Arterial Compliance and Continuous-Flow Left Ventricular Assist Device Pump Function.

Durable continuous-flow left ventricular assist devices (cfLVADs) demonstrate superior survival, cardiac functional status, and overall quality of life compared to medical therapy alone in advanced heart failure. Previous studies have not considered the impact arterial compliance may have on pump performance or developed arterial pressure. This study assessed the impact of alterations in arterial compliance, preload, and afterload on continuous-flow pump function and measured hemodynamics using an in-vitro pulsatile mock circulatory loop. Decreased arterial compliance was associated with a significant increase in arterial pressure pulsatility which was not evident in the flow pulsatility, as displayed in pump flow waveforms. There were marked changes in the pump flow waveforms due to the significant alteration in the aortoventricular gradient during diastole according to the changes in compliance. This study demonstrates that changes in systemic blood pressure, afterload, and left ventricular contractility each significantly affects the flow waveform. The association of hypertension with lower aortic compliance results in markedly decreased diastolic flow rates which may be important in contributing to a greater risk of adverse events under cfLVAD support.

Ex Vivo Assessment of Different Oral Anticoagulant Regimens on Pump Thrombosis in a HeartWare Ventricular Assist Device.

BACKGROUND: In light of decreased intracranial hemorrhage with direct oral anticoagulants and concerns about their safety in continuous flow left ventricular assist devices, we conducted an ex vivo study of thrombus formation using multiple anticoagulation agents. METHODS: A continuous flow left ventricular assist device (HeartWare ventricular assist device) hemocompatibility loop was run using human blood under 7 conditions: control (no anticoagulation or antiplatelet); in vitro addition of aspirin; in vitro addition of apixaban at low dose (equivalent 2.5 mg twice daily); addition of apixaban at high dose (equivalent 5 mg twice daily); patients on warfarin; patients on apixaban (5 mg twice daily); and patients on dabigatran (150 mg twice daily). The primary outcome was time to formation of intrapump thrombosis. Secondary outcomes were reduction in clotting times over 1 hour, hemolysis, reduced platelet aggregation, and von Willebrand activity. RESULTS: Twenty-one runs were completed. Times to thrombosis in median (interquartile range) were control, 131 (127-134.5); in vitro aspirin, 124 (114.5-137); and patients on dabigatran, 131 (130.5-135.5) minutes, respectively. Times in patients on warfarin were, 137 (136.5-143.5); in vitro low-dose apixaban, 141 (138.5-142); and patients on apixaban, 140 (138-142.5) minutes, respectively. No thrombus formed in the in vitro high-dose apixaban group. There were no significant differences between the individual groups. When all apixaban groups were compared with nonapixaban groups, the time to thrombosis formation was significantly longer, 143 (137-150) versus 133.5 (128.5-140) minutes, P=0.02. There were similar changes in lactate dehydrogenase levels and other secondary end points. CONCLUSIONS: In an in vitro study of anticoagulation using human blood in a mock loop with a HeartWare HVAD, we demonstrated similar thrombosis times for apixaban and warfarin. Time to clotting was longer in the combined apixaban groups compared with combined other groups, but thrombosis times between individual groups were not significantly different.

A RandomisEd ControLled TrIal of ChEwing Gum to RelieVE Thirst in Chronic Heart Failure (RELIEVE-CHF).

BACKGROUND: Thirst is a common and troublesome symptom of patients with chronic heart failure (CHF). To date, there are no interventions to help alleviate thirst in this cohort. Chewing gum is a novel intervention, which has been tested in people undergoing haemodialysis, also prescribed with a fluid restricted therapy. The aim of this study was to determine the effect of chewing gum on the level of thirst in the short-term (average of 24 hours each day for 4 days) and in the longer-term (Days 7, 14 and 28) individuals with CHF. METHODS: Seventy-one (71) individuals with CHF on oral loop diuretics were randomised to chewing gum (n=36) or control (n=35) for 2 weeks. Both groups were assessed for their level of thirst at Days 1-4, 7, 14 and 28. RESULTS: Significant improvements in the level of thirst of those who received chewing gum compared to the control group at Day 4 (p=0.04) and Day 14 (p=0.02) were observed. CONCLUSION: Chewing gum provided relief from thirst in the short-term and in the longer term. This trial provides important information to inform future clinical trials on ways to relieve thirst.

Insights Into Myocardial Oxygen Consumption, Energetics, and Efficiency Under Left Ventricular Assist Device Support Using Noninvasive Pressure-Volume Loops.

BACKGROUND: Assessment of left ventricular (LV) recovery under continuous-flow LV assist device therapy is hampered by concomitant pump support. We describe derivation of noninvasive pressure-volume loops in continuous-flow LV assist device patients and demonstrate an application in the assessment of recovery. METHODS AND RESULTS: Using pump controller parameters and noninvasive arterial pressure waveforms, central aortic pressure, outflow conduit pressure gradient, and instantaneous LV pressure were calculated. Instantaneous LV volumes were calculated from echocardiographic LV end-diastolic volume accounting for the integral of pump flow with respect to time and aortic ejection volume derived from the pump speed waveform. Pressure-volume loops were derived during pump speed adjustment and following bolus intravenous milrinone to assess changes in loading conditions and contractility, respectively. Fourteen patients were studied. Baseline noninvasive LV end-diastolic pressure correlated with invasive pulmonary arterial wedge pressure (r2=0.57, root mean square error 5.0 mm Hg, P=0.003). Measured noninvasively, milrinone significantly increased LV ejection fraction (40.3±13.6% versus 36.8±14.2%, P<0.0001), maximum dP/dt (623±126 versus 555±122 mm Hg/s, P=0.006), and end-systolic elastance (1.03±0.57 versus 0.89±0.38 mm Hg/mL, P=0.008), consistent with its expected inotropic effect. Milrinone reduced myocardial oxygen consumption (0.15±0.06 versus 0.16±0.07 mL/beat, P=0.003) and improved myocardial efficiency (43.7±14.0% versus 41.2±15.5%, P=0.001). Reduced pump speed caused increased LV end-diastolic volume (190±80 versus 165±71 mL, P<0.0001) and LV end-diastolic pressure (14.3±10.2 versus 9.9±9.3 mm Hg, P=0.024), consistent with a predictable increase in preload. There was increased myocardial oxygen consumption (0.16±0.07 versus 0.14±0.06 mL O2/beat, P<0.0001) despite unchanged stroke work (P=0.24), reflecting decreased myocardial efficiency (39.2±12.7% versus 45.2±17.0%, P=0.003). CONCLUSIONS: Pressure-volume loops are able to be derived noninvasively in patients with the HeartWare HVAD and can detect induced changes in load and contractility.

Choosing Between Left Ventricular Assist Devices and Biventricular Assist Devices.

Right ventricular failure following left ventricular assist devices implantation is a serious complication associated with high mortality. In patients with or at high risk of developing right ventricular failure, biventricular support is recommended. Because univentricular support is associated with high survival rates, biventricular support is often undertaken as a last resort. With the advent of newer right ventricular and biventricular systems under design and testing, better differentiation is required to ensure optimal patients care. Clear guidelines on patient selection, time of intervention and device selection are required to improve patient outcomes.

Pulsatile Conduit Pressure Gradients in the HeartWare HVAD.

We evaluated mean, peak, and instantaneous pressure gradients across the outflow conduit in a pulsatile mock circulation loop which incorporated Heartware HVADs for left ventricular (LV) and right ventricular (RV) support. Steady-state 50 Hz measurements of left ventricular assist device (LVAD) flow (Q) and pressures within the proximal and distal outflow conduit were obtained at varying pump speed, LV contractility, hematocrit (HCT), heart rate (HR), and conduit diameter and length. Experiments were conducted using polyvinyl chloride (PVC) tubing and results confirmed in HVAD Gelweave conduit. Conduit diameter was negatively and nonlinearly associated with mean and peak gradient in both the PVC and HVAD conduits. There were no significant differences between the PVC and HVAD conduits in terms of mean Q, systolic dQ/dt, mean conduit gradient, or peak gradient. Across the 10 mm HVAD conduit, mean gradient correlated linearly with mean Q, systolic dQ/dt, HCT, and conduit length (r = 0.91), whereas peak gradient correlated with mean Q, systolic dQ/dt, and conduit length (r = 0.93). A nonlinear model to determine instantaneous gradient was highly predictive (r = 0.83) across a range of pump and circulatory conditions. In summary, hemodynamically significant pressure gradients are observed across the LVAD outflow conduit under physiologic conditions, which may result in diminished pump flow.

Valvular Regurgitation in a Biventricular Mock Circulatory Loop.

Aortic regurgitation (AR), mitral regurgitation (MR), and tricuspid regurgitation (TR) after continuous-flow left ventricular assist device (LVAD) are common and may increase with prolonged LVAD support. The aim of this study was to simulate severe valvular regurgitation (AR, MR, and TR) within a 4-elemental pulsatile mock circulatory loop (MCL) and observe their impact on isolated LVAD and biventricular assist device (BiVAD) with HeartWare HVAD. Aortic regurgitation, MR, and TR were achieved via the removal of one leaflet from bileaflet mechanical valve from the appropriate valves of the left or right ventricles. The impact of alteration of LVAD pump speed (LVAD 2200-4000 RPM, right ventricular assist device [RVAD] 2400 RPM) and altered LVAD preload (10-25 mm Hg) was assessed. With each of the regurgitant valve lesions, there was a decrease in isolated LVAD pump flow pulsatility. Isolated LVAD provided sufficient support in the setting of severe MR or TR compared with control, and flows were enhanced with BiVAD support. In severe AR, there was no benefit of BiVAD support over isolated LVAD, and actual loop flows remained low. High LVAD flows combined with low RVAD flows and dampened aortic pressures are good indicators of AR. The 4-elemental MCL successfully simulated several control and abnormal valvular conditions using various pump speeds. Current findings are consistent with conservative management of MR and TR in the setting of mechanical support, but emphasize the importance of the correction of AR.

Outcomes of venopulmonary arterial extracorporeal life support as temporary right ventricular support after left ventricular assist implantation.

OBJECTIVES: We report our experience with temporary postoperative venopulmonary arterial extracorporeal life support as short-term right ventricular support in patients with biventricular failure undergoing HeartWare (HeartWare Inc, Framingham, Mass) left ventricular assist device implantation and compared these outcomes with isolated left ventricular assist device support and long-term biventricular assist device support. METHODS: A total of 112 consecutive patients were studied, 75 with the isolated HeartWare left ventricular assist device, 23 with a concomitant left ventricular assist device and venopulmonary arterial extracorporeal life support, and 14 with durable biventricular assist device support. The decision concerning short-term or durable biventricular support was based on the clinical characteristics, echocardiography, and hemodynamic profile. RESULTS: Patients who required venopulmonary arterial extracorporeal life support after left ventricular assist device insertion required the greatest support preoperatively and were more likely to have Interagency Registry for Mechanical Assisted Circulatory Support level 1 (left ventricular assist device 19%, venopulmonary arterial extracorporeal life support 48%, biventricular assist device 57%, P < .001). They were more likely to require preoperative mechanical support (left ventricular assist device 9%, venopulmonary arterial extracorporeal life support 43%, and biventricular assist device 29%, P < .001) or preoperative ventilation (9%, 38%, and 21%, respectively, P < .05). Preoperative echocardiographic and hemodynamic parameters were more similar to those requiring isolated left ventricular assist device, with patients requiring durable biventricular assist device support more likely to have elevated right atrial pressure (left ventricular assist device 14.3 ± 6.7 vs venopulmonary arterial extracorporeal life support 13.6 ± 4.8 vs biventricular assist device 18.7 ± 6.0 mm Hg, P < .05); right atrial/pulmonary capillary wedge pressure ratio (0.53 ± 0.23 vs 0.51 ± 0.17, vs 0.69 ± 0.22, respectively, P < .02); and tricuspid regurgitation grade (1.7 ± 1.5 vs 1.7 ± 1.6 vs 2.8 ± 1.6, respectively, P < .01). One-year survival was 84% for those with an isolated left ventricular assist device compared with 62% for those with venopulmonary arterial extracorporeal life support and 64.3% for biventricular assist device. CONCLUSIONS: In critically unwell patients requiring temporary biventricular support, planned venopulmonary arterial extracorporeal life support provides acceptable outcomes, similar to durable biventricular assist device support. Requirement for venopulmonary arterial extracorporeal life support is more determined by the level of preoperative acuity than echocardiographic or hemodynamic parameters.

Right Ventricular Failure Post LVAD Implantation Corrected with Biventricular Support: An In Vitro Model.

Right ventricular failure after left ventricular assist device (LVAD) implantation is associated with high mortality. Management remains limited to pharmacologic therapy and temporary mechanical support. Delayed right ventricular assist device (RVAD) support after LVAD implantation is associated with poorer outcomes. With the advent of miniaturized, durable, continuous flow ventricular assist device systems, chronic RVAD and biventricular assist device (BiVAD) support has been used with some success. The purpose of this study was to assess combined BiVAD and LVAD with delayed RVAD support within a four-elemental mock circulatory loop (MCL) simulating the human cardiovascular system. Our hypothesis was that delayed continuous flow RVAD (RVAD) would produce similar hemodynamic and flow parameters to those of initial BiVAD support. Using the MCL, baseline biventricular heart failure with elevated right and left filling pressures with low cardiac output was simulated. The addition of LVAD within a biventricular configuration improved cardiac output somewhat, but was associated with persistent right heart failure with elevated right-sided filling pressures. The addition of an RVAD significantly improved LVAD outputs and returned filling pressures to normal throughout the circulation. In conclusion, RVAD support successfully restored hemodynamics and flow parameters of biventricular failure supported with isolated LVAD with persistent elevated right atrial pressure.

A survey of views and opinions of health professionals managing thirst in chronic heart failure.

BACKGROUND: Thirst is a common and burdensome symptom of chronic heart failure (CHF) which affects adherence to self-care practices specifically fluid restriction. Despite this, there is no standard clinical practice for managing the symptom of thirst. AIMS AND OBJECTIVES: The aim is to identify the current strategies recommended by health professionals to help relieve thirst in CHF patients and their perceived usefulness of these strategies. METHODS: A survey was distributed to attendees of the 8th Annual Scientific Meeting of Australasian Cardiovascular Nursing College. RESULTS: There were 42 of 70 respondents to the survey. The majority (33 of 40; 82.5%) had recommended various strategies to alleviate thirst. The most recommended strategy was ice chips (36 of 38; 94.7%). Overall, the respondents reported 'some use' in all of the strategies. CONCLUSION: Information from this survey may help in the incorporation of thirst-relieving strategies into evidence-based guidelines; further improving the quality of care of patients.

Long-term biventricular HeartWare ventricular assist device support--Case series of right atrial and right ventricular implantation outcomes.

BACKGROUND: There is limited information on outcomes using the HeartWare ventricular assist device (HVAD; HeartWare, Framington, MA) as a biventricular assist device, especially with respect to site of right ventricular assist device (RVAD) implantation. METHODS: Outcomes in 13 patients with dilated cardiomyopathy and severe biventricular failure who underwent dual HVAD implantation as bridge to transplantation between August 2011 and October 2014 were reviewed. RESULTS: Of 13 patients, 10 were Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) Level 1, and 3 were INTERMACS Level 2. Mean age was 45 ± 11 years, and mean body mass index was 26 ± 4 kg/m(2). There were 7 patients on temporary mechanical support pre-operatively (extracorporeal life support, n = 5; intra-aortic balloon pump, n = 2). The median hospital length of stay was 53 days (interquartile range [IQR] 33-70 days) with a median intensive care unit length of stay of 14 days (IQR 8-36 days). The median length of support on device was 269 days (IQR 93-426 days). The right HVAD was implanted in the right ventricular (RV) free wall in 6 patients and in the right atrial (RA) free wall in 7 patients. Transplantation was successfully performed in 5 patients, and overall survival for the entire cohort was 54%. RVAD pump thrombosis occurred in 3 of 6 RV pumps and 1 of 7 RA pumps. No left ventricular assist device pump thrombosis was observed. Bleeding tended to be higher in the RV implantation group (3 of 6 vs 0 of 7). During follow up, 6 patients died (4 of 7 in the RA group vs 2 of 6 in the RV group). Cause of death was multiple-organ failure in 3 patients, sepsis in 2 patients, and intracerebral hemorrhage in 1 patient. CONCLUSIONS: Critically ill patients who require biventricular support can be successfully bridged to transplant using 2 HVADs. RA implantation may allow right heart support with lower pump thrombosis and bleeding complications, although this was at the expense of a higher mortality in this cohort.

Biventricular mechanical support devices--clinical perspectives.

Cardiac transplantation remains the optimal treatment for end stage heart failure in selected patients. However, the shortage of donor hearts, rigorous eligibility criteria and long waiting lists have increased the demand for alternative treatment strategies such as mechanical circulatory support. While many patients are adequately supported with left ventricular assist devices, frequently there is right heart failure or involvement of the right ventricle, requiring biventricular support. Pulsatile flow biventricular devices and total artificial hearts approved for temporary biventricular support have limitations including size, high rates of adverse events and restricted mobility which makes them unsuitable for long term support. A number of centres have reported dual continuous flow left ventricular assist devices as a means of supporting the left and right heart. This review will summarise the literature on the outcomes and complications from current biventricular support devices and assess the role of dual continuous flow VAD therapy, and the new continuous flow total heart replacement devices.

Peripheral arterial disease and chronic heart failure: a dangerous mix.

Chronic heart failure (CHF) is associated with a high comorbidity burden, adverse impact on quality of life and high health care utilisation. Peripheral arterial disease (PAD) and CHF share many risk, pathophysiological and prognostic features, and each has been associated with increased morbidity and mortality. PAD often goes undetected, and yet in spite of the availability of screening tools, this is not commonly considered in CHF care. A review of the electronic databases Medline, CINAHL and Cochrane CENTRAL was undertaken using the MeSH terms peripheral arterial disease, peripheral vascular disease, intermittent claudication and heart failure to identify studies examining the prevalence and clinical outcomes of coexisting PAD in patients with CHF. Five studies were identified. There are limited data describing the impact of PAD on CHF outcomes. As PAD may contribute to decreased capacity to exercise and other self-care behaviours, identifying those at risk and providing appropriate therapy are important. Based on this review, patients who are smokers and those with diagnosed coronary heart disease and diabetes should be targeted for the screening of PAD.