Post-cardiac arrest brain injury is driven by both global cerebral hypoperfusion and subsequent reperfusion. However, hyperacute blood-based neurobiomarker kinetics after precisely defined (very) low-flow intervals remain poorly characterized. During transcatheter aortic valve implantation (TAVI), rapid ventricular pacing (RVP) induces a transient pulseless ventricular tachycardia, functionally mimicking brief cardiac arrest. In this single-centre, prospective, self-controlled cohort study, adults undergoing TAVI were enrolled. RVP (120-200 bpm) was applied to transiently suppress forward flow. Invasive aortic pressure, common carotid- (CCA) and middle cerebral artery (MCA) flow were recorded continuously. Serum samples were obtained pre-procedure and 20, 65, 110 and 200 minutes after RVP. Neuron specific enolase (NSE), and S100 were measured as neurobiomarkers. In case of the 76 enrolled patients, median cumulative RVP duration was 60 s (IQR 41-92). During RVP, MCA and CCA flow showed a very low-flow state while aortic pressure fell below the presumed autoregulatory threshold. NSE concentrations increased progressively from baseline to 200 minutes (T0: 10.6 [9.1-13.0]; T20: 12.8 [11.6-15.5]; T65: 15.1 [13.0-18.6]; T110: 15.8 [13.8-18.6]; T200: 17.0 [14.2-20.5] µg/L). S100B concentrations showed an inverse U-shaped profile (T0: 0.05 [0.04-0.07]; T20: 0.13 [0.10-0.18]; T65: 0.14 [0.11-0.23]; T110: 0.11 [0.08-0.16]; T200: 0.08 [0.06-0.12] µg/L). No patient developed neurological deficits. Controlled (very) low-flow episodes during TAVI induce measurable, but clinically silent, elevations of NSE and S100. Neurobiomarkers reflects with distinct kinetics on ischaemia and reperfusion following a short, very low-flow cardiac arrest.

Background: Optical coherence tomography angiography (OCTA) provides quantitative metrics of the retinal microvasculature, most prominently vessel density (VD), that are increasingly used as biomarkers in ocular, systemic, and cerebrovascular disease. Because OCTA relies on the detection of flow-related motion contrast, image quality has emerged as a pervasive determinant of these metrics, yet its effect has been reported in fragmentary and non-comparable ways across the literature. Methods: We identified OCTA studies indexed in PubMed that examined the relationship between image quality and quantitative OCTA parameters, and we summarised their methods and findings across the macular, foveal avascular zone, and peripapillary regions and across vascular layers. We integrated directly comparable per-unit scan-quality effects using random-effects meta-analysis and separately synthesized direct cross-sectional Pearson correlations between manufacturer-reported image quality and macular vessel-density outcomes from independent healthy cohorts. Results: Higher image quality was associated with higher measured vessel density in every contributing dataset. On the Optovue scan-quality (SQ, 0–10) scale, superficial macular VD increased by 3.46% (95% CI 1.85–5.07) per SQ unit in controlled signal-attenuation experiments and by covariate-adjusted observational estimates ranging from 0.90% to 2.16% per SQ unit; a combined order-of-magnitude estimate across both estimator types was 1.64% (95% CI 1.15–2.12). Peripapillary estimates were heterogeneous and derived from only two independent cohorts; they were therefore summarised descriptively rather than pooled. Across three independent externally authored healthy cohorts reporting direct cross-sectional Pearson correlations, higher image quality was strongly associated with higher macular vessel-density outcomes (random-effects pooled r = 0.64, 95% CI 0.50–0.75; I² = 49%). Conclusions: Image quality is an important, directional confounder of VD-based OCTA metrics whose magnitude can rival the biological or physiological signal of interest. Platform-appropriate standardisation, transparent reporting, and consideration of image quality in acquisition and analysis are therefore important for the valid interpretation of vessel-density measurements, particularly in functional and longitudinal studies.