Haemodynamic significance of extrinsic outflow graft stenoses during HeartMate 3™ therapy.

Aims: The HeartMate 3 (HM3) implantable left ventricular assist device connects the left ventricle apex to the aorta via an outflow graft. Extrinsic obstruction of the graft (eOGO) is associated with serious morbidity and mortality and recently led to a Food and Drug Administration Class 1 device recall of HM3. This study aimed to provide a better understanding of the haemodynamic impact of extrinsic stenoses. Methods and results: Computed tomography (CT) images of two retrospectively identified patients with eOGO (29 and 36% decrease in cross-sectional area, respectively, by radiological evaluation) were acquired with a novel photon-counting CT system. Numerical evaluations of haemodynamics were conducted using a high-fidelity 3D computational fluid dynamics approach on both the patient-specific graft geometries and in two virtually augmented stenotic severities and three device flows. Visual analysis identified increased velocity, pressure, and turbulent flow in the outer anterior curvature of the outflow graft; however, changes in graft pressure gradients were slight (1-9 mmHg) across the range of stenosis severities and flow rates tested. Conclusion: Evidence of eOGO during HM3 support and the recent device recall can provoke clinical apprehension and interventions. The haemodynamic impact of a stenosis detected visually or by quantification of cross-sectional area reduction may be difficult to predict and easily overestimated. This numerical study suggests that, for clinically encountered flow rates and stenosis severities below 61% in cross-sectional area decrease, eOGO may have low haemodynamic impact. This suggests that patients without symptoms or signs consistent with haemodynamically significant obstruction might be managed expectantly.

Optimization of photon counting CT for cardiac imaging in patients with left ventricular assist devices: An in-depth assessment of metal artifacts.

PURPOSE: Photon counting CT (PCCT) holds promise for mitigating metal artifacts and can produce virtual mono-energetic images (VMI), while maintaining temporal resolution, making it a valuable tool for characterizing the heart. This study aimed to evaluate and optimize PCCT for cardiac imaging in patients during left ventricular assistance device (LVAD) therapy by conducting an in-depth objective assessment of metal artifacts and visual grading. METHODS: Various scan and reconstruction settings were tested on a phantom and further evaluated on a patient acquisition to identify the optimal protocol settings. The phantom comprised an empty thoracic cavity, supplemented with heart and lungs from a cadaveric lamb. The heart was implanted with an LVAD (HeartMate 3) and iodine contrast. Scans were performed on a PCCT (NAEOTOM Alpha, Siemens Healthcare). Metal artifacts were assessed by three objective methods: Hounsfield units (HU)/SD measurements (DiffHU and SDARTIFACT), Fourier analysis (AmplitudeLowFreq), and depicted LVAD volume in the images (BloomVol). Radiologists graded metal artifacts and the diagnostic interpretability in the LVAD lumen, cardiac tissue, lung tissue, and spinal cord using a 5-point rating scale. Regression and correlation analysis were conducted to determine the assessment method most closely associated with acquisition and reconstruction parameters, as well as the objective method demonstrating the highest correlation with visual grading. RESULTS: Due to blooming artifacts, the LVAD volume fluctuated between 27.0 and 92.7 cm3. This variance was primarily influenced by kVp, kernel, keV, and iMAR (R2 = 0.989). Radiologists favored pacemaker iMAR, 3 mm slice thickness, and T3D keV and kernel Bv56f for minimal metal artifacts in cardiac tissue assessment, and 110 keV and Qr40f for lung tissue interpretation. The model adequacy for DiffHU SDARTIFACT, AmplitueLowFreq, and BloomVol was 0.28, 0.76, 0.29, and 0.99 respectively for phantom data, and 0.95, 0.98, 1.00, and 0.99 for in-vivo data. For in-vivo data, the correlation between visual grading (VGSUM) and DiffHU SDARTIFACT, AmplitueLowFreq, and BloomVol was -0.16, -0.01, -0.48, and -0.40 respectively. CONCLUSION: We found that optimal scan settings for LVAD imaging involved using 120 kVp and IQ level 80. Employing T3D with pacemaker iMAR, the sharpest allowed vascular kernel (Bv56f), and VMI at 110 keV with kernel Qr40 yields images suitable for cardiac imaging during LVAD-therapy. Volumetric measurements of the LVAD for determination of the extent of blooming artifacts was shown to be the best objective method to assess metal artifacts.

Echocardiographic haemodynamic monitoring in the context of HeartMate 3™ therapy: a systematic review.

AIMS: While echocardiography remains essential within haemodynamic monitoring of durable mechanical circulatory support, previous echocardiographic guidelines are missing scientific evidence for the novel HeartMate 3™ (HM3) system. Accordingly, this review aims to summarize available echocardiographic evidence including HM3. METHODS AND RESULTS: This systematic review adhered to the PRISMA 2020 guidelines. Searches were conducted during August 2023 across PubMed, Embase, and Google Scholar using specific echocardiographic terms combined with system identifiers. Study quality was assessed using the Newcastle-Ottawa Scale (NOS) for cohort studies and Critical Appraisal Instrument (PCAI) for cross-sectional studies. Nine studies met the inclusion criteria, of which eight cohort studies and one cross-sectional study. Aortic regurgitation (AR) prevalence at approximately 12 months of support exhibited heterogenicity (33.5% (Δ 33%)) in a limited number of studies (n = 3). Several studies (n = 5) demonstrated an increasing prevalence and severity of AR during HM3 support, generating moderate to high level of evidence. One AR study showed a higher cumulative incidence of death and heart failure (HF) readmission compared with those without significant AR, hazard ratio 3.42 (95% CI 1.48-8.76). A second study showed that a worsening AR group had significantly lower survival-free from HF readmission (59% vs. 89%, P = 0.023) with a hazard ratio of 5.18 (95% CI 1.07-25.0), while a third study did not reveal any differences in cardiac-related hospitalizations in the 12 months follow-up or non-cardiac-related hospitalization. Mitral regurgitation (MR) prevalence at approximately 12 months of support exhibited good consistency 15.0% (Δ 0.8%) in both included studies, which did not reveal any significant pattern of changing prevalence over time. Tricuspid regurgitation (TR) prevalence at approximately 12 months of support exhibited fair consistency 28.5% (Δ 8.3%) in a limited number of studies (n = 2); both studies showed a statistically un-confirmed trend of increased TR prevalence over time. The evidence of general prevalence of right ventricular dysfunction (RVD) was insufficient due to lack of studies. CONCLUSIONS: There are few methodologically consistent studies with focus on long-term haemodynamic effects. Aortic regurgitation still seems to be a prevalent and potentially significant finding. The available evidence concerning right heart function is limited despite clinical relevance and potential prognostic value. Potential interventricular and haemodynamic interplay are identified as a white field for future research.

Enhancing students' understanding of cardiac physiology by using 4D visualization.

Difficulties in achieving knowledge about physiology and anatomy of the beating heart highlight the challenges with more traditional pedagogical methods. Recent research regarding anatomy education has mainly focused on digital three-dimensional models. However, these pedagogical improvements may not be entirely applicable to cardiac anatomy and physiology due to the multidimensional complexity with moving anatomy and complex blood flow. The aim of this study was therefore to evaluate whether high quality time-resolved anatomical images combined with realistic blood flow simulations improve the understanding of cardiac structures and function. Three time-resolved datasets were acquired using time-resolved computed tomography and blood flow was computed using Computational Fluid Dynamics. The anatomical and blood flow information was combined and interactively visualized using volume rendering on an advanced stereo projection system. The setup was tested in interactive lectures for medical students. Ninety-seven students participated. Summative assessment of examinations showed significantly improved mean score (18.1 ± 4.5 vs 20.3 ± 4.9, p = 0.002). This improvement was driven by knowledge regarding myocardial hypertrophy and pressure-velocity differences over a stenotic valve. Additionally, a supplementary formative assessment showed significantly more agreeing answers than disagreeing answers (p < 0.001) when the participants subjectively evaluated the contribution of the visualizations to their education and knowledge. In conclusion, the use of simultaneous visualization of time-resolved anatomy data and simulated blood flow improved medical students' results, with a particular effect on understanding of cardiac physiology and these simulations may be useful educational tools for teaching complex anatomical and physiological concepts.