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Modelling blood flow in the circle of Willis in continuous flow left ventricular assist devices: possible relevance
Srinivasan Krishna1, Komarakshi Balakrishnan2, Ramaratnam Krishna Kumar1
1Department of Engineering Design, Indian Institute of Technology Madras, Chennai, India.
Insights
Continuous flow left ventricular assist devices (CFLVADs) can cause hypertension and strokes. Adding pulsatility to CFLVAD flow may reduce blood pressure and stroke risk, especially with certain circle of Willis variations.
Area of Science:
- Biomedical Engineering
- Cardiovascular Physiology
- Neuroscience
Background:
- Continuous flow left ventricular assist devices (CFLVADs) are vital for heart failure treatment but are linked to adverse events like strokes.
- Hypertension is a common comorbidity in CFLVAD patients and a significant stroke risk factor.
- The relationship between CFLVAD hemodynamics, hypertension, and cerebral blood flow, particularly concerning circle of Willis anatomy, requires further investigation.
Purpose of the Study:
- To investigate the physical factors contributing to hypertension in CFLVAD patients.
- To determine if anatomical variations in the circle of Willis influence stroke risk in CFLVAD recipients.
- To explore the impact of pulsatile versus non-pulsatile flow on cerebral hemodynamics.
Main Methods:
- Utilized a one-dimensional blood flow model incorporating wave propagation and reflections.
- Analyzed cerebral circulation dynamics under both pulsatile and non-pulsatile CFLVAD flow conditions.
- Simulated the effects of anatomical variations, specifically the absence of the posterior communicating artery, on cerebral blood flow and pressure using the ADAN86 arterial network model.
Main Results:
- Non-pulsatile CFLVAD flow resulted in significantly higher mean arterial pressure compared to pulsatile flow.
- Increasing pulsatility in CFLVAD flow progressively decreased mean arterial pressure.
- The absence of the posterior communicating artery alone did not affect middle cerebral artery flow or pressure, but significantly reduced them when combined with ipsilateral carotid artery occlusion.
Conclusions:
- Incorporating physiological pulsatility into CFLVADs offers potential clinical benefits, including reduced blood pressure, and consequently, lower risks of stroke, pump thrombosis, GI bleeds, and aortic incompetence.
- Patient-specific anatomical variations of the circle of Willis, such as the absence of the posterior communicating artery, can critically impact regional cerebral perfusion under specific hemodynamic conditions.
- These findings highlight the importance of considering both device-generated hemodynamics and patient-specific cerebrovascular anatomy to mitigate adverse events in CFLVAD therapy.
Purpose:
Despite significant improvements in the design and performance of continuous flow left ventricular assist devices (CFLVADs), one of the most important reasons hampering further penetration of this technology is the occurrence of adverse events, especially strokes. One of the well-known risk factors for strokes is hypertension which is particularly common in patients undergoing a CFLVAD implant. While the device is implanted in the heart, strokes happen due to pathology in the brain and we hypothesised that modelling the blood flow in the circle of Willis might shed light on the causation of strokes in this situation.The aim of the study was two-fold:1. What is the reason for hypertension in CFLVADs? Are there physical factors at play, besides neurohumoral mechanisms?2. Do anatomical factors in the circle of Willis play a role in the causation of strokes in these patients?
Methods:
The circle of Willis is often incomplete and has a number of anatomical variations, the commonest being the absence of the posterior communicating artery. Hypertension is common after CFLVAD implantation and is also a well-known risk factor for strokes. We examined the blood pressure in the cerebral circulation with pulsatile and non-pulsatile flow for identical conditions and the effect of the absence of the posterior communicating artery on regional cerebral blood flow and pressure. One-dimensional blood flow model was used, taking into account wave propagation and reflections and physiological data obtained from anatomically detailed arterial network (ADAN86) which has data from 86 arteries including detailed cerebral network.
Results:
The mean arterial pressure was significantly higher in the non-pulsatile blood flow of CFLVADs compared to pulsatile flow, for identical conditions, across all arteries. With increasing imparted pulsatility to CFLVAD flow, the mean arterial pressure progressively decreased. Isolated absence of the posterior communicating artery had no effect on the flow as well as pressure in the middle cerebral artery. However, when combined with the absence of flow in the ipsilateral carotid artery, the flow as well as the pressure decreased very significantly in both continuous and pulsatile flow situations.
Conclusions:
Physiologically significant pulsatility in CFLVADs can have important clinical advantages in lowering of blood pressure which can lead to lower incidence of strokes, pump thrombosis, gastrointestinal (GI) bleeds, and aortic incompetence. Patient-specific anatomical variations in the circle of Willis, especially the absence of the posterior communicating artery, can have important consequences in regional cerebral perfusion under some circumstances.
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