Impeller (straight blade) design variations and their influence on the performance of a centrifugal blood pump

INTRODUCTION

The miniaturization of blood pumps has become a trend due to the advantage of easier transplantation, especially for pediatric patients. In small-scale pumps, it is much easier and more cost-efficient to manufacture the impeller with straight blades compared to spiral-profile blades.

METHODS

Straight-blade impeller designs with different blade angles, blade numbers, and impeller flow passage positions are evaluated using the computational fluid dynamics method. Blade angles (θ = 0°, 20°, 30°, and 40°), blade numbers (N = 5, 6, 7, and 8), and three positions of impeller flow passage (referred to as top, middle, and bottom) are selected as the studied parametric values.

RESULTS

The numerical results reveal that with increasing blade angle, the pressure head and the hydraulic efficiency increase, and the average scalar shear stress and the normalized index of hemolysis decrease. The minimum radial force and axial thrust are obtained when θ equals 20°. In addition, the minimum average scalar shear stress and normalized index of hemolysis values are obtained when N = 6, and the maximum values are obtained when N = 5. Regarding the impeller flow passage position, the axial thrust and the stagnation area forming in the impeller eye are reduced as the flow passage height declines.

CONCLUSION

The consideration of a blade angle can greatly improve the performance of blood pumps, although the influence of the blade number is not very easily determined. The bottom position of the impeller flow passage is the best design.

DURABLE MECHANICAL CIRCULATION SUPPORT AS AN ALTERNATIVE TO HEART TRANSPLANTATION

In the review a comparative analysis of the treatment of end-stage chronic heart failure using heart transplantation and durable mechanical circulatory is conducted. It shows the main advantages and limitations of heart transplantation and the prospects of application of durable mechanical circulatory support technology. The main directions of this technology, including two-stage heart transplant (bridge to transplant – BTT), assisted circulation for myocardial recovery (bridge to recovery – BTR) and implantation of an auxiliary pump on a regular basis (destination therapy, DT). 

Ventricular assist device implantation in the elderly

BACKGROUND

Dramatic advances in ventricular assist device (VAD) design and patient management have made mechanical circulatory support an attractive therapeutic option for the growing pool of elderly heart failure patients.

METHODS

A literature review of all relevant studies was performed. No time or language restrictions were imposed, and references of the selected studies were checked for additional relevant citations.

RESULTS

In concordance with the universal trend in mechanical circulatory support, continuous flow devices appear to have particular benefits in the elderly. In addition, the literature suggests that early intervention before the development of cardiogenic shock, important in all patients, is particularly paramount in older patients.

CONCLUSIONS

The ongoing refinement of patient selection, surgical technique, and post-operative care will continue to improve surgical outcomes, and absolute age may become a less pivotal criterion for mechanical circulatory support. However, clear guidelines for the use of mechanical circulatory support in the elderly remain undefined.

Survival in elderly patients supported with continuous flow left ventricular assist device as bridge to transplantation or destination therapy

BACKGROUND

Published data on mechanical circulatory support for elderly patients in continuous flow devices are sparse and suggest relatively poor survival. This study investigated whether LVADs can be implanted in selected patients over the age of 65 years with acceptable survival compared with published outcomes.

METHODS AND RESULTS

A single-center retrospective analysis was conducted in 64 consecutive patients ≥65 years of age implanted with a continuous-flow left ventricular assist device (CF-LVAD) as either bridge to transplantation or destination therapy from August 2005 to January 2012. Baseline laboratory and hemodynamic characteristics and follow-up data were obtained. Median survival was 1,090 days. Survival was 85%, 74%, 55%, and 45% at 6 months and 1, 2, and 3 years, respectively. Our cohort had a baseline mean Seattle Heart Failure Model (SHFM) score of 2.6 ± 0.9. Observed survival was significantly better than SHFM-predicted medical survival. Stratification by age subsets, renal function, SHFM, implantation intention, or etiology did not reveal significant differences in survival. The most common cause of death was sepsis and nonlethalcomplication was bleeding.

CONCLUSIONS

Our experience with patients over the age of 65 receiving CF-LVADs suggests that this group demonstrates excellent survival. Further research is needed to discern the specific criteria for risk stratification for LVAD support in the elderly.

Axial and centrifugal continuous-flow rotary pumps: a translation from pump mechanics to clinical practice

The recent success of continuous-flow circulatory support devices has led to the growing acceptance of these devices as a viable therapeutic option for end-stage heart failure patients who are not responsive to current pharmacologic and electrophysiologic therapies. This article defines and clarifies the major classification of these pumps as axial or centrifugal continuous-flow devices by discussing the difference in their inherent mechanics and describing how these features translate clinically to pump selection and patient management issues. Axial vs centrifugal pump and bearing design, theory of operation, hydrodynamic performance, and current vs flow relationships are discussed. A review of axial vs centrifugal physiology, pre-load and after-load sensitivity, flow pulsatility, and issues related to automatic physiologic control and suction prevention algorithms is offered. Reliability and biocompatibility of the two types of pumps are reviewed from the perspectives of mechanical wear, implant life, hemolysis, and pump deposition. Finally, a glimpse into the future of continuous-flow technologies is presented.

Flow field study comparing design iterations of a 50 cc left ventricular assist device

The Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure (REMATCH) study shows that implanted ventricular assist devices improve survival time and quality of life when used as a permanent therapy in patients who do not qualify for heart transplant. The success of the pulsatile 70 cc stroke volume left ventricular assist device (LVAD) developed by Penn State has led to the development of a 50 cc stroke volume pump for use in patients with smaller chest cavities to benefit a larger patient population. The initial 50 cc pump shows regions of in vivo thrombus formation, which correlate to low wall shear rates within the device. In an in vitro evaluation of three new designs (V-2, V-3, and V-4) of the 50 cc LVAD, identical except for the location and orientation of their outlet ports, particle image velocimetry (PIV) is used to capture planar flow field data within the pumps. V-2 has an outlet port that is located parallel to the inlet. In V-3, the outlet port is rotated away from the inlet port, with the intention of minimizing the amount of fluid turning needed to exit the device. With V-4 the outlet port is moved to the center of the pump to prolong the desirable rotational flow. PIV data were taken at six planar locations within the pump. Although the modifications to the outlet port locations serve their intended purpose, they also introduce unwanted changes in the flow. Poorer wall washing and weaker rotational flow are observed with V-3 and V-4. Although the differences between the devices are subtle, the device that has the most desirable flow characteristics is V-2.

Long-term mechanical circulatory support in 198 patients: largest single-center experience worldwide

During recent years, mechanical circulatory support (MCS) devices have been increasingly used for long-term support. Nevertheless, problems of embolic and bleeding complication, infections, and technical failure still inhibit successful permanent support. We analyzed the courses of 198 patients who were supported for >1 year by 12 different MCS devices. Of the 198 patients, 87 had first-generation MCS devices (pulsatile), 43 second-generation devices (nonpulsatile with standard bearings), and 68 third-generation devices (nonpulsatile with magnetic bearings), implanted between July 1994 and March 2009. The mean time on support of the total group was ∼ 2 years (690 ± 321 [366-1,875] days). Of the first generation, 83 patients (95%) could be discharged; in the second and third group, all patients could be discharged. Rehospitalizations were observed in all patients. Reasons for readmission were coagulation disorders, wound infections, stroke, and technical failure. Seventy-seven patients received heart transplantation, 66 are still receiving support, 53 died, and two patients have been weaned from the device. All types of devices can be used for extended periods of time. Device- and nondevice-related rehospitalizations were observed in all three groups of patients. Close outpatient monitoring and support are crucial to ensure good long-term results.