Peak flow measurements in patients with severe aortic stenosis: a prospective comparative study between cardiovascular magnetic resonance 2D and 4D flow and transthoracic echocardiography

Advance in the application of 4-dimensional flow MRI in atrial fibrillation

Atrial fibrillation (AF) is the most prevalent arrhythmia in world-wild places and is associated with the development of severe secondary complications such as heart failure and stroke. Emerging evidence shows that the modified hemodynamic environment associated with AF can cause altered flow patterns in left atrial and even systemic blood associated with left atrial appendage thrombosis. Recent advances in magnetic resonance imaging (MRI) allow for the comprehensive visualization and quantification of in vivo aortic flow pattern dynamics. In particular, the technique of 4- dimensional flow MRI (4D flow MRI) offers the opportunity to derive advanced hemodynamic measures such as velocity, vortex, endothelial cell activation potential, and kinetic energy. This review introduces 4D flow MRI for blood flow visualization and quantification of hemodynamic metrics in the setting of AF, with a focus on AF and associated secondary complications.

Moderate Aortic Stenosis-Advanced Imaging, Risk Assessment, and Treatment Strategies

Moderate aortic stenosis is increasingly recognized as a disease entity with poor prognosis. Diagnosis of moderate aortic stenosis may be complemented by laboratory tests and advanced imaging techniques focused at detecting signs of cardiac damage such as increase of cardiac enzymes (N-terminal pro-B-type Natriuretic Peptide, troponin), left ventricular remodeling (hypertrophy, reduced left ventricular ejection fraction), or myocardial fibrosis. Therapy should include guideline-directed optimal medical therapy for heart failure. Patients with signs of cardiac damage may benefit from early intervention, which is the focus of several ongoing randomized controlled trials. As yet, no evidence-based therapy exists to halt the progression of aortic valve calcification.

Thoracic aorta injury detected by 4D flow MRI predicts subsequent main adverse cardiovascular events in breast cancer patients receiving anthracyclines: A longitudinal study

PURPOSE

To investigate longitudinal thoracic aorta injury using 3-dimensional phase-contrast magnetic resonance imaging (4D flow MRI) parameters and to evaluate their value for predicting the subsequent main adverse cardiovascular events (MACEs) in breast cancer patients receiving anthracyclines.

METHODS

Between July 2020 and July 2021, eighty-eight female participants with breast cancer scheduled to receive anthracyclines with or without trastuzumab prospectively enrolled. Each subjects underwent 4D flow MRI at baseline, 3 and 6 months in relation to baseline. The diameter, peak velocity (Vpeak), wall shear stress (WSS), pulse wave velocity (PWV), energy loss (EL) and pressure gradient (PG) of thoracic aorta were measured. The association between these parameters and subsequent MACEs was performed by Cox proportional hazard models.

RESULTS

Ten participants had subsequently MACEs. The Vpeak and PG gradually decreased and the WSS, PWV and EL progressively increased at 3 and 6 months compared with baseline. Adjusted multivariable analysis showed that the WSS of the proximal, mid- and distal ascending aorta [HR, 1.314 (95% confidence interval (CI): 1.003, 1.898)], [HR, 1.320 (95% CI: 1.002, 1.801)] and [HR, 1.322 (95% CI: 1.001, 1.805)] and PWV of ascending aorta [HR, 2.223 (95% CI: 1.010, 4.653)] at 3 months were associated with subsequent MACEs. Combined WSS and PWV of ascending aorta at 3 months yielded the highest AUC (0.912) for predicting subsequent MACEs.

CONCLUSION

Combined WSS and PWV of ascending aorta at 3 months is helpful for predicting the subsequent MACEs in breast cancer patients treated by anthracyclines.

Quantitative 4D flow MRI-derived thoracic aortic normal values of 2D flow MRI parameters in healthy volunteers

PURPOSE

 To utilize 4 D flow MRI to acquire normal values of "conventional 2 D flow MRI parameters" in healthy volunteers in order to replace multiple single 2 D flow measurements with a single 4 D flow acquisition.

MATERIALS AND METHODS

 A kt-GRAPPA accelerated 4 D flow sequence was used. Flow volumes were assessed by forward (FFV), backward (BFV), and net flow volumes (NFV) [ml/heartbeat] and flow velocities by axial (VAX) and absolute velocity (VABS) [m/s] in 116 volunteers (58 females, 43 ± 13 years). The aortic regurgitant fraction (RF) was calculated.

RESULTS

 The sex-neutral mean FFV, BFV, NFV, and RF in the ascending aorta were 93.5 ± 14.8, 3.6 ± 2.8, 89.9 ± 0.6 ml/heartbeat, and 3.9 ± 2.9 %, respectively. Significantly higher values were seen in males regarding FFV, BFV, NFV and RF, but there was no sex dependency regarding VAX and VABS. The mean maximum VAX was lower (1.01 ± 0.31 m/s) than VABS (1.23 ± 0.35 m/s). We were able to determine normal ranges for all intended parameters.

CONCLUSION

 This study provides quantitative 4 D flow-derived thoracic aortic normal values of 2 D flow parameters in healthy volunteers. FFV, BFV, NFV, and VAX did not differ significantly from single 2 D flow acquisitions and could therefore replace time-consuming multiple single 2 D flow acquisitions. VABS should not be used interchangeably.

KEY POINTS

  · 4 D flow MRI can be used to replace 2 D flow MRI measurements.. · The parameter absolute velocities can be assessed by 4 D flow MRI.. · There are sex-dependent differences regarding forward, backward, net aortic blood flow and the aortic valve regurgitant fraction..

Is there a role for cardiovascular magnetic resonance imaging in the assessment of biological aortic valves?

Patients with biological aortic valves (following either surgical aortic valve replacement [SAVR] or trans catheter aortic valve implantation [TAVI]) require lifelong follow-up with an imaging modality to assess prosthetic valve function and dysfunction. Echocardiography is currently the first-line imaging modality to assess biological aortic valves. In this review, we discuss the potential role of cardiac magnetic resonance imaging (CMR) as an additional imaging modality in situations of inconclusive or equivocal echocardiography. Planimetry of the prosthetic orifice can theoretically be measured, as well as the effective orifice area, with potential limitations, such as CMR valve-related artefacts and calcifications in degenerated prostheses. The true benefit of CMR is its ability to accurately quantify aortic regurgitation (paravalvular and intra-valvular) with a direct and reproducible method independent of regurgitant jet morphology to accurately assess reverse remodelling and non-invasively detect focal and interstitial diffuse myocardial fibrosis. Following SAVR or TAVI for aortic stenosis, interstitial diffuse fibrosis can regress, accompanied by structural and functional improvement that CMR can accurately assess.

Multi-modality imaging in aortic stenosis: an EACVI clinical consensus document

In this EACVI clinical scientific update, we will explore the current use of multi-modality imaging in the diagnosis, risk stratification, and follow-up of patients with aortic stenosis, with a particular focus on recent developments and future directions. Echocardiography is and will likely remain the key method of diagnosis and surveillance of aortic stenosis providing detailed assessments of valve haemodynamics and the cardiac remodelling response. Computed tomography (CT) is already widely used in the planning of transcutaneous aortic valve implantation. We anticipate its increased use as an anatomical adjudicator to clarify disease severity in patients with discordant echocardiographic measurements. CT calcium scoring is currently used for this purpose; however, contrast CT techniques are emerging that allow identification of both calcific and fibrotic valve thickening. Additionally, improved assessments of myocardial decompensation with echocardiography, cardiac magnetic resonance, and CT will become more commonplace in our routine assessment of aortic stenosis. Underpinning all of this will be widespread application of artificial intelligence. In combination, we believe this new era of multi-modality imaging in aortic stenosis will improve the diagnosis, follow-up, and timing of intervention in aortic stenosis as well as potentially accelerate the development of the novel pharmacological treatments required for this disease.

4D Flow Versus 2D Phase Contrast MRI in Populations With Bi- and Tricuspid Aortic Valves

AIM

To compare 4D flow magnetic resonance imaging (MRI) and 2D phase contrast (PC) MRI when evaluating bicuspid (BAV) and tricuspid (TAV) aortic valves.

MATERIALS AND METHODS

A total of 83 subjects (35 BAV, 48 TAV) were explored with 4D flow and 2D PC MRI. Systolic peak velocity, peak flow and regurgitation fraction were analysed at two pre-defined aortic levels (aortic root, mid-tubular). Furthermore, the two methods of 4D flow analysis (Heart and Artery) were compared.

RESULTS

Correlation between the 2D PC MRI and 4D flow MRI derived parameters ranged from moderate (R=0.58) to high (R=0.90). 4D flow MRI yielded significantly higher peak velocities in the tubular aorta in both groups. Regarding the aortic root, peak velocities were significantly higher in the TAV group with 4D flow MRI, but in the BAV group 4D flow MRI yielded non-significantly lower values. Findings on peak flow differences between the two modalities followed the same pattern as the differences in peak velocities. 4D flow MRI derived regurgitation fraction values were lower in both locations in both groups. Interobserver agreement for different 4D flow MRI acquired parameters varied from poor (ICC=0.07) to excellent (ICC=1.0) in the aortic root, and it was excellent in the tubular aorta (ICC=0.8-1.0).

CONCLUSION

4D flow MRI seems to be accurate in comparison to 2D PC MRI in normal aortic valves and in BAV with mild to moderate stenosis. However, the varying interobserver reproducibility and impaired accuracy at higher flow velocities should be taken into account in clinical practice when using the 4D flow method.

The role of 4-dimensional flow in the assessment of bicuspid aortic valve and its valvulo-aortopathies

Bicuspid aortic valve is the most common congenital cardiac malformation and the leading cause of aortopathy and aortic stenosis in younger patients. Aortic wall remodelling secondary to altered haemodynamic flow patterns, changes in peak velocity, and wall shear stress may be implicated in the development of aortopathy in the presence of bicuspid aortic valve and dysfunction. Assessment of these parameters as potential predictors of disease severity and progression is thus desirable. The anatomic and functional information acquired from 4D flow MRI can allow simultaneous visualisation and quantification of the pathological geometric and haemodynamic changes of the aorta. We review the current clinical utility of haemodynamic quantities including velocity, wall sheer stress and energy losses, as well as visual descriptors such as vorticity and helicity, and flow direction in assessing the aortic valve and associated aortopathies.

Kat-ARC accelerated 4D flow CMR: clinical validation for transvalvular flow and peak velocity assessment

BACKGROUND

To validate the k-adaptive-t autocalibrating reconstruction for Cartesian sampling (kat-ARC), an exclusive sparse reconstruction technique for four-dimensional (4D) flow cardiac magnetic resonance (CMR) using conservation of mass principle applied to transvalvular flow.

METHODS

This observational retrospective study (2020/21-075) was approved by the local ethics committee at the University of East Anglia. Consent was waived. Thirty-five patients who had a clinical CMR scan were included. CMR protocol included cine and 4D flow using Kat-ARC acceleration factor 6. No respiratory navigation was applied. For validation, the agreement between mitral net flow (MNF) and the aortic net flow (ANF) was investigated. Additionally, we checked the agreement between peak aortic valve velocity derived by 4D flow and that derived by continuous-wave Doppler echocardiography in 20 patients.

RESULTS

The median age of our patient population was 63 years (interquartile range [IQR] 54-73), and 18/35 (51%) were male. Seventeen (49%) patients had mitral regurgitation, and seven (20%) patients had aortic regurgitation. Mean acquisition time was 8 ± 4 min. MNF and ANF were comparable: 60 mL (51-78) versus 63 mL (57-77), p = 0.310). There was an association between MNF and ANF (rho = 0.58, p < 0.001). Peak aortic valve velocity by Doppler and 4D flow were comparable (1.40 m/s, [1.30-1.75] versus 1.46 m/s [1.25-2.11], p = 0.602) and also correlated with each other (rho = 0.77, p < 0.001).

CONCLUSIONS

Kat-ARC accelerated 4D flow CMR quantified transvalvular flow in accordance with the conservation of mass principle and is primed for clinical translation.

Validation of aortic valve pressure gradient quantification using semi-automated 4D flow CMR pipeline

OBJECTIVE

Doppler echocardiographic aortic valve peak velocity and peak pressure gradient assessment across the aortic valve (AV) is the mainstay for diagnosing aortic stenosis. Four-dimensional flow cardiovascular magnetic resonance (4D flow CMR) is emerging as a valuable diagnostic tool for estimating the peak pressure drop across the aortic valve, but assessment remains cumbersome. We aimed to validate a novel semi-automated pipeline 4D flow CMR method of assessing peak aortic value pressure gradient (AVPG) using the commercially available software solution, CAAS MR Solutions, against invasive angiographic methods.

RESULTS

We enrolled 11 patients with severe AS on echocardiography from the EurValve programme. All patients had pre-intervention doppler echocardiography, invasive cardiac catheterisation with peak pressure drop assessment across the AV and 4D flow CMR. The peak AVPG was 51.9 ± 35.2 mmHg using the invasive pressure drop method and 52.2 ± 29.2 mmHg for the 4D flow CMR method (semi-automated pipeline), with good correlation between the two methods (r = 0.70, p = 0.017). Assessment of AVPG by 4D flow CMR using the novel semi-automated pipeline method shows excellent agreement to invasive assessment when compared to doppler-based methods and advocate for its use as complementary to echocardiography.