Strokes in LVADS. Insights from Modelling Flow in the Circle of Willis

Abstract

Purpose Strokes are a serious complication of LVADs and are especially known to occur with hypertension. Hypoperfusion of the innominate artery has been described in LVADS, especially in smaller diameter outflow grafts. (1) The normal circle of Willis is often incomplete and Hypoplasia of the posterior communicating artery is a common variant. Modelling flow in the circle of Willis may shed light on strokes in LVADS ( 1) Effect of Outflow Graft Size on Flow in the Aortic Arch and Cerebral Blood Flow in Continuous Flow Pumps: Possible Relevance to Strokes.ASAIO 63:2,144-149 Methods The arterial pulse wave propagation model was used to compare pressure and flow in the circle of Willis for 1.Normal pulsatile and nonpulsatile flow at 5 litres per minute 2. varying degrees of pulsatility in LVADS 3.Flow in the right and left cerebral arteries when the right carotid artery is having no flow, with and without a patent right posterior communicating artery Results The mean pressure in all the vessels is significantly higher for a non pulsatile compared to a pulsatile flow . Mean pressures are lower with increasing pulsatility. Absence of Posterior communicating AND Right common carotid artery flow lowered the pressure and flow drastically in the all the Right sided cerebral arteries but not the left. Conclusion Nonpulsatile flow increases the mean pressure in all the vessels including cerebral vessels . Increasing pulsatility attenuates this effect. Anatomical variations in the circle of willis may increase the vulnerability to strokes. Identifying these factors may help in lowering the risk of of strokes and diminition of cognitive function in long term LVAD therapy.