; mitral anulus < or = 9 mm; ascending aorta < or = 8 mm; left ventricular diameter < or = 13 mm) were related with the immediate poor outcome. At 7.6 years, survival and freedom with no valvular replacement nor reintervention probability rates were 83% and 67%, respectively.

CONCLUSIONS

2D echo Doppler provides essential information about the anatomic and functional lesions coexisting with severe or critical aortic stenosis in neonates. Patients with left heart hypoplasia and severe heart failure should not be candidates for balloon valvuloplasty. The degree of residual aortic regurgitation and endomyocardial abnormalities of the left ventricle play an important role in the mid-term follow-up.

Turbulent/viscous interactions control Doppler/catheter pressure discrepancies in aortic stenosis. The role of the Reynolds number

BACKGROUND

Despite good correlation between Doppler and catheter pressure drops in numerous reports, it is well known that Doppler tends to apparently overestimate pressure drops obtained by cardiac catheterization. Neither (1) simplification of the Bernoulli equation nor (2) pressure recovery effects can explain this dilemma when taken alone. This study addressed the hypothesis that a Reynolds number-based approach, which characterizes (1) and (2), provides a first step toward better agreement of catheter and Doppler assessments of pressure drops.

METHODS AND RESULTS

Doppler and catheter pressure drops were studied in an in vitro model designed to isolate the proposed Reynolds number effect and in a sheep model with varying degrees of stenosis. Doppler pressure drops in vitro correlated with the directly measured pressure drop for individual valves (r = .935, .960, .985, .984, .989, and .975) but with markedly different slopes and intercepts. A Bland-Altman type plot showed no useful pattern of discrepancy. The Reynolds number was successful in collapsing the data into the profile proposed in the hypothesis. Parallel results were found in the animal model.

CONCLUSIONS

Apparent overestimation of net pressure drop by Doppler is due to pressure recovery effects, and these effects are countered by both viscous effects and inertial/turbulent effects. Only by reconciliation of discrepancies by use of a quantity such as Reynolds number that embodies the relative importance of competing factors can the noninvasive and invasive methods be connected. This study shows that a Reynolds number-based approach accomplishes this goal both in the idealized in vitro setting and in a biological system.

Transesophageal echocardiography

This article presents an overview of the benefits and efficacy of transesophageal echocardiography (TEE) in the critically ill patient. The echocardiographic evaluation of ventricular function both regional and global, is discussed with special emphasis on ischemic heart disease; assessment of preload, interrogation of valvular heart disease (prosthetic and native) and its complications; endocarditis and its complications; intracardiac and extracardiac masses, including pulmonary embolism; aortic diseases (e.g., aneurysan, dissection, and traumatic tears); evaluation of patent foramen ovale and its association with central and peripheral embolic events; advancements in computer technology; and finally, the effect of TEE on critical care.