Non-Invasive Quantification of Ventricular Contractility, Arterial Elastic Function and Ventriculo-Arterial Coupling from a Single Diagnostic Encounter Using Simultaneous Arterial Tonometry and Magnetic Resonance Imaging

Pulsatile energy consumption as a surrogate marker for vascular afterload improves with time post transcatheter aortic valve replacement in patients with aortic stenosis

The effect of arterial stiffening on elevated pulsatile left ventricular afterload patients with aortic stenosis (AS) is pronounced beyond systemic hypertension. Circulatory afterload pulsatile efficiency (CAPE) is a marker of vascular function, defined as the ratio of steady state energy consumption (SEC) to maintain systemic circulation and pulsatile energy consumption (PEC). Twenty patients aged 80 ± 7 years were assessed at baseline and a median of 60 days post transcatheter aortic valve replacement (TAVR), with pulsatile vascular load calculated using simultaneous radial applanation tonometry derived aortic pressure and cardiac magnetic resonance phase-contrast imaging derived ascending aortic flow. Eight out of 20 patients had a reduction in PEC post TAVR, and the reduction of PEC correlated strongly with the number of days post TAVR (R = 0.62, P < 0.01). Patients assessed within the 100 days of TAVR had a rise in their PEC when compared to baseline (0.19 ± 0.09 vs 0.14 ± 0.08 W, P = 0.04). Baseline PEC correlated moderately with baseline SEC (R = 0.49, P = 0.03), and a high baseline PEC was predictive of post TAVR PEC reduction (R = 0.54, P =0.01). Overall, no significant differences were found between baseline and post TAVR for systolic aortic pressure (131 ± 20 vs 131 ± 20 mmHg), systemic vascular resistance (1894 ± 493 vs 2015 ± 519 dynes.s/cm⁵), aortic valve ejection time (337 ± 22 vs 324 ± 34 ms) or aortic characteristic impedance (120 ± 48 vs 107 ± 41 dynes.s/cm⁵). Improved flow profiles after TAVR likely unmask the true vascular properties by altering ventriculo-valvulo-arterial coupling, leading to downstream vascular remodelling secondary to flow conditioning, and results in eventual improvement of pulsatile afterload as reflected by our proposed index of CAPE.

A new integrative approach to assess aortic stenosis burden and predict objective functional improvement after TAVR

Background

A non-negligible rate of patients undergoing transcatheter aortic valve replacement (TAVR) do not report symptomatic improvement or even die in the short-midterm. We sought to assess the degree of objective functional recovery after TAVR and its prognostic implications and to develop a predictive model.

Methods

In a cohort of patients undergoing TAVR, a prospective evaluation of clinical, anatomical, and physiological parameters was conducted before and after the procedure. These parameters were derived from echocardiography, non-invasive analysis of arterial pulse waves, and cardiac tomography. Objective functional improvement 6 months after TAVR was assessed using a 6-min walk test and nitro-terminal pro-brain natriuretic peptide (NT-proBNP) levels. The derived predictive model was prospectively validated in a different cohort. A clinical follow-up was conducted at 2 years.

Results

Among the 212 patients included, objective functional improvement was observed in 169 patients (80%) and subjective improvement in 187 (88%). Patients with objective functional improvement showed a much lower death rate at 2 years (9% vs. 31% p = 0.0002). Independent predictors of improvement were as follows: mean aortic gradient of ≥40 mmHg, augmentation index₇₅ of ≥45%, the posterior wall thickness of ≤12 mm, and absence of atrial fibrillation. A simple integer-based point score was developed (GAPA score), which showed an area under the curve of 0.81 for the overall cohort and 0.78 for the low-gradient subgroup. In a validation cohort of 216 patients, these values were 0.75 and 0.76, respectively.

Conclusion

A total of 80% of patients experienced objective functional improvement after TAVR, showing a significantly lower 2-year mortality rate. A predictive score was built that showed a good discriminative performance in overall and low-gradient populations.

Arterial stiffness in aortic stenosis - complex clinical and prognostic implications

Arterial stiffness and degenerative aortic stenosis (AoS) are frequently associated leading to a combined valvular and vascular load imposed on the left ventricle (LV). Vascular load consists of a pulsatile load represented by arterial stiffness and a steady load corresponding to vascular resistance. Increased vascular load in AoS has been associated with LV dysfunction and poor prognosis in pre-intervention state, as well as after aortic valve replacement (AVR), suggesting that the evaluation of arterial load in AoS may have clinical benefits. Nevertheless, studies that investigated arterial stiffness in AoS either before or after AVR used various methods of measurement and their results are conflicting. The aim of the present review was to summarize the main pathophysiological mechanisms which may explain the complex valvulo-arterial interplay in AoS and their consequences on LV structure and function on the patients' outcome. Future larger studies are needed to clarify the complex hemodynamic modifications produced by increased vascular load in AoS and its changes after AVR. Prospective evaluation is needed to confirm the prognostic value of arterial stiffness in patients with AoS. Simple, non-invasive, reliable methods which must be validated in AoS still remain to be established before implementing arterial stiffness measurement in patients with AoS in clinical practice.

RBM20, a Therapeutic Target to Alleviate Myocardial Stiffness via Titin Isoforms Switching in HFpEF

Increased myocardial stiffness is critically involved in heart diseases with impaired cardiac compliance, especially heart failure with preserved ejection fraction (HFpEF). Myocardial stiffness mainly derives from cardiomyocyte- and extracellular matrix (ECM)-derived passive stiffness. Titin, a major component of sarcomeres, participates in myocardial passive stiffness and stress-sensitive signaling. The ratio of two titin isoforms, N2BA to N2B, was validated to influence diastolic dysfunction via several pathways. RNA binding motif protein 20 (RBM20) is a well-studied splicing factor of titin, functional deficiency of RBM20 in mice profile improved cardiac compliance and function, which indicated that RBM20 functions as a potential therapeutic target for mitigating myocardial stiffness by modulating titin isoforms. This minor review summarized how RBM20 and other splicing factors modify the titin isoforms ratio, therefore providing a promising target for improving the myocardial compliance of HFpEF.

New Evidence About Aortic Valve Stenosis and Cardiovascular Hemodynamics

Aortic stenosis (AS) is the most common degenerative valvular disease in western word. In patients with severe AS, small changes in aortic valve area can lead to large changes in hemodynamics. The correct understanding of cardiac hemodynamics and its interaction with vascular function is of paramount importance for correct identification of severe AS and to plan effective strategies for its treatment. In the current review with highlight the importance of pressure recovery phenomenon and valvular arterial impedance as novel tools in the evaluation of patients with aortic stenosis.

Ageing, Hypertension and Aortic Valve Stenosis: A Conscious Uncoupling

Aortic valve stenosis (AS) is no longer considered to be a disease of fixed left ventricular (LV) afterload (due to an obstructive valve), but rather, functions as a series circuit with important contributions from both the valve and ageing vasculature. Patients with AS are frequently elderly, with hypertension and a markedly remodelled aorta. The arterial component is sizable, and yet, the contribution of ventricular afterload has been difficult to determine. Arterial stiffening increases the speed of propagation of the blood pressure wave along the central arteries (estimated as the pulse wave velocity), which results in an earlier return of reflected waves. The effect is to augment blood pressure in the proximal aorta during systole, increasing the central pulse pressure and, in turn, placing even greater afterload on the heart. Elevated global LV afterload is known to have adverse consequences on LV remodelling, function and survival in patients with AS. Consequently, there is renewed focus on methods to estimate the relative contributions of local versus global changes in arterial mechanics and valvular haemodynamics in patients with AS. We present a review on existing and upcoming methods to quantify valvulo-arterial impedance and thereby global LV load in patients with AS.

Ageing, hypertension and aortic valve stenosis - Understanding the series circuit using cardiac magnetic resonance and applanation tonometry

BACKGROUND

Aortic stenosis (AS) is no longer considered to be a disease of fixed left ventricular (LV) afterload, but rather, functions as a series circuit, with important contributions from both the valve and vasculature. Patients with AS are typically elderly, with hypertension and a markedly remodelled aorta. The arterial component is sizeable, and yet, quantifying this to-date has been difficult to determine. We compared measurement of aortic pressure, flow and global LV load using a cardiac magnetic resonance (CMR)/applanation tonometry (AT) technique to uncouple ventriculo-arterial (VA) interactions.

METHODS

20 healthy elderly patients and 20 with AS underwent a CMR/AT protocol. CMR provided LV volume and aortic flow simultaneously with AT pressure acquisition. Aortic pressure was derived by transformation of the AT waveform. Systemic vascular resistance (SVR) and global LV load were determined as the relationship of pressure to flow in the frequency domain. Values from both cohorts were compared.

RESULTS

AS patients were older (p ​< ​0.01) albeit with no significant difference in brachial or central aortic pressure. SVR (14228 vs 19906 ​dyne ​s.cm-3; p ​= ​0.02) and load (740 vs 946 ​dyne ​s.cm-3; p ​= ​0.02) were higher in patients with AS, whilst aortic peak flow velocity was lower (38 vs 58 ​cm/s; p ​< ​0.01).

CONCLUSIONS

Quantification of aortic pressure, flow velocity and global LV load using a simultaneous CMR/AT technique is able to demonstrate the progressive effects of hypertension and aortic stiffening with advanced age and valvular stenosis. This technique may help to better identify future patients at risk of VA coupling mismatch after correction of AS.

A novel method to assess valvulo-arterial load in patients with aortic valve stenosis

INTRODUCTION

Ventricular function in elderly patients with aortic stenosis is impeded both by restricted aortic flow and arterial stiffening. A number of patients continue to have exertional intolerance after relief of aortic valvular obstruction due to unrecognized ventriculo-arterial coupling mismatch.

HYPOTHESIS

Quantification of valvulo-arterial load (VAL), using a simultaneous applanation tonometry/cardiac magnetic resonance (CMR) technique, can accurately assess the relative contributions of aortic stiffness and valve gradient in older patients with aortic stenosis.

METHODS

Elderly patients with aortic stenosis underwent a simultaneous applanation tonometry/CMR protocol. CMR provided left ventricular volume and aortic flow simultaneously with radial applanation tonometry pressure acquisition. Central aortic pressure was derived by transformation of the radial applanation tonometry waveform. VAL was determined as the relationship of derived aortic pressure to CMR aortic flow in frequency domain (central illustration).

RESULTS

Twenty patients (age 80 ± 9 years; 12 males; blood pressure 140/75 ± 20 mmHg) with aortic stenosis on transthoracic echocardiogram (16 severe; mean gradient 45 ± 16 mmHg; aortic valve area 0.8 ± 0.2 cm2) were enrolled. Derived aortic pressure and flow waveforms correlated well with invasive data. Increased VAL was significantly associated with advanced age (P = 0.04) and raised SBP (P < 0.01), irrespective of aortic stenosis severity.

CONCLUSION

Difficulties in the measurement and accuracy of ventriculo-arterial coupling means that it is not routinely measured in patients with aortic stenosis. We describe a new noninvasive index that provides an accurate assessment of valvular and arterial load on the left ventricle. VAL may help detect those at risk of ventriculo-arterial coupling mismatch and assist in selection of those most likely to benefit from an invasive procedure.

Impact of Aortic Stenosis on Myofiber Stress: Translational Application of Left Ventricle-Aortic Coupling Simulation

The severity of aortic stenosis (AS) has traditionally been graded by measuring hemodynamic parameters of transvalvular pressure gradient, ejection jet velocity, or estimating valve orifice area. Recent research has highlighted limitations of these criteria at effectively grading AS in presence of left ventricle (LV) dysfunction. We hypothesized that simulations coupling the aorta and LV could provide meaningful insight into myocardial biomechanical derangements that accompany AS. A realistic finite element model of the human heart with a coupled lumped-parameter circulatory system was used to simulate AS. Finite element analysis was performed with Abaqus FEA. An anisotropic hyperelastic model was assigned to LV passive properties, and a time-varying elastance function governed the LV active response. Global LV myofiber peak systolic stress (mean ± standard deviation) was 9.31 ± 10.33 kPa at baseline, 13.13 ± 10.29 kPa for moderate AS, and 16.18 ± 10.59 kPa for severe AS. Mean LV myofiber peak systolic strains were −22.40 ± 8.73%, −22.24 ± 8.91%, and −21.97 ± 9.18%, respectively. Stress was significantly elevated compared to baseline for moderate (p < 0.01) and severe AS (p < 0.001), and when compared to each other (p < 0.01). Ventricular regions that experienced the greatest systolic stress were (severe AS vs. baseline) basal inferior (39.87 vs. 30.02 kPa; p < 0.01), mid-anteroseptal (32.29 vs. 24.79 kPa; p < 0.001), and apex (27.99 vs. 23.52 kPa; p < 0.001). This data serves as a reference for future studies that will incorporate patient-specific ventricular geometries and material parameters, aiming to correlate LV biomechanics to AS severity.