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. Author manuscript; available in PMC: 2017 May 15.
Published in final edited form as: J Surg Res. 2016 Jan 20;202(2):363–371. doi: 10.1016/j.jss.2016.01.015

PHYSIOLOGIC EFFECTS OF CONTINUOUS-FLOW LEFT VENTRICULAR ASSIST DEVICES

Aaron H Healy a, Stephen H McKellar a, Stavros G Drakos b, Antigoni Koliopoulou a, Josef Stehlik b, Craig H Selzman a
PMCID: PMC4886545  NIHMSID: NIHMS777297  PMID: 27229111

Abstract

Background

Within the past ten years, continuous-flow Left Ventricular Assist Devices (LVADS) have replaced pulsatile-flow LVADs as the standard of care for both destination therapy and bridging patients to heart transplantation. Despite the rapid clinical adoption of continuous-flow LVADs, an understanding of the effects of continuous-flow physiology, as opposed to more natural pulsatile-flow physiology, is still evolving.

Materials and Methods

A thorough review of the relevant scientific literature regarding the physiologic and clinical effects of continuous-flow physiology was performed. These effects were analyzed on an organ system basis and include an evaluation of the cardiovascular, respiratory, hematologic, gastrointestinal, renal, hepatic, neurologic, immunologic, and endocrine systems.

Results

Continuous-flow physiology is, generally speaking, well tolerated over the long term. Several changes are manifest at the organ system level, however. While many of these changes are without appreciable clinical significance, other changes, such as an increased rate of gastrointestinal bleeding, appear to be associated with continuous-flow physiology.

Conclusions

Continuous-flow LVADs confer a significant advantage over their pulsatile-flow counterparts with regard to size and durability. From a physiologic standpoint, continuous-flow physiology has limited clinical effects at the organ system level. Though improved over previous generations, challenges with this technology remain. Approaching these problems with a combination of clinical and engineering solutions may be needed to achieve continued progression in the field of durable mechanical circulatory support.

Keywords: Cardiac surgery, Heart failure, Left ventricular assist device, Mechanical circulatory support, Physiology

1. Introduction

Heart failure affects 5.7 million Americans and is responsible for more than one million hospital admissions and 58,000 deaths annually [1]. As a means of treating heart failure, efforts to replicate and perfect artificial human circulation have been underway for several decades. The first successful use of mechanical circulation was by John Gibbon in 1954 when he used a heart-lung machine to repair an atrial septal defect [2]. Mechanical circulatory support evolved over the next 30 years to include left ventricular assist devices (LVADs) and permanently implantable artificial hearts [3,4]. In subsequent years, LVADs have advanced to become the predominant form of long-term mechanical circulatory support in use today [5].

The first several iterations of LVADs were volume displacement pumps. These devices were the workhorses of the field for many years and reached their clinical peak when they were approved for use in patients who were ineligible for heart transplantation, also known as destination therapy. The landmark REMATCH trial, published in 2001, demonstrated a profound survival benefit at one (52% vs. 25%) and two years (23% vs. 8%) after device implant compared to patients receiving optimal medical management [6].

Despite the dramatically improved survival offered by the use of these pulsatile-flow devices, there were several disadvantages associated with their use. First, the use of various bearings and valves employed in pulsatile designs were associated with limited durability, requiring many patients to undergo LVAD replacement surgery [7–9]. Second, pulsatile LVADs employed the use of a volume displacement chamber, resulting in a relatively large device. In turn, this required both a patient with a large body habitus and extensive dissection to accommodate implantation [10,11]. Third, owing to the mechanism of the volume displacement chamber, these pumps were often noisy.

In large part due to the limitations of pulsatile-flow designs, the clinical use of LVADs with continuous-flow mechanisms has been widely adopted over the last decade (Figure 1). Research into the use of continuous-flow designs, however, has been underway for more than fifty years. The first report on the development of a continuous flow device occurred in 1960 where it was described as “an ideal heart pump [12].” This claim has since been questioned, in part, because of the lack of pulsatile flow. Despite vastly improved pump designs and ever-increasing human experience, the controversy over the efficacy of continuous flow devices has remained. At one level, the rapid adoption of continuous flow pumps in the last 10 years makes sense. For anyone who places these devices, the ease of insertion and simplicity of patient management is greatly welcomed. Overlooked in this enthusiasm, however, is deference for the pulsatile circulatory system honed by nature. After a decade of experience with continuous-flow devices, we can conclude that continuous-flow circulation is generally safe and that challenging a human physiology designed for pulsatile flow with a continuous-flow LVAD is appropriate. Herein, we seek to summarize the evidence regarding continuous flow pumps at the level of each organ system to determine if Saxton was correct in his description of “an ideal heart pump.” To accomplish this, we thoroughly reviewed the available literature comparing pulsatile- and continuous-flow LVADs on an organ system basis. The results of these searches are summarized in the following sections.

Figure 1.

Figure 1

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Use of Durable Mechanical Circulatory Support Devices in Adults by Type Over Time. Reproduced from Kirklin, et al, [5] with permission.

2.1 Cardiovascular System

Unloading of the left ventricle and reestablishing normal cardiac output are primary reasons for implantation of an LVAD. While pressure unloading has been shown to be similar when comparing pulsatile- and continuous-flow LVADS, significantly greater volume unloading has been observed in pulsatile-flow devices, whether measured by either device flow rates or left ventricular end diastolic dimension (LVEDD) [13,14]. There is some conflicting evidence in this area, however, as other studies that show better unloading with pulsatile devices using a decrease in LVEDD on echocardiography could not confirm this finding with right ventricular catheterization [15]. Still other analyses showed no difference in pressure and volume unloading when comparing continuous- and pulsatile-flow LVADs [16]. A possible explanation for this discrepancy is the use of different continuous flow devices in the studies. Either way, left ventricular unloading using continuous-flow devices is sufficient enough to be associated with aortic valve commissural fusion of at least a mild degree in 48–89% of patients [17,18].

Examining the effect of continuous-flow LVADs on left ventricular unloading naturally leads to questions regarding how this type of flow affects myocardial recovery, particularly when compared to pulsatile-flow LVADs. Pulsatile flow devices have been associated with improved ejection fraction, with one study showing an improvement in average ejection fraction from 21% to 33%, while the ejection fraction of patients supported with continuous-flow devices remained static at 17% [19]. Similarly, a single-center, retrospective review evaluating factors associated with weaning from LVAD support showed a nearly three-fold increased probability of weaning in patients supported with pulsatile-flow LVADs [20]. The reasons for the observed differences in progression to myocardial recovery in patients supported with LVADs are unclear. Hypotheses include decreased coronary blood flow and myocardial atrophy [21,22], though the latter theory has largely been debunked [23,24].

Right ventricular dysfunction has historically occurred in approximately 40% of patients with LVADs and is a risk factor for increased mortality [25,26]. That being the case, there is some evidence to suggest that patients with continuous-flow LVADs may experience less right heart failure than patients with pulsatile-flow devices. A study of the HeartMate II LVAD (Thoratec Corporation, Pleasanton, CA) bridge to transplantation clinical trial showed only a 20% incidence of right ventricular failure among the study population, defined as insertion of a right ventricular assist device (6%), 14 or more days of inotropic support after implantation (7%), or inotropic support starting more than 14 days after implantation (7%) [27]. The randomized trial comparing continuous-flow and pulsatile flow pumps for destination therapy found that right heart failure managed with the extended use of inotropes was less in patients with continuous-flow devices (27% vs. 20%, p < 0.001). However, there was no difference in the incidence of right heart failure that was managed with a right ventricular assist device [28]. For patients with right ventricular (RV) dysfunction prior to continuous-flow LVAD implantation, it has been shown that RV function does not worsen after implantation of the LVAD and may actually improve [29,30]. Another study, which was a retrospective analysis of RV function and tricuspid regurgitation after continuous-flow LVAD implantation, found improvement in both parameters (Table 1) [31]. These improvements likely occurred as a result of decompression of the pulmonary vascular bed with a resultant drop in pulmonary vascular resistance.

Table 1.

Pre-Operative (n = 114) Post-Operative (n = 114) 3-Month Follow-Up (n = 71) 6-Month Follow-Up (n = 63) 12-Month Follow-Up (n = 52) P = (Post-Op vs. Pre-Op)
Right ventricular dysfunction (all patients) 2.09 ± 0.64 1.65 ± 0.71 1.67 ± 0.77 1.36 ± 0.88 1.64 ± 0.79 0.001
Right ventricular dysfunction (pre-op moderate or severe, n = 58) 2.46 ± 0.49 1.89 ± 0.55 1.79 ± 0.74 1.48 ± 0.80 1.75 ± 0.80 <0.00001
Tricuspid regurgitation (all patients) 1.48 ± 0.75 1.24 ± 0.50 1.05 ± 0.53 1.04 ± 0.42 0.75 ± 0.58 0.001
Tricuspid regurgitation (pre-op moderate or severe, n = 59) 2.17 ± 0.28 1.38 ± 0.60 1.14 ± 0.61 1.17 ± 0.47 0.71 ± 0.57 <0.000001
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Mean Preoperative, Immediate Postoperative, and Follow-Up Right Ventricular Dysfunction and Tricuspid Regurgitation Following Continuous Flow Left Ventricular Assist Device Implant. 0 = none, 1 = mild, 2 = moderate, 3 = severe. Reproduced from Atluri, et al, [31] with permission.

Further, in patients with intractable pulmonary hypertension, both pulsatile- and continuous-flow LVADs have been shown to alleviate pulmonary hypertension to a level that is compatible with heart transplant eligibility [31–34]. A retrospective study comparing the two flow types found that continuous-flow devices were associated with a greater decrease in pulmonary artery systolic pressure than pulsatile-flow devices [35]. No differences were found between the two groups with regard to right ventricular ejection fraction, grade of tricuspid insufficiency, or tricuspid annular plane systolic excursion.

The long-term effects of continuous-flow physiology on vessel morphology are unknown. Studies in a goat model showed diminished arterial constriction and aortic wall thickness in animals supported with continuous-flow physiology [36,37]. A comparison of aortic wall tissue at the time of insertion of a continuous-flow LVAD and at the time of transplantation/autopsy in humans showed increased foci of medial degeneration, smooth muscle cell depletion, elastic fiber fragmentation, medial fibrosis and atherosclerotic changes, but no difference in mean medial thickness [38]. At the time of transplantation, hearts supported with a continuous-flow LVAD had a reduction in the volume density of elastin and mucinous ground-substance, along with an increase in collagen, compared to hearts that were not supported with an LVAD prior to transplant [39]. These changes do not appear to be manifest at the end-organ level, however, as evidenced by a lack of difference in the vasculature with regard to perivascular infiltrates, intravascular infiltrates, wall thickness, thrombosis, endothelial cell swelling, vessel wall necrosis, or perivascular fibrosis [40]. However, larger vessels, such as the brachial artery, have been shown to have reduced flow-mediated vasodilation in patients with continuous flow LVADs compared to control patients without LVADs [41]. These differences could also be observed with regard to changes in vessel diameter (Figure 2). These different findings between the vasculature at the arterial and end organ levels may be due to the possibility that even in pulsatile-flow physiology, perfusion at the end-organ level has been sufficiently dampened by the arterioles to be essentially continuous. Therefore, the end-organ vasculature may not be experiencing any significant differences in flow type when a continuous-flow pump is placed in a patient accustomed to pulsatile physiology. Conversely, a recent study using a chronic ischemic heart failure bovine model found that end organ perfusion was improved when pulsatility was integrated into a continuous-flow LVAD by using variable speeds compared to the use of a constant speed [42]. In summary, what clinical significance, if any, changes to the arterial vasculature signify remains to be seen.

Figure 2.

Figure 2

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Brachial Artery Flow-Mediated Dilation in New York Heart Association Functional Class II Heart Failure Patients, Class III/IV Heart Failure Patients, Class III/IV Heart Failure Patients Post-LVAD Implantation, and Healthy Control Subjects. * denotes a significant difference compared to controls, while † denotes a significant difference from the Class II Heart Failure Group. HFrEF = Heart Failure with Reduced Ejection Fraction. Reproduced from Witman, et al, [41] with permission.

2.2 Respiratory System

The effect of non-pulsatile flow on pulmonary circulation has been clinically studied in the setting of Fontan procedures. Fontan physiology, a pulseless pulmonary circulation, is well tolerated. Studies of continuous-flow physiology in newborn lambs shows that non-pulsatile circulation is associated with a smaller decrease in pulmonary vascular resistance as flow rates are increased compared to pulsatile flow physiology [43]. Pulsatility loss in a porcine model is associated with pulmonary hypertension and increased pulmonary resistance [44]. Hemodynamic changes in pulmonary and systemic circulation during non-pulsatile flow don’t seem to affect gas exchange or intrapulmonary shunt ratio [45].

From a purely clinical standpoint, the type of flow has little to no clinical effect on the rate of respiratory complications. A single center retrospective review of 182 patients found that there was no difference in the rate of prolonged intubation after LVAD placement (defined as 6 or more days of ventilator support), reintubation, or tracheostomy in patients with continuous flow LVADs compared to those with pulsatile flow LVADs [46]. Likewise, no difference was observed in the rate of respiratory failure when devices with the two flow types were compared in a randomized, controlled trial of destination therapy LVAD patients [28].

2.3 Hematologic System

Given the devastating consequences of bleeding and thromboembolism (TE), the hematologic effects of LVAD support are a major concern. Continuous-flow VADs require anticoagulation and are prone to thrombus formation in the pump housing chamber. Rate of TE events vary among different technologies. Pulsatile VADs with mechanical valves required high levels of anticoagulation while the HeartMate XVE (Thoratec Corporation, Pleasanton, CA) needed only anti-platelet therapy. Data from the HeartMate II bridge to transplant trial reported event/rates per patient year as follows: bleeding requiring surgery = 0.78, bleeding requiring ≥ 2 units of packed red blood cells = 2.09, ischemic stroke = 0.13, hemorrhagic stroke = 0.05, transient ischemic attack = 0.10, peripheral nonneurologic thromboembolism = 0.15, and device thrombosis = 0.05 [47]. Over the next few years following this study, clinicians perceived an increase in the rate of pump thrombosis of the HeartMate II device, prompting a formal analysis of the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS). This showed that freedom from device exchange or death due to thrombosis at 6 months after device implant had decreased from 99% in 2009 to 94% in 2012 [48]. Overall survival in patients with the HeartMate II was 80% at one year after device placement.

Owing to the mechanism of a rapidly spinning axial/centrifugal rotor in continuous-flow devices, hemolysis is found in a greater degree than in patients with pulsatile-flow LVADs. Fibrinolytic markers such as D-dimer, fibrinogen, plasma-free hemoglobin, and red blood cell sedimentation rate are generally highest just after implant of continuous-flow devices and then undergo a relative decrease with ongoing VAD support [49]. Despite laboratory evidence of increased hemolysis with the use of continuous-flow LVADs, most patients are not clinically affected. An analysis of the INTERMACS registry using 4,850 patients found that freedom from clinically significant hemolysis, defined as a plasma-free hemoglobin greater than 40 mg/dL in setting of clinical evidence of hemolysis occurring more than 72 hours after device implantation, was 91% at two years. For those patients who did experience hemolysis, it was associated with higher rates of device malfunction, device exchange, and mortality [50]. Further, lactate dehydrogenase and plasma-free hemoglobin levels have been shown to be significantly elevated in patients who were being admitted for LVAD thrombosis [51].

2.4 Gastrointestinal System

The most common adverse event associated with continuous-flow LVAD support is bleeding [52]. Gastrointestinal bleeds, in particular, occur in 15–30% of continuous-flow LVAD patients at a rate of 0.45 events/patient-year [53,54] and are a major driver of readmission and thromboembolic events [55–58]. The reasons for increased rates of gastrointestinal bleeding are likely multifactorial and include chronic anticoagulation, mucosal ischemia, loss of von Willebrand factor activity, and an increased rate of angiodysplasia [59]. Acquired von Willebrand syndrome, due to proteolysis of von Willebrand factor secondary to sheer stress, has even been observed in short-term support using continuous-flow LVADs [60]. Interestingly, a higher pulsatility index – which is a measure of the degree of residual pulsatility present in patients with continuous flow LVADs, has been shown to be associated with a lower rate of nonsurgical bleeding (Figure 3).

Figure 3.

Figure 3

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Survival Free from Non-surgical Bleeding in Continuous-flow Left Ventricular Assist Device Patients. PI = Pulsatility Index. Reproduced from Wever-Pinzon, et al, [58] with permission.

A study of post-implantation nutritional status comparing the HeartMate XVE and HeartMate II demonstrated that patients with the HeartMate II had higher albumin levels after 6 months of support [61]. It was suggested that this might be the result of early satiety due to the larger size of the HeartMate XVE and the pressure effect on the stomach and upper GI tract.

2.5 Renal System

Several groups have studied kidney function in continuous-flow LVAD patients. A comparison of pre- and post-implant levels of serum urea nitrogen and creatinine demonstrated that kidney function was either maintained or improved in patients awaiting transplantation [53,62]. In a cohort of continuous-flow LVAD patients supported for at least one year, creatinine and blood urea nitrogen levels initially declined, then gradually increased over the following year. The values at one year, however, remained significantly lower than their baseline values [63]. Other studies that directly compared pulsatile- and continuous-flow LVADs have used serum urea nitrogen, creatinine, creatinine clearance, and glomerular filtration rate as outcomes. They uniformly demonstrated that there was no difference in kidney function between the two groups [64–66]. Conversely, a randomized, controlled evaluation of continuous- and pulsatile-flow devices for use in destination therapy showed a significantly lower rate of post-implant renal failure in patients with continuous-flow devices [28]. Long-term data from the INTERMACS registry also describes an approximately 50% reduction in the rate of renal dysfunction in patients with continuous-flow LVADs compared to pulsatile-flow LVADs [52].

2.6 Hepatic System

Studies of hepatic function in continuous flow LVAD patient populations have produced similar results to those of renal function. Using total bilirubin, serum glutamico-oxaloacetic transaminase (SGOT), serum glutamic-pyruvic transaminase (SGPT), alanine aminotransferase (ALT), and aspartate aminotransferase (AST), it has been shown that hepatic function is improved or maintained over the duration of continuous-flow LVAD support [53,62]. Direct comparisons of liver perfusion using continuous- and pulsatile-flow LVADs have used albumin, total bilirubin, SGOT, SGPT, AST, and ALT as outcome measures but have not shown any difference between the two groups [64,66]. INTERMACS data describes the rate of hepatic dysfunction in continuous flow device patients as 0.60/100 patient-months compared to a rate of 1.32 events/100 patient-months in patients with pulsatile-flow devices [52]. In patients supported with a continuous-flow device for a year, total bilirubin declined continuously over the course of LVAD support [63]. In addition, synthetic function of the liver was observed to improve, as evidenced by a continuously increasing serum albumin level.

2.7 Neurologic System

Effects on the neurologic system can be divided into two categories, those that are the direct result of continuous-flow per se and those that are secondary effects due to having a continuous flow device. Regarding the former category, there are a few studies performed during the early clinical application of continuous-flow devices that do shed some light on the subject. Using markers of brain injury such as protein S-100B and neuron-specific enolase, it has been shown that there is no difference in continuous and pulsatile-flow LVADs in the first fourteen days of support [67]. Interestingly, while microembolic signals detected using transcranial Doppler were shown to be predictive of thromboembolic events in patients with pulsatile Novacor LVADs [68] there is no correlation between microembolic signals and thromboembolic events in patients with continuous-flow DeBakey LVADs [69]. It is not know whether these findings apply to the current widely used continuous flow LVADs.

A more recent study evaluated the effect of sympathetic activation during tilt-table testing among patients with continuous- and pulsatile-flow LVADs. Those patients with continuous-flow LVADs had marked increases in sympathetic activation, thought to be due to baroreceptor unloading. These authors speculated that chronic sympathetic activation may contribute to decreased end organ function over the long term [70]. Autoregulation of cerebral perfusion does not appear to depend on flow type, despite a noted reduction in pulsatility among patients with continuous-flow LVADS compared to patients with pulsatile-flow LVADs [71].

With regard to secondary effects of continuous-flow physiology, most clinical events are consequences of LVAD management – the balance between bleeding and thrombosis. That being the case, rates of neurologic dysfunction are lower over long-term follow-up in continuous-flow LVAD patients than in pulsatile-flow patients according to INTERMACS data [52]. Prospective studies of neurologic outcomes in LVAD patients are sparse, thought the HeartMate II Destination therapy trial found no difference in stroke rate when comparing continuous- and pulsatile-flow LVAD patients. There was also no difference between the two groups when strokes were subdivided into ischemic and hemorrhagic categories [28].

2.8 Immunologic System

Whereas LVADs are frequently used to bridge patients to transplantation, any effect that flow physiology may have on the immunologic system can have considerable relevance. To this end, a retrospective comparison of pulsatile- and continuous flow patients who were bridged to transplant evaluated post-transplant incidence of treated rejection and the mean number of rejection episodes per patient. No differences were observed by either measure [72]. Other studies have found different results. Our group has previously demonstrated that patients transplanted after being bridged with a continuous-flow LVAD have similar overall rejection rates as patients bridged with pulsatile-flow LVADs, but have a lower rate of clinically relevant rejection according to the International Society for Heart and Lung Transplantation revised cardiac allograft rejection scale (Table 2) [73,74]. Conversely, another retrospective study found that episodes of severe rejection were significantly more frequent in patients who were bridged to transplant with a continuous-flow LVAD compared to those who were bridged with a pulsatile-flow LVAD [75].

Table 2.

Rejection Pulsatile (n = 77) Continuous (n = 34) p Value
1R-3R 2.00 ± 1.43 1.50 ± 1.16 0.076
2R-3R 0.49 ± 0.72 0.12 ± 0.33 <0.001
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Cardiac Allograft Rejection Rates in the First Year After Transplantation in Patients Who Received an LVAD as a Bridge to Transplantation. Rates are episodes per year as determined by pathologic tissue analysis. 1R = Mild Rejection, 2R = Moderate Rejection, 3R = Severe Rejection, LVAD = Left Ventricular Assist Device. Reproduced from Healy, et al, [73] with permission.

2.9 Endocrine System

Most studies of endocrine function associated with continuous-flow physiology come from research involving cardiopulmonary bypass. Studies show variable changes to the function of the adrenocortical system. For example, evidence exists of a reduction in cortisol secretion during non-pulsatile bypass that can be corrected through the use of pulsatile bypass [76]. In contrast, other studies comparing hypothermic pulsatile and nonpulsatile cardiopulmonary bypass found no differences between the two groups with regard to cortisol, renin, or adrenocorticotropic hormone levels [77,78]. Evidence of the effect of continuous-flow physiology using durable LVADs is limited, though at least one study exists evaluating the administration of hypothalamic releasing hormones in continuous-flow LVAD patients. This demonstrated a normal response of adrenocorticotropic hormone, thyroid-stimulating hormone, luteinizing hormone, and prolactin, and a slightly diminished response of growth hormone [79]. Though other studies of this area are lacking, and absence of evidence is not evidence of absence, it seems reasonable to conclude that given the widespread use of continuous-flow LVADs in the treatment of modern heart failure, the effects of continuous-flow physiology on endocrine function are clinically negligible.

3.1 Conclusions

Over the last 10 years, continuous-flow LVADs have become the standard of care when long-term mechanical support is required. They have several mechanical advantages over pulsatile-flow devices, including decreased size, increased durability, and ease of implantation. From a physiologic standpoint, continuous-flow is generally well tolerated, even over extended periods of several years. Though some differences exist among various organ system parameters (Table 3), most of these differences likely have minimal clinical significance. In a minority of situations, such as with gastrointestinal bleeding, continuous-flow physiology presents challenges that are not seen as frequently as in patients with pulsatile-flow. Effective treatment and prevention of these events mark some the current clinical difficulties in managing patients with continuous-flow physiology.

Table 3.

Organ System
Cardiovascular

  • CF and PF devices have similar pressure unloading, but volume unloading may be better in PF devices

  • Possibly higher rates of progression to myocardial recovery with PF LVADs

  • Possibly lower rates of right heart failure in patients with CF LVADs

  • Comparable alleviation of pulmonary hypertension in CF and PF LVADs

  • Increased degeneration of aortic wall tissue in CF LVADS, significance unknown

Respiratory

  • Pulseless pulmonary circulation is well tolerated

  • No difference in rates of post-operative respiratory complications

Hematologic

  • Pump thrombosis a concern with particular CF LVADs

  • Higher degree of hemolysis with CF LVADS, usually not clinically significant

Gastrointestinal

  • Relatively high rate of gastrointestinal bleeding with CF LVADs

Renal

  • Comparable improvement in preoperative renal dysfunction after device placement

  • Decreased rates of renal dysfunction in patients with CF LVADs after device placement

Hepatic

  • Comparable improvement in preoperative hepatic dysfunction after device placement

  • Decreased rates of hepatic dysfunction in patients with CF LVADs after device placement

Neurologic

  • Little evidence that continuous-flow per se affects neurologic function

  • No difference in stroke rates between CF and PF LVADs

  • Possibly lower rates of neurologic dysfunction in patients with CF LVADs

Immunologic

  • Possibly lower rates of clinically significant rejection in patients with CF LVADs

Endocrine

  • Little evidence available; likely no difference

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Summary of Differences in Physiology Depending on Flow Type. CF = Continuous-Flow, LVADs = Left Ventricular Assist Devices, PF = Pulsatile-Flow

While continuous-flow LVADs clearly have several mechanical advantages over pulsatile LVADs, it may well be that a hybrid approach would provide the most optimal patient outcomes. For example, a combination of continuous-flow pump design with software algorithms to generate pump speed variations to create pulsatility may prove to be advantageous. The needed frequency of pulsatility to optimize outcomes, whether similar to the human heart or just a few times per minute, is not known. What is clear is that despite the significant benefit that continuous-flow technology has provided to patients with end-stage heart failure, some large clinical hurdles remain and will be the subject of considerable research in the coming years.

Acknowledgments

This work is funded, in part, by the NIH/NHLBI 4R01 HL089592 (CHS), Doris Duke Foundation Clinical Scientist Grant 2013108 (SGD), VA Merit Review Award, 1I01CX000710-01A1 (JS, SGD), American College of Surgeons and American Association of Thoracic Surgeons (SHM), Deseret Foundation #00571 (SGD).

Footnotes

Author Contributions:

Healy: conception and study design, acquisition and interpretation of data, drafting and revising of article, final approval

McKellar: conception and study design, final approval

Drakos: conception and study design, final approval

Koliopoulou: revising of article, final approval

Stehlik: revising of article, final approval

Selzman: conception and study design, interpretation of data, revising of article, final approval

Disclosures:

The authors report no proprietary or commercial interest in any product mentioned or concept discussed in this article.

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Contributor Information

Aaron H. Healy, Email: aaron.healy@hsc.utah.edu.

Stephen H. McKellar, Email: stephen.mckellar@hsc.utah.edu.

Stavros G. Drakos, Email: stavros.drakos@hsc.utah.edu.

Antigoni Koliopoulou, Email: antigone.koliopoulou@hsc.utah.edu.

Josef Stehlik, Email: josef.stehlik@hsc.utah.edu.

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