VADs are also called blood pumps, cardiac assist devices, or mechanical circulatory support. The VADs are similar to the mechanical pump in that they can support either the failing left or right ventricle without having to remove the patient’s natural heart. Depending on the individual patient’s condition, the VAD can support either the right ventricle, the left ventricle, or both ventricles at the same time. Whereas an implantable device known as a Total Artificial Heart (TAH) takes over the function of the natural heart and requires the ventricles to be removed before it can be put in place.
Heart Failure
A symptom of chronic heart failure, also known as congestive heart failure (CHF), is the weakening of the cardiac muscles and the ensuing decreased ability to contract. Fatigue and shortness of breath are brought on by a CHF-related inadequate blood supply. Backflow to the heart brought on by insufficient blood flow pressure congests tissues. A condition known as “Edema” can result from this extra fluid swelling the legs, feet, and ankles. Another place where this fluid can build up and result in a blockage is in the lungs.
Hypertension, diabetes, and CHF may all result from coronary artery disease. This illness affects the elderly, according to the US National Hospital Discharge Surveys. Hospitalizations are mostly caused by this factor.
VADs Need
Depending on the severity of the condition, people with CHF have a range of treatment options, including medication, lifestyle modifications, transcatheter procedures, and heart transplants. The best course of therapy for CHF patients is a heart transplant, unfortunately there are not many donors available. While the number of patients tends to rise each year, the supply of donor hearts is essentially stable. Therefore, the discrepancy between the demand for hearts and the supply of accessible hearts from donors may be filled by mechanical circulatory support systems. Whereas, the TAH is most suitable for the patients in the end stages of CHF, for whom transplantation is not possible.
Indication for Use
VADs are referred to as LVAD, RVAD, and BIVAD depending on whether they assist the left ventricle, right ventricle, or both. The ventricular assist devices (VADs) can be used as a bridge-to-recovery (BTR) in the event that myocardial recovery occurs, as a bridge to heart transplantation (BTT), or for the long term use as destination therapy (DT) for patients who need a circulatory support system. As a result, these devices have a wide range of applications in the treatment of a wide variety of heart conditions. The criteria for using such devices depends on the heart conditions and judgments of clinicians.
VADs Types
In general, VADs are categorized according to the features of their outflow, which may be either pulsatile (volume displacement) or non-pulsatile (rotary or continuous). Other methods of categorization are based on the kinds of help that are required, the duration of the application, the therapeutic goal, and the source of the power. The rotary blood pumps are popular in ventricular assist devices (VADs) due to their compact size, ease of implantation, and low infection rates. The following information on rotary VADs is given for your perusal and consideration.
The rotary pump may be divided into two distinct types of pumps: centrifugal pumps and axial flow pumps.
The centrifugal pumps are able to create larger pressures while operating at lower rotating speeds. On the other hand, the axial pump requires higher rotational speeds in order to provide the same pressure difference that is necessary for the desired flow rate. In axial pumps, higher rotating speeds may lead to higher shear stress, which in turn raises the risk of hemolysis. On the other hand, higher rotational speed results in a shorter exposure period due to the pump’s comparably smaller volume, which is beneficial. Because of their slower speeds, centrifugal pumps are beneficial in some applications; however, the major benefits of the axial pump, such as its smaller size and lower power consumption, make these pumps appropriate for implantation in both adult and pediatric applications. Thus, the type of rotary pump application is patient-specific and determined by clinician judgment.
Additionally, scientists have described a brand-new VAD application magnetically levitated device based on a passive magnetic spherical bearing, known as the nutating blood pump or nutating disc pump. Additionally, it demonstrated appropriate hemolysis and thrombosis levels for the projected values of flow rate and wall shear stress. However, more research and technological enhancements are required to got its practical VAD application.
Main Challenges
1. Hemolysis is the process that causes haemoglobin to be released from red blood cells (RBCs) into the plasma. RBCs are the cells that carry haemoglobin. If the quantity of free haemoglobin that is released is more than a specific critical threshold, then it might be harmful to the kidney. It is possible for it to result in the failure of many organs in the worst-case scenario. Shear stress is responsible for the deformation and fragmentation of red blood cells, which leads to the mechanism of hemolysis. The primary cause of hemolysis in the blood pump is sublethal damage to the red blood cells (RBCs), and catastrophic damage may occur when shear rates surpass the certain range.
2.Thrombosis in the blood pumps is a major concern, and researchers and medical experts have been working hard to investigate it. White thrombus and red thrombus are the two most common forms of thrombosis issues that might arise with the blood pumps. When platelets are exposed to shear, they get activated, which leads to the creation of a white thrombus. On the other hand, the formation of a red thrombus is caused by blood that has been allowed to pool. Platelets are subjected to shear stress that is mechanically created, and when this stress is maintained for an extended period of time, it causes thrombus development, platelet aggregation, and platelet deposition.
3.The size of axial blood pump may be further reduced, which will be highly advantageous from the point of view of both implantation and operation. The smaller axial blood pump implant will have a lower power need in comparison to its predecessors due to the pump’s decreased size.
4.It is possible to imitate the pulsatility of a normal heart by modulating the speed of the impeller in such a way that it simulates the continuous rotational velocity of a normal heart. This is something that may be accomplished by including an appropriate speed modulation algorithm into the design of the pump.
5.The design of the blood pump components such as impeller and diffuser can be modified to improve the hydraulic performance, clinical performance and make the blood pump smaller overall.
Future Prospects
The above discussed challenges can be overcome using a computational simulation tool called computational fluid dynamics (CFD). it is an excellent technique for creating VADs since it enables various designs to describe and enhance in-silico performance. Preprocessing, solver, and postprocessing are all included in a CFD study of a computational domain. These are the basic steps, and concerned engineers and researchers are well aware about these things. All these analyses are performed in virtual environments, and many assumptions and constraints are involved during the simulation process. So, to improve the design of blood pumps, a better link between simulation and optimization methodologies is required. The need for the blood pump prototype will increase as new blood pump designs are introduced and computationally modelled. The validation and comparison of thrombosis and hemolysis data with simulation findings and actual computed data on patients and animals will become essential when the simulation procedure is completed.