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At least 19 recordsLinked to original sources
PubMed1997

Estimation of the minimum pump speed to prevent regurgitation in the continuous flow left ventricular assist device: left ventricular drainage versus left atrial drainage.

Due to the fact that centrifugal and axial pumps do not require valves, there is a possibility of back flow when the pump speed is low. To estimate the minimum required pump speed to prevent this regurgitation, an in vitro simulation test was conducted. A pulsatile pump simulated the natural heart while a centrifugal pump simulated the continuous flow left ventricular assist device (LVAD). The LVAD flow was attained from the left atrial (LA) drainage or left ventricular (LV) drainage. The minimum or regurgitate flow was observed in the systolic phase with LA drainage and in the diastolic phase with LV drainage. LV drainage always provided higher flow than LA drainage at the same pump speed. These differences are due to the various total pressure heads of the LVAD. To prevent the regurgitation, the LVAD should maintain a certain pump speed which can create positive flow against the aortic systolic pressure with LA drainage and against the aortic diastolic pressure with LV drainage. These required pump speeds can be identified by the LVAD flow-pressure curve.

Aortic Valve Insufficiency↗
PubMedDate not supplied

Intravascular ultrasound imaging of the Heartmate 1000 IP left ventricular assist device.

Left ventricular assist devices are increasingly used as a bridge to transplantation in patients with end-stage cardiac disease. Potential complications of these devices include thromboembolism and infection. Because conventional cardiac diagnostic techniques cannot be used to obtain an image of the interior of a left ventricular assist device, we assessed the ability of intravascular ultrasonography to obtain an image of the interior of the Heartmate 1000 IP left ventricular assist device. Feasibility of intravascular ultrasound imaging was initially demonstrated in vitro on a left ventricular assist device immersed in water. Five soft rubber masses were then placed in the device intake port adherent to the wall, and their images were obtained by intravascular ultrasonography. Excellent correlation between actual size and size as measured by intravascular ultrasonography was noted (long-axis, r = 0.98, short-axis, r = 0.89). After the device was implanted in two calves, intravascular ultrasound imaging was performed in vivo in the animals. The catheter was easily advanced through the device, and excellent images were obtained. In conclusion, intravascular ultrasonography can easily be used to obtain an image of the left ventricular assist device interior and can accurately assess the presence and size of abnormal masses inside the device. Intravascular ultrasonography may be clinically useful in evaluating cases of thrombus or vegetation related to left ventricular assist devices.

Animals↗
PubMed2003

Timing of transesophageal echocardiography in diagnosing patent foramen ovale in patients supported with left ventricular assist device.

Left ventricular assist devices unload the left ventricle and decrease left atrial pressure. This hemodynamic change may cause a right to left atrial shunt and hypoxemia in patients with patent foramen ovale. We prospectively studied the best time for performing diagnostic transesophageal echocardiography in left ventricular assist device patients. Intraoperative transesophageal echocardiography was performed in 14 patients before cardiopulmonary bypass was initiated and after left ventricular assist device was implanted. No patent foramen ovale was detected when transesophageal echocardiography was done before bypass, but a patent foramen ovale was found in 3 patients when transesophageal echocardiography was performed after left ventricular assist device was activated. Patent foramen ovale was confirmed by inspection in all three patients and surgically closed during the same procedure. There were no patent foramen ovale closure-related complications.

Cardiac Surgical Procedures↗
PubMed1996

Activation of coagulation and fibrinolytic pathways in patients with left ventricular assist devices.

Left ventricular assist devices have provided successful supportive therapy for patients awaiting cardiac transplantation for extended periods of time. Although thromboembolic events have complicated support with these devices, the HeartMate left ventricular assist device developed by Thermo Cardiosystems, Inc., Woburn, Massachusetts, was specifically designed with a textured blood-contacting surface to minimize this risk. Clinical experience with this device has been encouraging, inasmuch as minimal thromboembolic complications have occurred despite the absence of anticoagulation. The coagulation and fibrinolytic pathways in these individuals were investigated to better understand the hematologic status of patients treated with the Thermo Cardiosystems device. Despite apparently normal prothrombin and activated partial thromboplastin times, as well as platelet counts, evidence of significant thrombin generation and fibrinolysis was present. To eliminate underlying cardiac failure as the responsible factor for these abnormalities, we made similar measurements in patients with end-stage heart failure who were not supported by an assist device or anticoagulation. These measurements revealed no evidence of thrombin generation or fibrinolysis. These data demonstrate that patients supported with a left ventricular assist device, while successfully sustained without systemic anticoagulation, nevertheless have evidence of activation of coagulation. These phenomena appear to be related to the presence of the device rather than to the underlying cardiac abnormalities. Although procoagulant and fibrinolytic pathways are apparently balanced in these patients, these data underscore the potential for the development of bleeding or thrombosis in clinically relevant settings.

Adolescent↗
PubMed2005

Imaging of left ventricular assist devices.

Left ventricular assist devices are used as a bridge to recovery, a bridge to transplant, or a permanent alternative to cardiac transplant. This exhibit demonstrates the imaging appearance of commonly used left ventricular assist devices and their complications.

Brain↗
PubMed2002

[Myocardial alterations with mechanical left ventricular assist devices].

Left ventricular assist devices (LVAD) have been used to "bridge" patients with end-stage heart failure to transplantation. Although several reports have suggested that the native ventricular function recovers after long-term LVAD support, a process called "reverse remodeling", the underlying biological mechanisms are still unclear. Various molecular pathways of the human myocardium associated with apoptosis, response to stress, or matrix changes are known to be altered under conditions of heart failure, and some have been shown to be reversibly regulated during left ventricular mechanical support, suggesting that the descriptive term "reverse remodeling" is, at least in parts, a reversible mechanism. The reduction of volume and pressure overload with a decrease of ventricular wall stress leading to an improvement of myocardial blood supply under mechanical circulatory assistance, may be one explanation for the molecular myocardial changes and may reflect one possible cause for the phenomenon of "reverse remodeling".

Animals↗
PubMed1993

The PUCA pump: a left ventricular assist device.

Left ventricular assist devices (LVADs) that are being used clinically still have specific drawbacks. Therefore, a new concept for mechanical circulatory support was developed, the pulsatile catheter (PUCA) pump. It consists of an extracorporeally placed, pneumatically driven membrane pump that is connected to a valved catheter. The catheter is introduced into an easily accessible artery and positioned with its distal tip in the left ventricle. Blood is aspirated from the left ventricle and ejected into the ascending aorta. Potential advantages of the catheter pump are its simple design and its fast application with minimal surgery. Preliminary in vitro tests with a first prototype showed that it is possible to create a pulsatile flow of 3 L/min and proved that further developing the PUCA pump will be worthwhile.

Heart-Assist Devices↗
PubMedDate not supplied

Exercise capacity recovers slowly but fully in patients with a left ventricular assist device.

Left ventricular assist devices (LVAD) are used increasingly as bridges to cardiac transplantation. The typical LVAD candidate is a bedridden, critically ill, New York Heart Association (NYHA) Class IV patient with congestive heart failure (CHF) who is dependent upon intravenous, inotropic, and, in many cases, intra-aortic balloon support. The LVAD provides the potential for pre transplant rehabilitation by allowing the patient to become ambulatory, and by improving muscle tone, muscle mass, and nutritional status before transplantation. However, whether the abnormal exercise capacity of these patients improves after implantation has not been elucidated. The purpose of the present study was to evaluate the exercise capacity of patients with CHF after LVAD implantation (n = 10) using peak oxygen consumption during maximal exercise (MVO2), and comparing the results with those of a group of NYHA Class III patients with CHF (n = 14). After 2 months of implantation, MVO2 of the patients with LVAD was 12.8 +/- 0.3 ml/kg/min, which was comparable to that of the NYHA Class III patients with CHF (12.5 +/- 0.5 ml/kg/min). Four of 10 patients with LVAD were monitored for more than 5 months when MVO2 rose to 15.4 +/- 1.0 ml/kg/min (p < 0.05 vs NYHA Class III). In conclusion, the exercise capacity of patients with LVAD recovers slowly but significantly after 5 months of implantation, promising the potential for complete recovery from heart failure in patients supported with an LVAD.

Adult↗
PubMedDate not supplied

Assessment of biventricular cardiac function in patients with a Novacor left ventricular assist device.

Novacor left ventricular assist devices were implanted in 10 patients. We used blood-pool radionuclide angiography and echocardiography to evaluate the response of the left and right ventricle to the left ventricular assist. Radionuclide angiography was done before and after implantation of the Novacor left ventricular assist devices in all cases. All patients had diffuse left ventricular enlargement; the mean left ventricular ejection fraction before Novacor left ventricular assist device implantation was 17% +/- 7%. After implantation of the Novacor left ventricular assist devices the left ventricular ejection fraction improved to 47% +/- 19%, with the pump on a 1:1 assist ratio (p < 0.005). The right ventricular ejection fraction before the Novacor left ventricular assist device implantation was 21%, which improved to 32% with the Novacor left ventricular assist devices (p < 0.01). Doppler echocardiography was carried out in nine patients with the left ventricular assist devices. In five patients the aortic valve remained closed throughout systole. In four patients partial aortic valve opening was noted. At an assist ratio of 1:3, complete opening of the aortic valve was noted in all cases (n = 9); the left ventricular ejection fraction decreased to 31%. We conclude that the Novacor left ventricular assist device substantially improves both right ventricular ejection fraction and left ventricular ejection fraction, although the aortic valve typically remains closed.

Echocardiography↗
PubMed1997

Development of a direct mechanical left ventricular assist device for left ventricular failure.

We have developed a direct mechanical left ventricular assist device (DMLVAD) for severe left ventricular failure. The DMLVAD was attached to the left ventricle and compressed the heart by a pneumatic driving unit. In a mock circulation model with an extracted nonbeating heart, a cardiac output (CO) of 1.93 L/min was obtained at a driving pressure of 200 mm Hg. In a canine left ventricular failure model induced by injection of sodium hydroxide into the myocardium, the systolic arterial pressure, systolic left ventricular pressure, maximum LV dP/dt, peak flow, and CO increased by 21, 24, 58, 144, and 37%, respectively. The mean left atrial pressure also decreased by 15% when the DMLVAD was driven. These effects were most prominent when the mean left atrial pressure was over 15 mm Hg, and the driving pressure was over 100 mm Hg. Compression at late systole was more effective in obtaining greater CO. We suggest that the DMLVAD could be an optional circulatory assist device for patients with left ventricular failure awaiting heart transplantation.

Animals↗
PubMedDate not supplied

Assessment of timing right ventricular assist device withdrawal using left ventricular assist device filling characteristics.

Right ventricular assist devices (RVAD) are often needed on a short term basis in patients who develop RV failure after left ventricular assist device (LVAD) implantation. The purpose of this study was to use LVAD filling characteristics to help determine the timing for weaning a patient from RVAD support. Eleven patients (age 50 years +/- 15) supported with an LVAD (Novacor) and an RVAD (Biomedicus or ABIOMED) were studied. Eight patients (RV recovery group) were studied before RVAD removal and all were successfully weaned from RVAD support. Five patients (RV failure group) were studied at the time of RVAD placement to determine baseline characteristics of RV failure. Simultaneous measures of LVAD volume and routine hemodynamics were recorded during periods of high and low RVAD flow. The LVAD filling was assessed as the first derivative of LVAD volume and the mean filling rate for each cardiac cycle was calculated and averaged over 10 sec periods at both RVAD flows. The mean pump rate corrected filling rates did not change in the RV recovery group (89 +/- 13 vs. 87 +/- 8 ml/beat) and significantly decreased in the RV failure group (84 +/- 19 vs. 62 +/- 22 ml/ beat) (p < 0.001) with decreasing RVAD flow. These data suggest that LVAD filling rates may be used to assess RV systolic function and the proper timing of RVAD removal in selected patients.

Adult↗
PubMed2003

Immunologic sensitization in recipients of left ventricular assist devices.

OBJECTIVE: Left ventricular assist device implantation is associated with an increased risk of development of circulating anti-HLA class I and II antibodies (sensitization). We investigated the impact of sensitization on posttransplantation outcomes in 105 consecutive left ventricular assist device recipients. METHODS: Five hundred twenty-one consecutive adult cardiac allograft recipients between 1992 and 1999 were retrospectively studied. Of these, 105 were supported with a left ventricular assist device. Pretransplantation and posttransplantation antibody production, time to transplantation after listing, rejection, freedom from transplant coronary artery disease, and survival were evaluated by Kaplan-Meier analysis. Among sensitized left ventricular assist device recipients, 26 were treated with a pretransplantation immunomodulatory regimen consisting of intravenous immunoglobulin and cyclophosphamide. RESULTS: There were no significant differences between left ventricular assist device recipients and nonbridged recipients with respect to pretransplantation demographic characteristics and ABO and HLA matching. Among left ventricular assist device recipients, 66% (69/105) were sensitized before transplantation; in contrast, only 6% (24/399) of nonbridged recipients were sensitized (P <.001). Sensitized untreated left ventricular assist device recipients had both a prolongation of waiting time to transplantation and an increased risk of acute rejection. Pretransplantation immunomodulatory therapy reduced both the increased waiting time and the increased risk of acute rejection. However, sensitization or the use of immunomodulatory therapy in left ventricular assist device-bridged recipients did not influence posttransplantation survival relative to nonbridged recipients. CONCLUSIONS: Left ventricular assist device recipients have survival outcomes similar to those of nonbridged recipients after cardiac transplantation, despite their significantly higher immunologic risk. The reduced rate of transplantation and the increased incidence of rejection observed in sensitized left ventricular assist device recipients are prevented by immunomodulatory therapy. Sensitization will remain an important issue with increased use of left ventricular assist devices, and improved understanding of this is essential to achieve better outcomes in the management of patients with end-stage heart failure.

Actuarial Analysis↗
PubMed2001

The use of muscle flaps to treat left ventricular assist device infections.

Left ventricular assist devices have become an important adjunct in the therapeutic armamentarium for patients with end-stage heart failure. Although they may provide a bridge to transplantation, they are prone to certain problems, expecially infection. Because these are life-sustaining devices, changing the device or simple explantation may be a risky, if not impossible, option. Therefore, we evaluated the effectiveness of a surgical alternative, namely, coverage of infected devices with muscle or myocutaneous flaps. Eighty-two consecutive patients who underwent the insertion of 88 left ventricular assist devices at our institution over a 6.5-year period were evaluated. Follow-up was provided for all patients and ranged from 1 to 7.5 years. The duration of ventricular support ranged from 0 to 434 days. All patients who demonstrated clinical evidence of infection were identified. Overall, 54 patients (66 percent) had infections locally at the device site, at distant sites, or systemically during support. Cultured organisms included gram-positive and -negative bacteria, fungi, and viruses. Of the 56 infections in these 54 patients, 21 (38 percent) were device-related, i.e., in the pocket created by the device, in the device itself, or from the driveline. Thus, 24 percent (21 of 88) of all ventricular support devices inserted demonstrated device infection during use. Therapeutic modalities used to combat device-related infection included both nonsurgical management with antibiotics alone and surgical procedures such as device change or relocation, device explant, and flap coverage. Eight of the 20 patients in whom the 21 device-related infections occurred underwent surgical intervention. Four of these eight patients undenwent local flap coverage of their infected left ventricular assist devices. All four patients also had evidence of systemic infection, or "device endocarditis." Coverage was successfully achieved in all cases with pedicled rectus abdominis flaps. There were no perioperative complications. Two patients later underwent successful transplantation; the other two died from causes unrelated to the flap. In conclusion, the treatment of infected left ventricular assist devices currently includes both nonsurgical and surgical alternatives. Of the latter, muscle flaps should be considered a first-line intervention to assist in eradicating infection by providing well-vascularized tissue. Although there were no perioperative complications, the 50 percent mortality rate is consistent with that reported for patients with "device endocarditis." It may be that flap coverage of infected ventricular assist devices, if instituted at an earlier stage in the therapeutic process, could help prevent systemic infection in these patients and, therefore, improve their overall outcome.

Adolescent↗
PubMedDate not supplied

Gastrointestinal consequences of left ventricular assist device placement.

Left ventricular assist devices effectively improve hemodynamic function and reverse renal and hepatic dysfunction; however, their effects upon the gastrointestinal (Gl) system have not been addressed. We evaluated Gl function in 27 left ventricular assist device recipients using interviews, Gl contrast studies, endoscopy, and 99mTc sulfur colloid studies of esophageal transit and gastric emptying. While on left ventricular assist device support (mean duration of 84 days), 19 patients reported early satiety and/or nausea, and 1 was unable to tolerate oral intake. Esophageal transit time (normal, < 10 sec) was borderline slow at 14 +/- 4 (mean +/- standard error of the mean) and gastric emptying (normal < 90 min) was prolonged (range of 106-506 min, mean = 283 +/- 69 min). In a 1-38 month follow-up, gastric function subjectively improved in all. Six patients had intraperitoneal device placement. One died of aspiration pneumonia secondary to small bowel obstruction, and one had prolonged inability to tolerate oral intake, which required feeding jejunostomy tube placement. The 21 patients with pre peritoneal placement of the device did not require Gl operative interventions and had no catastrophic Gl events; they had mild to no Gl complaints. Pre peritoneal placement may mitigate early satiety and obviate serious Gl complications.

Digestive System Physiological Phenomena↗
PubMed2006

Progress versus precision: challenges in clinical trial design for left ventricular assist devices.

New left ventricular assist devices promise fewer adverse events but, currently, only minor improvements in survival. Small (survival) treatment effects, limited patient populations, and the increasing number of left ventricular assist devices in development challenge the efficient conduct of premarketing trials (especially in destination therapy) and, maybe more importantly, hamper innovation. Novel trial designs would facilitate this process. Among a range of trial designs, we opt for small randomized trials, which would preserve the advantages of randomization and also allow for a shorter enrollment period. We also advocate an evidence shift toward postmarketing studies, with the Interagency Registry of Mechanically Assisted Circulatory Support providing a robust infrastructure.

Biomarkers↗