In vitro atrial flow dynamics: normal conditions versus atrial fibrillation.

AIMS: The flow dynamics in the atrium is poorly described. The reasons are principally due to the complicated geometry of the cavity and its contractility. The present in vitro study focuses on the description of the flow in the left atrium in normal conditions (NC) and in atrial fibrillation (AF). The final objective is to give leads to understand, from the hemodynamic point of view, complications in case of AF. METHODS AND RESULTS: An atrio-ventricular dual activation system is used to simulate physiological flow in the left atrium. The cavities are compliant and transparent. Velocity measurements are performed with Particle Image Velocimetry. Systolic peak of the pulmonary venous flow is about 0.4 m s(-1) and diastolic peak 0.6 m s(-1) in magnitude. Vortices appear during diastasis and systole and are of normal size and duration. In early and late diastole, the ventricular filling (in NC and AF) and the atrial contraction (in NC only) create a characteristic flow pattern that consists in directed flow towards the mitral valve. In AF an increased resident time (500 ms versus 300 ms) and a slow helical flow pattern (about 0.1 m s(-1)), similar to what is measured using ultrasound echocardiography are observed. CONCLUSION: This study uses atrial flow dynamics description to help understand why thromboembolisms occur in AF.

Assessment of the trackability, flexibility, and conformability of coronary stents: a comparative analysis.

The efficacy and safety of coronary stent implantation depend on the mechanical features of these devices when deployed in atheromatous lesions of various morphologies. We evaluated the trackability, flexibility, and conformability of 17 coronary stents using specific mechanical bench tests. The quantifications used a dynamometer for assessment of trackability (maximal strength) and flexibility (stiffness) and a 3D optical gauging machine for assessment of conformability (distance between stent and arterial wall in a curvature). The maximal strength (measuring the trackability) ranged respectively from 0.24 +/- 0.06 and 0.38 +/- 0.03 N (Seaquest) to 1.31 +/- 0.42 and 1.34 +/- 0.35 N (Carbostent), concerning respectively curvatures of 90 degrees (P < 0.0001) and 135 degrees (P < 0.0001). The stiffness (measuring the flexibility) ranged from 0.53 +/- 0.16 (Seaquest) to 1.28 +/- 0.10 N/mm (NIR Royal; P < 0.0001). The mean distance between stent and external curvature (external conformability) ranged from 0.15 +/- 0.06 mm (S7) to 0.57 +/- 0.4 mm (NIR Royal; P < 0.0001). The mean distance between stent and internal curve (internal conformability) ranged from 0.26 +/- 0.13 (S7) to 0.44 +/- 0.12 mm (S670; P < 0.0001). These results may influence the choice of a particular stent adapted to a specific coronary anatomy.