An early relook identifies high-risk trajectories in ambulatory advanced heart failure

INTRODUCTION

Patients with ambulatory advanced heart failure (HF) are increasingly considered for durable mechanical circulatory support (MCS) and heart transplantation and their effective triage requires careful assessment of the clinical trajectory.

METHODS

REVIVAL, a prospective, observational study, enrolled 400 ambulatory advanced HF patients from 21 MCS/transplant centers in 2015-2016. Study design included a clinical re-assessment of Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) profile within 120 days after enrollment. The prognostic impact of a worsening INTERMACS Profile assigned by the treating physician was assessed at 1 year after the Early Relook.

RESULTS

Early Relook was done in 325 of 400 patients (81%), of whom 24% had a worsened INTERMACS Profile, associated with longer HF history and worse baseline INTERMACS profile, but no difference in baseline LVEF (median 0.20), 6-minute walk, quality of life, or other baseline parameters. Early worsening predicted higher rate of the combined primary endpoint of death, urgent MCS, or urgent transplant by 1 year after Early Relook, (28% vs 15%), with hazard ratio 2.2 (95% CI 1.2- 3.8; p = .006) even after adjusting for baseline INTERMACS Profile and Seattle HF Model score. Deterioration to urgent MCS occurred in 14% vs 5% (p = .006) during the year after Early Relook.

CONCLUSIONS

Early Relook identifies worsening of INTERMACS Profile in a significant population of ambulatory advanced HF, who had worse outcomes over the subsequent year. Early reassessment of ambulatory advanced HF patients should be performed to better define the trajectory of illness and inform triage to advanced therapies.

Predictive Value of Cardiopulmonary Exercise Testing Parameters in Ambulatory Advanced Heart Failure

OBJECTIVES

This study sought to determine cardiopulmonary exercise (CPX) predictors of the combined outcome of durable mechanical circulatory support (MCS), transplantation, or death at 1 year among patients with ambulatory advanced heart failure (HF).

BACKGROUND

Optimal CPX predictors of outcomes in contemporary ambulatory advanced HF patients are unclear.

METHODS

REVIVAL (Registry Evaluation of Vital Information for ventricular assist devices [VADs] in Ambulatory Life) enrolled 400 systolic HF patients, INTERMACS (Interagency Registry for Mechanically Assisted Circulatory Support) profiles 4-7. CPX was performed by 273 subjects 2 ± 1 months after study enrollment. Discriminative power of maximal (peak oxygen consumption [peak VO₂]; VO₂ pulse, circulatory power [CP]; peak systolic blood pressure • peak VO₂], peak end-tidal pressure CO₂ [PEtCO₂], and peak Borg scale score) and submaximal CPX parameters (ventilatory efficiency [VE/VCO₂ slope]; VO₂ at anaerobic threshold [VO₂AT]; and oxygen uptake efficiency slope [OUES]) to predict the composite outcome were assessed by univariate and multivariate Cox regression and Harrell's concordance statistic.

RESULTS

At 1 year, there were 39 events (6 transplants, 15 deaths, 18 MCS implantations). Peak VO₂, VO₂AT, OUES, peak PEtCO₂, and CP were higher in the no-event group (all p < 0.001), whereas VE/VCO₂ slope was lower (p < 0.0001); respiratory exchange ratio was not different. CP (hazard ratio [HR]: 0.89; p = 0.001), VE/VCO₂ slope (HR: 1.05; p = 0.001), and peak Borg scale score (HR: 1.20; p = 0.005) were significant predictors on multivariate analysis (model C-statistic: 0.80).

CONCLUSIONS

Among patients with ambulatory advanced HF, the strongest maximal and submaximal CPX predictor of MCS implantation, transplantation, or death at 1 year were CP and VE/VCO_2, respectively. The patient-reported measure of exercise effort (Borg scale score) contributed substantially to the prediction of outcomes, a surprising and novel finding that warrants further investigation. (Registry Evaluation of Vital Information for VADs in Ambulatory Life [REVIVAL]; NCT01369407).

Impact of Socioeconomic Factors on Patient Desire for Early LVAD Therapy Prior to Inotrope Dependence

BACKGROUND

Worsening heart failure (HF) and health-related quality of life (HRQOL) have been shown to impact the decision to proceed with left ventricular assist device (LVAD) implantation, but little is known about how socioeconomic factors influence expressed patient preference for LVAD.

METHODS AND RESULTS

Ambulatory patients with advanced systolic HF (n=353) reviewed written information about LVAD therapy and completed a brief survey to indicate whether they would want an LVAD to treat their current level of HF. Ordinal logistic regression analyses identified clinical and demographic predictors of LVAD preference. Higher New York Heart Association (NYHA) class, worse HRQOL measured by Kansas City Cardiomyopathy Questionnaire, lower education level, and lower income were significant univariable predictors of patients wanting an LVAD. In the multivariable model, higher NYHA class (OR [odds ratio]: 1.43, CI [confidence interval]: 1.08-1.90, P = .013) and lower income level (OR: 2.10, CI: 1.18 - 3.76, P = .012 for <$40,000 vs >$80,000) remained significantly associated with wanting an LVAD.

CONCLUSION

Among ambulatory patients with advanced systolic HF, treatment preference for LVAD was influenced by level of income independent of HF severity. Understanding the impact of socioeconomic factors on willingness to consider LVAD therapy may help tailor counseling towards individual needs.

Quality of life and treatment preference for ventricular assist device therapy in ambulatory advanced heart failure: A report from the REVIVAL study

BACKGROUND

The Registry Evaluation of Vital Information for Ventricular Assist Devices (VADs) in Ambulatory Life study is a prospective multicenter cohort of 400 ambulatory patients with advanced chronic systolic heart failure (HF). The aim of the study is to better understand disease trajectory and optimal timing of advanced HF therapies. We examined patient health-related quality of life (HRQOL) data collected at enrollment and their association with patient treatment preferences for VAD placement.

METHODS

Baseline assessment of HRQOL included the Kansas City Cardiomyopathy Questionnaire (KCCQ) and the EuroQol EQ-5D-3L Visual Analogue Scale (VAS), along with patient self-assessment of remaining life (PSARL). Descriptive statistics were used to present baseline HRQOL data and Spearman correlation tests to assess the association between KCCQ, VAS, and VAD treatment preference with patient clinical characteristics of interest.

RESULTS

The median age was 60 years, 75% were male, and the median left ventricular ejection fraction was 20%. The median (25th percentile, 75th percentile), baseline KCCQ summary score was 64 (48, 78), VAS score 65 (50, 75), and PSARL 7 years (5, 10). There were statistically significant associations of baseline KCCQ and VAS with New York Heart Association class and Interagency Registry of Mechanically Assisted Circulatory Support profile (p < 0.005 for all comparisons). Baseline KCCQ and VAS revealed a modest association with PSARL (correlation = 0.45 and 0.35, respectively; p < 0.001), and many patients were overly optimistic about their expected survival. VAD treatment preference was associated with KCCQ scores (p < 0.031), but the absolute differences were small. VAD treatment preference was independent of other key clinical characteristics such as subject age, VAS, and PSARL.

CONCLUSIONS

We found a lack of strong association between HRQOL and patient preference for VAD therapy. Better understanding of patients' perceptions of their illness and how this relates to HRQOL outcomes, clinician risk assessment, and patient decision-making is needed. This may in turn allow better guidance toward available HF therapies in this vulnerable population.

Registry Evaluation of Vital Information for VADs in Ambulatory Life (REVIVAL): Rationale, design, baseline characteristics, and inclusion criteria performance

INTRODUCTION

Improved understanding of the clinical course of ambulatory advanced chronic systolic heart failure may improve the provision of appropriate care and is central to the design of clinical trials in this population.

METHODS

Twenty-one implanting ventricular assist device (VAD) centers enrolled 400 subjects in the Registry Evaluation of Vital Information for VADs in Ambulatory Life (REVIVAL), a prospective, observational study in ambulatory, chronic, advanced systolic heart failure, designed to identify a cohort with an approximately 25% 1-year risk of the primary composite outcome of death, urgent transplant, or durable mechanical circulatory support. Inclusion criteria utilized only information collected during routine clinical care. Exclusion criteria identified patients with contraindications to VAD. Study inclusion required at least 1 of 10 high-risk criteria derived from established hospitalization and non-hospitalization markers of increased mortality risk. We evaluated the test performance characteristics of the high-risk criteria.

RESULTS

Data on 373 subjects evaluable for the primary composite outcome at the 1-year visit are presented. Baseline data were consistent with a less advanced cohort than Medical Arm for Mechanically Assisted Circulatory Support or Risk Assessment (MedaMACS) and Comparative Effectiveness of Left Ventricular Assist Device and Medical Management in Ambulatory Heart Failure Patients (ROADMAP). Freedom from the primary composite outcome was 75.9%. Non-hospitalization inclusion criteria identified 89% of patients with events.

CONCLUSIONS

Using routinely obtained clinical information for enrollment, REVIVAL successfully recruited an ambulatory chronic systolic heart failure cohort with an approximately 25% annual risk of the primary composite outcome. Information from this registry will be relevant to the planning of future trials of earlier VAD use and of other interventions in this population.

Current and Future Considerations in the Use of Mechanical Circulatory Support Devices: An Update, 2008–2018

Our review in the 2008 volume of this journal detailed the use of mechanical circulatory support (MCS) for treatment of heart failure (HF). MCS initially utilized bladder-based blood pumps generating pulsatile flow; these pulsatile flow pumps have been supplanted by rotary blood pumps, in which cardiac support is generated via the high-speed rotation of computationally designed blading. Different rotary pump designs have been evaluated for their safety, performance, and efficacy in clinical trials both in the United States and internationally. The reduced size of the rotary pump designs has prompted research and development toward the design of MCS suitable for infants and children. The past decade has witnessed efforts focused on tissue engineering–based therapies for the treatment of HF. This review explores the current state and future opportunities of cardiac support therapies within our larger understanding of the treatment options for HF.

Ambulatory Advanced Heart Failure in Women: A Report From the REVIVAL Registry

OBJECTIVES

This study sought to explore clinical characteristics and outcomes in women and men with ambulatory advanced heart failure (HF).

BACKGROUND

Women have been underrepresented in studies of advanced HF and have an increased mortality on the transplant waiting list and early after mechanical circulatory support (MCS). An increased understanding of the differential burden of HF between women and men is required to inform the use of mechanical circulatory support in ambulatory advanced HF patients.

METHODS

REVIVAL (Registry Evaluation for Vital Information on Ventricular Assist Devices in Ambulatory Life) is a prospective, observational study of 400 outpatients with chronic systolic HF, New York Heart Association functional class II to IV, and 1 additional high-risk feature. Clinical characteristics, quality of life, and functional capacity were compared between women and men, as was a primary composite endpoint of death, durable MCS, or urgent heart transplantation at 1 year.

RESULTS

REVIVAL enrolled 99 women (25% of the cohort) who had similar age, ejection fraction, INTERMACS (Interagency Registry for Mechanically Assisted Circulatory Support) profiles, medication use, and willingness to consider MCS as the men enrolled; however, women reported significantly greater limitations in quality of life with respect to physical limitation, reduced 6-min walk distance, and more frequent symptoms of depression. Nevertheless, 1-year combined risk of death, durable MCS, or urgent transplantation did not differ between women and men (24% vs. 22%; p = 0.94).

CONCLUSIONS

This study represents the largest report to date of women with ambulatory advanced HF receiving contemporary therapies. Systematic elicitation of patient-reported outcome measures uncovered an added burden of HF in women and may be an appropriate target of augmented support and intervention.

Closing in on the PumpKIN Trial of the Jarvik 2015 Ventricular Assist Device

The Infant Jarvik ventricular assist device (VAD; Jarvik Heart, Inc., New York, NY) has been developed to support the circulation of infants and children with advanced heart failure. The first version of the device was determined to have elevated hemolysis under certain conditions. The objective of this work was to determine appropriate modifications to the Infant Jarvik VAD that would result in acceptably low hemolysis levels. In vitro hemolysis testing revealed that hemolysis was related to the shape of the pump blade tips and a critical speed over which hemolysis would occur. Various design modifications were tested and a final design was selected that met the hemolysis performance goal. The new version was named the Jarvik 2015 VAD. Chronic in vivo tests, virtual fit studies, and a series of other performance tests were carried out to assess the device's performance characteristics. In vivo test results revealed acceptable hemolysis levels in a series of animals and virtual fit studies showed that the device would fit into children 8 kg and above, but could fit in smaller children as well. Additional FDA-required testing has been completed and all of the data are being submitted to the FDA so that a clinical trial of the Jarvik 2015 VAD can begin. Development of a Jarvik VAD for use in young children has been challenging for various reasons. However, with the hemolysis issue addressed in the Jarvik 2015 VAD, the device is well-poised for the start of the PumpKIN clinical trial in the near future.

Eighth annual INTERMACS report: Special focus on framing the impact of adverse events

BACKGROUND

The Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) database now includes >20,000 patients from >180 hospitals.

METHODS

The eighth annual report of INTERMACS updates the first decade of patient enrollment.

RESULTS

In the current era, >95% of implants are continuous flow devices. Overall survival continues to remain >80% at 1 year and 70% at 2 years. Review of major adverse events shows minimal advantage for patients with ambulatory heart failure pre-implant. Stroke, major infection, and continued inotrope requirement during the first 3 months have a major effect on subsequent survival.

CONCLUSIONS

Greater application of durable devices to patients with ambulatory heart failure will mandate more effective neutralization or prevention of major adverse events.

Advancing the Science of Myocardial Recovery With Mechanical Circulatory Support: A Working Group of the National, Heart, Lung, and Blood Institute

The medical burden of heart failure (HF) has spurred interest in clinicians and scientists to develop therapies to restore the function of a failing heart. To advance this agenda, the National Heart, Lung, and Blood Institute (NHLBI) convened a Working Group of experts from June 2 to 3, 2016, in Bethesda, Maryland, to develop NHLBI recommendations aimed at advancing the science of cardiac recovery in the setting of mechanical circulatory support (MCS). MCS devices effectively reduce volume and pressure overload that drives the cycle of progressive myocardial dysfunction, thereby triggering structural and functional reverse remodeling. Research in this field could be innovative in many ways, and the Working Group specifically discussed opportunities associated with genome-phenome systems biology approaches; genetic epidemiology; bioinformatics and precision medicine at the population level; advanced imaging modalities, including molecular and metabolic imaging; and the development of minimally invasive surgical and percutaneous bioengineering approaches. These new avenues of investigations could lead to new treatments that target phylogenetically conserved pathways involved in cardiac reparative mechanisms. A central point that emerged from the NHLBI Working Group meeting was that the lessons learned from the MCS investigational setting can be extrapolated to the broader HF population. With the precedents set by the significant effect of studies of other well-controlled and tractable subsets on larger populations, such as the genetic work in both cancer and cardiovascular disease, the work to improve our understanding of cardiac recovery and resilience in MCS patients could be transformational for the greater HF population.

Seventh INTERMACS annual report: 15,000 patients and counting

The seventh annual report of the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) summarizes the first 9 years of patient enrollment. The Registry includes >15,000 patients from 158 participating hospitals. Trends in device strategy, patient profile at implant and survival are presented. Risk factors for mortality with continuous-flow pumps are updated, and the major causes/modes of death are presented. The adverse event burden is compared between eras, and health-related quality of life is reviewed. A detailed analysis of outcomes after mechanical circulatory support for ambulatory heart failure is presented. Recent summary data from PediMACS and MedaMACS is included. With the current continuous-flow devices, survival at 1 and 2 years is 80% and 70%, respectively.

Sixth INTERMACS annual report: a 10,000-patient database

The sixth annual report of the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) summarizes the first 8 years of patient enrollment. The analysis is based on data from >10,000 patients and updates demographics, survival, adverse events and risk factors. Among patients with continuous-flow pumps, actuarial survival continues to be 80% at 1 year and 70% at 2 years. The report features a comparison of two eras of continuous-flow durable devices in the USA in terms of device strategy, patient profiles, adverse event burden, survival and quality of life.

Fifth INTERMACS annual report: risk factor analysis from more than 6,000 mechanical circulatory support patients

The 5th annual report of the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) summarizes and analyzes the first 6 years of patient and data collection. The current analysis includes more than 6000 patients and updated risk factors for continuous flow pumps. Among continuous flow pumps, actuarial survival is 80% at 1 year and 70% at 2 years. Quality of life indicators are generally favorable and adverse event burden will likely influence patient selections of advanced heart failure therapies.

The Fourth INTERMACS Annual Report: 4,000 implants and counting

The Fourth Annual Report of the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) summarizes and analyzes the first 5 years of patient and data collection. With more than 4,000 patients entered into the database, the evolution of pump technology, strategy at implant, and pre-implant patient profiles are chronicled. A risk factor analysis of the entire adult primary implant population is provided, and the recent composition of patient profiles is examined. Current actuarial survival with continuous-flow pumps exceeds 80% at 1 year and 70% at 2 years.

Third INTERMACS Annual Report: the evolution of destination therapy in the United States

The third annual report of the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) provides documentation of the current landscape of durable mechanical circulatory support in the United States. With nearly 3,000 patients entered into the database, the transition to continuous-flow pump technology is evident and dramatic. This report focuses on the rapidly expanding experience with mechanical circulatory support as destination therapy. The current 1-year survival of 75% with continuous-flow destination therapy provides a benchmark for the evolving application of this therapy.

NHLBI's program for VAD therapy for moderately advanced heart failure: the REVIVE-IT pilot trial

BACKGROUND

Ventricular assist devices (VADs) are used to bridge heart failure patients to transplantation, to allow their own hearts to recover, or as permanent ("destination") therapy. To date, the use of VADs has been limited to late-stage heart failure patients because of the associated device risks. In 2008, a National Heart, Lung, and Blood Institute (NHLBI) working group met to evaluate the treatment of heart failure using VADs and to advise the institute on how therapy for heart failure may be best advanced by clinical trials involving the devices.

METHODS AND RESULTS

Recognizing the improvements in VAD technology and in patient care and selection over the past decade, the working group recommended that a trial be performed to assess the use of chronic VAD therapy in patients who are less ill than those currently eligible for destination therapy. The hypothesis proposed for the trial is that VAD therapy may improve both survival and quality of life in moderately advanced heart failure patients who are neither inotrope-dependent nor exercise-intolerant and have not yet developed serious consequences such as malnourishment, end-organ damage, and immobility.

CONCLUSION

Based on the group's recommendations, NHLBI issued an RFP in 2009 for the REVIVE-IT Pilot Trail, which will serve to test the hypothesis and inform the pivotal trial.

Novel engineering approaches to obesity, overweight, and energy balance: public health needs and research opportunities

The obesity epidemic is one of the most rapidly evolving public health problems of our day. At present, 2/3 of American adults and 1/6 of American children and adolescents are considered either overweight or obese. Public health concern about obesity is high and reflects documented increased risk of cardiovascular disease, type 2 diabetes, many forms of cancer, gallbladder disease, and osteoarthritis, and increased mortality from these ailments, especially among the most obese. Innovative engineering technologies are needed to address a large range of problems in energy balance, intake, and expenditure that are associated with the obesity epidemic. Excess adipose tissue, representing fat storage, ultimately derives from an imbalance between energy intake and energy expenditure. Novel sensors, devices, imaging technologies, nanotechnology, biomaterials, and other approaches need to be developed and evaluated through multidisciplinary collaborations between engineers, physical scientists, and scientists with expertise in obesity and nutrition. The goal is to encourage research to develop useful technologies and tools to facilitate research and eventually to support therapeutic advances and behavioral change. Furthermore, the possibility of re-engineering the "built environment" to encourage higher levels of physical activity has been suggested as another promising and important approach to which engineers can contribute (see http://www.obesityresearch.nih.gov).

High-Risk Medical Devices, Children and the FDA: Regulatory Challenges Facing Pediatric Mechanical Circulatory Support Devices

Pediatric mechanical circulatory support is a critical unmet need in the United States. Infant- and child-sized ventricular assist devices are currently being developed largely through federal contracts and grants through the National Heart, Lung, and Blood Institute (NHLBI). Human testing and marketing of high-risk devices for children raises epidemiologic and regulatory issues that will need to be addressed. Leaders from the US Food and Drug Administration (FDA), NHLBI, academic pediatric community, and industry convened in January 2006 for the first FDA Workshop on the Regulatory Process for Pediatric Mechanical Circulatory Support Devices. The purpose was to provide the pediatric community with an overview of the federal regulatory process for high-risk medical devices and to review the challenges specific to the development and regulation of pediatric mechanical circulatory support devices. Pediatric mechanical circulatory support present significant epidemiologic, logistic, and financial challenges to industry, federal regulators, and the pediatric community. Early interactions with the FDA, shared appreciation of challenges, and careful planning will be critical to avoid unnecessary delays in making potentially life-saving devices available for children. Collaborative efforts to address these challenges are warranted.

Engineering approaches to energy balance and obesity: opportunities for novel collaborations and research: report of a joint national science foundation and national institutes of health workshop

Energy balance disorders account for a large public health burden. The obesity epidemic in particular is one of the most rapidly evolving public health problems of our day. At present, two-thirds of American adults and one-sixth of American children and adolescents are considered either overweight or obese. Public health concern about obesity is high because of the increased risk and increased mortality of cardiovascular disease, Type 2 diabetes, many forms of cancer, gallbladder disease, and osteoarthritis. These risks increase with the severity of the obesity. Excess adipose tissue, representing fat storage, ultimately derives from an imbalance between energy intake and energy expenditure. Conversely, undesirable and inadvertent loss of body weight and muscle mass, as seen in aging and cachectic states of chronic diseases such as heart failure and cancer, have serious clinical and functional consequences without satisfactory clinical or behavioral solutions. Innovative engineering technologies could help to address unresolved problems in energy balance, intake, and expenditure. Novel sensors, devices, imaging technologies, nanotechnologies, biomaterials, technologies to detect biochemical markers of energy balance, mathematical modeling, systems biology, and other approaches could be developed, evaluated, and leveraged through multidisciplinary collaborations. Engineers, physical scientists, and mathematicians can work with scientists from other relevant disciplines who possess expertise in obesity and nutrition. Furthermore, the possibility of re-engineering the "built environment" to encourage higher levels of physical activity has been suggested as another promising and important approach to which engineers can contribute (see http://www.obesityresearch.nih.gov). Ultimately, systematic application of the "Engineering Approach" can help in developing the needed technologies and tools to facilitate research and eventually support therapeutic advances and behavioral change. This article summarizes important public health concerns related to disordered energy balance and describes research priorities identified at a recent National Science Foundation-National Institutes of Health workshop. Research funding opportunities are described as posted on the NIH Guide to Grants and Contracts (see http://www.nih.gov/grants/guide).

The National Heart, Lung, and Blood Institute Pediatric Circulatory Support Program

Options for the circulatory support of pediatric patients under the age of 5 years are currently limited to short-term extracorporeal devices, the use of which is often complicated by infection, bleeding, and thromboembolism. Recognizing this void, the National Heart, Lung, and Blood Institute solicited proposals for the development of novel circulatory support systems for infants and children from 2 to 25 kg with congenital or acquired cardiovascular disease. Five contracts were awarded to develop a family of devices that includes (1) an implantable mixed-flow ventricular assist device designed specifically for patients up to 2 years of age, (2) another mixed-flow ventricular assist device that can be implanted intravascularly or extravascularly depending on patient size, (3) compact integrated pediatric cardiopulmonary assist systems, (4) apically implanted axial-flow ventricular assist devices, and (5) pulsatile-flow ventricular assist devices. The common objective for these devices is to reliably provide circulatory support for infants and children while minimizing risks related to infection, bleeding, and thromboembolism. The devices are expected to be ready for clinical studies at the conclusion of the awards in 2009.

Fluid dynamics of the CarboMedics kinetic bileaflet prosthetic heart valve

OBJECTIVE

To compare hydrodynamic characteristics of a new bileaflet heart valve, the CarboMedics kinetic cardiac valve prosthesis, with those of a St. Jude Medical (SJM) heart valve.

METHODS

Hydrodynamic characteristics were determined in the mitral and aortic positions of a Vivitro Systems pulse duplicator for size 23 Kinetic aortic values, size 23 SJM aortic valves, size 29 Kinetic mitral valves and size 29 SJM mitral valves. Test conditions were 72 beats per min with cardiac outputs of 2, 5 and 7 l/min. Values of forward flow pressure drop (delta P), regurgitant and energy loss were determined for each valve. The test results for the two valve designs were compared by valve size.

RESULTS

The test results show that both the size 23 and size 29 Kinetic valves have 8-14% lower delta P values and 5-10% greater effective orifice area (EOA) values. The size 29 Kinetic mitral valve has a 1-2 ml lower regurgitant volume, while the size 23 Kinetic aortic valve has a 0.5 ml greater regurgitant volume than the corresponding SJM values. These factors combine to provide a 5-10% lower energy loss for size 23 Kinetic aortic valves and a 15-25% lower energy loss for size 29 Kinetic mitral valves over the cardiac cycle than for corresponding sizes of SJM valves.

CONCLUSIONS

The Kinetic valve's fluid dynamics are superior to equivalent sizes of SJM valves. This is especially impressive considering that the tissue annulus diameters for Kinetic valves are approximately 0.5 mm less than equivalent size SJM valves. The primary reasons for the superior hydrodynamic performance of Kinetic valves are (1) the larger orifices which result in lower forward flow delta P values and (2) the opening angles, which have been customized for each valve size to minimize energy loss.

LDA measurements of mean velocity and Reynolds stress fields within an artificial heart ventricle

Laser Doppler Anemometry measurements of mean (ensemble average) velocities and turbulent (Reynolds) stresses at 140 locations within the left ventricle of the Penn State 70 cc electric artificial heart/ventricular assist device are reported at 8 times during the cardiac cycle. Mean velocity patterns indicate that the surfaces of the blood sac and valve tracts are exposed to significant levels of wall shear stress (good wall washing) during some portion of the flow cycle, and there is no location where the flow is stagnant over the entire flow cycle. This implies that thrombus deposition within the artificial heart should be suppressed. Turbulent stresses in the main pumping chamber and the outflow tracts of the tilting disk valves do not exceed 2000 dynes/cm2. The highest turbulent stresses (20,000 dynes/cm2) and smallest turbulent microscales (6 microns) are found in the regurgitant jets on the minor orifice side of the aortic valve during diastole and the mitral valve during systole. Taken together, the data suggest that improvements in artificial heart fluid mechanics will come through valve design and pump operating conditions, not pumping chamber design.

Determination of principal reynolds stresses in pulsatile flows after elliptical filtering of discrete velocity measurements

The purpose of this study was to develop a method to accurately determine mean velocities and Reynolds stresses in pulsatile flows. The pulsatile flow used to develop this method was produced within a transparent model of a left ventricular assist device (LVAD). Velocity measurements were taken at locations within the LVAD using a two-component laser Doppler anemometry (LDA) system. At each measurement location, as many as 4096 realizations of two coincident orthogonal velocity components were collected during preselected time windows over the pump cycle. The number of realizations was varied to determine how the number of data points collected affects the accuracy of the results. The duration of the time windows was varied to determine the maximum window size consistent with an assumption of pseudostationary flow. Erroneous velocity realizations were discarded from individual data sets by implementing successive elliptical filters on the velocity components. The mean velocities and principal Reynolds stresses were determined for each of the filtered data sets. The filtering technique, while eliminating less than 5 percent of the original data points, significantly reduced the computed Reynolds stresses. The results indicate that, with proper filtering, reasonable accuracy can be achieved using a velocity data set of 250 points, provided the time window is small enough to ensure pseudostationary flow (typically 20 to 40 ms). The results also reveal that the time window which is required to assume pseudostationary flow varies with location and cycle time and can range from 100 ms to less than 20 ms.(ABSTRACT TRUNCATED AT 250 WORDS)

Mean velocities and Reynolds stresses within regurgitant jets produced by tilting disc valves

Fluid velocities were measured with a two-component laser Doppler anemometry system in the regurgitant jet regions of Bjork-Shiley Delrin monostrut tilting disc valves mounted within a Plexiglas model of the 70 cm3 Penn State electric left ventricular assist device. At each measurement location, 250 instantaneous velocity realizations were collected at times when regurgitation through the valves occurred. The maximum Reynolds shear and normal stresses were calculated after filtering the data. Results show that Reynolds shear and normal stresses proximal to the mitral valve were elevated to magnitudes of 9,000 dynes/cm2 and 20,000 dynes/cm2, respectively. The peak Reynolds stresses near the mitral valve occurred during early systole, when regurgitant jet velocities reached magnitudes as high as 440 cm/sec. The Reynolds shear and normal stresses proximal to the aortic valve reached magnitudes of 9,900 dynes/cm2 and 20,500 dynes/cm2, respectively. The peak Reynolds stresses near the aortic valve occurred during early diastole, when regurgitant jet velocities were as high as 280 cm/sec. These high Reynolds stresses created by turbulent regurgitant flow have the potential to cause significant blood damage.

Estimation of Reynolds stresses within the Penn State left ventricular assist device

Fluid velocities were measured using a two-component laser Doppler anemometery (LDA) system at 129 locations within a Plexiglas model of a 70 cm3 Penn State electric Left Ventricular Assist Device (LVAD). The LVAD was driven by a pulsatile piston pump acting on an attached segmented polyurethane diaphragm. Bjork-Shiley tilting disc valves were used to provide unidirectional flow through the inlet and outlet ports. A seeded blood analog fluid, which matched the kinematic viscosity of blood at high shear rates and the refractive index of Plexiglas, was used to make the measurements. At each location, 250 instantaneous velocity realizations were collected at eight instances during the pump cycle. The maximum Reynolds shear and normal stresses were calculated for each pump cycle time and location after filtering the data. The results reveal that the highest Reynolds shear and normal stresses occur in the near wall region just proximal to the aortic valve during diastole, and reach values of 5,300 dynes/cm2 and 10,800 dynes/cm2, respectively. The elevated turbulent stresses are observed during the period of regurgitant flow through the aortic valve, with peak stress values arising during the period of peak regurgitant flow. This supports the hypothesis that a regurgitant turbulent jet is formed near the wall of the prosthetic aortic valve and may be contributing to blood damage.

Hot-film wall shear probe measurements inside a ventricular assist device

Wall shear rates at eleven sites within the Penn State Electric Ventricular Assist Device (EVAD) were determined with the pump operating under conditions of 30 and 50 percent systolic duration and a mean flow rate of 5.8 L/min using a flush-mounted hot-film probe. Probe calibrations were performed with the hot-film in two orientations relative to the flow direction: a standard orientation and an orientation in which the hot-film was rotated by 90 deg from the standard orientation. The magnitude and direction of the wall shear stress at each site within the EVAD were estimated from ensemble averaged voltage data recorded for similar standard and rotated film orientations. The results indicate that, during diastole the wall shear stress direction around the pump's periphery for both operating conditions is predominantly perpendicular to the inflow-outflow plane (in the direction of the pusher plate motion) and reaches a peak value of approximately 350 dynes/cm2. The highest wall shear stresses were found near the prosthetic aortic valve (inside the EVAD) under the 30 percent systolic duration condition and are estimated to be as high as 2700 dynes/cm2. Peak shear stress values of 1400 dynes/cm2 were observed in the vicinity of the prosthetic mitral valve under both operating conditions. The results suggested that the valve regions are substantially more hemolytic than other wall regions of the EVAD; the magnitudes of the wall shear stresses are sensitive to operating conditions; and that wall shear in the direction of pusher plate motion can be significant.