Comparison of valvular resistance, stroke work loss, and Gorlin valve area for quantification of aortic stenosis. An in vitro study in a pulsatile aortic flow model

Prognostic value of flow-status in severe aortic stenosis patients undergoing percutaneous intervention

PURPOSE

Low-flow status is a mortality predictor in severe aortic stenosis (SAS) patients, including after transcatheter aortic valve implantation (TAVI) treatment. However, the best parameter to assess flow is unknown. Recent studies suggest that transaortic flow rate (FR) is superior to currently used stroke volume index (SVi) in defining low-flow states. Therefore, we aimed to evaluate the prognostic value of FR and SVi in patients undergoing TAVI.

METHODS

A single-centre retrospective analysis of all consecutive patients treated with TAVI for SAS between 2011 and 2019 was conducted. Low-FR was defined as < 200 mL/s and low-SVi as < 35 mL/m2. Primary endpoint was all-cause five-year mortality, analyzed using Kaplan-Meier curves and Cox regression models. Secondary endpoint was variation of NYHA functional class six months after procedure. Patients were further stratified according to ejection fraction (EF < 50%).

RESULTS

Of 489 cases, 59.5% were low-FR, and 43.1% low-SVi. Low-flow patients had superior surgical risk, worse renal function, and had a higher prevalence of coronary artery disease. Low-FR was associated with mortality (hazard ratio 1.36, p = 0.041), but not after adjustment to EuroSCORE II. Normal-SVi was not associated with survival, despite a significative p-trend for its continuous value. No associations were found for flow-status and NYHA recovery. When stratifying according to preserved and reduced EF, both FR and SVi did not predict all-cause mortality.

CONCLUSION

In patients with SAS undergoing TAVI, a low-FR state was associated with higher mortality, as well as SVi, but not at a 35 mL/m2 cut off.

Prognostic value of transvalvular flow rate in patients with low-gradient severe aortic stenosis: A dobutamine stress echocardiography study

BACKGROUNDS

There are limited data on the clinical relevance of transvalvular flow rate (Qmean ) at rest (Qrest) and at peak stress (Qstress ) during dobutamine stress echocardiography (DSE) in patients with low-gradient severe aortic stenosis (LG-SAS).

METHODS

We retrospectively analyzed the clinical data of patients with LG-SAS who underwent DSE. LG-SAS was defined as an aortic valve (AV) area index of < .6 cm2 /m2 and a mean AV pressure gradient (AVPG) of < 40 mm Hg. The primary endpoint included all-cause death and heart failure hospitalization.

RESULTS

Of 100 patients (mean age 79.5 ± 7.3 years; men, 45.0%; resting left ventricular ejection fraction [LVEF] 52.1% ± 15.9%; resting stroke volume index 35.8 ± 7.7 mL/m2 ; Qrest 171.8 ± 34.9 mL/s), the primary endpoint occurred in 51 patients during a median follow-up of 2.84 (interquartile range 1.01-5.21) years. When the study patients were divided into three subgroups based on Qrest and Qstress , the multivariate analysis showed that Qrest < 200 mL/s and Qstress ≥200 mL/s (hazard ratio 3.844; 95% confidence interval 1.143-12.930; p = .030), as well as Qrest and Qstress < 200 mL/s (hazard ratio 9.444; 95% confidence interval 2.420-36.850; p = .001), were significantly associated with unfavorable outcomes with Qrest and Qstress ≥200 mL/s as a reference after adjusting for resting LVEF, resting mean AVPG, chronic kidney disease, New York Heart Association functional class III/IV, and AV replacement.

CONCLUSIONS

Flow conditions based on the combination of Qrest and Qstress are helpful for risk stratification in LG-SAS patients.

Using Augmented Mean Arterial Pressure to Identify High Mortality Risk Patients With Moderate Aortic Stenosis

OBJECTIVE

To study the usefulness of a novel echocardiographic marker, augmented mean arterial pressure (AugMAP = [(mean aortic valve gradient + systolic blood pressure) + (2 × diastolic blood pressure)] / 3), in identifying high-risk patients with moderate aortic stenosis (AS).

PATIENTS AND METHODS

Adults with moderate AS (aortic valve area, 1.0-1.5 cm2) at Mayo Clinic sites from January 1, 2010, through December 31, 2020, were identified. Baseline demographic, echocardiographic, and all-cause mortality data were retrieved. Patients were grouped into higher and lower AugMAP groups using a cutoff value of 80 mm Hg for analysis. Kaplan-Meier and Cox regression models were used to assess the performance of AugMAP.

RESULTS

A total of 4563 patients with moderate AS were included (mean ± SD age, 73.7±12.5 years; 60.5% men). Median follow-up was 2.5 years; 36.0% of patients died. The mean ± SD left ventricular ejection fraction (LVEF) was 60.1%±11.4%, and the mean ± SD AugMAP was 99.1±13.1 mm Hg. Patients in the lower AugMAP group, with either preserved or reduced LVEF, had significantly worse survival performance (all P<.001). Multivariate Cox regression showed that AugMAP (hazard ratio, 0.962; 95% CI, 0.942 to 0.981 per 5-mm Hg increase; P<.001) and AugMAP less than 80 mm Hg (hazard ratio, 1.477; 95% CI, 1.241 to 1.756; P<.001) were independently associated with all-cause mortality.

CONCLUSION

AugMAP is a simple and effective echocardiographic marker to identify high-risk patients with moderate AS independent of LVEF. It can potentially be used in the candidate selection process if moderate AS becomes indicated for aortic valve intervention in the future.

Echocardiographic assessment of aortic stenosis: a practical guideline from the British Society of Echocardiography

The guideline provides a practical step-by-step guide in order to facilitate high-quality echocardiographic studies of patients with aortic stenosis. In addition, it addresses commonly encountered yet challenging clinical scenarios and covers the use of advanced echocardiographic techniques, including TOE and Dobutamine stress echocardiography in the assessment of aortic stenosis.

At what flow rate does the aortic valve gradient become severely elevated? Implications for guideline recommendations on aortic valve area cutoffs

Introduction

Aortic stenosis (AS) is considered severe when the aortic valve area (AVA) is < 1.0 cm2 and the mean aortic valve gradient (mAVG) exceeds 40 mm Hg. Since many patients with AVA < 1.0 cm2 do not manifest an mAVG > 40 mm Hg, we sought to determine the AVA at which mAVG tends to exceed 40 mm Hg in a sample of subjects with varied transvalvular flow rates.

Material and methods

Our echocardiography database was queried for subjects with native valve AS. We selected 200 subjects with an AVA < 1.0 cm2. The sample was selected to include subjects with varied mean systolic flow (MSF) rates. Linear regression was performed to determine the relationship between MSF and mAVG. Since this relationship varied by AVA, the regression was stratified by AVA (critical < 0.6 cm2, severe 0.6-0.79 cm2, moderately severe 0.8-0.99 cm2).

Results

The study sample was 79 ±12 years old and was 60% female. The MSF rate at which mAVG tended to exceed 40 mm Hg was 120 ml/s for critical AVA, 183 ml/s for severe AVA and 257 ml/s for moderately severe AVA. Those with moderately severe AVA rarely (8%) had an mAVG > 40 mm Hg at a wide range of MSF. In contrast, those with severe AVA typically (75%) had mAVG > 40 mm Hg when MSF was normal (> 200 ml/s). Those with critical AVA frequently (44%) had mAVG > 40 mm Hg, even when MSF was reduced.

Conclusions

Subjects with AVA of 0.8 and 0.9 cm2 rarely had mAVG > 40 mm Hg, even when the transvalvular flow rate was normal. Using current guidelines, it is not clear if such cases should be classified as severe.

Sex differences in transaortic flow rate and association with all-cause mortality in patients with severe aortic stenosis

AIMS

It is not known whether transaortic flow rate (FR) in aortic stenosis (AS) differs between men and women, and whether the commonly used cut-off of 200 mL/s is prognostic in females. We aimed to explore sex differences in the determinants of FR, and determine the best sex-specific cut-offs for prediction of all-cause mortality.

METHODS AND RESULTS

Between 2010 and 2017, a total of 1564 symptomatic patients (mean age 76 ± 13 years, 51% men) with severe AS were prospectively included. Mean follow-up was 35 ± 22 months. The prevalence of cardiovascular disease was significantly higher in men than women (63% vs. 42%, P < 0.001). Men had higher left ventricular mass and lower left ventricular ejection fraction compared to women (both P < 0.001). Men were more likely to undergo an aortic valve intervention (AVI) (54% vs. 45%, P = 0.001), while the death rates were similar (42.0% in men and 40.6% in women, P = 0.580). A total of 779 (49.8%) patients underwent an AVI in which 145 (18.6%) died. In a multivariate Cox regression analysis, each 10 mL/s decrease in FR was associated with a 7% increase in hazard ratio (HR) for all-cause mortality (HR 1.07; 95% CI 1.03-1.11, P < 0.001). The best cut-off value of FR for prediction of all-cause mortality was 179 mL/s in women and 209 mL/s in men.

CONCLUSION

Transaortic FR was lower in women than men. In the group undergoing AVI, lower FR was associated with increased risk of all-cause mortality, and the optimal cut-off for prediction of all-cause mortality was lower in women than men.

Transvalvular Flow Rate Determines Prognostic Value of Aortic Valve Area in Aortic Stenosis

BACKGROUND

Aortic valve area (AVA) ≤1.0 cm² is a defining characteristic of severe aortic stenosis (AS). AVA can be underestimated at low transvalvular flow rate. Yet, the impact of flow rate on prognostic value of AVA ≤1.0 cm² is unknown and is not incorporated into AS assessment.

OBJECTIVES

This study aimed to evaluate the effect of flow rate on prognostic value of AVA in AS.

METHODS

In total, 1,131 patients with moderate or severe AS and complete clinical follow-up were included as part of a longitudinal database. The effect of flow rate (ratio of stroke volume to ejection time) on prognostic value of AVA ≤1.0 cm² for time to death was evaluated, adjusting for confounders. Sensitivity analysis was performed to identify the optimal cutoff for prognostic threshold of AVA. The findings were validated in a separate external longitudinal cohort of 939 patients.

RESULTS

Flow rate had a significant effect on prognostic value of AVA. AVA ≤1.0 cm² was not prognostic for mortality (p = 0.15) if AVA was measured at flow rates below median (≤242 ml/s). In contrast, AVA ≤1.0 cm² was highly prognostic for mortality (p = 0.003) if AVA was measured at flow rates above median (>242 ml/s). Findings were irrespective of multivariable adjustment for age, sex, and surgical/transcatheter aortic valve replacement (as time-dependent covariates); comorbidities; medications; and echocardiographic features. AVA ≤1.0 cm² was also not an independent predictor of mortality below median flow rate in the validation cohort. The optimal flow rate cutoff for prognostic threshold was 210 ml/s.

CONCLUSIONS

Transvalvular flow rate determines prognostic value of AVA in AS. AVA measured at low flow rate is not a good prognostic marker and therefore not a good diagnostic marker for truly severe AS. Flow rate assessment should be incorporated into clinical diagnosis, classification, and prognosis of AS.

In vitro correlation between the effective and geometric orifice area in aortic stenosis

BACKGROUND

Planimetry of aortic stenosis can be performed when Doppler measurements are unavailable. We sought to evaluate if, as advised in guidelines, the geometric orifice area (GOA) threshold value of 1 cm² was concordant with the threshold of 1 cm² of the effective orifice area (EOA), and the factors influencing the contraction coefficient (EOA/GOA ratio).

METHODS

In an in vitro mock circulatory system, we tested 6 degrees of AS severity (3 severe and 3 non-severe), and 3 levels of flow (<150 ml/s, 150-200 ml/s, >250 ml/s). The EOA was calculated by Doppler-echocardiography, and the GOA was measured with dedicated software after camera acquisition.

RESULTS

In all but the very low flow condition, an EOA of 1 cm² corresponded to a GOA of 1.2 cm². The contraction coefficient increased with both the flow and the stenosis severity. For very severe stenoses, the EOA and the GOA were interchangeable.

CONCLUSION

As observed in clinical studies, the GOA was larger than the EOA, and a GOA between 1 and 1.2 cm² should not discard the possibility of severe aortic stenosis.

Age related structural and functional changes in left ventricular performance in healthy subjects: a 2D echocardiographic study

Left ventricular (LV) adaptation to aging is currently poorly understood. We aimed to characterize age related changes in LV structure and function by studying a large group of healthy subjects across a wide age range. Prospectively enrolled healthy volunteers (n = 778, 327 females; age 18 to 100 years, mean age 49.8 ± 18.1 years), were divided into 4 age groups: 18 to 34 years (n = 165); 35 to 49 years (n = 242), 50 to 79 years (n = 334) and ≥ 80 years (n = 40). All subjects underwent clinical examination, as well as comprehensive transthoracic echocardiogram [TTE]. Body mass index, systolic blood pressure (BP), and left atrial volume (p < 0.0001) increased with age while diastolic BP (p < 0.0001) decreased over time. LV mass/body surface area (BSA) and relative wall thickness increased with age (p < 0.0001) coincident with worsening parameters of diastolic function (E/A and E/Em, p < 0.0001). The ejection fraction and Sm did not change significantly. Stroke volume, ejection time index, flow rate and stroke work significantly increased with age (p < 0.01). The arterial elastance (Ea), a measure of ventricular afterload, and ventricular elastance (Ees), an index of LV systolic stiffness did not change with age nor did their ratio (Ees/Ea) the latter being an expression of ventricular-arterial coupling. Age, gender and LVM were the main independent variables associated with LV systolic function. In conclusion, LV adaptation to aging in a healthy cohort is characterized by concentric LV remodeling, increased contractility and preserved ventricular-arterial coupling.

Hydrodynamic and Geometric Behavior of Two Pericardial Prostheses Implanted in Small Aortic Roots

Hydrodynamic performance of stented bioprostheses is far below that of the native valve. One of the reasons is that the internal diameter of the prosthesis is usually smaller than that of the native valve. However, other valve characteristics are also important in generating the pressure drop. We aimed to assess, in an ex vivo pulsatile mock loop, the hydrodynamic behavior of two bioprostheses, Trifecta and Mitroflow, to ascertain which geometric terms are limiting factors in hydrodynamic performance. At stroke volumes between 30 and 60 ml, Trifecta showed lower pressure drop, energy dissipation and valve resistance, and greater effective orifice area. This trend was overturned at higher stroke volumes, with Mitroflow slightly outperforming Trifecta. The geometric determinants were consistent with these results. Trifecta achieved its maximum opening area already at the lowest stroke volumes, featuring a divergent shape at the systolic peak. Mitroflow showed a complex opening pattern, featuring a convergent shape at the systolic peak for lower stroke volumes, while reaching its maximum opening area at higher stroke volumes, with a divergent shape. The two bioprostheses, although similar in design, displayed different biomechanical behaviors. The internal diameter of each bioprosthesis did not show to be strictly correlated with its hydrodynamic characteristics.

Classification of Aortic Stenosis by Flow and Gradient Patterns Provides Insights into the Pathophysiology of Disease

Different patterns of flow and valve gradients can lead to diagnostic uncertainty about the severity of aortic stenosis (AS). Consecutive patients with severe AS (valve area <1 cm(2)) underwent echocardiography and computed tomography. Patients were classified into 4 groups (high-gradient/normal flow [HGNF], high-gradient/low flow [HGLF], low-gradient/normal flow [LGNF], and low-gradient/low flow [LGLF]). Low flow was defined as stroke volume index <35 mL/m(2) and low gradient as a mean aortic gradient <40 mm Hg. Aortic valve calcification (AVC) was calculated using the Agatston score. Of 181 patients, 56, 30, 46, and 49 had HGNF, HGLF, LGNF and LGLF with median AVC of 2048, 2015, 1366, and 1178 AU/m(2) (P < .0001) and valvuloarterial impedance of 4.5, 6.4, 4.2, and 5.9, respectively (P < .0001). Among those with LGLF, AVC was lower in patients with preserved compared to reduced left ventricular ejection fraction (1018 vs 2550 AU/m(2); P < .0001), but valvuloarterial impedance was similar (P = .33). The LGLF AS with preserved ejection fraction is associated with lower AVC and may identify patients with less severe AS in association with an adaptive ventricular response to high afterload.

3D pulsatile flow in a curved tube with coexisting model of aortic stenosis and coarctation of the aorta

Coarctation of the aorta is a congenital heart disease defined as an obstruction of the aorta distal to the left subclavian artery (between the aortic arch and descending aorta). It is usually associated with other diseases such as bicuspid and tricuspid aortic stenosis. If the coarctation remains uncorrected it can lead to hypertension, left ventricular failure and aortic dissection. Numerous investigations pointed out that there is a relationship between the genesis and the progression of cardiovascular disease and the locally irregular flow occurring at the diseased zone. Therefore, to examine the relationship between arterial disease and hemodynamics conditions, detailed quantitative studies on flow dynamics in arterial models are clearly inquired. In this study we numerically investigate pulsatile blood flow in a simplified model of the aorta (curved pipe) with coexisting coarctation of the aorta and aortic stenosis. Three severities of aortic stenoses (0.61 cm(2), 1.0 cm(2) and 1.5 cm(2)) coexisting with aortic coarctations (50%, 75% and 90% by area) are investigated. An experimentally validated numerical model from literature is used and baseline results are validated against it. To ensure having a physiologically relevant model using this geometry, flow properties are set so that the Dean number falls in the physiological range for the aorta. The results show that the coexistence of these pathologies significantly modifies the flow in a curved pipe. The maximal velocity is shifted towards the outer wall and can reach values as high as 5m/s just downstream of the coarctation. The wall shear stress distribution is significantly modified compared to the normal, unobstructed case. Finally, a clinically significant pressure gradient is induced by the curvature of the tube (up to 36 mmHg). This can lead to an overestimation of the severity of the coarctation using catheterization.

Trileaflet valve hydrodynamic resistance assessment

Valve hydrodynamic performance is usually assessed by effective orifice area, transvalvular resistance, regurgitation and blood damage effect. Some studies suggest effects in effective orifice area due to cardiovascular resistance, compliance and angle position of the valve. We suppose that silicone rubber valves under study have a good performance under different cardiovascular resistance conditions. Two in vitro experiments were made to test this hypothesis under constant and pulsatile flow rate. Transvalvular gradient pressure, transvalvular resistance, Gorling effective orifice area, effective orifice area in the ascending aorta and Reynolds numbers were estimated in both flow rates. Results suggest that cardiovascular resistance has no significant effect for this kind of valves, however resistance effect is observed in pumping pressure. Small transvalvular resistance and transvalvular pressure gradients were found. Gorlin effective orifice areas greater than 0.3 cm(2) have not viscosity effect. P-value 0.001 was found between Gorlin effective orifice area under constant and pulsatile flow rate.

Stroke-Work Loss Underestimates Hemodynamic Significance of Aortic Stenosis in Patients with Hypertension

BACKGROUND

Stroke-work loss (SWL) represents the amount of energy the left ventricle dissipates as heat because of outflow obstruction. Recent studies suggest that SWL > 25% was the most clinically efficient Doppler measure for predicting hemodynamic significance, symptomatic status, and outcome in patients with aortic stenosis (AS). However, SWL may be affected by systolic blood pressure (SBP).

OBJECTIVE

To determine if SWL reliably predicts hemodynamic significance of AS in patients with hypertension.

METHODS

We studied 42 consecutive patients with hemodynamically significant AS requiring aortic valve replacement (AVR). Data on demographics, preoperative hemodynamics, and echocardiographic parameters were obtained. SWL was measured using the formula SWL = 100 x mean PG/ (mean PG + SBP), where PG is transaortic pressure gradient. Patients were considered hypertensive if their BP > 140/90 mmHg or if they are on antihypertensive medications.

RESULTS

There were 27 males (64%) and mean age was 68 +/- 11 years. Twenty-four patients (57%) were hypertensive. Mean SBP was 134 +/- 24 mmHg, mean transaortic PG 47 +/- 20 mmHg, effective valve orifice area (EOA) by Doppler estimation 0.74 +/- 0.23 cm(2), and SWL 26 +/- 9%. Patients with hypertension had smaller SWL than normotensives (table I). SWL was >25% in 20 (49%) patients, and fewer patients with hypertension have SWL >25% (33% vs 71%, P = 0.019). Of note, patients with SWL < or =25% had significantly higher SBP (145 +/- 21 mmHg vs 122 +/- 22 mmHg, P = 0.02).

CONCLUSION

SWL underestimates the hemodynamic significance of aortic stenosis in the majority of patients with hypertension.

Low-flow, low-gradient aortic stenosis: from evaluation to treatment

PURPOSE OF REVIEW

Valve replacement improves symptoms and survival in symptomatic severe aortic stenosis. Low-flow, low-gradient aortic stenosis, however, is an especially challenging subset as valve replacement has a significant risk, and may fail to alleviate symptoms or improve left ventricular function. This article reviews the potential problems in evaluating aortic stenosis severity in low-flow, low-gradient aortic stenosis, the utility of dobutamine challenge to identify patients most likely to benefit from surgery, and the factors predicting patient outcome.

RECENT FINDINGS

Low-flow, low-gradient aortic stenosis consists of a heterogeneous group of patients with 'true' severe aortic stenosis, in whom afterload mismatch results from a severely stenotic valve; and 'pseudo-severe' aortic stenosis, where the valve is only mildly or moderately stenotic, but appears severe due to limitations in determining disease severity under low-flow conditions. Valve replacement is likely to benefit the former group, but may have little benefit to the latter. Dobutamine challenge can distinguish 'true' and 'pseudo-severe' aortic stenosis, and can evaluate contractile reserve, one of the strongest predictors of patient outcome. Strategies to avoid prosthesis-patient mismatch should be considered to optimize postoperative outcome.

SUMMARY

Dobutamine challenge can identify low-flow, low-gradient aortic stenosis patients most likely to benefit from valve replacement and provides important prognostic information on the operative risks and long-term outcome.

Impact of blood pressure on the Doppler echocardiographic assessment of severity of aortic stenosis

OBJECTIVE

To investigate the impact of blood pressure (BP) on the Doppler echocardiographic (Doppler-echo) evaluation of severity of aortic stenosis (AS).

METHODS

Handgrip exercise or phenylephrine infusion was used to increase BP in 22 patients with AS. Indices of AS severity (mean pressure gradient (DeltaP(mean)), aortic valve area (AVA), valve resistance, percentage left ventricular stroke work loss (% LVSW loss) and the energy loss coefficient (ELCo)) were measured at baseline, peak BP intervention and recovery.

RESULTS

From baseline to peak intervention, mean (SD) BP increased (99 (8) vs 121 (10) mm Hg, p<0.001), systemic vascular resistance (SVR) increased (1294 (264) vs 1552 (372) dynexs/cm(5), p<0.001) and mean (SD) transvalvular flow rate (Q(mean)) decreased (323 (67) vs 306 (66) ml/s, p = 0.02). There was no change in DeltaP(mean) (36 (13) vs 36 (14) mm Hg, p = NS). However, there was a decrease in AVA (1.15 (0.32) vs 1.09 (0.33) cm(2), p = 0.02) and ELCo (1.32 (0.40) vs 1.24 (0.42) cm(2), p = 0.04), and an increase in valve resistance (153 (63) vs 164 (74) dynexs/cm(5), p = 0.02), suggesting a more severe valve stenosis. In contrast, % LVSW loss decreased (19.8 (6) vs 16.5 (6)%, p<0.001), suggesting a less severe valve stenosis. There was an inverse relationship between the change in mean BP and AVA (r = -0.34, p = 0.02); however, only the change in Q(mean) was an independent predictor of the change in AVA (r = 0.81, p<0.001).

CONCLUSIONS

Acute BP elevation due to increased SVR can affect the Doppler-echo evaluation of AS severity. However, the impact of BP on the assessment of AS severity depends primarily on the associated change in Q(mean), rather than on an independent effect of SVR or arterial compliance, and can result in a valve appearing either more or less stenotic depending on the direction and magnitude of the change in Q(mean).

Small aortic annulus: The hydrodynamic performances of 5 commercially available tissue valves

BACKGROUND

In vivo comparison of the performance of heart valve prostheses is confounded by several factors, such as different nominal size, patients' characteristics and hemodynamics, surgical techniques, and study design. The aim of this study was to compare the in vitro hydrodynamic performances of 5 different tissue valves that would fit a 21-mm-diameter valve holder of the Sheffield pulse duplicator.

METHODS

Three samples of 5 supra-annular production-quality tissue valves, including the sewing ring cuffs, were tested in the aortic chamber of the Sheffield pulse duplicator. The prostheses fitting a 21-mm valve holder, which is comparable with a 21-mm aortic annulus, were as follows: 20-mm Sorin Soprano, 21-mm Carpentier-Edwards Magna, 21-mm SJM-Biocor-Epic-Supra, 21-mm Medtronic Mosaic, and 23-mm Mitroflow. The tests were carried out at a fixed pulse rate (70 beats/min) and at increasing cardiac outputs of 2, 4, 5, and 7 L/min. Each valve was tested 10 times for each different cardiac output. This resulted in a total of 40 tests for each valve and 120 tests for each valve model. Forward flow pressure decrease, effective orifice area, stroke work loss, and total regurgitant, closing, and leakage volumes were recorded while the valve operated under each cardiac output.

RESULTS

Pericardial valves showed significantly lower transvalvular gradients than porcine valves, unlike the SJM-Biocor-Epic-Supra valve at 2 L/min of cardiac output. Although the Carpentier-Edwards Magna valve provided the best performance at 2 and 4 L/min, the Mitroflow valve exhibited the lowest mean and peak gradients at 5 to 7 L/min. Total regurgitant and leakage volumes were higher for the Carpentier-Edwards Magna valve and lower for the SJM-Biocor-Epic-Supra and Mitroflow valves. Between 2 and 4 L/min, the calculated effective orifice area and stroke work loss were better for the Carpentier-Edwards Magna valve, whereas between 5 and 7 L/min, they were significantly superior with the Mitroflow prosthesis. Among the porcine bioprostheses, the SJM-Biocor-Epic-Supra valve showed significantly better results when compared with the Medtronic Mosaic valve at each cardiac output.

CONCLUSION

Assuming that the valve holder is comparable with a defined aortic annulus of 21 mm in which a spread of supra-annular tissue valves could be fitted, this hydrodynamic evaluation model allows comparison of the efficiency of currently available bioprostheses with a definite tissue annulus diameter. Pericardial valves exhibited the best performances, and the Mitroflow valve showed the lowest gradients and stroke work loss at increasing cardiac output.

Low-gradient aortic valve stenosis: value and limitations of dobutamine stress testing

Aortic valve stenosis has already reached endemic proportions in Western countries. As the prognosis of low-flow aortic valve stenosis under medical treatment is dismal, surgery is recommended in most patients. Preoperative dobutamine stress testing may help to assess surgical risk, but there is no strong scientific evidence to deny surgery based exclusively on the results of this test. The problems associated with clinical decision making in this condition are reviewed.

Flow-Dependent Changes in Doppler-Derived Aortic Valve Effective Orifice Area Are Real and Not Due to Artifact

OBJECTIVES

We sought to determine whether the flow-dependent changes in Doppler-derived valve effective orifice area (EOA) are real or due to artifact.

BACKGROUND

It has frequently been reported that the EOA may vary with transvalvular flow in patients with aortic stenosis. However, the explanation of the flow dependence of EOA remains controversial and some studies have suggested that the EOA estimated by Doppler-echocardiography (EOA(Dop)) may underestimate the actual EOA at low flow rates.

METHODS

One bioprosthetic valve and three rigid orifices were tested in a mock flow circulation model over a wide range of flow rates. The EOA(Dop) was compared with reference values obtained using particle image velocimetry (EOA(PIV)).

RESULTS

There was excellent agreement between EOA(Dop) and EOA(PIV) (r2 = 0.94). For rigid orifices of 0.5 and 1.0 cm2, no significant change in the EOA was observed with increasing flow rate. However, substantial increases of both EOA(Dop) and EOA(PIV) were observed when stroke volume increased from 20 to 70 ml both in the 1.5 cm2 rigid orifice (+52% for EOA(Dop) and +54% for EOA(PIV)) and the bioprosthetic valve (+62% for EOA(Dop) and +63% for EOA(PIV)); such changes are explained either by the presence of unsteady effects at low flow rates and/or by an increase in valve leaflet opening.

CONCLUSIONS

The flow-dependent changes in EOA(Dop) are not artifacts but represent real changes in EOA attributable either to unsteady effects at low flow rates and/or to changes in valve leaflet opening. Such changes in EOA(Dop) can be relied on for clinical judgment making.

Preliminary experience in the assessment of aortic valve calcification by ECG-gated multislice spiral computed tomography

BACKGROUND

The aim was to correlate the degree of valvular calcification in patients with aortic stenosis determined by retrospectively electrocardiogram (ECG)-gated multislice spiral computed tomography with stenosis severity assessed by cardiac catheterization.

METHODS

Prospective study on 41 patients (18 men, mean age 71+/-8 years) with aortic stenosis, who underwent four detector row multislice spiral computed tomography and cardiac catheterization. Severity of aortic stenosis was classified by cardiac catheterization. Aortic valve area, peak to peak and mean transvalvular gradients were correlated with the degree of calcification determined by multislice spiral computed tomography. Aortic valve calcification was assessed using aortic Agatston score, aortic mass score and aortic volume score.

RESULTS

All measured aortic valve calcification scores were significantly higher in patients with severe aortic stenosis (n=29) than in patients with moderate (n=7) or mild aortic stenosis (n=5, p<0.001). Aortic valve calcification scores correlated significantly with aortic valve area (r=-0.49, p=0.001 for aortic mass score) and with peak to peak (r=0.68, p<0.001) and mean (r=0.60, p<0.001) transvalvular gradients.

CONCLUSIONS

Severity of aortic valve calcification assessed by cardiac multislice spiral computed tomography is inversely related to aortic valve area and positively correlated with transvalvular gradients. Based on this preliminary data larger studies should be performed with echocardiography as a reference standard in order to validate this new information and its utility in the clinical management of the patient.

A ventricular-vascular coupling model in presence of aortic stenosis

In patients with aortic stenosis, the left ventricular afterload is determined by the degree of valvular obstruction and the systemic arterial system. We developed an explicit mathematical model formulated with a limited number of independent parameters that describes the interaction among the left ventricle, an aortic stenosis, and the arterial system. This ventricular-valvular-vascular (V3) model consists of the combination of the time-varying elastance model for the left ventricle, the instantaneous transvalvular pressure-flow relationship for the aortic valve, and the three-element windkessel representation of the vascular system. The objective of this study was to validate the V3 model by using pressure-volume loop data obtained in six patients with severe aortic stenosis before and after aortic valve replacement. There was very good agreement between the estimated and the measured left ventricular and aortic pressure waveforms. The total relative error between estimated and measured pressures was on average (standard deviation) 7.5% (SD 2.3) and the equation of the corresponding regression line was y = 0.99 x − 2.36 with a coefficient of determination r2 = 0.98. There was also very good agreement between estimated and measured stroke volumes ( y = 1.03 x + 2.2, r2 = 0.96, SEE = 2.8 ml). Hence, this mathematical V3 model can be used to describe the hemodynamic interaction among the left ventricle, the aortic valve, and the systemic arterial system.

The effects of hypertension on aortic valve stenosis

Hypertension not only can modify the exploratory findings of aortic stenosis, but may also interfere with the assessment of severity, and even have an impact on patient outcome.

Small aortic annulus: The hydrodynamic performances of 5 commercially available bileaflet mechanical valves

OBJECTIVE

Hemodynamic performances of mechanical valve prostheses in patients with aortic valve stenosis and a small aortic annulus are crucial. We analyzed the in vitro hydrodynamics of 5 currently available bileaflet mechanical prostheses that fitted a 21-mm-diameter valve holder of a Sheffield pulse duplicator.

METHODS

Three samples of 5 high-performance production-quality prostheses, including the sewing ring cuffs, were tested in the aortic chamber of a Sheffield pulse duplicator. Sizes of the prostheses fitting the 21-mm valve holder were as follows: 18-mm ATS, 19-mm SJM Regent, 19-mm Sorin Bicarbon Slimline, 19-mm On-X, and 21-mm Carbomedics Top Hat. The tests were carried out at a fixed pulse rate (70 beats/min) and at increasing cardiac outputs of 2, 4, 5, and 7 L/min. Each valve was tested 10 times for each different cardiac output. This resulted in a total of 40 tests for each valve and 120 tests for each valve model. The aortic pressure was set at 120/80 mm Hg (mean pressure, 100 mm Hg) throughout the experiment for all cardiac outputs. Forward flow pressure decrease, total regurgitant volume, closing and leakage volumes, effective orifice area, and stroke work loss were recorded while the valve operated under each cardiac output.

RESULTS

The SJM Regent valve and the Sorin Bicarbon Slimline prosthesis showed the lowest mean and peak gradients at increasing cardiac outputs. The closure volume was higher for the SJM Regent and Sorin Bicarbon Slimline prostheses, unlike with the ATS prosthesis at 7 L/min of cardiac output. The ATS and SJM Regent prostheses showed the largest regurgitant volume, whereas the Sorin Bicarbon Slimline prosthesis showed the lowest regurgitant volume. The calculated effective orifice area and stroke work loss were significantly better with the SJM Regent and Sorin Bicarbon Slimline prostheses.

CONCLUSION

Assuming that the 21-mm valve holder in which all the tested prostheses were accommodated is comparable with a defined aortic valve size, this hydrodynamic evaluation model allowed us to compare the efficiency of currently available valve prostheses, and among these, the SJM Regent and the Sorin Bicarbon Slimline exhibited the best performances.

Clinical efficacy of Doppler-echocardiographic indices of aortic valve stenosis: a comparative test-based analysis of outcome

OBJECTIVES

This study was designed to assess which hemodynamic index best accounts for clinical severity of aortic stenosis (AS) and to analyze the value of low-dose dobutamine testing.

BACKGROUND

Pressure gradient and valve area are suboptimal because they depend on flow rate, correlate poorly with symptoms, and provide limited prognostic information. Recently, new indices and low-dose inotropic stimulation have been introduced, but their clinical value remains uncertain.

METHODS

A total of 307 consecutive patients with AS were included in an ambispective study design (71 +/- 12 years old; peak jet velocity: 3.7 +/- 1.1 m/s). Clinical and Doppler-echocardiographic data were obtained, as well as results of low-dose dobutamine infusion (47 patients). Using receiver-operator-characteristic curve analysis, we evaluated jet velocity, pressure gradient, valve area, resistance, stroke-work loss (SWL), and dobutamine-induced increase in area for predicting 1) symptomatic status at entry, 2) early (</=3 months) cardiovascular death or aortic valve replacement, and 3) long-term outcome. Logistic regression and Cox models were designed multivariate and adjusted by bootstrapping.

RESULTS

Only 28% of patients were alive without valve replacement at the end of the follow-up period (22 +/- 4 months). The decision for valve replacement was made by the referring physician, blinded to the SWL, valve resistance, and dobutamine results. Non-flow-corrected indices performed better than valve area and valve resistance. Among them, SWL best predicted the defined end points. Odds/hazard ratios associated with a SWL Delta = 17% were 5.14 for presenting AS symptoms, 4.68 for early events, and 2.31 for late outcome. A cutoff value of SWL >25% best discriminated clinical end points. Other independent predictors of prognosis were symptomatic status and left ventricular ejection fraction. Dobutamine testing added no value to baseline models.

CONCLUSIONS

Non-flow-corrected indices show the highest clinical efficacy in aortic stenosis. Among these, SWL best predicts symptomatic status and outcome and therefore should be incorporated to aid patient management in unclear situations.

Effect of three-dimensional valve shape on the hemodynamics of aortic stenosis: three-dimensional echocardiographic stereolithography and patient studies

OBJECTIVES

This study tested the hypothesis that the impact of a stenotic aortic valve depends not only on the cross-sectional area of its limiting orifice but also on three-dimensional (3D) valve geometry.

BACKGROUND

Valve shape can potentially affect the hemodynamic impact of aortic stenosis by altering the ratio of effective to anatomic orifice area (the coefficient of orifice contraction [Cc]). For a given flow rate and anatomic area, a lower Cc increases velocity and pressure gradient. This effect has been recognized in mitral stenosis but assumed to be absent in aortic stenosis (constant Cc of 1 in the Gorlin equation).

METHODS

In order to study this effect with actual valve shapes in patients, 3D echocardiography was used to reconstruct a typical spectrum of stenotic aortic valve geometrics from doming to flat. Three different shapes were reproduced as actual models by stereolithography (computerized laser polymerization) with orifice areas of 0.5, 0.75, and 1.0 cm(2) (total of nine valves) and studied with physiologic flows. To determine whether valve shape actually influences hemodynamics in the clinical setting, we also related Cc (= continuity/planimeter areas) to stenotic aortic valve shape in 35 patients with high-quality echocardiograms.

RESULTS

In the patient-derived 3D models, Cc varied prominently with valve shape, and was largest for long, tapered domes that allow more gradual flow convergence compared with more steeply converging flat valves (0.85 to 0.90 vs. 0.71 to 0.76). These variations translated into differences of up to 40% in pressure drop for the same anatomic area and flow rate, with corresponding variations in Gorlin (effective) area relative to anatomic values. In patients, Cc was significantly lower for flat versus doming bicuspid valves (0.73 +/- 0.14 vs. 0.94 +/- 0.14, p < 0.0001) with 40 +/- 5% higher gradients (p < 0.0001).

CONCLUSIONS

Three-dimensional valve shape is an important determinant of pressure loss in patients with aortic stenosis, with smaller effective areas and higher pressure gradients for flatter valves. This effect can translate into clinically important differences between planimeter and effective valve areas (continuity or Gorlin). Therefore, valve shape provides additional information beyond the planimeter orifice area in determining the impact of valvular aortic stenosis on patient hemodynamics.

Hemodynamic stability of valve area, valve resistance, and stroke work loss in aortic stenosis: a comparative analysis

BACKGROUND

Although aortic valve area (AVA) has provided the standard index for assessing aortic stenosis severity, valve resistance and percent left ventricular stroke work (%LVSW) loss have been proposed as alternative flow independent indices of stenosis severity that may provide a more stable measure under diverse hemodynamic conditions. In 30 patients with moderate or severe aortic stenosis (AVA < or = 1.2 cm(2)), Doppler echocardiography indices of AVA, valve resistance, and %LVSW loss were measured at multiple transvalvular flow rates during dobutamine infusions (0-10 microg/kg/min) to compare their hemodynamic stability.

RESULTS

From baseline to maximum dobutamine dose in the 30 patients, transvalvular flow rate increased 43% and resulted in a 42% increase in mean transvalvular pressure gradient, a 15% increase in Doppler AVA, and a 26% increase in %LVSW loss. Group mean valve resistance did not change for the total cohort. For individual patients, AVA and %LVSW loss demonstrated a linear relationship with transvalvular flow (median r = 0.74 and 0.84, respectively). In contrast, both flow-mediated increases and decreases in valve resistance were observed in individual patients, resulting in the apparent stability of the group mean valve resistance in the total cohort. For individual patients, Doppler AVA and valve resistance demonstrated comparable stability in response to changes in hemodynamic conditions and were significantly more stable than mean transvalvular pressure gradient and %LVSW loss.

CONCLUSION

Doppler AVA and valve resistance provide stenotic indices of equivalent hemodynamic stability. However, transvalvular flow has a predictable directional effect on AVA and an unpredictable directional effect on valve resistance, potentially limiting valve resistance as a measure of hemodynamic severity.

Prediction of symptom-onset in aortic stenosis: a comparison of pressure drop/flow slope and haemodynamic measures at rest

To compare the pressure drop/flow slope with peak and mean pressure drop, effective orifice area and aortic valve resistance for the prediction of symptom-onset we performed resting and dobutamine stress echocardiography in 49 asymptomatic patients with aortic stenosis (peak aortic velocity>2.5 m/s). The end-point was progression to symptoms requiring surgery and patients were followed for a mean 21.2 (5.2) months. A total of 23 (47%) patients progressed to symptoms requiring aortic valve replacement and 26 remained asymptomatic. There was no significant difference in age, gender, fractional shortening or the presence or absence of coronary artery disease between these groups. There were differences in peak aortic velocity (P<0.0001), peak and mean pressure drop (P<0.0001), effective orifice area (P=0.03), aortic valve resistance (P=0.001) and pressure drop/flow slope (P<0.0001). On Cox regression analysis, the pressure drop/flow slope (P<0.0001), peak aortic velocity (P=0.005) and peak pressure gradient (P=0.02) were independent predictors. Mean event-free survival at 2 years for peak velocity >4.0 m/s was 17% and for pressure drop/flow slope >0.10 mmHg/ms(-1) was 20%. Of 13 patients reporting symptoms during dobutamine stress, 10 (77%) developed spontaneous symptoms during follow-up compared with 13 of 36 (36%) with no symptoms (P=0.11). The pressure drop/flow slope is a better independent predictor of symptom onset than resistance, mean pressure difference and effective orifice area, but is similar to peak velocity.

Comparison of valve resistance with effective orifice area regarding flow dependence

Aortic valve resistance has been proposed to represent the severity of aortic stenosis because some studies observed that it was less affected by change in flow than the valve-effective orifice area, but this issue remains controversial. The objective of this study was to systematically analyze the theoretical and practical determinants of these parameters in relation to changes in flow. Valve area and resistance in different valves were studied in vitro in a pulse duplicator system at different flow rates and in vivo in 90 subjects referred to either exercise or dobutamine infusion. Theoretical analysis and experimental results both demonstrated a unique relation between resistance (RES), valve-effective orifice area (EOA), and flow rate (Q): RES = K x (Q/EOA(2)). Accordingly, in fixed stenoses or in mechanical valves, resistance increased markedly with flow rate both in vitro (+0.88 +/- 0.26%/% of flow increase) and in vivo (mechanical valves: +2.09 +/- 4.61, fixed stenotic valves: +0.59 +/- 0.32%/%), whereas valve area did not change significantly (<0.2%/%). In contrast, in valves with a flexible orifice (bioprostheses and some patients with aortic stenosis), resistance was less increased due to the increase in valve area. Thus, both from a theoretical and a practical standpoint, valve resistance is much more flow dependent than valve area, particularly in fixed stenoses. Situations in which resistance does not increase with flow rate are unpredictable and are found in flexible valves when there is a concomitant increase in valve area.

Timing of surgery in aortic stenosis

In adults with valvular stenosis, the importance of prompt aortic valve replacement once symptoms occur is well known. The operative mortality for aortic valve replacement has improved dramatically over the past 4 decades and remains the only effective therapy for severe symptomatic aortic stenosis. Aortic valve replacement in patients with left ventricular dysfunction has a high operative mortality, although those patients who do not undergo surgery at all have an even worse outcome. While issues to consider include the presence or absence of coronary artery disease and expected hemodynamics of the prosthetic valve compared with the native valve, when in doubt, one should err on the side of surgical intervention. Elderly age is not a contraindication to aortic valve replacement for severe symptomatic aortic stenosis, although there is a higher prevalence of comorbid disease and higher operative mortality. Life expectancy is significantly prolonged and quality of life is significantly improved in the elderly who survive surgery. Indications for surgery in asymptomatic patients are controversial. We do not recommend valve replacement in asymptomatic patients at this time due to the known risks of surgery and a prosthetic valve and the lack of evidence for benefit of early surgery. Patients undergoing coronary bypass surgery should be considered for concomitant aortic valve surgery for moderate aortic stenosis that is expected to progress to severe stenosis in less than 5 years.

Flow dynamics of stenotic aortic valves assessed by signal processing of Doppler spectrograms

Clinical assessment of aortic stenosis (AS) is sometimes challenging, because all hemodynamic indexes of severity are modified by flow rate. However, the mechanisms underlying flow dependence remain controversial. Analysis of instantaneous flow dynamics has provided crucial information in a number of cardiovascular disorders and may add new insight into this phenomenon. This study was designed to analyze in vivo the effects of flow interventions on instantaneous valvular dynamics of stenotic valves. For this purpose, a custom algorithm for signal processing of Doppler spectrograms was developed and validated against a control population. Digital Doppler recordings at the aortic valve and left ventricular outflow tract were obtained in 15 patients with AS, at baseline and during low-dose dobutamine infusion; 10 normal subjects were studied as controls. Spectrograms were processed by signal averaging, time alignment, modal-velocity enhancement, envelope tracing, and numerical interpolation. Instantaneous relative aortic valve area (rAVA) was obtained by the continuity equation and plotted against normalized ejection time. Curves were classified as either type A (rapid, early-systolic opening) or type B (slow, end-systolic opening). Curves from controls closely matched prior knowledge of normal valve dynamics, but curves from patients were clearly different: all controls except 2 (80%) had type A, whereas all patients except 3 (80%) had a type B pattern (p = 0.03). Dobutamine infusion in patients increased and slightly anticipated peak rAVA by accelerating valve opening. Despite similar values of area and pressure difference, type B dynamics were associated with lower blood pressure (p = 0.01) and worse long-term outcome (>3 years) than type A flow dynamics (p = 0.02). Signal processing of Doppler spectrograms allows a comprehensive assessment of aortic flow dynamics. Differences in timing of valve aperture and in maximal leaflet excursion account for flow-mediated changes in valve area, suggesting complementary effects of inertia and elasticity on the kinetics of stenotic aortic valves. Flow-dynamic analysis provides novel clinical information regarding physiology of AS unavailable to conventional indexes.

Stress Echocardiography in Aortic Stenosis: Insights into Valve Mechanics and Hemodynamics

Stress interventions have been classically combined with cardiac catheterization recordings to understand the hemodynamic principles of valvular stenosis. Indices of aortic stenosis such as pressure gradient and valve area were based on simple hydraulic principles and have proved to be clinically useful for patient management during a number of decades. With the advent of Doppler echocardiography, these hemodynamic indices can be readily obtained noninvasively. Abundant evidence obtained using exercise and pharmacological stress echocardiography has demonstrated that the assumptions of classic hemodynamic models of aortic stenosis were wrong. Consequently, it is recognized that conventional indices may be misleading indicators of aortic stenosis significance in particular clinical situations. To improve diagnostic accuracy, several alternative hemodynamic models have been developed in the past few years, including valve resistance and left ventricular stroke work loss, among others. Nevertheless, these more-accurate indices should be obtainable noninvasively and need to demonstrate greater diagnostic and prognostic power than conventional indices; preliminary data suggest such superiority. Stress echocardiography is well established as the tool of choice for testing hypothesis and physical models of cardiac valve function. Although the final role of alternative indices is not yet well established, the new insights into valvular hemodynamics provided by this technique may change the clinical assessment of aortic stenosis.

The relation between transaortic pressure difference and flow during dobutamine stress echocardiography in patients with aortic stenosis

OBJECTIVE

To investigate the relation between transaortic pressure difference and flow in patients with aortic stenosis.

METHODS

50 asymptomatic patients with all grades of aortic stenosis were studied using dobutamine stress echocardiography. Individual plots of mean pressure drop against flow were drawn. Comparisons were made between grades of aortic stenosis as defined by the continuity equation.

RESULTS

A significant linear relation between pressure difference and flow was found in 34 patients (68%). There was a significant curvilinear relation in four (8%), while no significant regression line could be fitted in 12 (24%). In the 34 patients with linear fits, the slopes (mean (SD)) were 0.08 (0.07) in mild, 0.10 (0.04) in moderate, and 0.22 (0.16) in severe aortic stenosis (p = 0. 0055).

CONCLUSIONS

Transaortic pressure difference can be related directly to flow in many patients with all grades of aortic stenosis. However, there are individual differences in slope and intercept suggesting that resistance calculated at rest may not always be representative. Raw pressure drop/flow plots may be an alternative method of describing valve function.

Real-time 3-dimensional volumetric ultrasound imaging of the vena contracta for stenotic valves with the use of echocardiographic contrast imaging: in vitro pulsatile flow studies

The purpose of our study was to investigate the utility of real-time 3-dimensional volumetric ultrasound coupled with echo contrast imaging to visualize and quantify effective flow areas for stenotic valves in vitro. Real-time 3-dimensional ultrasound imaging has recently emerged as a promising method for increasing the quantitative accuracy of echocardiography. Since the technique currently does not process Doppler information, its use for quantifying flow has not been studied. However, the use of contrast agents to visualize cardiac flows with the use of echocardiography should allow determination of mass-dependent flow parameters such as effective flow area (vena contracta area) for stenotic lesions. We used real-time 3-dimensional imaging in an in vitro stenotic valve model (areas 0.785 to 1.767 cm2) under pulsatile flow conditions (60 bpm; 40 to 80 mL/beat). An echo contrast agent was used to visualize the distal jet. Real-time 3-dimensional imaging provides simultaneous views of long-axis and short-axis (C-scan) image planes of the jet. The vena contracta was identified and measured by placing the C-scan line immediately distal to the orifice and measuring the cross-sectional flow area. System gain and postprocessing curve shape affected 3-dimensional areas; minimal gain and a custom curve produced best agreement to actual vena contracta areas measured with a previously validated laser method (y = 0.939x + 0.089; r = 0.98; standard error of estimate = 0.158 cm2). We conclude that real-time 3-dimensional ultrasound imaging coupled with a contrast agent can be used as an accurate yet simple clinical means of measuring effective flow areas for stenotic valves.

Particle trace visualization of intracardiac flow using time-resolved 3D phase contrast MRI

The flow patterns in the human heart are complex and difficult to visualize using conventional two-dimensional (2D) modalities, whether they depict a single velocity component (Doppler echocardiography) or all three components in a few slices (2D phase contrast MRI). To avoid these shortcomings, a temporally resolved 3D phase contrast technique was used to derive data describing the intracardiac velocity fields in normal volunteers. The MRI data were corrected for phase shifts caused by eddy currents and concomitant gradient fields, with improvement in the accuracy of subsequent flow visualizations. Pathlines describing the blood pathways through the heart were generated from the temporally resolved velocity data, starting from user-specified locations and time frames. Flow trajectories were displayed as 3D particle traces, with simultaneous demonstration of morphologic 2D slices. This type of visualization is intuitive and interactive and may extend our understanding of dynamic and previously unrecognized patterns of intracardiac flow.

Effects of exercise on Doppler-derived pressure difference, valve resistance, and effective orifice area in different aortic valve prostheses of similar size

The effects of increased transvalvular volume flow on Doppler-derived measurements were compared in similarly sized, normally functioning, mechanical prostheses, stented and stentless porcine bioprostheses, and homografts. Homograft and stentless valves showed the largest effective orifice area and the lowest pressure differences and valve resistance at rest and during exercise-induced increase in flow rates.