Acute effects of transcatheter aortic valve replacement on the ventricular-aortic interaction

Transcatheter aortic valve replacement (TAVR) is increasingly used to treat severe aortic stenosis (AS) patients. However, little is known regarding the direct effect of TAVR on the ventricular-aortic interaction. In the present study, we aimed to investigate changes in central hemodynamics after successful TAVR. We retrospectively examined 33 cases of severe AS patients (84 +/- 6 yr) who underwent TAVR. Invasive measurements of left ventricular and aortic pressures as well as echocardiographic aortic flow were acquired before and after TAVR (maximum within 5 days). We examined alterations in key features of central pressure and flow waveforms, including the aortic augmentation index (AIx), and performed wave separation analysis. Arterial parameters were determined via parameter-fitting on a two-element Windkessel model. Resolution of AS resulted in direct increase in the aortic systolic pressure and maximal aortic flow (131 +/- 22 vs. 157 +/- 25 mmHg and 237 +/- 49 vs. 302 +/- 69 mL/s, P < 0.001 for all), whereas the ejection duration decreased (P < 0.001). We noted a significant decrease in the AIx (from 42 +/- 12 to 19 +/- 11%, P < 0.001). Of note, the arterial properties remained unchanged. There was a comparable increase in both forward (61 +/- 20 vs. 77 +/- 20 mmHg, P < 0.001) and backward ( 35 +/- 14 vs. 42 +/- 10 mmHg, P = 0.013) pressure wave amplitudes, while their ratio, i.e., the reflection coefficient, was preserved. Our results highlight the impact of TAVR on the ventricular-aortic interaction by affecting the amplitude, shape, and related attributes of the aortic pressure and flow pulse and challenge the interpretation of AIx as a solely vascular measure in AS patients. NEW & NOTEWORTHY Transcatheter aortic valve replacement (TAVR) is linked with an immediate increase in aortic systolic blood pressure and maximal flow, as well as steeper aortic pressure and flow wave upstrokes. After TAVR, the forward wave pumped by the heart is enhanced. Although the arterial properties remain unchanged, the central augmentation index (AIx) is markedly decreased after TAVR. This challenges the interpretation of AIx as a solely vascular measure in patients with aortic valve stenosis.

Hemodynamics of ageing, ventricular-arterial coupling and noninvasive assessment of key hemodynamical and cardiac quantities

Stamatia Zoi Pagoulatou

Ageing is a natural process that affects both the anatomical and functional properties of the cardiovascular system and alters the coupling characteristics between the heart and the aorta. These alterations may predispose the cardiovascular system in the development and progression of cardiovascular diseases (CVD), such as hypertension and left ventricular (LV) hypertrophy. CVDs are currently the leading cause of morbidity and mortality globally, and with the population of elderly steadily increasing, they are expected to become socio-economic burden in the near future. Accordingly, the presented body of research aimed at providing novel insights into the evolution of hemodynamics with ageing (Part I) and the physiology of the ventricular-arterial interaction (Part II) by leveraging the potential of a state-of-the-art one-dimensional (1D) model of the systemic circulation. A major goal of this dissertation was also the development, implementation and validation of novel noninvasive tools for monitoring biomarkers of importance (Part III), as well as the evaluation of existing or novel techniques to derive aortic biomechanical properties (Part IV). In Part I, we presented a validated 1D model of the systemic circulation that was adjusted to account for the effects of ageing, as reported by previous literature. The ageing model was found highly consistent with published data from large-scale studies. Examination of the wave reflection profile revealed an increase in the forward wave amplitude over time, which constitutes the principal determinant of the age-induced increase in systolic pressure. Additionally, we highlighted the importance of considering the heterogeneous effects of ageing on the arterial distensibility when adapting the properties of the arterial tree model, in order to predict correctly central hemodynamics. In Part II, we focused on the effect of cardiac systolic function on central and peripheral hemodynamics under physiological and pathological conditions. By means of our computational 1D model, we showed that a physiological increase in cardiac contractility leads to a steeper forward pressure wave pumped by the heart, which, subsequently, drastically alters central and peripheral hemodynamics. These computational results were in good agreement with our subsequent in vivo study, conducted in a group of aortic valve stenosis patients subjected to Transcatheter Aortic Valve Replacement. Part III of this thesis was devoted to the design, development, testing and validation of a method to achieve cardiac and hemodynamic monitoring based on simple, readily available, noninvasive measurements. The concept is based on the personalization of the parameters of the mathematical model of the cardiovascular system according to patient data, and the subsequent derivation of cardiovascular properties in a reverse-engineering approach. Finally, in Part IV, we evaluated existing and novel methods for the assessment of the biomechanical properties of the aorta. We first investigated whether local aortic area compliance, measured as lumen area changes over pulse pressure, is an appropriate index of volume compliance or distensibility when applied to the proximal aorta. In a second analysis, we focused our attention on measures of regional aortic compliance. More specifically, we examined the potential of using compressed-sensing 4D Flow MRI to reliably estimate aortic pulse wave velocity.

EPFL2020

Noninvasive estimation of aortic hemodynamics and cardiac contractility using machine learning

Vasiliki Bikia, Stamatia Zoi Pagoulatou, Georgios Rovas, Nikolaos Stergiopulos

Cardiac and aortic characteristics are crucial for cardiovascular disease detection. However, noninvasive estimation of aortic hemodynamics and cardiac contractility is still challenging. This paper investigated the potential of estimating aortic systolic pressure (aSBP), cardiac output (CO), and end-systolic elastance (E-es) from cuff-pressure and pulse wave velocity (PWV) using regression analysis. The importance of incorporating ejection fraction (EF) as additional input for estimating E-es was also assessed. The models, including Random Forest, Support Vector Regressor, Ridge, Gradient Boosting, were trained/validated using synthetic data (n = 4,018) from an in-silico model. When cuff-pressure and PWV were used as inputs, the normalized-RMSEs/correlations for aSBP, CO, and E-es (best-performing models) were 3.36 +/- 0.74%/0.99, 7.60 +/- 0.68%/0.96, and 16.96 +/- 0.64%/0.37, respectively. Using EF as additional input for estimating E-es significantly improved the predictions (7.00 +/- 0.78%/0.92). Results showed that the use of noninvasive pressure measurements allows estimating aSBP and CO with acceptable accuracy. In contrast, E-es cannot be predicted from pressure signals alone. Addition of the EF information greatly improves the estimated E-es. Accuracy of the model-derived aSBP compared to in-vivo aSBP (n = 783) was very satisfactory (5.26 +/- 2.30%/0.97). Future in-vivo evaluation of CO and E-es estimations remains to be conducted. This novel methodology has potential to improve the noninvasive monitoring of aortic hemodynamics and cardiac contractility.

2020

Role of total arterial compliance and peripheral resistance in the determination of systolic and diastolic aortic pressure

Nikolaos Stergiopulos, Nico Westerhof

The goal of the study was to define the major arterial parameters that determine aortic systolic (Ps) and diastolic (Pd) pressure in the dog. Measured aortic flows were used as input to the two-element windkessel model of the arterial system, with peripheral resistance calculated as mean pressure over mean flow and total arterial compliance calculated from the decay time in diastole. The windkessel model yielded an aortic pressure wave from which we obtained the predicted systolic (Ps, wk) and diastolic (Pd, wk) pressure. These predicted pressures were compared with the measured systolic and diastolic pressures. The measurements and calculations were carried out in 7 dogs in control conditions, during aortic occlusion at four locations (the trifurcation, between trifurcation and diaphragm, the diaphragm and the proximal descending thoracic aorta) and during occlusion of both carotid arteries. Under all conditions studied the predicted systolic and diastolic pressure matched the experimental ones very well: Ps, wk = (1.000 +/- 0.0055) Ps with r = 0.958 and Pd, wk = (1.024 +/- 0.0035) Pd with r = 0.995. Linear regression for pulse pressure gave PPwk = (0.99 +/- 0.016) PP (r = 0.911). We found the accuracy of prediction equally good under control conditions and in presence of aortic or carotid artery occlusions. Multiple regression between pulse pressure and arterial resistance and total arterial compliance yielded a poor regression constant (r2 = 0.19) suggesting that the two arterial parameters alone cannot explain pulse pressure and that flow is an important determinant as well. We conclude that, for a given ejection pattern (aortic flow), two arterial parameters, total arterial resistance and total arterial compliance are sufficient to accurately describe systolic and diastolic aortic pressure.

1999

Hemodynamics of ageing, ventricular-arterial coupling and noninvasive assessment of key hemodynamical and cardiac quantities

Stamatia Zoi Pagoulatou

EPFL2020