Effects of Left Ventricular Assist and Aortic Graft Angle on Aortic Valve: A Hemodynamic Study / 医用生物力学

Objective To investigate the effect of left ventricular assist device (LVAD) and aortic graft angle on hemodynamics of aortic valve. Methods Three models of aorta and aortic valve with 45°, 60° and 90° anastomosis angles between LVAD and aorta were constructed, and an in vitro pulsating table was built for in vitro experiments. Using particle image velocimetry (PIV) system, three moments in the cardiac cycle ( T1 systolic peak, T rapid closure, T3 diastolic peak), were selected to study the hemodynamic state of aortic valve. Results Velocity vector, vorticity and viscous shear stress were used to evaluate the effect of LVAD anastomosis angle on hemodynamics of aortic valve. During the period of rapid valve closure, with the increase of graft angle, the blood flow velocity near the valve wall, the average vorticity and the maximum viscous shear stress all increased. Conclusions When the graft angle is lower, the impact velocity of blood on the valve is smaller, and the shear force on the valve decreases, so that the valve is in a better hemodynamic environment. This study provides references for the selection of anastomotic angles in clinical operations.

Learning Curve in Left Ventricular Assist Device Implantation: Low Volumes Do Not Equate Bad Outcomes

ABSTRACT Introduction: Most implantations of left ventricular assist devices (LVAD) are performed in low-volume centers. This study aimed to evaluate the procedural learning curve of HeartMate II (HM2) implantations by comparing outcomes between two time periods in a low-volume center. Methods: All 51 consecutive patients undergoing HM2 implantation between January 2009 and December 2017 were reviewed and allocated into 2 groups: early-era group (from 2009 to 2014; n=25) and late-era group (from 2015 to 2017; n=26). The primary outcome was the 90-day mortality rate, and the secondary outcome was a composite of mortality, neurological event, reoperation for bleeding, need for temporary right ventricular assist device, and pump thrombosis at 90 days. Median follow-up time was 51 months (0-136). A cumulative sum (CUSUM) control analysis was used to establish a threshold of implantations that optimizes outcomes. Results: Patients in the early era had a higher rate of diabetes, previous stroke, and inotrope support before HM2 implantation. The 90-day mortality rate was not significantly higher in the early era (24% vs. 15%, P=0.43), but the composite endpoint was significantly higher (76% vs. 42%, P=0.01). The CUSUM analysis found a threshold of 23 operations after which the composite endpoint was optimized. Conclusion: Patients undergoing HM2 implantation in a low-volume center have improving outcomes with number of cases and optimized results after a threshold of 23 cases. Significant changes in patient selection, surgical techniques, and patient management might lead to improved outcomes after LVAD implantation.

Early outcomes of heart transplantation in critical patients: single center experience of Fuwai Hospital / 器官移植

Objective To analyze the early outcomes of heart transplantation in critical patients and its significance in donor allocation decision. Methods Clinical data of 449 recipients undergoing heart transplantation were retrospectively analyzed. According to preoperative status, all patients were divided into the critical status group (n=64) and general status group (n=385). The incidence of critical status was summarized. Clinical data of recipients were statistically compared between two groups. Postoperative survival and causes of death in recipients between two groups were analyzed. Perioperative results of critical recipients undergoing different mechanical circulation support as a bridge to heart transplantation were compared. Results Critical patients accounted for 14.3% of the total number of transplant recipients. The proportion of critical patients gradually increased in recent 5 years. Compared with the general status group, the recipients in critical status group had a lower proportion of smoking history, a higher proportion of cardiac surgery history, a higher serum level of creatinine, and a higher proportion of primary diseases of heart failure before heart transplantation(all P≤0.01). The proportion of undergoing mechanical circulation support was higher, the incidence of complications was higher, the stay time in intensive care unit (ICU) was longer and the in-hospital fatality was higher after heart transplantation in the critical status group (all P≤0.01). The 1-year survival rate of recipients in critical status group was significantly lower than that in general status group (83% vs. 95%, P < 0.01). The fatality of recipients due to infection and multiple organ failure in critical status group was higher than that in general status group. Among 64 critical recipients, 1 recipient received ventilator alone, and 63 recipients underwent mechanical circulation support devices as a bridge to heart transplantation. Among them, intra-aortic balloon pump (IABP) alone was applied in 49 cases (77%), 8 cases (13%) of extracorporeal membrane oxygenation (ECMO) combined with IABP, 4 cases (6%) of ECMO alone, and 2 cases (3%) of left ventricular assist device (LVAD) alone. Critical patients who received preoperative ECMO and ECMO combined with IABP bridging to heart transplantation have a higher proportion of postoperative complications, a longer ICU stay time, a longer mechanical ventilation time, and a higher proportion of hospital deaths. Conclusions The overall prognosis of critical patients undergoing heart transplantation is relatively poor. Effective preoperative management may reverse the high-risk status of critical patients in a certain extent. The limited quantity of donor heart should be allocated to the most urgent patients who can obtain the greatest benefit from heart transplantation.

Hemodynamic Analysis on Meglev Left Ventricular Assist Device of a New Generation / 医用生物力学

Objective To reduce the thrombosis probability and hemolysis risk of the meglev left ventricular assist device (LVAD), so as to increase the efficiency of blood supply. Methods The influences of the pump outlet diameter, exit angle, fillet size between the outlet and the inner wall of the pump, as well as gap between the rotor and the shell on internal flow field of the pump were studied by using the computational fluid dynamics (CFD) method, so as to optimize the internal structure and improve the hydrodynamic performance of the pump. Results Compared with pump of the previous generation, the maximum wall shear stress (WSS) of the pump inner wall, the maximum WSS of the pump rotor, the area with WSS >200 Pa were reduced by 23.6%, 47.4%, 76.2%, respectively, while the outlet flow was increased by 14.4%. Conclusions For the meglev LVAD of the new generation, its internal blood flow tended to be smooth, and the hemodynamic performance of blood flow was improved comprehensively. The research findings provide references for optimization design of the meglev LVAD and related experimental researches in the future.

Two Cases of Bioprosthetic Valve Stenosis of the Aortic Valve Position Found on Weaning of a Nipro Left Ventricular Assist Device / 日本心臓血管外科学会雑誌

The first case was a 67-year-old woman. She had been given a diagnosis of fulminant myocarditis and received a biventricular assist device as a bridge to recovery. A Nipro ventricular assist device (VAD) was implanted into her left heart. She was also found to have moderate aortic insufficiency before the operation, so she received aortic valve replacement (AVR) with a bioprosthetic valve (CEP Magna Ease 21 mm) at the same time. Her cardiac function recovered gradually. Therefore, a weaning operation was scheduled for three months after the VAD implantation. However, her left ventricle motion was very poor when she was taken off of the extracorporeal circulation after removing the VAD, and transesophageal echocardiography (TEE) revealed severe bioprosthetic valve stenosis. When her heart was stopped again and the bioprosthetic valve was observed, the leaflets of the bioprosthetic valve were fused. Commissural fusion of bioprosthetic valve was able to be released using forceps, and the punnus extending under the leaflet was removed. In this way, the function of the bioprosthetic valve was restored. Her cardiac motion became good, and removal from extracorporeal circulation was easily achieved. She left the hospital 100 days after weaning from the VAD. The second case was a 68-year-old woman. She also had fulminant myocarditis. She underwent biventricular assist device implantation and AVR (CEP Magna Ease 19 mm). Her cardiac function recovered, and a weaning operation was scheduled on the 73rd-postoperative day. Preoperative TEE before the weaning of VAD showed severe bioprosthetic valve stenosis. The commissural fusion of the bioprosthetic valve was released and the punnus extending under the leaflet removed at the same time as the VAD was removed. Re-valve replacement was not required. We should therefore consider the possibility of bioprosthetic valve stenosis when VAD implantation and AVR with a bioprosthetic valve are performed at the same time in patients with an extremely reduced cardiac function.

Exercise Therapy for an Older Patient With Left Ventricular Assist Device

A left ventricular assist device (LVAD) is a mechanical circulation support implanted for patients with end-stage heart failure. It may be used either as a bridge to cardiac transplantation or as a destination therapy. The health of a 75-year-old man with a medical history of systolic heart failure worsened. Therefore, he was recommended to have implanted a LVAD (Thoratec Corp.) as a destination therapy. After the surgery, he was enrolled in patient cardiac rehabilitation for the improvement of dyspnea and exercise capacity. In results, there is an improvement on his exercise capacity and quality of life. For the first time in Korea, we reported a benefit of exercise therapy after being implanted with a LVAD.

A Case of Long Term Survival for Left Ventricular Assist Device Related Mediastinitis with Negative Pressure Wound Therapy / 日本心臓血管外科学会雑誌

A 44-year-old man who received left ventricular assist device (LVAD) implantation for end-stage heart failure due to dilated cardiomyopathy suffered from mediastinitis. Computed tomography confirmed mediastinitis. His mediastinum was reopened and irrigated. Negative pressure wound therapy (NPWT) was applied to the wound without closing the chest. This system enabled the patient to receive early physical rehabilitation. One year after LVAD implantation, under NPWT, the patient could walk in the general ward, and was waiting for cardiac transplantation. We used some useful materials for NPWT including a coatable non-alcoholic film, flexible sealing sheet, soft exudate absorber, in order to control wound clean, keep air-tight, prevent damage to the skin and to reduce mediastinal instability. LVAD implantation is usually performed as a bridge to transplantation or recovery. One of the most critical complications is intractable mediastinitis. We described a successful infection control of LVAD related mediastinitis with the NPWT.

Theoretical Estimation of Cannulation Methods for Left Ventricular Assist Device Support as a Bridge to Recovery

Left ventricular assist device (LVAD) support under cannulation connected from the left atrium to the aorta (LA-AA) is used as a bridge to recovery in heart failure patients because it is non-invasive to ventricular muscle. However, it has serious problems, such as valve stenosis and blood thrombosis due to the low ejection fraction of the ventricle. We theoretically estimated the effect of the in-series cannulation, connected from ascending aorta to descending aorta (AA-DA), on ventricular unloading as an alternative to the LA-AA method. We developed a theoretical model of a LVAD-implanted cardiovascular system that included coronary circulation. Using this model, we compared hemodynamic responses according to various cannulation methods such as LA-AA, AA-DA, and a cannulation connected from the left ventricle to ascending aorta (LV-AA), under continuous and pulsatile LVAD supports. The AA-DA method provided 14% and 18% less left ventricular peak pressure than the LA-AA method under continuous and pulsatile LVAD conditions, respectively. The LA-AA method demonstrated higher coronary flow than AA-DA method. Therefore, the LA-AA method is more advantageous in increasing ventricular unloading whereas the AA-DA method is a better choice to increase coronary perfusion.

The Leaving Hospital Program of the Patient with LVAD for Destination Therapy / 日本心臓血管外科学会雑誌

The left ventricle assist device (LVAD) has become an important therapeutic option in the treatment of acute or chronic heart failure. It is usually used as bridge to transplantation or recovery. At present, destination therapy with LVAD has been a therapeutic option in patients with heart failure in whom transplantation is not indicated. We describe a patient, who received destination therapy with LVAD, and was able to go home temporarily. The patient was a 63-year-old man with low output syndrome after acute myocardial infarction. An LVAD (TOYOBO) was implanted at Oita University Hospital, however the patient suffered from MRSA mediastinitis 6 months later. He and his family wished for him to temporarily go home to Ibaraki. The patient, supported by LVAD, was transferred from Oita to Ibaraki by a regular commercial flight and ambulance. Rehabilitation training involved stretching, in-bed muscle strength training, maintaining a standing position, walking on flat ground with a walker and going up and down ramps. All training was measured at the patient's home. The patient was out of hospital for 5 hours, and this period was uneventful upon leaving hospital. The patient also took an active part in rehabilitation after discharge. This program can help to improve the quality of life (QOL) of patients with implanted LVADs for destination therapy.