The angle of the outflow graft to the aorta can affect recirculation due to aortic insufficiency under left ventricular assist device support

Aortic insufficiency (AI) is a crucial complication during continuous-flow left ventricular assist device (LVAD) support. Our previous clinical study suggested that a larger angle between the outflow graft and the aorta (O–A angle) could cause AI progression. This study examined the effect of the O–A angle on the hemodynamics of AI under LVAD support in an acute animal experimental model. An LVAD was installed in seven calves, with the inflow cannula inserted from the LV apex and with the outflow graft sutured at the ascending aorta. The AI model was made using a temporary inferior vena cava filter inserted from the LV apex and placed at the aortic valve. Cardiac dysfunction was induced by continuous beta-blocker infusion. Hemodynamic values and the myocardial oxygen extraction rate (O₂ER) were evaluated at three O–A angles (45°, 90°, and 135°) over three levels of AI (none, Sellers I–II AI, and Sellers III–IV AI). The recirculation rate, defined as the percentage of regurgitation flow to LVAD output, was calculated. Systemic flow tended to decrease with a larger O–A angle. The recirculation rate was significantly increased with a larger O–A angle (22, 23, and 31% at 45°, 90°, and 135° in Sellers III–IV AI, respectively). Coronary artery flow was decreased at a larger O–A angle (86, 76 and 75 mL/min at 45°, 90°, and 135° in Sellers I–II AI, respectively, and 77, 67, and 56 mL/min at 45°, 90°, and 135° in Sellers III–IV AI, respectively). O₂ER tended to increase with a larger O–A angle (40, 43, and 49% at 45°, 90°, and 135° in Sellers III–IV AI, respectively). A larger O–A angle can increase the recirculation due to AI and can be disadvantageous to LVAD-AI hemodynamics and myocardial oxygen metabolism.     

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.     

Left ventricular assist device support induces acute changes in myocardial electrolytes in heart failure

The regulation of myocardial electrolyte concentrations is critical to proper cardiac function. Myocardial ischemia is associated with deranged ion transport. Left ventricular assist device (LVAD) therapy improves myocyte bioenergetics in chronic heart failure (CHF), which may manifest as electrolyte alterations; however, rapid electrolyte shifts may place critically ill patients at risk for arrhythmias upon initiation of LVAD support. We examine the effect of incremental increases in LVAD support on acute changes in myocardial arteriovenous electrolytes in CHF. CHF was induced in sheep via coronary microembolization. Four months later, sheep underwent acute LVAD implantation. LVAD support was incrementally increased (0%, 25%, 50%, 75% support). Paired arterial and coronary sinus blood samples were obtained at each increment and analyzed for K+, Ca2+, and Na+ concentrations. Arteriovenous electrolyte concentrations (mmol/l) were inverted in CHF before LVAD support: K+ (-0.08), Ca2+ (-0.04), and Na+ (0.04). These imbalances were corrected within 20 minutes and with as little as 25% LVAD support: K+ (0.06), Ca2+ (0.012), and Na+ (-0.80). The arteriovenous differences further widened as LVAD support was increased. In conclusion, LVAD support in CHF induces acute alterations in myocardial electrolytes. Rapid shifts myocardial arteriovenous electrolyte balances during LVAD support may in part explain the incidence of post-LVAD arrhythmias observed clinically in humans.     

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.     

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.     

Intermittent aortic insufficiency as an aid to diagnosing obstruction in a HeartMate II continuous-flow left ventricular assist device

This report details two cases of left ventricular assist device (LVAD)-related fungal infection. In both cases, the infection occurred within the device and formed an obstruction resulting in intermittent variation in the output of the LVAD. This was manifested by a change in the pattern of aortic insufficiency (AI) from continuous to intermittent on transesophageal echocardiography. Recognition of this finding may allow for noninvasive diagnosis of LVAD flow obstruction.     

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.     

Effects of continuous flow left ventricular assist device support on skin tissue microcirculation and aortic hemodynamics

Continuous flow ventricular assist devices (CFVADs) are thought to be the next generation of circulatory assist devices. With many now in various stages of development or clinical trial, it is important that the physiologic aspects of these pumps be critically analyzed. In this study, 15 calves were divided into two groups. One group received a CFVAD, and the other a sham implant. Two additional animals were used in an acute study to examine aortic blood flow patterns from a CFVAD. Tissue perfusion was measured on all animals before surgery and then weekly thereafter. Before surgery, there was no difference in hemodynamics or tissue perfusion between studied animals. Postoperatively, CFVAD animals had statistically significant increased diastolic pressure. Significantly decreased pulse pressure, pulse index, and tissue perfusion were also observed in CFVAD animals. Results from the flow pattern studies suggested that at moderate levels of pump support (40-75%), the amount of blood flow distal to the outflow graft anastomosis decreased approximately 25% because of increased regurgitant blood flow in the aorta. These results suggest that the diminished tissue perfusion is likely due to changes in aortic hemodynamics and provide some insight into the distribution of flow from CFVADs.     

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...     

Development of a new left ventricular assist device: the dynamic aortic valve

We have been developing a new left ventricular assist device, an axial flow pump implanted at the aortic valve position. Since the device is intended for long-term use, its motor unit and pump are physically separated. The device consists of a "rotor-impeller" and a support cage. The rotor joins the impeller at one end and provides torque needed to spin the impeller. The support cage consists of a cantilever, a cantilever shaft, a top ring, and an end ring. The support cage is designed to fit within the ascending aorta and sutured to the aortic annulus during implantation. The magnetic rotor will rotate in the presence of alternating magnetic fields generated by an electric motor. The assembly also serves as a valve by maintaining the appropriate pressure drop across the aortic orifice. A prototype device was fabricated and tested in vitro. It produced a flow rate up to 5 L/min with a rotation rate of 12,600 rpm at a pressure difference of 100 mm Hg. The results proved the feasibility of the new device.     

Four-year paracorporeal left ventricular assist device (LVAD) support for heart failure after Rastelli operation

It is well known that heart failure can occur after a conventional Rastelli operation (using an anatomical right ventricle as a systemic ventricle) in patients with congenitally corrected transposition of the great arteries (CCTGA). At present, heart transplantation (HTx) is the only definitive therapy known to save such patients. The left ventricular assist device (LVAD) has been employed for patients presenting with acute deterioration of chronic heart failure as a bridge to transplantation when early HTx is not feasible. LVAD implantation in postoperative cases and/or in patients with dextrocardia is often difficult because of the complex anatomy. We report the case of a 26-year-old male patient with CCTGA who presented with heart failure after a conventional Rastelli operation and in whom paracorporeal LVAD implantation was undertaken for the management of right (systemic) ventricular failure. The patient recovered from the heart failure and remained on the HTx list for approximately 4 years with LVAD support.     

Fibrinolytic activation during long-term support with the HeartMate II left ventricular assist device

Human physiologic responses to pulsatile left ventricular assist devices (LVADs) are well understood; responses to the newer continuous flow pumps are not. Therefore, we evaluated the long-term effects of continuous flow LVAD support on fibrinolytic activation. Twelve recipients of an axial flow LVAD as destination therapy were assessed for fibrinolytic activation at 1, 3, 6, 9, and 12 months postimplantation. The fibrinolytic response and changes were assessed in terms of fibrinogen, D-dimer, plasma free hemoglobin, international normalized ratio (INR), and red blood cell (RBC) sedimentation rate. Bleeding and thromboembolic events were recorded. All fibrinolytic response parameters were elevated at baseline; mean RBC sedimentation rate was 51.8 mm/h, mean D-dimer was 3.95 nmol/L, and the mean fibrinogen was 356 mg/dl. The D-dimer and fibrinogen levels increased after LVAD implantation but returned to near-normal levels by 12 months. Red blood cell sedimentation rates increased indicating ongoing inflammation. Plasma free hemoglobin values decreased and remained low, an indicator of low shear rates and hemolysis. Three nonfatal bleeding events but no thromboembolic events were observed. Fibrinolytic responses initially increase after LVAD implantation but then gradually normalize.     

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.     

Clinical potential of hemodynamic ramp test by simultaneous echocardiography and right heart catheterization for aortic insufficiency in a patient with continuous-flow left ventricular assist device

Journal of Artificial Organs - Aortic insufficiency (AI) is an important adverse event in patients with continuous-flow (CF) left ventricular assist device (LVAD) support. AI is often progressive,...     

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.     

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.