Clinical applications of intra-cardiac four-dimensional flow cardiovascular magnetic resonance: A systematic review

Abstract

Background: Four-dimensional flow cardiovascular magnetic resonance (4D flow CMR) is an emerging non-invasive imaging technology used to visualise and quantify intra-cardiac blood flow. The aim of this systematic review is to assess the literature on the current clinical applications of intra-cardiac 4D flow CMR.

Methods: A systematic review was conducted to evaluate the literature on the intra-cardiac clinical applications of 4D flow CMR. Structured searches were carried out on Medline, EMBASE and the Cochrane Library in October 2016. A modified Critical Skills Appraisal Programme (CASP) tool was used to objectively assess and score the included studies. Studies were categorised as 'highly clinically applicable' for scores of 67-100%, 'potentially clinically applicable' for 34-66% and 'less clinically applicable' for 0-33%.

Results: Of the 1608 articles screened, 44 studies met eligibility for systematic review. The included literature consisted of 22 (50%) mechanistic studies, 18 (40.9%) pilot studies and 4 (9.1%) diagnostic studies. Based on the modified CASP tool, 27 (62%) studies were 'highly clinically applicable', 9 (20%) were 'potentially clinically applicable' and 8 (18%) were 'less clinically applicable'.

Conclusions: There are many proposed methods for using 4D flow CMR to quantify intra-cardiac flow. The evidence base is mainly mechanistic, featuring single-centred designs. Larger, multi-centre studies are required to validate the proposed techniques and investigate the clinical advantages that 4D flow CMR offers over standard practices. PROSPERO=CRD42016051438.

Keywords: 4D flow CMR; 4D flow MRI; Cardiovascular magnetic resonance; Four-dimensional; Intra-cardiac; Systematic review.

Fig. 1

Overview of study selection process. Panel A = Article screening algorithm. Two reviewers independently screened the titles and abstracts of 936 studies using this system. The number of studies excluded at each stage is shown. Panel B = Flow diagram used for identifying the included studies. The full-texts of the 73 studies that were identified from the screening process were assessed. Of these, 4 (5.5%) were excluded as being irrelevant to the systematic review. The remaining 69 studies underwent citation tracking through the OvidSP databases, as well as manual reference searching. This process identified a further 4 relevant studies for inclusion. Of the final 73 studies included, 44 (60.3%) were full studies, whereas 29 (39.7%) were abstracts only. Flow diagram adapted from Moher et al. . Preferred reporting items for systematic reviews and meta-analyses: The PRISMA Statement. PLOS Medicine 2009. 6 (7):e1000097. The PRISMA Statement is distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium.

Fig. 2

Graphical representations of the percentage of clinical applicability against various study design factors, Panel A = against study type, Panel B = against study year, Panel C = against the 4D flow methods used and Panel D = against intra-cardiac structure. KE = kinetic energy, TKE = turbulent kinetic energy, Haem forces = haemodynamic forces, RVT = retrospective valve tracking, JSLD = jet shear layer detection method, VT = volume tracking, RV = regurgitant volume, LA = left atrium, LV = left ventricle, MV = mitral valve, AV = aortic valve, TV = tricuspid valve, PV = pulmonary valve, RA = right atrium, RV = right ventricle.

Fig. 3

4D flow streamline visualisation and retrospective valve tracking quantification. Panels A and B = Four-dimensional mitral inflow in a patient with mitral regurgitation. Panel A shows the mitral regurgitation (yellow arrow) as well as tricuspid regurgitation (red arrow). Panel B = Mitral valve inflow quantification using retrospective valve-tracking. Panels C and D = Four-dimensional aortic flow in a patient with aortic root dilatation. Panel C shows pathological vortex formation in the ascending aorta (red arrow) as well as aortic regurgitation (yellow arrow). Panel D = Aortic valve flow quantification using retrospective valve-tracking.