Effect of heart rate on hemodynamics in patient-specific intracranial aneurysms: An in vitro study

The rupture of an intracranial aneurysm (IA) has been linked to local hemodynamic environments, but it remains unclear how transient physiological states such as elevated heart rate modulate those environments, and whether different aneurysm geometries respond similarly. Here, we used volumetric particle tracking velocimetry (PTV) to measure 3D velocity fields in two patient-specific IA phantoms, a right middle cerebral artery (MCA) aneurysm and a left vertebral artery (LVA) aneurysm, under three heart rates representative of rest (60 bpm), active movement (100 bpm), and exercise (137 bpm). From these measurements, we quantified coherent structures, turbulent kinetic energy (TKE), wall shear stress (WSS), and oscillatory shear index (OSI). Increasing heart rate did not simply increase peak inflow; it altered the temporal organization of the flow. In the MCA aneurysm, higher heart rates produced a stronger, more anchored intra-saccular vortex and elevated coherent-structure strength and TKE that persisted into mid- and end-diastole, along with broader spatial coverage of elevated WSS that remained high beyond peak systole. The LVA aneurysm exhibited a more muted response, with minimal changes in streamline topology and WSS across heart rates. These results show that heart rate can drive prolonged high-shear, high-energy loading within the cardiac cycle, but that this amplification is morphology-dependent and non-monotonic rather than universal.