Experimental Assessment of Right Ventricular Function in Normal Pigs with a Left Ventricular Assist Device

Abstract: Right ventricular (RV) failure during the use of a left ventricular assist device (LVAD) is the leading cause of death in circulatory support patients. Previous work, both experimentally and clinically, has shown the difficulties in predicting the behavior of the right ventricle at the start of LVAD. An experimental study has been designed to evaluate RV functional changes during LVAD and its relation to preload changes. The model used adult mongrel pigs (n = 10). Right ventricular functional parameters were measured with a thermodilution RV ejection fraction catheter. The left ventricle was supported by a Nippon Zeon blood pump. Two groups were studied, the first one was the LVAD–off group (n = 5) and the other was the LVAD–on group (n = 5) which was supported by LVAD at maximum flow. Change of cardiac output, mean pulmonary artery pressure (PAP), RV stroke work, and RV ejection fraction in both groups were not significantly different. However, the relationship between right ventricular end–diastolic pressure (RV–EDP) and right ventricular stroke volume (RVSV) was significantly changed at a high level of RV–EDP. When RV–EDP was over 6. 5 mm Hg in the LVAD–off group, RVSV decreased to 52. 3 ± 11. 5 ml while in the LVAD–on group, RVSV increased to 97. 2 ± 22. 0 ml. The change in PAP in the LVAD–on group was lower than in the LVAD–off group. We conclude that, at the volume overload state, LVAD can reduce the afterload of the right ventricle and maintain Frank–Starling's effect, thus having a beneficial effect on right ventricular performance.     

Efficacy and mechanisms of biventricular and left/right direct cardiac compression in acute heart failure sheep

Direct cardiac compression (DCC) with implanted heart patches has previously demonstrated efficacy of biventricular (BiV) support in acute heart failure (HF) sheep. We hypothesized that this was primarily due to a left ventricular (LV) effect. This study compared BiV, LV, and right ventricular (RV) assists in terms of hemodynamic and energetic response. Ten sheep underwent instrumentation and device implantation at least 1 week prior to study. HF (50% reduction in cardiac output) was maintained with intravenous esmolol infusion. BiV, LV, and RV assists were activated randomly with intervening stable HF periods. BiV assist was more effective than either LV or RV assist in restoring hemodynamic parameters; however, there was no difference in efficacy of LV and RV support. RV assist preserved left coronary flow patterns and chamber geometry compared to other assist conditions, but increased LV preload. These results suggest that LV and RV support each make a significant contribution to the efficacy of BiV assist, albeit through different mechanisms.     

Development of a Direct Mechanical Left Ventricular Assist Device for Left Ventricular Failure

Abstract: 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 non-beating 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.     

Therapeutic and Physiological Artificial Heart: Future Prospects

Abstract: Current left ventricular assist devices (LVADs) have demonstrated admirable results. However, approximately one-fourth of the patients who require LVADs suffer from right heart failure and require additional right ventricular (RV) assist devices (RVADs). The RV failure impairs the splanchnic circulation, subsequently developing into multiorgan failure (MOF). An aggressive application of a biventricular assist device (BVAD) is the best way to avoid and treat MOF because the BVAD reduces splanchnic congestion. Also, because the BVAD allows retention of the natural heart, recovery of the heart function can be expected after long-term assist. This benefit cannot be expected from conventional total artificial hearts. Although there are no implantable clinical BVAD systems in existence today, present advanced technologies in rotary blood pumps can enable these systems to be totally implantable. So, we should focus on developing a totally implantable BVAD system. The implantable BVAD will be a therapeutic and physiological total artificial heart, and it will be a common home health care device in the near future.     

Clinical Outcomes of Patients Treated With Pulmonary Vasodilators Early and in High Dose After Left Ventricular Assist Device Implantation

Right ventricular failure (RVF) is common after left ventricular assist device (LVAD) implantation and a major determinant of adverse outcomes. Optimal perioperative right ventricular (RV) management is not well defined. We evaluated the use of pulmonary vasodilator therapy during LVAD implantation. We performed a retrospective analysis of continuous‐flow LVAD implants and pulmonary vasodilator use at our institution between September 2004 and June 2013. Preoperative RVF risk was assessed using recognized variables. Sixty‐five patients (80% men, 50 ± 14 years) were included: 52% HeartWare ventricular assist device (HVAD), 11% HeartMate II (HMII), 17% VentrAssist, 20% Jarvik. Predicted RVF risk was comparable with contemporary LVAD populations: 8% ventilated, 14% mechanical support, 86% inotropes, 25% BUN >39 mg/dL, 23% bilirubin ≥2 mg/dL, 31% RV : LV (left ventricular) diameter ≥0.75, 27% RA : PCWP (right atrium : pulmonary capillary wedge pressure) >0.63, 36% RV stroke work index <6 gm‐m/m²/beat. The majority (91%) received pulmonary vasodilators early and in high dose: 72% nitric oxide, 77% sildenafil (max 200 ± 79 mg/day), 66% iloprost (max 126 ± 37 μg/day). Median hospital stay was 26 (21) days. No patient required RV mechanical support. Of six (9%) patients meeting RVF criteria based on prolonged need for inotropes, four were transplanted, one is alive with an LVAD at 3 years, and one died on day 35 of intracranial hemorrhage. Two‐year survival was 77% (92% for HMII/HVAD): transplanted 54%, alive with LVAD 21%, recovery/explanted 2%. A low incidence of RVF and excellent outcomes were observed for patients treated early during LVAD implantation with combination, high‐dose pulmonary vasodilators. The results warrant further investigation in a randomized controlled study.     

Right ventricular assist system feedback flow control parameter for a rotary blood pump

At least 25-30% of patients with a permanent implantable left ventricular assist device (LVAD) experience right ventricular failure; therefore, an implantable biventricular assist system (BiVAS) with small centrifugal pumps is being developed. Many institutions are focusing and developing a control system for a left ventricular assist system (LVAS) with rotary blood pumps. These authors feel that the right ventricular assist system (RVAS) with rotary blood pumps should be developed simultaneously. A literature search indicated no recent reports on the effect of hemodynamics and exercise with this type of nonpulsatile implantable RVAS. In this study, a calf with an implantable right ventricular assist system (RVAS) was subjected to 30 min of exercise on a treadmill at 1.5 mph, resulting in excellent hemodynamics. The input voltage remained unchanged. Hemodynamic recordings were taken every 5 min throughout the testing period, and blood gas analysis was done every 10 min. Oxygen uptake (VO2), oxygen delivery (DO2), and oxygen extraction (O2ER) were calculated and analyzed. Two different pump flows were investigated: Group 1 low assist (<3.5 L/min) and Group 2 high assist (>3.5 L/min). In both groups, the RVAS flow rates were unchanged while the pulmonary artery (PA) flow increased during exercise; also, the heart rate and right atrial pressure (RAP) increased during exercise. There were no significant differences in the 2 groups. The PA flow correlates to the heart rate during exercise. In all of the tests, the VO2 and DO2 increased during exercise. Regarding VO2, no changes were observed during the different flow conditions; however, the DO2 of Group 2 was higher than that of Group 1. Because the implantable RVAS did not have pump flow changes during the test conditions, it was necessary to incorporate a flow control system for the implantable RVAS. During exercise with an implantable RVAS rotary blood pump, incorporating the heart rate and VO2 as feedback parameters is feasible for controlling the flow rate.     

Prevention of Right Heart Failure After Left Ventricular Assist Device Implantation by Phosphodiesterase 5 Inhibitor

Right ventricular (RV) function immediately after left ventricular assist device (LVAD) implantation is a crucial prognostic factor. RV failure is linked to increased mortality and worse outcome. A phosphodiesterase 5 inhibitor, sildenafil, was shown to decrease pulmonary vascular resistance and pulmonary artery pressure post‐LVAD. We report on a series of heart failure patients, and the effect of sildenafil on the incidence of RV failure after LVAD implantation. We retrospectively analyzed the data of end‐stage heart failure patients who underwent LVAD implantation with pulmonary hypertension and RV dysfunction prior to surgery. Patients were divided into two groups; group 1: patients who received sildenafil perioperatively, and group 2: patients who did not receive sildenafil. Hemodynamic and echographic data were collected before and after surgery. Fourteen patients were included, 8 patients in group 1 and 6 in group 2. Sildenafil was administered with a mean dose of 56.2 ± 9.4 mg in group 1 and was able to significantly reduce right heart failure incidence, and to demonstrate a significant reduction in pulmonary vascular resistance, pulmonary artery pressure, transpulmonary gradient, and a significant increase in cardiac output. In conclusion, sildenafil seems to have a promising role perioperatively in preventing acute RV failure postsurgery in patients with RV dysfunction and pulmonary hypertension, requiring LVAD therapy.     

Banding the Right Ventricular Assist Device Outflow Conduit: Is It Really Necessary With Current Devices?

Implantable left ventricular assist devices (LVADs) have been adapted clinically for right‐sided mechanical circulatory support (RVAD). Previous studies on RVAD support have established the benefits of outflow cannula restriction and rotational speed reduction, and recent literature has focused on assessing either the degree of outflow cannula restriction required to simulate left‐sided afterload, or the limitation of RVAD rotational speeds. Anecdotally, the utility of outflow cannula restriction has been questioned, with suggestion that banding may be unnecessary and may be replaced simply by varying the outflow conduit length. Furthermore, many patients have a high pulmonary vascular resistance (PVR) at the time of ventricular assist device (VAD) insertion that reduces with pulmonary vascular bed remodeling. It is therefore important to assess the potential changes in flow through an RVAD as PVR changes. In this in vitro study, we observed the use of dual HeartWare HVAD devices (HeartWare Inc., Framingham, MA, USA) in biventricular support (BiVAD) configuration. We assessed the pumps' ability to maintain hemodynamic stability with and without banding; and with varying outflow cannulae length (20, 40, and 60 cm). Increased length of the outflow conduit was found to produce significantly increased afterload to the device, but this was not found to be necessary to maintain the device within the manufacturer's recommended operational parameters under a simulated normal physiological setting of mild and severe right ventricular (RV) failure. We hypothesize that 40 cm of outflow conduit, laid down along the diaphragm and then up over the RV to reach the pulmonary trunk, will generate sufficient resistance to maintain normal pump function.     

Effects of Left Ventricular Assist Device on Cardiac Function: Experimental Study of Relationship between Pump Flow and Left Ventricular Diastolic Function

The left ventricular assist device (LVAD) with centrifugal pump has two characteristics. One is a pump flow wave of the centrifugal pump, consisting of the pulsatile flow of the native heart and the nonpulsatile flow of the centrifugal pump. The other is that the centrifugal pump fills from the native heart not only in the systolic phase, but also in the diastolic phase. In the case of the apex outlet LVAD with centrifugal pump, blood flows from the left atrium through the left ventricle to the pump. Pump flow is regulated by preload, and preload is regulated by diastolic hemodynamics. The aim of this study is to analyze the relationship between pump flow and the diastolic hemodynamics of the native heart. Ten anesthetized intact pigs were studied after placement of an LVAD. Data were recorded with the LVAD off (control) and the LVAD on. The assist rate was changed to 25%, 50%, and 75%. The indexes of left ventricular (LV) diastolic function included LV myocardial relaxation (time constant of isovolumic pressure decay [Tau] and maximum negative dP/dt [LV dP/dt min]) and LV filling (peak filling rate [PFR], time to peak filling rate [tPFR], and diastolic filling time [DFT]). Stroke volume decreased significantly in 75% assist. LV end-systolic pressure decreased significantly in 50% and 75% assist. LV end-diastolic volume decreased as assist rate increased, but there were no significant changes. Stroke work decreased significantly in 50% and 75% assist. LV dP/dt min decreased significantly in 50% and 75% assist. Tau prolonged as assist rate increased, but there were no significant changes. DFT shortened significantly in 75% assist. PFR increased significantly in 75% assist. tPFR shortened significantly in 50% and 75% assist. In this study, LV relaxation delayed as an increasing of pump assist rate, but it suggested a result of reduction of cardiac work. Also, it was suggested that LVAD increases the pressure difference between the left atrium and the left ventricle in the diastolic phase. This phenomenon is due to the filling of the left ventricle. In this study it was suggested that as pump assist rate increases, it is more effective to keep cardiac function in the diastolic phase.     

The use of a biventricular assist device for postcardiotomy profound biventricular failure

A 58-year-old woman who could not be weaned from cardiopulmonary bypass was treated with a biventricular assist device (BVAD) using a centrifugal pump for the left side and a pneumatic pulsatile pump for the right side. At the initiation of the BVAD support, predominant right ventricular failure was recognized and therefore weaning was begun from the left side. The left ventricular assist device was discontinued after 87 h and the patient was finally weaned from the right ventricular assist device after 205 h. Despite the complete recovery of cardiac function, the patient developed renal failure followed by an intractable infection and died of multiple organ failure on the 59th postoperative day (POD).     

Evaluation of Inflow Cannulation Site for Implantation of Right‐Sided Rotary Ventricular Assist Device

Right heart dysfunction is one of the most serious complications following implantation of a left ventricular assist device, often leading to the requirement for short‐ or long‐term right ventricular assist device (RVAD) support. The inflow cannulation site induces major hemodynamic changes and so there is a need to optimize the site used depending on the patient's condition. Therefore, this study evaluated and compared the hemodynamic influence of right atrial cannulation (RAC) and right ventricular cannulation (RVC) inflow sites. An in vitro variable heart failure mock circulation loop was used to compare RAC and RVC in mild and severe biventricular heart failure (BHF) conditions. In the severe BHF condition, higher ventricular ejection fraction (RAC: 13.6%, RVC: 32.7%) and thus improved heart chamber and RVAD washout were observed with RVC, which suggested this strategy might be preferable for long‐term support (i.e., bridge‐to‐transplant or destination therapy) to reduce the risk of thrombus formation. In the mild BHF condition, higher pulmonary valve flow (RAC: 3.33 L/min, RVC: 1.97 L/min) and lower right ventricular stroke work (RAC: 0.10 W, RVC: 0.13 W) and volumes were recorded with RAC. These results indicate an improved potential for myocardial recovery, thus RAC should be chosen in this condition. This in vitro study suggests that RVAD inflow cannulation site should be chosen on a patient‐specific basis with a view to the support strategy to promote myocardial recovery or reduce the risk of long‐term complications.     

Systematic Review of Phosphodiesterase‐5 Inhibitor Use in Right Ventricular Failure Following Left Ventricular Assist Device Implantation

Our aim was to identify relevant literature supporting the use of phosphodiesterase‐5 (PDE5) inhibitors in patients with persistent pulmonary hypertension with signs of postprocedural right ventricular (RV) dysfunction following left ventricular assist device (LVAD) implantation. We searched MEDLINE, SCOPUS, and Web of Science from inception through November 27, 2014 for citations evaluating patients with end‐stage heart failure necessitating LVAD, continuous and pulsatile, who received a PDE5 inhibitor to prevent RV failure. Outcomes of interest included changes in mean pulmonary artery pressure, pulmonary vascular resistance, central venous pressure, cardiac index, and mean arterial pressure. Results are presented qualitatively. Four citations (n = 83 patients) were included. These included a single case report, two retrospective case series, and a prospective open‐label study with a historical control. All four studies utilized the PDE5 inhibitor sildenafil with various doses for up to 3 months. Sildenafil routinely reduced mean pulmonary artery pressures as soon as 90 min after administration. Reductions in pulmonary vascular resistance were also seen shortly after the procedure and maintained through 12–15 weeks. While one study saw improvements in postoperative central venous pressures, another did not. Evidence supporting PDE5 inhibitor use to attenuate RV failure in patients requiring an LVAD is weak.     

In vivo experimental testing of a microaxial blood pump for right ventricular support

The incidence of isolated right ventricular (RV) failure is rare in postcardiotomy patients, but high in patients undergoing implantation of a left ventricular assist device or cardiac transplantation. Therefore, we have developed a new microaxial flow device and report on our first in vivo animal trials. Six healthy adult female sheep weighing 80-90 kg underwent implantation of the microaxial blood pump for partial unloading of the right ventricle. This pump is a miniaturized rotary blood pump with a diameter of only 6.4 mm and a weight of 11 g. The inner volume of the pump is limited to 12 mL, and the inner artificial blood contacting surface is 65 cm(2). The pump consists of a rotor driven by an incorporated brushless direct current motor, the housing of the rotor, the inflow cage, the outflow cannula, and the driveline. At the maximum speed of 32,500 rotations/min, a flow of 6 L/min can be delivered. The inflow and outflow conduit were anastomosed to the right atrium and the main pulmonary artery, respectively. Hemodynamic and echocardiographic data as well as blood samples were measured over the whole test period of 7 days. The hearts and lungs as well as the pump were explanted for a thorough examination at the end of the trial. Systemic arterial blood pressures remained unchanged during the entire test period. RV cardiac output was diminished significantly as demonstrated by the echocardiographic studies. The number of platelets decreased perioperatively, but recovered within the test period. The free hemoglobin was not enhanced postoperatively indicating no significant hemolysis. Liver function was only slightly impaired due to operative reasons (increase in bilirubin on the first postoperative day but normalization within the test period). The pathologic examination revealed some clots at the inflow cage and fibrin depositions on the impeller as well as on the inner surface of the outflow graft without an impairment of pump function. Our results demonstrate that this newly developed microaxial blood pump is a promising device for RV support, but it cannot be driven without any anticoagulation.     

What Is the Optimal Setting for a Continuous‐Flow Left Ventricular Assist Device in Severe Mitral Regurgitation?

Excessive left ventricular (LV) volume unloading can affect right ventricular (RV) function by causing a leftward shift of the interventricular septum in patients with mitral regurgitation (MR) receiving left ventricular assist device (LVAD) support. Optimal settings for the LVAD should be chosen to appropriately control the MR without causing RV dysfunction. In this study, we assessed the utility of our electrocardiogram‐synchronized rotational speed (RS) modulation system along with a continuous‐flow LVAD in a goat model of MR. We implanted EVAHEART devices after left thoracotomy in six adult goats weighing 66.4 ± 10.7 kg. Severe MR was induced through inflation of a temporary inferior vena cava filter placed within the mitral valve. We evaluated total flow (TF; the sum of aortic flow and pump flow [PF]), RV fractional area change (RVFAC) calculated by echocardiography, left atrial pressure (LAP), LV end‐diastolic pressure (LVEDP), LV end‐diastolic volume (LVEDV), and LV stroke work (LVSW) with a bypass rate (PF divided by TF) of 100% under four conditions: circuit‐clamp, continuous mode, co‐pulse mode (increased RS during systole), and counter‐pulse mode (increased RS during diastole). TF tended to be higher in the counter‐pulse mode. Moreover, RVFAC was significantly higher in the counter‐pulse mode than in the co‐pulse mode, whereas LAP was significantly lower in all driving modes than in the circuit‐clamp condition. Furthermore, LVEDP, LVEDV, and LVSW were significantly lower in the counter‐pulse mode than in the circuit‐clamp condition. The counter‐pulse mode of our RS modulation system used with a continuous‐flow LVAD may offer favorable control of MR while minimizing RV dysfunction.     

A Right Ventricular Hemopump Restores Right Ventricular Function with Pulmonary Artery Banding

Abstract: We investigated the ability of the Hemopump to support the right ventricle during acute, partial, pulmonary artery obstruction. In 6 pigs, a 14 Fr size Hemopump was placed through the pulmonary artery into the right ventricle. Control measurements were made. A band around the pulmonary artery proximal to the outflow port of the Hemopump was tightened, and measurements were repeated with the Hemopump at minimum and then maximum speed. With banding, right ventricular stroke volume and output decreased (43 [SD,7] to 28 [SD,8] ml, p < 0.001; 4.9 [SD,0.8] to 3.7 [SD,1.0] L/min, p < 0.01 respectively), but they were restored with the Hemopump (38 [SD,5] ml and 4.5 [SD,0.6] L/min; both p = NS vs control). Increases in right ventricular peak systolic (28 [SD,10] to 42 [SD,17] mm Hg; p < 0.01) and end-diastolic pressure (2 [SD,1] to 12 [SD,6] mm Hg; p < 0.02) were reversed by the Hemopump (29 [SD,8] and 4 [SD,2] mm Hg; both p = NS vs control). Right ventricular pressure rate product almost doubled with banding (3,199 [SD,1,252] to 5,962 [SD,2,796] mm Hg; p < 0.01), but it decreased with the Hemopump (3,368 [SD,767] mm Hg; p = NS vs control). With acute partial pulmonary artery banding, a right ventricular Hemopump restores output from and offloads the right ventricle.     

Impact of Residual Mitral Regurgitation on Right Ventricular Systolic Function After Left Ventricular Assist Device Implantation

Significant mitral regurgitation (MR) is thought to decrease after left ventricular assist device (LVAD) implantation, and therefore repair of mitral valve is not indicated in current practice. However, residual moderate and severe MR leads to pulmonary artery pressure increase, thereby resulting in right ventricular (RV) dysfunction during follow‐up. We examined the impact of residual MR on systolic function of the right ventricle by echocardiography after LVAD implantation. This study included 90 patients (mean age: 51.7 ± 10.9 years, 14.4% female) who underwent LVAD implantation (HeartMate II = 21, HeartWare = 69) in a single center between December 2010 and June 2014. Echocardiograms obtained at 3–6 months and over after implantation were analyzed retrospectively. RV systolic function was graded as normal, mild, moderate, and severely depressed. MR (≥moderate) was observed in 43 and 44% of patients at early and late period, respectively. Systolic function of the RV was severely depressed in 16 and 9% of all patients. Initial analysis (mean duration of support 174.3 ± 42.5 days) showed a statistically significant correlation between less MR and improved systolic function of RV (P = 0.01). Secondary echocardiographic analysis (following a mean duration of support of 435.1 ± 203 days) was also statistically significant for MR degree and RV systolic dysfunction (P = 0.008). Residual MR after LVAD implantation may cause deterioration of RV systolic function and cause right‐sided heart failure symptoms. Repair of severe MR, in selected patients such as those with severe pulmonary hypertension and depressed RV, may be considered to improve the patient's clinical course during pump support.     

In‐Series Versus In‐Parallel Mechanical Circulatory Support for the Right Heart: A Simulation Study

Right heart failure (RHF) is a serious health issue with increasing incidence and high mortality. Right ventricular assist devices (RVADs) have been used to support the end‐stage failing right ventricle (RV). Current RVADs operate in parallel with native RV, which alter blood flow pattern and increase RV afterload, associated with high tension in cardiac muscles and long‐term valve complications. We are developing an in‐series RVAD for better RV unloading. This article presents a mathematical model to compare the effects of RV unloading and hemodynamic restoration on an overloaded or failing RV. The model was used to simulate both in‐series (sRVAD) and in‐parallel (pRVAD) (right atrium‐pulmonary artery cannulation) support for severe RHF. The results demonstrated that sRVAD more effectively unloads the RV and restores the balance between RV oxygen supply and demand in RHF patients. In comparison to simulated pRVAD and published clinical and in silico studies, the sRVAD was able to provide comparable restoration of key hemodynamic parameters and demonstrated superior afterload and volume reduction. This study concluded that in‐series support was able to produce effective afterload reduction and preserve the valve functionality and native blood flow pattern, eliminating complications associated with in‐parallel support.     

In Vitro and In Vivo Testing of an Implantable Motor-Driven Left Ventricular Assist Device

Abstract: A totally implantable motor-driven left ventricular assist device (LVAD) has been developed and tested. The performance of this LVAD was tested in a mock circulatory system. This pump provided 8 L/min of output against a mean afterload of 120 mm Hg with a filling pressure of 20 mm Hg when the pump was operated in the fill/empty mode. The right and left pumps were tested in a mock loop. The right pump afterload was kept in the range from 23–32 mm Hg. With increase in the left pump afterload, the pump power output varied from 1.64 to 2.37 W. The instantaneous motor power input varied from 22.6 to 30.6 W with the total system efficiency ranging from 6.7 to 9.4%. To date, 4 in vivo studies have been conducted for up to 12 h. Two animals survived 12 and 10 h, respectively. Termination was due to bleeding in 1 animal, vent tube obstruction in 1, and respiratory failure in 2. All animals died of technical failure. Another experiment is to be undertaken, and a newly designed cannula is now being manufactured.     

The Effect of Left Ventricular Bypass on the Right Ventricular Function: Experimental Analysis of the Effects of Ischemic Injuries to the Right Ventricular Free Wall and Interventricular Septum

The right ventricular (RV) function during left heart bypass (LHB) was examined in open-chest anesthetized mongrel dogs (average weight, 11.8 kg). The LHB was carried out by a left ventricle (LV) to femoral artery bypass using a centrifugal pump for 90 min, and the bypass flow was kept maximum to obtain almost complete decompression of the LV. The RV function was evaluated by hemodynamic parameters and pressure-dimension (sonomicrometry) relationship at pre-LHB (control) and 30, 60, and 90 min after LHB (LHB-30, LHB-60, and LHB-90). The materials were divided into three groups after LHB-30: intact heart (group 1, n = 5), RV free wall ischemia (group 2, n = 5), and interventricular septum (IVS) ischemia group (group 3, n = 8). No significant changes in mean right atrial pressure (mRAP), RV end-diastolic pressure (RVEDP), RV maximum derivative pressure, or RV fractional shortening (RVFS) were found between pre-LHB and post-LHB in groups 1 and 2. On the contrary, group 3 showed significant increases in mRAP and RVEDP, and a decrease in RVFS at LHB-90 compared to both pre-LHB and LHB-30. The RV end-systolic dimension (percentage of pre-LHB) showed significant increases at LHB-90 compared to LHB-30 in groups 2 and 3. These results indicate that the LHB itself does not depress the RV function in the intact heart and in the RV free wall ischemic heart, while the impairment of the IVS during LHB appears to lead to RV dysfunction.     

Mechanical Circulatory Support for Postcardiotomy Ventricular Failure: The Heart Institute of Japan Experience 1984–1992

Abstract: In the last 9 years, 30 patients received assisted circulation or a ventricular assist device after open-heart operations at the Heart Institute of Japan. After cardiovascular surgery, 9 of those patients underwent venoarterial bypass, 10 had biventricular bypass, 7 had left ventricular bypass, and the remaining 4 received a left ventricular assist device. Of the first 15 patients, only 3 (20%) were discharged from the hospital. In contrast, 7 (46.7%) of the last 15 patients were discharged without major complications. With respect to complications, bleeding and ventricular arrhythmia (immature weaning) decreased with low-heparinized isolated left ventricular supports. However, profound biventricular failure, infection, and multiple organ failure remain as possible complications with any type of assisted circulation. These results suggest that early application of circulatory support and appropriate selection of the mode of support and devices used are important for successful circulatory support.