Dynamic causal modelling for functional near-infrared spectroscopy.

Functional near-infrared spectroscopy (fNIRS) is an emerging technique for measuring changes in cerebral hemoglobin concentration via optical absorption changes. Although there is great interest in using fNIRS to study brain connectivity, current methods are unable to infer the directionality of neuronal connections. In this paper, we apply Dynamic Causal Modelling (DCM) to fNIRS data. Specifically, we present a generative model of how observed fNIRS data are caused by interactions among hidden neuronal states. Inversion of this generative model, using an established Bayesian framework (variational Laplace), then enables inference about changes in directed connectivity at the neuronal level. Using experimental data acquired during motor imagery and motor execution tasks, we show that directed (i.e., effective) connectivity from the supplementary motor area to the primary motor cortex is negatively modulated by motor imagery, and this suppressive influence causes reduced activity in the primary motor cortex during motor imagery. These results are consistent with findings of previous functional magnetic resonance imaging (fMRI) studies, suggesting that the proposed method enables one to infer directed interactions in the brain mediated by neuronal dynamics from measurements of optical density changes.

Comparison between transcatheter and surgical prosthetic valve implantation in patients with severe aortic stenosis and reduced left ventricular ejection fraction.

BACKGROUND: Patients with severe aortic stenosis and reduced left ventricular ejection fraction (LVEF) have a poor prognosis with conservative therapy but a high operative mortality when treated surgically. Recently, transcatheter aortic valve implantation (TAVI) has emerged as an alternative to surgical aortic valve replacement (SAVR) for patients considered at high or prohibitive operative risk. The objective of this study was to compare TAVI and SAVR with respect to postoperative recovery of LVEF in patients with severe aortic stenosis and reduced LV systolic function. METHODS AND RESULTS: Echocardiographic data were prospectively collected before and after the procedure in 200 patients undergoing SAVR and 83 patients undergoing TAVI for severe aortic stenosis (aortic valve area ≤1 cm(2)) with reduced LV systolic function (LVEF ≤50%). TAVI patients were significantly older (81±8 versus 70±10 years; P<0.0001) and had more comorbidities compared with SAVR patients. Despite similar baseline LVEF (34±11% versus 34±10%), TAVI patients had better recovery of LVEF compared with SAVR patients (ΔLVEF, 14±15% versus 7±11%; P=0.005). At the 1-year follow-up, 58% of TAVI patients had a normalization of LVEF (>50%) as opposed to 20% in the SAVR group. On multivariable analysis, female gender (P=0.004), lower LVEF at baseline (P=0.005), absence of atrial fibrillation (P=0.01), TAVI (P=0.007), and larger increase in aortic valve area after the procedure (P=0.01) were independently associated with better recovery of LVEF. CONCLUSION: In patients with severe aortic stenosis and depressed LV systolic function, TAVI is associated with better LVEF recovery compared with SAVR. TAVI may provide an interesting alternative to SAVR in patients with depressed LV systolic function considered at high surgical risk.

Right ventricular systolic to diastolic duration ratio: A novel predictor of outcome in adult idiopathic pulmonary arterial hypertension.

BACKGROUND: The systolic to diastolic (SD) duration ratio reflects global RV performance in pulmonary arterial hypertension (PAH) yet limited data exists on its application to adult non-congenital PAH. We measured SD ratios on echocardiogram in idiopathic PAH (IPAH) to establish its response to pulmonary vasodilator therapy and prognostic value at diagnosis and follow up. METHODS: Incident patients with IPAH undergoing echocardiogram, haemodynamic and exercise assessments were identified within our centre between 2005 and 2018. SD ratios were adjusted for heart rate at diagnosis and follow up. RESULTS: In 98 patients at diagnosis, the mean SD ratio was 1.03 ±â€¯0.37 decreasing to 0.85 ±â€¯0.25, p < 0.001 at follow-up echocardiogram performed at a median interval of 9.0 months. The SD ratio at diagnosis correlated weakly with RV basal diameter (r = 0.24, p = 0.04) and 6MWD (r = 0.23, p = 0.04). At follow up, the mean SD ratio was lower in those receiving combination vs monotherapy pulmonary vasodilator treatment (71 ±â€¯25 vs 92 ±â€¯22% baseline respectively, p < 0.001). After a median follow-up of 4.8 years, 3 patients were transplanted and 23 patients died. The SD ratio at diagnosis and follow up predicted an increased risk of death/transplantation (HR 2.41 (1.09-5.29), p = 0.03; HR 5.02 (1.27-19.77), p = 0.02 respectively), retaining its predictive value at diagnosis in bivariate models with 6MWD (HR 2.18 (1.06-4.08)), WHO Functional Class (HR 2.33 (1.04-5.21)) and TAPSE (HR 2.36 (1.07-5.19)), all p < 0.05. CONCLUSIONS: The SD ratio carries prognostic value at diagnosis and follow up in IPAH. Its further evaluation alongside current PAH risk stratification parameters should be considered.

Prevalence and prognostic implication of restenosis or dilatation at the aortic coarctation repair site assessed by cardiovascular MRI in adult patients late after coarctation repair.

BACKGROUND: Cardiovascular magnetic resonance (CMR) is ideal for assessing patients with repaired aortic coarctation (CoA). Little is known on the relation between long-term complications of CoA repair as assessed by CMR and clinical outcome. We examined the prevalence of restenosis and dilatation at the repair site and the long-term outcome in patients with repaired CoA. METHODS AND RESULTS: CMR imaging and clinical data for adult CoA patients (247 patients aged 33.0 ± 12.8 years, 60% male), were analyzed. The diameter of the aorta at the repair site was measured on CMR and its ratio to the aortic diameter at the diaphragm (repair site-diaphragm ratio, RDR) was calculated. Restenosis (RDR≤70%) was present in 31% of patients (and significant in 9% [RDR<50%]), and dilatation (RDR>150%) in 13.0%. A discrete aneurysm at the repair site was observed in 9%. Restenosis was more likely after resection and end-end anastomosis, whereas dilatation after patch repair. Systemic hypertension was present in 69% of patients. Of the hypertensive patients, blood pressure (133 ± 20/73 ± 10 mm Hg) was well controlled in 93% with antihypertensive therapy. Mortality rate over a median length of 5.9 years was low (0.69% per year, 95% CI: 0.33-1.26), but significantly higher than age-matched healthy controls (standardised mortality ratio 2.86, CI 1.43-5.72, p<0.001). CONCLUSION: Restenosis or dilatation at the CoA repair site as assessed by CMR is not uncommon. Medium term survival remains good, however, albeit lower than in the general population. Life-long follow-up and optimal blood pressure control are likely to secure a good longer term outlook in these patients.