CARD27: The Effect of Permissive Hypertension on Cerebral Perfusion in VAD Patients with Embolic Stroke

Abstract

Study: This study aims to investigate the effect of permissive hypertension, a deliberate rise in Mean Arterial Pressure (MAP), on cerebral perfusion in Left Ventricular Assist Device (LVAD) patients with embolic stroke. Methods: A previously published Lumped Parameter Model (LPM) of the human circulation, including pulmonary and systemic circulation, as well as all four cardiac chambers and an LVAD, is divided into circulation of the upper and lower body. The upper circulation is further divided into extracranial and intracranial vessels to study brain perfusion as a function of MAP, as well as peripheral and intracranial resistance. Actual LVAD H-Q characteristic curves model the instantaneous LVAD response to a rise in MAP and the differential increase in resistance between the intracranial region suffering a stroke and the remaining circulation. The resulting changes in intracranial flow rate as MAP increases and vascular resistance is altered are analyzed. Increased resistance in intracranial vasculature is incorporated into a model of a typical embolic stroke, and its influence on cerebral perfusion is studied for a range of LVAD speeds and MAP values. Results: In LVAD patients with embolic stroke, intracranial flow significantly decreases as MAP is allowed to rise. These findings are robust at any LVAD speed, consistent with a significant reduction in LVAD flow with increased afterload. This counterintuitive result of permissive hypertension in LVAD patients is captured by the LPM model of embolic stroke, whereby the increase in intracranial resistance decreases cerebral perfusion even further via a decrease in total cardiac output associated with the increase in MAP. Third-generation LVADs are known to be afterload sensitive. Our results show that a mere increase in MAP from 70 to 80 mmHg decreases cerebral blood flow by a commensurate 15%, thus increasing infarct size, which is quite deleterious (see Fig. 1). Our study confirms there is no role for permissive hypertension in LVAD patients with embolic stroke. Figure 1. Cranial flow rate (Qcranial) as a function of MAP for no embolism (purple) and embolism (teal) cases and for 2400 RPM (circles) and 2800 RPM (squares) LVAD speeds.