Effects of left ventricular assist device support and outflow graft location upon aortic blood flow

Although continuous flow (CFVAD) and pulsatile (PVAD) ventricular assist devices (VADs) are being clinically used, their effects upon aortic blood flow as a measure of overall blood distribution remain unclear. The objective of this study was to compare the effects of CFVAD and PVAD support for ascending (AscA) and descending (DA) aorta outflow cannulation upon mean aortic blood flow and waveform morphology. Six experiments were conducted in a normal, acute calf model, in which an inflow cannula was implanted in the left ventricle apex and outflow cannulae were anastomosed to both the AscA and DA. Flow probes were placed around the pulmonary artery, pump outflow, brachiocephalic trunk, and aorta proximal and distal to the DA outflow. For each acute experiment, calves received randomly selected levels of VAD support (0-100% of cardiac output) and pump failure (VAD off and outflow cannula unclamped) for each of four randomly selected test conditions: (1) PVAD and AscA, (2) PVAD and DA, (3) CFVAD and AscA, and (4) CFVAD and DA. Regardless of pump type or support level, proximal and distal aorta mean flows were lower (p < 0.05) for DA compared with the AscA. No differences in mean aortic flows between pump types at either outflow graft location were discerned. Differences in morphologic features of blood flow waveforms between PVAD and CFVAD were observed. During simulated pump failure, retrograde aortic blood flow in both the aortic arch and DA was observed. Partial ventricular suction was also observed during the greatest levels of CFVAD support and suggested pronounced effects upon both the right and left ventricle. Collectively, these findings imply that VAD outflow location may have an important role in patient response and recovery. Investigation of the long-term pathophysiologic responses to pump type and outflow location is ongoing.     

Readmissions after continuous flow left ventricular assist device implantation

Continuous flow left ventricular assist device (CF-LVAD) therapy has improved the survival of patients with advanced heart failure. However, the readmission rate of CF-LVAD patients is still relatively high. A total of 90 patients who received CF-LVADs between April 2011 and March 2016 at our institute and were discharged home were analyzed retrospectively. They were followed up through March 2017. Clinical data, including frequency, length and etiology of readmission, were obtained from medical records. The mean observation period after initial discharge was 713 ± 322 days. In total, 73 patients (81%) had 236 readmissions, 214 unplanned and 22 planned. The overall and unplanned readmission rates were 1.34 and 1.22 per patient-year, respectively. The rate of freedom from unplanned first readmission at 1 year after initial discharge was 39%. The median interval between the previous hospital discharge and first and second readmissions was 311 and 213 days, respectively (log-rank test, p = 0.117). The rate of readmission after more than three readmissions was significantly higher than that of first or second readmission (log-rank test, p < 0.001). The most common etiology of readmission was driveline infection (DLI) (36%), followed by stroke (9%). The median length of hospital stay due to DLI was 23 days. The patients with repeated unplanned readmissions had significantly lower EuroQol 5 dimensions questionnaire utility score than those with no or just one readmission. Readmission was common in CF-LVAD patients, and the most common etiology of readmissions was DLI. The interval to the next readmission seemed shorter for patients with repeated readmissions.     

Aortic valve closure for rapidly deteriorated aortic insufficiency after continuous flow left ventricular assist device implantation

A patient underwent aortic valve closure for de novo aortic insufficiency that had deteriorated to severe insufficiency during six months of support with a continuous flow left ventricular assist device (cf-LVAD). Aortic insufficiency was initially noted one month after LVAD implantation, and then deterioration quickly developed. Right heart catheterization revealed that when the rotational speed of the cf-LVAD was increased, the cardiac index was decreased by an increase in regurgitant volume, as shown by echocardiography. During surgery, fusion and shortening of the aortic leaflets as well as left coronary ostial occlusion were observed. Direct aortic closure improved hemodynamics. Thrombus formation on the aortic valve shown by echocardiography in the early postoperative period may be a trigger of aortic insufficiency. Control of the cf-LVAD rotational speed is likely required to prevent aortic insufficiency.     

The effect of aortic valve incompetence on the hemodynamics of a continuous flow ventricular assist device in a mock circulation

There is evidence that the incidence of aortic valve incompetence (AI) and other valvular pathologies may increase as more patients are submitted to longer periods of ventricular assist device (VAD) support. There is a need to better understand the mechanisms associated with the onset of these conditions and other possible complications related to the altered hemodynamics of VAD patients. In this study, the effect of AI on the hemodynamic response of continuous flow VAD (C-VAD) patients was measured in a mock loop over a range of pump speeds and level of native cardiac function. Our results showed that, in the presence of sufficient ventricular function, decreasing the C-VAD speed can allow a transition from series to parallel flow. Our study demonstrated that AI reduces the aortic pressure and flow when system impedance is unchanged. AI produces wasteful recirculation that substantially increases the pump work and decreases systemic perfusion, in particular during series flow conditions coupled with higher C-VAD speeds. The hematologic consequence of this regurgitant flow is a much higher exposure to shear for the blood, increasing the likelihood of hemolysis and thrombosis. While a certain degree of AI can be tolerated by a heart with good cardiac function, the consequences of AI for patients with VADs and poor cardiac function are much greater. Valve dysfunction in VAD patients may be related to structural changes in the tissue induced by altered biomechanics and excessive stress.     

The influence of pump rotation speed on hemodynamics and myocardial oxygen metabolism in left ventricular assist device support with aortic valve regurgitation

Aortic valve regurgitation (AR) is a serious complication under left ventricular assist device (LVAD) support. AR causes LVAD-left ventricular (LV) recirculation, which makes it difficult to continue LVAD support. However, the hemodynamics and myocardial oxygen metabolism of LVAD support with AR have not been clarified, especially, how pump rotation speed influences them. An animal model of LVAD with AR was newly developed, and how pump rotation speed influences hemodynamics and myocardial oxygen metabolism was examined in acute animal experiments. Five goats (55 ± 9.3 kg) underwent centrifugal type LVAD, EVAHEART implantation. The AR model was established by placing a vena cava filter in the aortic valve. Hemodynamic values and the myocardial oxygen consumption, delivery, and oxygen extraction ratio (O₂ER) were evaluated with changing pump rotation speeds with or without AR (AR+, AR?). AR+ was defined as Sellers classification 3 or greater. AR was successfully induced in five goats. Diastolic aortic pressure was significantly lower in AR+ than AR? (p = 0.026). Central venous pressure, mean left atrial pressure, and diastolic left ventricular pressure were significantly higher in AR+ than AR? (p = 0.010, 0.047, and 0.0083, respectively). Although systemic flow did not improve with increasing pump rotation speed, LVAD pump flow increased over systemic flow in AR+, which meant increasing pump rotation speed increased LVAD-LV recirculation and did not contribute to effective systemic circulation. O₂ER in AR? decreased with increasing pump rotation speed, but O₂ER in AR+ was hard to decrease. The O₂ER in AR+ correlated positively with the flow rate of LVAD-LV recirculation (p = 0.012). AR caused LVAD-LV recirculation that interfered with the cardiac assistance of LVAD support and made it ineffective to manage with high pump rotation speed.     

Development of aortic insufficiency in patients supported with continuous flow left ventricular assist devices

Development of aortic insufficiency (AI) in patients supported with continuous flow left ventricular assist devices (LVAD) can adversely affect pump performance. In this study, we examined the incidence of new AI after LVAD implant at our institution. Pre- and postoperative echocardiograms of 66 patients who received HeartMate II or Heartware LVAD at our institution since June 2008 were reviewed for presence of new AI. Median LVAD support duration was 221 days. New AI developed in 6 patients (9.5%) after a median time of 374.5 days of support. There were no cases of severe or symptomatic AI. There was no significant difference between the AI incidence between HeartMate II and Heartware recipients. For patients who remained on LVAD support at 6 and 12 months, freedom from AI was 100% and 68.4%, respectively. Age, destination therapy status, and duration of support were predictors of new AI after LVAD implant. In conclusion, AI develops frequently during long-term support with continuous flow LVADs, particularly in those supported for longer than 6 months. As we move to the era of long-term LVAD support and destination therapy, further studies with longer follow-ups are required to determine the progression and clinical significance of AI in these patients.     

Outcomes of midterm circulatory support by left ventricular assist device implantation with descending aortic anastomosis

For some patients undergoing left ventricular assist device (LVAD) implantation, the perfusion tube is anastomosed to the descending aorta instead of the currently more prevalently used ascending aorta. Purpose of this study was to assess retrospectively the outcomes of LVAD patients with descending aortic anastomosis. Between March 2007 and March 2010, six patients underwent LVAD implantation with descending aortic anastomosis with Toyobo or Jarvik 2000 LVAD at our institute. Their average circulatory support time was 434 (range 82–751) days. Both types of LVAD afforded adequate circulatory support, and inotrope treatment and mechanical ventilation were discontinued relatively early. Echocardiograms of the three patients with Jarvik 2000 LVAD revealed antegrade flow in the ascending aorta during the intermittent low-speed period. Among them, one patient developed infarction in the right brain hemisphere because of thromboembolism, whereas another patient developed pneumonia in the left lung followed by a lethal systemic infection. One patient on Toyobo LVAD support reached heart transplantation without morbidity. Another patient implanted with Toyobo LVAD, whose left ventricular function was too poor to generate forward flow through aortic valve, developed thrombus in the ascending aorta. No embolic events were observed in the organs below the diaphragm. In conclusion, descending aortic anastomosis of the perfusion tube can be used for LVAD implantation for some patients, but considerable risks of morbidities, including thromboembolic events and/or infection, should be recognized.     

Myocardial size and fibrosis changes during left ventricular assist device support

Previous studies have demonstrated that left ventricular assist device (LVAD) implantation significantly decreases myocyte size and reduces fibrosis of the left ventricle (LV). The objectives of the present study were to evaluate LV functional recovery after LVAD implantation and to assess its predictive factors, including histological findings of LV. Six patients with idiopathic cardiomyopathy underwent LVAD support with an EVAHEART implantable centrifugal pump (Sun Medical Technology Research, Nagano, Japan) for an average support duration of 2.91 years. Histologic samples were obtained from their LV apexes at the time of implantation. At 1 month and at 24 months after implantation, brain natriuretic peptide (BNP) and echocardiographic parameters were evaluated. Brain natriuretic peptide values, LV end-diastolic dimension, LV end-systolic dimension, functional shortening, and right ventricular systolic pressure (RVSP) were improved after LVAD implantation. Patients with developing fibrosis had longer durations of heart-failure history and higher pulmonary artery pressures. Patients with hypertrophic myocytes had smaller FS preoperatively. There was a correlation between the amount of fibrosis and the rate of BNP value change after LVAD implantation. In patients with less fibrosis and smaller myocytes preoperatively, improvement in LV function was observed during LVAD support.     

Design of a continuous flow centrifugal pediatric ventricular assist device

Thousands of pediatric patients suffering from cardiomyopathy or single ventricular physiologies secondary to debilitating heart defects may benefit from long-term mechanical circulatory support due to the limited number of donor hearts available. This article presents the initial design of a fully implantable centrifugal pediatric ventricular assist device (PVAD) for 2 to 12 year olds. Conventional pump design equations, including a nondimensional scaling approach, enabled performance estimations of smaller scale versions (25 mm and 35 mm impeller diameters) of our adult support VAD. Based on this estimated performance, a computational model of the PVAD with a 35 mm impeller diameter was generated. Employing computational fluid dynamics (CFD) software, the flow paths through the PVAD and overall performance were analyzed for steady state flow conditions. The numerical simulations involved flow rates of 2 to 5 LPM for rotational speeds of 2750 to 3250 RPM and incorporated a k-epsilon fluid turbulence model with a logarithmic wall function to characterize near-wall flow conditions. The CFD results indicated best efficiency points ranging from 25% to 28%, which correlate well with typical values of blood pumps. The results further demonstrated that the pump could deliver 2 to 5 LPM at 70 to 95 mmHg for desired physiologic conditions in resting 2 to 12 year olds. Scalar stress levels remained below 300 Pa, thereby signifying potentially low levels of hemolysis. Several flow regions in the pump exhibited signs of vortices, retrograde flow, and stagnation points, which require optimization and further study. This CFD model represents a reasonable starting point for future model enhancements, leading to prototype manufacturing and experimental validation.     

Central aortic valve closure successfully treated aortic insufficiency of the patient with Jarvik 2000 continuous flow left ventricular assist device: a case report

Aortic insufficiency (AI) is a significant complication of long-term support of continuous flow left ventricular assist device (CF-LVAD) for patients with end-stage heart failure. A 26-year-old female with osteogenesis imperfecta (OI) was diagnosed with dilated phase hypertrophic cardiomyopathy (d-HCM)) and was implanted with Jarvik 2000, for bridge to transplantation. AI gradually developed and surgical intervention was indicated. We performed central aortic valve closure (CAVC) instead of valve replacement 20 months after CF-LVAD implantation. Patient’s symptoms dramatically improved postoperatively. This is the first report of CAVC for a patient supported with Jarvik 2000.     

Quantification of interventricular dyssynchrony during continuous-flow left ventricular assist device support

Journal of Artificial Organs - Under continuous-flow left ventricular assist device (CF-LVAD) support, the ventricular volume change and cardiac cycle between the left ventricle (LV) and right...     

Myocardial hemodynamics, physiology, and perfusion with an axial flow left ventricular assist device in the calf

The Jarvik 2000 axial flow left ventricular assist device (LVAD) is used clinically as a bridge to transplantation or as destination therapy in end-stage heart disease. The effect of the pump's continuous flow output on myocardial and end-organ blood flow has not been studied experimentally. To address this, the Jarvik 2000 pump was implanted in eight calves and then operated at speeds ranging from 8,000 to 12,000 rpm. Micromanometry, echocardiography, and blood oxygenation measurements were used to assess changes in hemodynamics, cardiac dimensions, and myocardial metabolism, respectively, at different speeds as compared with baseline (pump off, 0 rpm) in this experimental model. Microsphere studies were performed to assess the effects on heart, kidney, and brain perfusion at different speeds. The Jarvik 2000 pump unloaded the left ventricle and reduced end-diastolic pressures and left ventricular dimensions, particularly at higher pump speeds. The ratio of myocardial oxygen consumption to coronary blood flow and the ratio of subendocardial to subepicardial blood flow remained constant. Optimal adjustment of pump speed and volume status allowed opening of the aortic valve and contribution of the native left ventricle to cardiac output, even at the maximum pump speed. Neither brain nor kidney microcirculation was adversely affected at any pump speed. We conclude that the Jarvik 2000 pump adequately unloads the left ventricle without compromising myocardial metabolism or end-organ perfusion.     

一种经皮植入式左心辅助装置的泵流量测试

目的 研究设计一种能用于心血管急危重症的经皮植入式左心辅助装置（血泵）。方法 根据机翼理论,设计一种经皮植入的左心辅助装置,通过测量3种不同参数（叶片旋转角度、血泵出水口距离、血泵出水口长度）的血泵所能产生的流量,最终选择最优化的血泵设计。结果 经过简易流量测定装置测量,当血泵采取单叶设计,血泵叶片的旋转角度为720°时,或血泵出水口与叶片的距离为0 mm时,血泵出水口长度为4 mm时,血泵流量最大。结论 选择能产生最大流量的参数值,研制出一种可在体外正常运转的经皮植入式左心辅助装置,为最终研制一种可用于临床的经皮植入式左心辅助装置提供理论和数据支持。     

Prognostic value of left ventricular apical tissue removed for HeartMate II left ventricular assist device placement

BackgroundWith the increasing use of left ventricular assist devices, the left ventricular apical core has become a more frequently encountered surgical pathology tissue. We investigated the prognostic value of this cardiac tissue in short-term patient mortality. Previous studies have shown that the degree of cardiac fibrosis correlates with improvements in ejection fraction and the likelihood of weaning from an assist device.MethodsLeft ventricular apical core tissues from 29 sequential subjects who received a HeartMate II continuous axial flow left ventricular assist device were studied retrospectively to determine whether interstitial fibrosis, replacement fibrosis (scar), the presence of mural thrombus, or other histopathologic findings were associated with hemodynamic changes or mortality in this population. Patients received left ventricular assist devices as bridges to transplantation or as destination therapy. Interstitial fibrosis was determined by observer scoring and digital scoring methods. Before and after left ventricular assist device procedure, right heart catheterizations were reviewed for clinical cardiac data.ResultsThe presence of replacement fibrosis in the apical core tissue significantly correlated with decreased improvement in pulmonary capillary wedge pressure after left ventricular assist device placement (P=.02). Ten subjects died over the course of this study. No specimen variables, including scar, interstitial fibrosis, and the presence of mural thrombosis, correlated with patient mortality.ConclusionsPathologic findings in left ventricular apical cores have little prognostic utility in guiding patient management as related to overall 1-year mortality, but may indicate patients who are more likely to positively remodel their hearts.     

Improvement in early oxygen uptake kinetics with left ventricular assist device support

Sustained myocardial recovery and reversal of heart failure has been reported with the use of left ventricular assist devices (LVADs). However, clinical predictors of sustained recovery have not been clearly defined, and little information exists regarding exercise improvement in LVAD patients. Therefore, we sought to determine whether peripheral oxygen delivery and utilization were improved with LVAD support. Eleven patients with available pre- and post-LVAD cardiopulmonary exercise (CPX) data were studied retrospectively. Five patients received a HeartMate XVE for destination therapy (DT) and six patients received a Thoratec PVAD pneumatic LVAD for bridge-to-recovery (BTR). Oxygen uptake kinetics was assessed by fitting a single exponential function to the VO2 response. There was a significant improvement in several key parameters of cardiac performance including peak VO2, VO2 at anaerobic threshold (AT), oxygen kinetics as measured by mean response time (MRT), and oxygen deficit during LVAD support. Oxygen deficiency improved from 0.29 +/- 0.16 ml/kg to 0.16 +/- 0.06 ml/kg (p = 0.023), as did MRT 68 +/- 47.7 seconds to 35.8 +/- 13.3 seconds (p = 0.046) with LVAD support. Improved oxygen kinetics suggests improved peripheral utilization of oxygen, and may offer an additional clinical parameter to predict the likelihood of sustained recovery.     

Papillary muscle rupture after myocardial infarction during left ventricular assist device support

We report a rare case of papillary muscle rupture due to myocardial infarction during left ventricular assist device support. A 69-year-old woman with cardiogenic shock due to acute myocardial infarction requiring venoarterial extracorporeal membrane oxygenation support was transferred for further surgical intervention. Six days after the event, extracorporeal membrane oxygenation was decannulated, and an extracorporeal left ventricular assist device was implanted. On postoperative day 11, she suffered from sudden onset hypoxia due to pulmonary edema. Transesophageal echocardiography showed new onset severe mitral regurgitation. No further surgical intervention was performed according to the family’s wishes, and she passed away on the 22nd postoperative day. Autopsy findings revealed papillary muscle rupture. Although the left ventricle is unloaded by the left ventricular assist device, papillary muscle rupture should be recognized as a possible complication after myocardial infarction.     

Outflow graft anastomosis site design could be correlated to aortic valve regurgitation under left ventricular assist device support

Aortic valve regurgitation (AR) is a critical complication during circulatory support with a left ventricular assist device (LVAD). The time-course of AR and related factors, including outflow graft anastomosis site design, were investigated. Twenty-three patients who had continuous-flow LVAD implantation and were supported for more than 6 months were investigated. AR grade (none, 0; trivial, 0.5; mild, 1; mild-moderate, 1.5; moderate, 2; moderate-severe, 2.5; severe, 3) and aortic valve opening were evaluated with echocardiography. Computed tomography was performed to all the patients postoperatively. The angle of the outflow graft to the aorta (O-A angle, parallel 0; tangent 90°, 0–180°), aortic diameter at the anastomosis site, sino-tubular junction (STJ) diameter, distance between the STJ and the anastomosis site, and distance between the anastomosis site and the brachiocephalic artery were measured. The patients’ age was 38?±?11 years. Support duration was 686?±?354 days. Mean AR grade after continuous-flow LVAD implantation was increased to around mild and was maintained thereafter. No patient needed any intervention to the aortic valve. The aortic valves of 82.6% of patients were closed continuously. The O-A angle (83?±?14) was positively correlated with maximum AR grade (p?=?0.0095). The O-A angle was significantly smaller in patients with maximum AR grade of 1 or less (77?±?9°) than in those with 1.5 or greater (94?±?15°, p?=?0.021). The other CT measurements had no correlation with AR grade. In conclusion, the O-A angle was correlated with AR grade progression. The O-A angle appears to be one of the important factors related to AR under continuous-flow LVAD support.     

Arterial pulsatility improvement in a feedback-controlled continuous flow left ventricular assist device: An ex-vivo experimental study

Continuous flow left ventricular assist devices (CF-LVADs) reduce arterial pulsatility, which may cause long-term complications in the cardiovascular system. The aim of this study is to improve the pulsatility by driving a CF-LVAD at a varying speed, synchronous with the cardiac cycle in an ex-vivo experiment. A Micromed DeBakey pump was used as CF-LVAD. The heart was paced at 140 bpm to obtain a constant cardiac cycle for each heartbeat. First, the CF-LVAD was operated at a constant speed. At varying-speed CF-LVAD assistance, the pump was driven such that the same mean pump output was generated. For synchronization purposes, an algorithm was developed to trigger the CF-LVAD each heartbeat. The pump flow rate was selected as the control variable and a reference model was used for regulating the CF-LVAD speed. Continuous and varying-speed CF-LVAD assistance provided the same mean arterial pressure and flow rate, while the index of pulsatility doubled in both arterial pressure and pump flow rate signals under pulsatile pump speed support. This study shows the possibility of improving the pulsatility in CF-LVAD support by regulating pump speed over a cardiac cycle without compromising the overall level of support.