Long-term circulatory support to promote recovery from profound heart failure

Cardiological Challenges Related to Long-Term Mechanical Circulatory Support for Advanced Heart Failure in Patients with Chronic Non-Ischemic Cardiomyopathy

Long-term mechanical circulatory support by a left ventricular assist device (LVAD), with or without an additional temporary or long-term right ventricular (RV) support, is a life-saving therapy for advanced heart failure (HF) refractory to pharmacological treatment, as well as for both device and surgical optimization therapies. In patients with chronic non-ischemic cardiomyopathy (NICM), timely prediction of HF's transition into its end stage, necessitating life-saving heart transplantation or long-term VAD support (as a bridge-to-transplantation or destination therapy), remains particularly challenging, given the wide range of possible etiologies, pathophysiological features, and clinical presentations of NICM. Decision-making between the necessity of an LVAD or a biventricular assist device (BVAD) is crucial because both unnecessary use of a BVAD and irreversible right ventricular (RV) failure after LVAD implantation can seriously impair patient outcomes. The pre-operative or, at the latest, intraoperative prediction of RV function after LVAD implantation is reliably possible, but necessitates integrative evaluations of many different echocardiographic, hemodynamic, clinical, and laboratory parameters. VADs create favorable conditions for the reversal of structural and functional cardiac alterations not only in acute forms of HF, but also in chronic HF. Although full cardiac recovery is rather unusual in VAD recipients with pre-implant chronic HF, the search for myocardial reverse remodelling and functional improvement is worthwhile because, for sufficiently recovered patients, weaning from VADs has proved to be feasible and capable of providing survival benefits and better quality of life even if recovery remains incomplete. This review article aimed to provide an updated theoretical and practical background for those engaged in this highly demanding and still current topic due to the continuous technical progress in the optimization of long-term VADs, as well as due to the new challenges which have emerged in conjunction with the proof of a possible myocardial recovery during long-term ventricular support up to levels which allow successful device explantation.

Weaning from ventricular assist device support after recovery from left ventricular failure with or without secondary right ventricular failure

Although complete myocardial recovery after ventricular assist device (VAD) implantation is rather seldom, systematic search for recovery is worthwhile because for recovered patients weaning from VADs is feasible and can provide survival benefits with long-term freedom from heart failure (HF) recurrence, even if a chronic cardiomyopathy was the primary cause for the drug-refractory HF necessitating left ventricular (LVAD) or biventricular support (as bridge-to-transplantation or definitive therapy) and even if recovery remains incomplete. LVAD patients explanted for myoacardial recovery compared to those transplanted from LVAD support showed similar survival rates and a significant proportion of explanted patients can achieve cardiac and physical functional capacities that are within the normal range of healthy controls. In apparently sufficiently recovered patients, a major challenge remains still the pre-explant prediction of the weaning success which is meanwhile reliably possible for experienced clinicians. In weaning candidates, the combined use of certain echocardiography and right heart catheterization parameters recorded before VAD explantation can predict post-weaning cardiac stability with good accuracy. However, in the absence of standardization or binding recommendations, the protocols for assessment of native cardiac improvement and also the weaning criteria differ widely among centers. Currently there are still only few larger studies on myocardial recovery assessment after VAD implantation. Therefore, the weaning practice relies mostly on small case series, local practice patterns, and case reports, and the existing knowledge, as well as the partially differing recommendations which are based mainly on expert opinions, need to be periodically systematised. Addressing these shortcomings, our review aims to summarize the evidence and expert opinion on the evaluation of cardiac recovery during mechanical ventricular support by paying special attention to the reliability of the methods and parameters used for assessment of myocardial recovery and the challenges met in both evaluation of recovery and weaning decision making.

Development of a hybrid decision support model for optimal ventricular assist device weaning

BACKGROUND

Despite the small but promising body of evidence for cardiac recovery in patients that have received ventricular assist device (VAD) support, the criteria for identifying and selecting candidates who might be weaned from a VAD have not been established.

METHODS

A clinical decision support system was developed based on a Bayesian Belief Network that combined expert knowledge with multivariate statistical analysis. Expert knowledge was derived from interviews of 11 members of the Artificial Heart Program at the University of Pittsburgh Medical Center. This was supplemented by retrospective clinical data from the 19 VAD patients considered for weaning between 1996 and 2004. Artificial Neural Networks and Natural Language Processing were used to mine these data and extract sensitive variables.

RESULTS

Three decision support models were compared. The model exclusively based on expert-derived knowledge was the least accurate and most conservative. It underestimated the incidence of heart recovery, incorrectly identifying 4 of the successfully weaned patients as transplant candidates. The model derived exclusively from clinical data performed better but misidentified 2 patients: 1 weaned successfully, and 1 that needed a cardiac transplant ultimately. An expert-data hybrid model performed best, with 94.74% accuracy and 75.37% to 99.07% confidence interval, misidentifying only 1 patient weaned from support.

CONCLUSIONS

A clinical decision support system may facilitate and improve the identification of VAD patients who are candidates for cardiac recovery and may benefit from VAD removal. It could be potentially used to translate success of active centers to those less established and thereby expand use of VAD therapy.

Which factors predict the recovery of natural heart function after insertion of a left ventricular assist system?

BACKGROUND

Recent reports have demonstrated that use of a left ventricular assist system (LVAS) can initiate recovery of cardiac function, and subsequent weaning from the LVAS has attracted considerable interest. In this study we investigated reliable predictors of LVAS weaning.

METHODS

Eighty-two patients underwent LVAS implantation between April 1994 and July 2006 at our institution. Cardiac function was restored in 8 patients, who were weaned from LVAS after a mean of 5 months (Group R). Thirty-three patients remained on LVAS support for >1 year (Group N) because natural heart function did not show adequate improvement. We retrospectively evaluated the differences between these two groups. Group R was younger, and had a shorter duration of heart failure than Group N (23.4 vs 36.7 years and 13.3 vs 56.1 months, p < 0.01, respectively). Pathologic findings showed that the interstitial fibrosis score was lower in Group R (p < 0.01). Three months after LVAS insertion, B-type natriuretic peptide (BNP) and fractional shortening (FS) were more favorable (66.6 +/- 46 vs 264.5 +/- 170 pg/ml, p < 0.01, and 23 +/- 17.1 vs 12 +/- 9.1%, p < 0.05, respectively) in Group R. Furthermore, Group R received a higher dose of beta-blocker (15.4 +/- 8.4 vs 5.8 +/- 3.9 mg, p < 0.05).

CONCLUSIONS

Younger age, shorter history of heart failure, and less interstitial fibrosis were effective predictors of weaning from LVAS. Restoration of natural heart function was more rapid and more persistent in candidates for LVAS explantation, and presence of beta-blocker played a prominent role in improving cardiac function after LVAS implantation.

Effects of ventricular unloading on apoptosis and atrophy of cardiac myocytes1

BACKGROUND

Ventricular unloading decreases cardiac ventricular mass. This loss of ventricular mass can be due to either atrophy (a reversible process) or apoptosis (an irreversible process) of the cardiac myocytes. We investigated the effect of ventricular unloading on atrophy and apoptosis of cardiac myocytes, using working and nonworking transplant heart models in rats.

MATERIALS AND METHODS

ACI rats underwent heterotopic heart transplantation with two different techniques to create working and nonworking cardiac grafts. Cardiac grafts were harvested at different time points after transplantation. TUNEL, caspase-3 assay, and electron microscopy were used to assess the degree of apoptosis while cellular atrophy was estimated by calculation of the cytoplasmic index (CI = mean sectional cytoplasmic area/nucleus).

RESULTS

Ventricular mass reduction was more pronounced in nonworking than in working hearts (P < 0.05). Apoptotic index and caspase-3 activities increased in both groups, peaking at 3 days after transplantation, but were not significantly different between the two models. The cytoplasmic index was significantly lower in nonworking than in working grafts (P < 0.05).

CONCLUSIONS

These data suggest that cellular atrophy is the primary mechanism that accounts for myocardial weight reduction following ventricular unloading. The inference is that ventricular unloading by ventricular assist devices may not cause permanent loss of cardiac myocytes, thus allowing for functional recovery.

Mechanical cardiac support system for patients with postcardiotomy cardiogenic shock

OBJECTIVE

Mechanical cardiac support system (MCSS) has been used for adult patients in postcardiotomy cardiogenic shock and has been shown to provide excellent oxygenation and hemodynamic support. However, MCSS has a number of disadvantages that include high incidence rate of complications (e.g. stroke, bleeding) and limited duration of sufficient support. The objective of this study is to identify perioperative and postoperative factors for survival in patients having MCSS.

METHODS

From January 1991 to April 2001, MCSS has been applied to 22 adult patients in postcardiotomy cardiogenic shock. These patients' charts were retrospectively reviewed.

RESULTS

Of 22 patients, 9 patients (41%) were successfully weaned, and 6 (27%) were hospital survivors. The duration of assist ranged from 21 to 211 hours (median 66 hours). In 7 (78%) out of 9 patients who could be weaned from MCSS, MCSS were required for less than 3 days. Major complications were reexploration for bleeding (18%), leg ischemia (45%), renal dysfunction (77%), liver dysfunction (59%), infection (31.8%), hypoxia due to lung dysfunction (36%) and cerebral dysfunction (41%). pH, base excess, HCO3-, urine output, transfused platelets at first 24 hours of MCSS and preoperative body surface area were significant predictors for survival.

CONCLUSION

The indices of insufficient hemodynamic support such as progression of acidosis or poor urine output are significant predictors for early death. Early conversion from MCSS to long-term assist device, such as left ventricular assist device, should be considered when these factors are associated with poor cardiac recovery.

Newly developed ventricular assist device with linear oscillatory actuator

The goal of this study was to develop a new direct electromagnetic left ventricular assist device (DEM-LVAD) with a linear oscillatory actuator (LOA). The DEM-LVAD is a pulsatile pump with a pusher plate. The pusher plate is driven directly by the mover of the LOA. The LOA provides reciprocating motion without using any movement converter such as a roller screw or a hydraulic system. It consists of a stator with a single winding excitation coil and a mover with two permanent magnets. The simple structure of the LOA is based on fewer parts to bring about high reliability and smaller size. The mover moves back and forth when forward and backward electric current is supplied to the excitation coil. The pump housings have been designed using three-dimensional computer aided design software and fabricated with the aid of computer aided manufacturing technology. Monostrut valves (Bjork-Shiley #21) were used for the prototype. The DEM-LVAD dimension is 96 mm in diameter and 50 mm thick with a mass of 0.62 kg and a volume of 280 ml. An in vitro test (afterload 100 mm Hg; preload 10 mm Hg; input power 10 W) demonstrated more than 6 L/minute maximum output and 15% maximum efficiency at 130 beats per minute (bpm). Dynamic stroke volume ranged between 40 and 60 ml. The feasibility of the DEM-LVAD was confirmed.

Estimation of left ventricular recovery level based on the motor current waveform analysis on circulatory support with centrifugal blood pump

In a mock circulatory loop simulating the left heart bypass using a centrifugal blood pump, analysis of the motor current waveform of the centrifugal pump was performed to derive a useful parameter to evaluate the status of ventricular function. The relationship between the peak, amplitude, and the peak of the fundamental frequency of the power spectral density of the periodic motor current waveform (MCpsdP) that reflected the pulsatile ventricular pressure, and the peak of the left ventricular pressure (LVP) was examined. Although both peak and amplitude of the motor current waveform showed an excellent correlation with the peak LVP, they failed to predict the opening of the aortic valve. The MCpsdP that corresponds to the frequency of the heart rate showed an excellent correlation with the peak LVP throughout the LVP levels, but the slope between them changed with the opening of the aortic valve. Thus, it is possible to follow the change in the LVP and detect even the opening of the aortic valve, and, hence, the recovery of the left ventricle. However, the slope of the linear regression equation varied, depending on the pump speed. This result implies that the MCpsdP can be possibly used to follow the change of ventricular function during circulatory assistance with a centrifugal blood pump as well as to control the pump speed in response to varying ventricular function.

Control strategy for rotary blood pumps

The control strategy for ventricular support with a centrifugal blood pump was examined in this study. The control parameter was the pump rpm that determines pump flow. Optimum control of pump rpm that reflects the body's demand is important for long-term, effective, and safe circulatory support. Moreover, continuous, reliable monitoring of ventricular function will help successfully wean the patients from the ventricular assist device (VAD). The control strategy in this study includes determination of the target pump rpm that can provide the flow required by the body, fine-rpm-tuning to minimize deleterious effects such as suction in the ventricle, and assessment of ventricular function for successful weaning from VADs. To determine the target pump rpm, we proposed to use the relation between the native heart rate and cardiac output, and the relation between the pump rpm and centrifugal pump output. For fine-tuning of the pump rpm, the motor current waveform was used. We computed the power spectral density of the motor current waveform and calculated the ratio of the fundamental to the higher order components. When this ratio was larger than approximately 0.2, we assumed there would be a suction effect in the ventricle. As for assessment of ventricular function, we used the amplitude of the motor current waveform. The control system implemented using a DSP functioned properly in the mock circulatory loop as well as in acute animal experiments. The motor current also showed a good correlation with the ventricular pressure in acute animal experiments.

Bridging-to-recovery

BACKGROUND

Patients with end-stage heart failure placed on a cardiac assist device show at least some degree of improvement of cardiac function. In a subgroup of selected patients, some hearts recovered considerable function. In these patients the device was removed and cardiac transplantation was no longer necessary. We report our long-term experience with these weaned patients.

METHODS

As of today, 512 cardiac assist devices of various types (Berlin Heart, Berlin, Germany; Novacor, World Heart, Ottawa, Ontario, Canada; TCI, ThermoCardio Systems, Inc, Woburn, MA; DeBakey, Micromed Technology Inc, Houston, TX) were implanted in patients with end-stage heart failure in our institution. Of these, 95 patients belonged to a subgroup of patients with nonischemic, idiopathic, dilated cardiomyopathy who were implanted with a left ventricular support system (Novacor 84, TCI 10, Berlin Heart 1) between 1994 and 2000. All were routinely examined by echocardiography for improvement of cardiac function. The left ventricular diameter in diastole (LVIDd) and left ventricular ejection fraction (LVEF) served as the main parameters to assess changes in cardiac performance. Under the conditions of a running device, an LVIDd below 60 mm and an LVEF above 40% were the criteria to do further echocardiographic studies when the pump was turned off for up to 20 minutes.

RESULTS

Twenty-eight patients (26 men, 2 women; ages 18 to 64 yrs; history of heart failure, 1 to 17 yrs) fulfilled the criteria of improved cardiac performance and were weaned from the device. Since then, 16 patients have continued "normal" heart function with follow-up times ranging from 1 month to 5.5 years (group B). Three patients died of noncardiac causes (group C). Eight patients were transplanted from 1 to 17 months later and one died on the waiting list (group A). Statistically significant differences between groups A and B were calculated for the duration of heart failure (9 versus 2 years, p = 0.0002). Differences in LVIDd before removal of the device (57 versus 51 mm, p = 0.0420), LVEF after 2 months of unloading (30 versus 49%, p = 0.0300), and LVEF preexplantation (43 versus 52%, p = 0.0001) were significant. Overall, 17% of the cohort of 95 patients were weaned successfully.

CONCLUSIONS

Weaning from cardiac assist devices is feasible for selected patients; it saves donor hearts and is preferred to cardiac transplantation. However, as of today no reliable parameter predicts outcome after weaning and none determines the possibility of device removal before implantation in advance.

Healing the heart with ventricular assist device therapy: mechanisms of cardiac recovery

As experience has grown with the use of mechanical circulatory support systems in patients with cardiogenic shock, many anecdotes have been noted where myocardial recovery occurred and devices could be removed with reasonable residual cardiovascular performance and resolution of the shock syndrome. Indeed, when first used, ventricular assist devices were inserted to bridge patients unable to be separated from cardiopulmonary bypass to eventual recovery. Many successes with ventricular support systems have been recorded in individuals with postcardiotomy cardiogenic shock, acute myocarditis, and in the periinfarction period where stunning of potentially viable myocardial tissue contributed to severe heart failure. From an experimental standpoint, recovery of myocyte function and restoration of more normal myocardial geometry and constitution have been noted. There are many explanations for this, but principally, benefit is related to amelioration of circulatory insufficiency with attenuation of perturbed humoral networks and reduction of myocardial wall stress. It is important to understand how ventricular assist device implantation in select advanced heart failure patients might precipitate recovery of depressed myocardial function.

A new method of monitoring recovery and weaning the Thoratec left ventricular assist device

BACKGROUND

Recent scientific and clinical data suggest that chronic mechanical ventricular unloading may lead to myocardial recovery. Evaluating and monitoring patients for myocardial recovery and the optimal methods of weaning the left ventricular assist device are not well defined.

METHODS

Six patients with advanced heart failure and severe mitral regurgitation have undergone successful bridge to recovery using a Thoratec left ventricular assist device. Data that details their monitoring for myocardial recovery and weaning from the left ventricular assist device were prospectively collected.

RESULTS

Clinical data collected during the recovery phase included chest roentgenogram, echocardiography, plasma norepinephrine, tumor necrosis factor-alpha, bioimpedance, and cardiopulmonary exercise testing (peak oxygen consumption). Normalization of these variables with a 10% increase in the peak oxygen consumption was obtained before weaning. The Thoratec device rate and percent systole were manipulated to allow gradual reloading of the ventricle. The weaning process occurred for more than 5 to 10 days to allow time for observation of the ventricle and its response to the increasing workload.

CONCLUSIONS

Select patients with advanced congestive heart failure and severe mitral insufficiency can benefit from mechanical device support. We describe our technique of monitoring for myocardial recovery using clinical variables. Our technique of weaning allows for gradual reloading of the ventricle and a longer period of observation before device removal. Additional research is needed to determine which variables will accurately predict long-term myocardial recovery and the optimal weaning method.

Midterm follow-up of patients who underwent removal of a left ventricular assist device after cardiac recovery from end-stage dilated cardiomyopathy

OBJECTIVE

Cardiac recovery in end-stage idiopathic dilated cardiomyopathy recently occurred after temporary support with a left ventricular assist device. We report the case histories of patients who underwent removal of the device more than 4 years ago.

METHODS

Since June 1994, 23 patients with end-stage idiopathic dilated cardiomyopathy who were supported by a left ventricular assist device or biventricular assist device for 1 to 26 months (mean, 6 months) underwent removal of the device after complete or extensive cardiac recovery, as revealed by echocardiography.

RESULTS

Seven patients (group A) had recurrent cardiac failure after 4 to 24 months. Transplantation was performed in 6 patients, and one died while on the waiting list. Three patients died of noncardiac causes within a period of 4 months and 3 days after removal of the assist device. Stable cardiac recovery occurred in 13 patients (group B) for 3 to 49 months (mean, 23 months). At the time of implantation, there were no significant differences between the groups with regard to age, hemodynamics, left ventricular ejection fraction, left ventricular internal diameter in diastole, and autoantibody levels. The increase of ejection fraction and the decrease of left ventricular internal diameter in diastole after 2 months were highly significant. The patients in group A had longer histories of heart failure and first cardiac symptoms and duration of assist when compared with group B. Group B demonstrated a quicker cardiac recovery on the assist device, and thus support was shorter. Also, the degree of recovery at assist device explantation was more complete in group B. The age at the time of device placement was the only influencing factor for duration on the assist device. The probability of recurrence of heart failure was influenced by the duration of heart failure.

CONCLUSIONS

In selected patients with idiopathic dilated cardiomyopathy, lasting recovery can be achieved after unloading with a left ventricular assist device. Lasting cardiac recovery seems to be related to functional normalization and a more rapid recovery during the unloading period.

Relationship of blood pressure and pump flow in an implantable centrifugal blood pump during hypertension

The purpose of this study was to evaluate the real time relationship between pump flow and pump differential pressure (D-P) during experimentally induced hypertension (HT). Two calves (80 and 68 kg) were implanted with the EVA-HEART centrifugal blood pump (SunMedical Technology Research Corp., Nagano, Japan) under general anesthesia. Blood pressure (BP) in diastole was increased to 100 mm Hg by norepinephrine to simulate HT. Pump flow, D-P, ECG, and BP were measured at pump speeds of 1,800, 2,100, and 2,300 rpm. All data were separated into systole and diastole, and pump flow during HT was compared with normotensive (NT) conditions at respective pump speeds. Diastolic BP was increased to 99.3+/-4.1 mm Hg from 66.5+/-4.4 mm Hg (p<0.01). D-P in systole was under 40 mm Hg (range of change was 10 to 40 mm Hg) even during HT. During NT, the average systolic pump flow volume was 60% of the total pump flow. However, during HT, the average systolic pump flow was 100% of total pump flow volume, although the pump flow volume in systole during HT decreased (33.1+/-5.7 vs. 25.9+/-4.0 ml/systole, p<0.01). In diastole, the average flow volume through the pump was 19.6+/-6.9 ml/diastole during NT and -2.2+/-11.1 ml/diastole during HT (p<0.01). The change in pump flow volume due to HT, in diastole, was greater than the change in pump flow in systole at each pump speed (p<0.001). This study suggests that the decrease of mean pump flow during HT is mainly due to the decrease of the diastolic pump flow and, to a much lesser degree, systolic pump flow.

Evaluation of cardiac function during left ventricular assist by a centrifugal blood pump

In this study, the effects on varying cardiac function during a left ventricular (LV) bypass from the apex to the descending aorta using a centrifugal blood pump were evaluated by analyzing the left ventricular pressure and the motor current of the centrifugal pump in a mock circulatory loop. Failing heart models (preload 15 mm Hg, afterload 40 mm Hg) and normal heart models (preload 5 mm Hg, afterload 100 mm Hg) were simulated by adjusting the contractility of the latex rubber left ventricle. In Study 1, the bypass flow rate, left ventricular pressure, aortic pressure, and motor current levels were measured in each model as the centrifugal pump rpm were increased from 1,000 to 1,500 to 2,000. In Study 2, the pump rpm were fixed at 1,300, 1,500, and 1,700, and at each rpm, the left ventricular peak pressure was increased from 40 to 140 mm Hg by steps of 20 mm Hg. The same measurements as in Study 1 were performed. In Study 1, the bypass flow rate and mean aortic pressure both increased with the increase in pump rpm while the mean left ventricular pressure decreased. In Study 2, a fairly good correlation between the left ventricular pressure and the motor current of the centrifugal pump was obtained. These results suggest that cardiac function as indicated by left ventricular pressure may be estimated from a motor current analysis of the centrifugal blood pump during left heart bypass.

A small pulsatile blood pump for ventricular support during end-stage heart failure

A displacement blood pump to support the natural heart of patients for recovery from end-stage heart failure has been developed. This electromechanical pusher plate pump has a very compact and extremely flat design. The design goal was achieved by developing a novel gear system based on the principle of a swash plate. The blood pump and cannulae can be placed within the thoracic cavity between the lungs and ribcage. The first labtype model delivers an output of 3.1 L/min against an aortic pressure of 100 mm Hg at 120 bpm.

Cardiac recovery in dilated cardiomyopathy by unloading with a left ventricular assist device

BACKGROUND

Lasting recovery from intractable end-stage dilated cardiomyopathy, which occurs with ventricular unloading, has recently been demonstrated in 5 patients. Here our extended clinical experience with the "weaning" concept is presented.

METHODS

In 19 patients (23 to 65 years) with intractable end-stage dilated cardiomyopathy, ventricular assist devices were explanted after support periods of up to 26 months, when repeat off-pump studies had shown either restoration of cardiac function (left ventricular ejection fraction, > 45%) and dimensions (left ventricular internal diameter in diastole, < 55 mm) or partial recovery (left ventricular ejection fraction between 35% and 40%) with serious complications on the device. At the time of device placement left ventricular ejection fraction was below 20% and left ventricular internal diameter in diastole more than 64 mm and bridge-to-transplantation had been planned.

RESULTS

Seven patients with persistently restored cardiac function for more than 8 months and 5 patients for less than 5 months after weaning were studied. Five patients with recurrent heart failure died within 4 to 8 months after explantation. Four patients had to be transplanted and 2 died for reasons unrelated to cardiac function. An individual optimal left ventricular ejection fraction and left ventricular internal diameter in diastole was reached before pump removal was actually conducted in all patients. These parameters gradually deteriorated until pump removal.

CONCLUSIONS

Lasting recovery can be reached by ventricular unloading in a subset of patients with intractable end-stage dilated cardiomyopathy. Obviously, there is an individual optimum of recovery that cannot be further improved by prolonged unloading.

Ventricular assistance for recovery of cardiac failure

Mechanical assist devices have been used increasingly to support patients who await heart transplantation. The initial goal was to provide sufficient circulatory function to keep these patients alive and to allow them to recover from secondary organ dysfunction. A recent observation showed an improvement in native heart performance in some transplant candidates who receive support with mechanical assist devices. Under these conditions, myocardial recovery has been mostly restricted to patients with primary dilated cardiomyopathy and with extended periods of ventricular support. Also, the exact mechanisms that lead to substantial myocardial recovery remain unknown. Several investigations have demonstrated improved myocyte performance, reduced fibrosis, reduced cytokine levels, and reduced autoantibodies during long-term mechanical support; therefore, the observation of cardiac recovery during mechanical support is in accordance with currently discussed models of end-stage heart failure.

In vivo evaluation of the miniaturized Gyro centrifugal pump as an implantable ventricular assist device

A miniaturized Gyro centrifugal pump has been developed to be incorporated into a totally implantable artificial heart. The Gyro PI (permanently implantable) model is a pivot bearing supported centrifugal pump with a priming volume of 20 ml. With the miniaturized actuator, the pump-actuator package has a height of 53 mm, a diameter of 65 mm, and a displacement volume of 145 ml. To evaluate the hemocompatibility and efficiency of the Gyro PI pump system, a plastic prototype (Gyro PI-601) was implanted into a bovine model as a left or right ventricular assist device (LVAD or RVAD), bypassing from the left ventricular apex to the descending aorta or from the right ventricular infundibulum to the main pulmonary artery. The calves were anticoagulated with heparin to maintain activated clotting times from 150 to 200 s. Four calves were supported for 23, 24, and 50 days in the LVAD studies, and 40 days in the RVAD study. The first calf died due to intrathoracic bleeding associated with sepsis. The second calf was euthanized for a low flow rate less than 2 L/min due to an obstructed inflow with growing pannus. The third and fourth calves were euthanized as scheduled. Renal and hepatic functions remained normal, and plasma free hemoglobin values were less than 8 mg/dL throughout the experiments. The fourth case showed flow rates of 4.83 +/- 0.57 L/min, input power of 6.16 +/- 0.49 W, and the inside temperature of the actuator of 43.5 +/- 0.52 degrees C. The pumps implanted in the fourth calf demonstrated no thrombus formation at the autopsy. These in vivo experiments revealed that the Gyro PI pump can provide adequate flow as an easily implantable, efficient, antithrombogenic, and nonhemolytic centrifugal LVAD or RVAD with miniaturized actuators.

Development of a flow estimation and control system of an implantable centrifugal blood pump for circulatory assist

A bypass flow rate estimation and control system (BECS) for an implantable centrifugal blood pump (ICBP) has been developed in our institute. The estimated flow rate (EF) of the ICBP was derived from the electric power consumption, the rotating speed of a motor, and the blood viscosity presumed by the hematocrit and body temperature. The error in the EF was 0.5 +/- 0.4 L/min in in vivo experiments for 40 days. The rotating speed of the motor was controlled automatically every 200 ms to bring the EF in accord with the desired flow rate (DF). The reactivity and accuracy of the BECS were investigated in in vitro and in vivo experiments. The ICBP was operated by the BECS in a mock circuit in parallel with a pulsatile ventricular assist device (PVAD) to simulate left heart bypass. The reactivity was evaluated by changing the DF from 7 L/min to 5 L/min at an afterload of 160/97 mm Hg. To evaluate the accuracy of the BECS, the ICBP was driven under the aortic pressure of 110/85 mm Hg in the abdominal wall of an adult goat (70 kg). The DF was set at 5 L/min for 4 min for the goat in an awake condition. It took 13 s to change the flow rate in the in vitro experiment. The measured flow rate (MF) was maintained at 5.0 +/- 0.2 L/min by the BECS in vivo. In conclusion, the BECS has moderate reactivity and accuracy.

[Temporary mechanical left heart support. Recovery of heart function in patients with end-stage idiopathic dilated cardiomyopathy]

BACKGROUND

Implantation of a mechanical cardiac support system (MCSS) in patients with idiopathic dilated cardiomyopathy (IDC) may improve cardiac function and allow explantation of the device. Our experience now includes 13 patients who have been "weaned" from MCSS and we report about the overall results of this treatment as well as the effects of ventricular unloading on cardiac function, anti-beta 1-adrenoceptor-autoantibody (A-beta 1-AAB) level and the degree of myocardial fibrosis.

METHODS

13 patients with non-ischemic IDC who had been admitted here in cardiogenic shock (CI < 1.61.min-1.m2, left ventricular ejection fraction [LVEF] < 16% and left ventricular internal diameter in diastole [LVIDd] > 68 mm) and who all tested positive for A-beta 1-AABs were implanted with an uni-(12 patients) or a biventricular (1 patient) mechanical assist device. Echocardiographic evaluation and A-beta 1-AAB-level-monitoring was routinely performed after implantation and explantation of the MCSS and the degree of myocardial fibrosis was assessed at the time of implantation and after explantation.

RESULTS

During a mean duration of mechanical support of 236 +/- 201 days (range: 30 to 794 days), LV-EF improved to a mean of 46% and LVIDd decreased to a mean value of 56 mm in these 13 patients. A-beta 1-AABs decreased and disappeared 11.7 weeks after implantation of the device and did not reincrease thereafter. The highly pathologic degree of fibrosis at the time of implantation diminished to normal values about 1 year after explantation. One patient died of anesthesiologic complications and another patient shortly presented with a new episode of cardiac insufficiency 6 months after explantation. He was implanted again with an univentricular assist device was successfully transplanted 3 weeks later. Mean observation period of the remaining 11 patients now amounts to 12.6 +/- 9.77 (range: 3 to 26) months after explantation of the device--as of May, 31, 1997--with a cumulative observation period of 139 patient months.

CONCLUSION

Temporary implantation of a MCSS may normalize cardiac function in selected patients with IDC. The striking degree of myocardial fibrosis can reduce to normal values after explantation of the device. A-beta 1-AABs disappear during ventricular unloading and do not increase thereafter. "Weaning" from mechanical device may constitute an alternative treatment to cardiac transplantation in selected patients.

Weaning from mechanical cardiac support in patients with idiopathic dilated cardiomyopathy

BACKGROUND

Implantation of mechanical cardiac support systems (MCSS) in patients with idiopathic dilated cardiomyopathy (IDC) may improve cardiac function and allow explantation of the device. We report of long-term effects of ventricular unloading on cardiac function, humoral anti-beta1-adrenoceptor autoantibodies (A-beta1-AABs), and myocardial fibrosis.

METHODS AND RESULTS

Seventeen patients in New York Heart Association functional class IV with nonischemic IDC received MCSS. All had a cardiac index of < 1.6 L x min(-1) x m(-2) of body surface area, a left ventricular ejection fraction (LVEF) of <16%, and a left ventricular internal diameter in diastole (LVIDd) of >68 mm and tested positive for A-beta1-AABs. Echocardiographic evaluation, serum tests for A-beta1-AABs, and histological assessment of myocardial fibrosis were performed before and after MCSS implantation. The mean support duration was 230+/-201 days. Six patients died, four were transplanted, and two are still on MCSS. Five patients with significant cardiac recovery (mean LVIDd, 54+/-2.3 mm; LVEF, 47+/-3.7%) were weaned after 160 to 794 days and are now device free for 51 to 592 days. A-beta1-AABs disappeared gradually during MCSS without increase after weaning; cardiac function and volume density of fibrosis remained normal. Nine patients' cardiac function hardly improved during ventricular unloading.

CONCLUSIONS

Cardiac function can be normalized in selected patients with end-stage IDC by MCSS. The degree of preoperative myocardial fibrosis may be an indicator for outcome; A-beta1-AABs can be used to monitor myocyte recovery. Weaning from MCSS offers an alternative to cardiac transplantation in certain patients.

Long-term evaluation of a nonpulsatile mechanical circulatory support system

Antithrombogenicity of a centrifugal pump (CP) developed in our institute is provided by a central balancing hole (BH) in the impeller. A current CP, the National Cardiovascular Center (NCVC)-2, was ameliorated to improve antithrombogenicity, whereby the BH diameter was widened to improve self washout flow velocity, and an edge of the thrust bearing was rounded off to minimize flow separation. Effects of these modifications were assessed in a long-term in vivo experiment. The antithrombogenicity, hemolytic property, and mechanical durability of the NCVC-2 were investigated in 3 goats. The NCVC-2 was installed paracorporeally between the left atrium and the aorta and driven as long as possible at rotating speeds of about 2,800 rpm. The NCVC-2 ran for 50, 200, and 367+ days. The mean bypass flow rates were 6.8, 5.0, and 5.3 L/min, respectively. Creatinine, blood urea nitrogen (BUN), glutamic-oxaloacetic transaminase (GOT), and glutamic-pyruvic transaminase (GPT) did not increase until one week before termination. Plasma free hemoglobin was kept to a level less than 15 mg/dl, except for the last week of the second case. These results indicate that the NCVC-2 has excellent antithrombogenicity, an acceptable hemolytic property and the necessary durability for prolonged use.

Control of centrifugal blood pump based on the motor current

In this study, centrifugal pump performance was examined in a mock circulatory loop to derive an automatic pump rotational speed (rpm) control method. The pivot bearing supported sealless centrifugal pump was placed in the left ventricular apex to aorta bypass mode. The pneumatic pulsatile ventricle was used to simulate the natural ventricle. To simulate the suction effect in the ventricle, a collapsible rubber tube was placed in the inflow port of the centrifugal pump in series with the apex of the simulated ventricle. Experimentally, the centrifugal pump speed (rpm) was gradually increased to simulate the suction effect. The pump flow through the centrifugal pump measured by an electromagnetic flowmeter, the aortic pressure, and the motor current were continuously digitized at 100 Hz and stored in a personal computer. The analysis of the cross-spectral density between the pump flow and motor current waveforms revealed that 2 waveforms were highly correlated at the frequency range between 0 and 4 Hz, with the coherence and phase angles being close to 1.0 and 0 degree, respectively. The fast Fourier transform analysis of the motor current indicated that the second harmonic component of the motor current power density increased with the occurrence of the suction effect in the circuit. The ratio of the fundamental to the second harmonic component decreased less than 1.3 as the suction effect developed in the circuit. It is possible to detect and prevent the suction effect of the centrifugal blood pump in the natural ventricle through analysis of the motor current waveform.

Flow characteristics and required control algorithm of an implantable centrifugal left ventricular assist device

As the clinical application of LVADs has increased, attempts have been made to develop smaller, less expensive, more durable and efficient implantable devices using rotary blood pumps. Since chronic circulatory support with implantable continuous-flow LVADs will be established in the near future, we need to determine the flow characteristics through an implantable continuous-flow LVAD. This study describes the flow characteristics through an implantable centrifugal blood pump as a left ventricular assist device (LVAD) to obtain a simple non-invasive algorithm to control its assist flow rate adequately. A prototype of the completely seal-less and pivot bearing-supported centrifugal blood pump was implanted into two calves, bypassing from the left ventricle to the descending aorta. Device motor speed, voltage, current, flow rate, and aortic blood pressure were monitored continuously. The flow patterns revealed forward flow in ventricular systole and backward flow in diastole. As the pump speed increased, an end-diastolic notch became evident in the flow profile. Although the flow rate (Q [l/min]) and rotational speed (R [rpm]) had a linear correlation (Q = 0.0042R - 5.159; r = 0.96), this linearity was altered after the end-diastolic notch was evident. The end-diastolic notch is considered to be a sign of the sucking phenomenon of the centrifugal pump. Also, although the consumed current (I [A]) and flow rate had a linear correlation (I = 0.212Q + 0.29; r = 0.97), this linearity also changed after the end-diastolic notch was evident. Based upon the above findings, we propose a simple algorithm to maintain submaximal flow without inducing sucking. To maintain the submaximal flow rate without measuring flow rate, the sucking point is determined by monitoring consumed current according to gradual increases in voltage.