Systemic pressure does not directly affect pressure gradient and valve area estimates in aortic stenosis in vitro

In-silico modelling of the impact of hypertension on the mean transvalvular gradients in aortic stenosis

INTRODUCTION

The influence of hypertension on the diagnostic assessment of aortic stenosis (AS) severity is unclear, yet clinically relevant. To clarify the effect of hypertension on transvalvular gradients, requires a better understanding of the impact that blood pressure change has on mean flow rate. Also, the effect of various degrees of AS severity, the valve geometry and intrinsic left ventricular contractile function (elastance) on this interaction, needs to be clarified. The current work aims to assess this interaction and the magnitude of these effects.

METHODS

A validated, zero-dimensional electro-hydraulic analogue computer model of the human cardiovascular circulatory system was generated. It was used to assess the impact of blood pressure changes on left ventricular pressure and transvalvular gradients at various flow rates, left ventricular elastances, a range of aortic valve areas and for different aortic valve morphologies.

RESULTS AND DISCUSSION

The magnitude of the impact of hypertension induced changes on the mean gradient (MG) is influenced by the mean flow rate, the AS severity, the hydraulic effective valve orifice area and the left ventricular elastance. Generally, for a given change in systemic arterial pressure, the impact on MG will be the most marked for lower flow rate states such as is expected in more severe degrees of AS, for worse intrinsic left ventricular (LV) contractility, shorter ejection times and lower end diastolic LV volumes. Given the above conditions, the magnitude of the effect will be more for a larger aortic sinus diameter, and also for a typical degenerative valve morphology compared to a typical rheumatic valve morphology.

CONCLUSION

The interaction between hypertension and mean gradients in AS is complex. The current work places previous recommendations in perspective by quantifying the magnitude of the effect that the changes in blood pressure has on mean gradient in various pathophysiological states. The work creates a framework for the parameters that should be considered in future clinical research on the topic.

Normalizing arterial blood pressure in patients with aortic stenosis does not prevent grading discrepancies between pre-cardiopulmonary bypass transesophageal echocardiography and transthoracic echocardiography

Background

Aortic stenosis (AS) grading discrepancies exist between pre-cardiopulmonary (pre-CPB) transesophageal echocardiography (TEE) and preoperative transthoracic echocardiography (TTE). Prior studies have not systematically controlled blood pressure.

Aims

We hypothesized that normalizing arterial blood pressure during pre-CPB TEE for patients undergoing valve replacement for AS would result in equivalent grading measurements when compared to TTE.

Setting

Single University Hospital.

Design

Prospective, Interventional.

Methods

Thirty-five adult patients underwent procedures for valvular AS between February 2017 and December 2020 at Medical University of South Carolina. Study participants had a TTE within 90 days of their procedure that documented blood pressure, peak velocity (Vp), mean gradient (PGm), aortic valve area (AVA), and dimensionless index (DI). During pre-CPB TEE, if a patient's mean arterial pressure (MAP) fell more than 20% below their baseline blood pressure obtained during TTE, measurements were recorded as "out of range." Phenylephrine was administered to restore MAP to the baseline range and repeat TEE measurements were recorded as "in-range."

Statistical Analysis

Differences between imaging modalities and grading parameters were examined using a series of linear mixed models. P values were Bonferroni-adjusted to account for multiple comparisons.

Main Results

Significant discrepancies between TEE and TTE were observed for Vp, PGm, and DI despite blood pressure normalization across all subjects and for out-of-range measures and corrected measures. There were no statistically significant differences between TEE and TTE for AVA.

Conclusions

Blood pressure normalization during pre-CPB TEE is not sufficient to avoid AS grading discrepancies with preoperative TTE.

Arterial Wave Reflection and Aortic Valve Stenosis: Diagnostic Challenges and Prognostic Significance

Introduction

Arterial wave reflection is an important component of the left ventricular afterload, affecting both pressure and flow to the aorta. The aim of the present study was to evaluate the impact of wave reflection on transvalvular pressure gradients (TPG), a key parameter for the evaluation of aortic valve stenosis (AS), as well as its prognostic significance in patients with AS undergoing a transcatheter aortic valve replacement (TAVR).

Materials and Methods

The study population consisted of 351 patients with AS (mean age 84 ± 6 years, 43% males) who underwent a complete hemodynamic evaluation before the TAVR. The baseline assessment included right and left heart catheterization, transthoracic echocardiography, and a thorough evaluation of the left ventricular afterload by means of wave separation analysis. The cohort was divided into quartiles according to the transit time of the backward pressure wave (BWTT). Primary endpoint was all-cause mortality at 1 year.

Results

Early arrival of the backward pressure wave was related to lower cardiac output (Q1: 3.7 ± 0.9 lt/min vs Q4: 4.4 ± 1.0 lt/min, p < 0.001) and higher aortic systolic blood pressure (Q1: 132 ± 26 mmHg vs Q4: 117 ± 26 mmHg, p < 0.001). TPG was significantly related to the BWTT, patients in the arrival group exhibiting the lowest TPG (mean TPG, Q1: 37.6 ± 12.7 mmHg vs Q4: 44.8 ± 14.7 mmHg, p = 0.005) for the same aortic valve area (AVA) (Q1: 0.58 ± 0.35 cm2 vs 0.61 ± 0.22 cm2, p = 0.303). In multivariate analysis, BWTT remained an independent determinant of mean TPG (beta 0.3, p = 0.002). Moreover, the prevalence of low-flow, low-gradient AS with preserved ejection fraction was higher in patients with early arterial reflection arrival (Q1: 33.3% vs Q4: 14.9%, p = 0.033). Finally, patients with early arrival of the reflected wave (Q1) exhibited higher all-cause mortality at 1 year after the TAVR (unadjusted HR: 2.33, 95% CI: 1.17–4.65, p = 0.016).

Conclusion

Early reflected wave arrival to the aortic root is associated with poor prognosis and significant aortic hemodynamic alterations in patients undergoing a TAVR for AS. This is related to a significant decrease in TPG for a given AVA, leading to a possible underestimation of the AS severity.

Impact of blood pressure on coronary perfusion and valvular hemodynamics after aortic valve replacement

OBJECTIVE

Our objective was to evaluate the impact of various blood pressures (BPs) on coronary perfusion and valvular hemodynamics following aortic valve replacement (AVR).

BACKGROUND

Lower systolic and diastolic (SBP/DBP) pressures from the recommended optimal target range of SBP < 120-130 mmHg and DBP < 80 mmHg after AVR have been independently associated with increased cardiovascular and all-cause mortality.

METHODS

The hemodynamic assessment of a 26 mm SAPIEN 3 transcatheter aortic valve (TAV), 29 mm Evolut R TAV, and 25 mm Magna Ease surgical aortic valve (SAV) was performed in a pulsed left heart simulator with varying SBP, DBP, and heart rate (HR) conditions (60 and 120 bpm) at 5 L/min cardiac output (CO). Average coronary flow (CF), effective orifice areas (EOAs), and valvulo-arterial impedance (Zva) were calculated.

RESULTS

At HR of 60 bpm, at SBP < 120 mmHg and DBP < 60 mmHg, CF decreased below the physiological lower limit with several different valves. Zva and EOA were found to increase and decrease respectively with increasing SBP and DBP. The same results were found with an HR of 120 bpm. The trends of CF variation with BP were similar in all valves however the drop below the lower physiological CF limit was valve dependent.

CONCLUSION

In a controlled in vitro system, with different aortic valve prostheses in place, CF decreased below the physiologic minimum when SBP and DBP were in the range targeted by blood pressure guidelines. Combined with recent observations from patients treated with AVR, these findings underscore the need for additional studies to identify the optimal BP in patients treated with AVR for AS.

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.

Impact of Arterial Blood Pressure on Ultrasound Hemodynamic Assessment of Aortic Valve Stenosis Severity

BACKGROUND

Aortic stenosis (AS) severity assessment is based on several indices. Aortic valve area (AVA) is subject to inaccuracies inherent to the measurement method, while velocities and gradients depend on hemodynamic status. There is controversy as to whether blood pressure directly affects common indices of AS severity.

OBJECTIVES

The study objective was to assess the effect of systolic blood pressure (SBP) variation on AS indices, in a clinical setting.

METHODS

A prospective, single-center study included 100 patients with at least moderately severe AS with preserved left ventricle ejection fraction. Patients underwent ultrasound examination during which AS severity indices were collected, with three hemodynamic conditions: (1) low SBP: <120 mm Hg; (2) intermediate SBP: between 120 and 150 mm Hg; (3) high SBP: ≥150 mm Hg. For each patient, SBP profiles were obtained by injection of isosorbide dinitrate or phenylephrine.

RESULTS

At baseline state, 59% presented a mean gradient (G_mean) ≥ 40 mm Hg, 44% a peak aortic jet velocity (V_peak) ≥4 m/sec, 66% a dimensionless index (DI) ≤0.25, and 87% an indexed AVA (AVAi) ≤ 0.6 cm²/m². Compared with intermediate and low SBP, high SBP induced a significant decrease in G_mean (39 ± 12 vs 43 ± 12 and 47 ± 12 mm Hg, respectively; P < .05) and in V_peak (3.8 ± 0.6 vs 4.0 ± 0.6 and 4.2 ± 0.6 mm Hg; P < .05). Compared with the baseline measures, in 16% of patients with an initial G_mean< 40 mm Hg, gradient rose above 40 mm Hg after optimization of the afterload (low SBP; P < .05). Conversely, DI and AVAi did not vary with changes in hemodynamic conditions. Flow rate, not stroke volume was found to impact G_mean and V_peak but not AVA and DI (P < .05).

CONCLUSIONS

Hemodynamic conditions may affect the AS ultrasound assessment. High SBP, or afterload, leads to an underestimation of AS severity when based on gradients and velocities. Systolic blood pressure monitoring and control are crucial during AS ultrasound assessment.

Aortic Stenosis, Aortic Regurgitation and Arterial Hypertension

BACKGROUND

Hypertension (HT) is an important risk factor for cardiovascular disease and might precipitate pathology of the aortic valve.

OBJECTIVE

To investigate the association of HT with aortic dysfunction (including both aortic regurgitation and stenosis) and the impact of antihypertensive treatment on the natural course of underlying aortic disease.

METHODS

We performed a systematic review of the literature for all relevant articles assessing the correlation between HT and phenotype of aortic disease.

RESULTS

Co-existence of HT with aortic stenosis and aortic regurgitation is highly prevalent in hypertensive patients and predicts a worse prognosis. Certain antihypertensive agents may improve haemodynamic parameters (aortic jet velocity, aortic regurgitation volume) and remodeling of the left ventricle, but there is no strong evidence of benefit regarding clinical outcomes. Renin-angiotensin system inhibitors, among other vasodilators, are well-tolerated in aortic stenosis.

CONCLUSION

Several lines of evidence support a detrimental association between HT and aortic valve disease. Therefore, HT should be promptly treated in aortic valvulopathy. Despite conventional wisdom, specific vasodilators can be used with caution in aortic stenosis.

Impact of concomitant mitral regurgitation on transvalvular gradient and flow in severe aortic stenosis: a systematic ex vivo analysis of a subentity of low-flow low-gradient aortic stenosis

AIMS

Evaluation of aortic stenosis (AS) is based on echocardiographic measurement of mean pressure gradient (MPG), flow velocity (Vmax) and aortic valve area (AVA). The objective of the present study was to analyse the impact of systemic haemodynamic variables and concomitant mitral regurgitation (MR) on aortic MPG, Vmax and AVA in severe AS.

METHODS AND RESULTS

A pulsatile circulatory model was designed to study function and interdependence of stenotic aortic (AVA: 1.0 cm², 0.8 cm² and 0.6 cm²) and insufficient mitral prosthetic valves (n=8; effective regurgitant orifice area [EROA] <0.2 cm² vs. >0.4 cm²) using Doppler ultrasound. In the absence of severe MR, a stepwise increase of stroke volume (SV) and a decrease of AVA was associated with a proportional increase of aortic MPG. When MR with EROA <0.2 cm² vs. >0.4 cm² was introduced, forward SV decreased significantly (70.9±1.1 ml vs. 60.8±1.6 ml vs. 47.4±1.1 ml; p=0.02) while MR volume increased proportionally. This was associated with a subsequent reduction of aortic MPG (57.1±9.4 mmHg vs. 48.6±13.8 mmHg vs. 33.64±9.5 mmHg; p=0.035) and Vmax (5.09±0.4 m/s vs. 4.91±0.73 m/s vs. 3.75±0.57 m/s; p=0.007). Calculated AVA remained unchanged (without MR: AVA=0.53±0.04 cm² vs. with MR: AVA=0.52±0.05 cm²; p=ns). In the setting of severe AS without MR, changes of vascular resistance (SVR) and compliance (C) did not impact on aortic MPG (low SVR and C: 66±13.8 mmHg and 61.1±20 mmHg vs. high SVR and C: 60.9±9.2 mmHg and 71.5±13.5 mmHg; p=ns) In concomitant severe MR, aortic MPG and Vmax were not significantly reduced by increased SVR (36.6±2.2 mmHg vs. 34.9±5.6 mmHg, p=0.608; 3.89±0.18 m/s vs. 3.96±0.28 m/s; p=ns).

CONCLUSIONS

Systemic haemodynamic variables and concomitant MR may potentially affect diagnostic accuracy of echocardiographic AS evaluation. As demonstrated in the present study, MPG and Vmax are flow-dependent and significantly reduced by a reduction of forward SV from concomitant severe MR, resulting in another entity of low-flow low-gradient aortic stenosis. In contrast, calculated AVA appears to be a robust parameter of AS evaluation if severe MR is present. Changes of SVR and C did not affect the diagnostic accuracy of AS evaluation.

Recommendations on the echocardiographic assessment of aortic valve stenosis: a focused update from the European Association of Cardiovascular Imaging and the American Society of Echocardiography

Echocardiography is the key tool for the diagnosis and evaluation of aortic stenosis. Because clinical decision-making is based on the echocardiographic assessment of its severity, it is essential that standards are adopted to maintain accuracy and consistency across echocardiographic laboratories. Detailed recommendations for the echocardiographic assessment of valve stenosis were published by the European Association of Echocardiography and the American Society of Echocardiography in 2009. In the meantime, numerous new studies on aortic stenosis have been published with particular new insights into the difficult subgroup of low gradient aortic stenosis making an update of recommendations necessary. The document focuses in particular on the optimization of left ventricular outflow tract assessment, low flow, low gradient aortic stenosis with preserved ejection fraction, a new classification of aortic stenosis by gradient, flow and ejection fraction, and a grading algorithm for an integrated and stepwise approach of artic stenosis assessment in clinical practice.

Quantification of congenital aortic valve stenosis in pediatric patients: comparison between cardiac magnetic resonance imaging and transthoracic echocardiography

Previous studies showed the reliability of cardiac magnetic resonance imaging (cMRI) in the quantification of aortic valve stenosis in adults. The aim of this retrospective study was to assess the ability of cMRI in the quantification of congenital aortic valve stenosis (CAS) in children. Nineteen patients (mean age 14.0 ± 3.2 years, 15 boys and 4 girls) with CAS were imaged by cMRI and transthoracic echocardiography (TTE). cMRI was performed on a 1.5-Tesla MR scanner (Magnetom Avanto; Siemens Healthcare, Erlangen, Germany) using cine steady-state free precession sequences for the assessment of the aortic valve area (AVA) by MR planimetry and left-ventricular function. Phase-contrast measurement was used in cMRI to assess peak flow velocity above the aortic valve. A positive correlation was found between maximum systolic pressure gradient (MPG) as assessed by cMRI and TTE (28.9 ± 21.2 vs. 41.3 ± 22.7 mmHg, r = 0.84, p = 0.001) with a mean underestimation of 12.4 mmHg by cMRI. Only a weak correlation could be observed between AVA by cMRI and MPG at the aortic valve by TTE (r = -0.50, p = 0.029) and cMRI (r = -0.27, p = 0.40). Furthermore, a positive correlation between myocardial mass (cMRI) and MPG (TTE, r = 0.57, p = 0.01), but not between myocardial mass (cMRI) and AVA (cMRI, r = 0.07, p = 0.77), was found. The assessment of MPG by cMRI in patients with CAS is feasible with a trend toward underestimatation compared with TTE. Moreover, MPG seems to be a more accurate parameter than AVA regarding the prediction of myocardial hypertrophy.

Aortic valve stenosis and arterial hypertension: a synopsis in 2013

Systemic hypertension and aortic valve stenosis (AVS) are both age-related diseases. The pathophysiology of AVS shares some similarities with essential hypertension, which might be the link between the two diseases. Although AS is usually related with low blood pressure levels, approximately one third of patients with severe AS suffer from arterial hypertension, a percentage that can increase up to 50 % according some studies. This review will summarize various aspects regarding the prevalence the pathophysiology and the natural history of those two diseases that seems to be linked, as well as the effect of blood pressure and antihypertensive treatment on various echocardiographic parameters in patients with AVS.

Impact of afterload on the assessment of severity of aortic stenosis

BACKGROUND

Aortic stenosis (AS) is increasingly diagnosed in current aging society. Echocardiography is the most important tool in the assessment of AS and its severity. However, load-dependency of Doppler measurement could affect the accuracy of AS severity assessment. We tried to evaluate the impact of afterload on the assessment of AS severity by modification of afterload using pneumatic compression (Pcom).

METHODS

Forty patients diagnosed as moderate or severe AS [effective orifice area of aortic valve (EOA_AV) by continuity equation of < 1.5 cm²] were consecutively enrolled. Patients with severely uncontrolled hypertension, severe left ventricular (LV) dysfunction, and other significant valve disease were excluded. Comprehensive echocardiography was performed at baseline to assess AS severity. Then, pneumatic compression of the lower extremities by 100 mmHg was applied to increase LV afterload. After 3 minutes, echocardiography was repeated to assess AS severity.

RESULTS

Mean blood pressure was significantly increased under Pcom (p < 0.001), while heart rate remained unchanged. Peak aortic valve velocity (V_max) was slightly, but significantly decreased under Pcom (p = 0.03). However, Doppler velocity index and EOA_AV by continuity equation were not affected by Pcom.

CONCLUSION

AS severity assessment by echocardiography was not dependent on the change of LV afterload imposed by Pcom. AV V_max was slightly decreased with LV afterload increment, but these changes were too small to alter treatment plan of AS patients. EOA_AV and Doppler velocity index are more stable parameters for AS severity assessment.

Design and validation of a novel bioreactor to subject aortic valve leaflets to side-specific shear stress

Hemodynamic stresses are presumed to play an important role in the development of calcific aortic valve disease (CAVD). The elucidation of the shear stress mechanisms involved in the pathogenesis of CAVD has been hampered by the complexity of the native unsteady and side-specific valvular flow environment. To address this gap, this article describes the design and validation of a novel device to expose leaflet samples to time-dependent side-specific shear stress. The device built on a double cone-and-plate geometry was dimensioned based on our previous single-sided shear stress device that minimizes secondary flow effects inherent to this geometry. A fluid-structure interaction (FSI) model was designed to predict the actual shear stress produced on a tissue sample mounted in the new device. Staining was performed on porcine leaflets conditioned in the new bioreactor to assess endothelial integrity and cellular apoptosis. The FSI results demonstrated good agreement between the target (native) and the actual side-specific shear stress produced on a tissue sample. No significant difference in endothelial integrity and cellular apoptosis was detected between samples conditioned for 96 h and fresh controls. This new device will enable the investigation of valvular response to normal and pathologic hemodynamics and the potential mechano-etiology of CAVD.

The effects of arterial hypertension on aortic valve stenosis

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