Review on Electrical Motor and Pump Assemblies in Ventricular Assist Devices & Total Artificial Hearts

Author Name(s): R. Basanth, Anil K. Puppala
Author Email: basanth246@gmail.com

Abstract

Pump and motor assembly plays a vital role in the design of the Ventricular Assist Devices (VAD) & Total Artificial Hearts (TAH). Heart’s pulsatile blood flow was first mimicked by pulsatile flow devices. However, due to the compact sizing of the continuous flow devices, have shown significant decrease in the mortality rate. Pulsatile and continuous flow devices differ in their motors and drive systems. This paper presents a review of different motor structures that were used in both the systems.

Introduction

HEART disease is one of the major cause of death. Because of less availability of donor hearts, developments and advancements in mechanical circulatory system (Ventricular Assist Devices – VADs, Total Artificial Hearts -TAHs) is going on from past 50 to 60 years[1][2].  Importance of Mechanical Circulatory System (MCS) has increased to enhance or replace myocardial performance. A mile stone in artificial organ development arose in 1943 [3]. The quest for an artificial heart started in 1957. The field of (MCS) was first introduced in 1964 [4][5]. The Patients receiving a mechanical circulatory support device (MCSD) place their lives in the hands of the engineers who design the MCSDs and the physicians who manage the MCSDs [6]. Due to shortages in donor organ availability, advanced heart-failure patients are at high risk  often leading to death while awaiting transplantation, this motivates the engineers to develop MCSDs. Statistics on mortaility because of heart diseases is shown in Table 1, indicates that there’re will be a 127% and 115% increase in the mortaility in India in Men and women respectively.[7]

The primary or initially artificial hearts were a great extent mechanical devices, these devices were extremely unwieldy, electrical power is given to implantable devices through outer pneumatic cables.  These are introduced with pulsatile flow innovation. These devices are problematic as little exhaustion splits which forms in bladder walls, finally they leads to premature death of patient [8]. The pumps lifetime with this type of technology is about one to two years only.  By considering these issues, the biomedical group investigated for elective approach, and the new designs are in minimized structure and mechanically reliable design, as opposed to depending on to a largely mechanical devices with their characteristic weakness to weariness disappointments.

Conclusion

Continuous flow VADs (CFVADs) are smaller due to avoiding of larger mechanical elements, and also CFVADs are more durable, reliable than pulsatile flow VADs (PFVADs) [29]. However, CFVADs produce continuous-flow (CF) and diminished pulsatility systemically. pulsatile flow is the basic nature of human heart. In view of these perceptions, there is at present an enthusiasm for creating control techniques for CFVADs as a method to generate a pulse pressure (PP) [11]. HeartMate 3 (St. Jude Medical Inc.) is a smaller profile, fully magnetically levitated centrifugal pump that is undergoing an IDE trial in the USA (Momentum 3 IDE Trial) and is already approved for clinical use in European Union. The pump incorporates artificial pulse technology, which may reduce some of the complications that are attributed to lack of adequate pulse pressure in patients supported with current centrifugal pumps [17]. And it is required to improve the performance of electromagnet bearing system.

Newer devices should have to overcome the current disadvantages of the TAHs and VADs which are:

  1. Bulky and may not fit in many patients in need.
  2. Patients are tethered to the driver (Cardiowest TAH) which interferes with quality of life.
  3. If considered for destination therapy, durability is not illustrated.
  4. Thromboembolism, infections are secondary complications.

5.Quiet inconvenience from sound-related unsettling influences.

  1. Lack of pressure flow relationship that mimics native heart to adjust for varying loading conditions. [30]

The motor which is used in MCSD should be able to achieve pulsatile flow or continues flow.  Motor should be very small size and it have to provide required force to pump the blood. Most motors and pump assemblies reported to achieve the pulsatality are not compact as they require externally placed drive. Implantable drives would lead to infection. Compact motor and pump assemblies without the need for external drive would help a long way in decreaseing the patient’s mortality rate because of Heart failure.

 

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