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Ann Thorac Surg 1996;61:317-322
© 1996 The Society of Thoracic Surgeons

Experience With Devices With Limited Availability

Ventricular Assist Systems: Experience in Japan With Toyobo Pump and Zeon Pump

Hisateru Takano, MD, PhD, Takeshi Nakatani, MD, PhD

National Cardiovascular Center Research Institute, Osaka, Japan

Abstract

Background. Two types of ventricular assist systems have been approved for use by the Japanese government.

Methods. The two government-approved ventricular assist systems, the Toyobo pump (National Cardiovascular Center type) and the Zeon pump (Tokyo University type), were applied to 219 patients in Japan as of October 20, 1994.

Results. Adult-sized were used in 211 patients and pediatric ones in 8 patients. Left ventricular assist systems was performed in most cases (82.6%). The predominant indication was failure to be weaned from cardiopulmonary bypass (65.8%). The duration of ventricular assist system application ranged from 1 hour to 70 days, and the mean was 7.3 days, excluding the patients with cardiomyopathy. The weaning rate was 48.8% and the survival rate was 25.6%. Main causes of death were heart failure including unrecoverable heart failure and multiple organ failure. In 12 cardiomyopathy patients, Toyobo pumps were applied as left ventricular assist systems. Support duration was from 13 days to 192 days (ongoing). One patient was bridged to transplantation successfully and 1 was weaned after 3 months of support.

Conclusions. From these data, the Toyobo pump and the Zeon pump are useful for short-term support for acute, profound heart failure. The Toyobo pump also may provide sufficient support as a bridge to transplantation for the medium term.

An artificial heart program in Japan started to attempt replacement of the whole heart in the late 1950s by Tokyo University group [1]. From the clinical side, a ventricular assist system (VAS) was desired to maintain the normal circulation and to restore the failing heart after cardiac operations [2–4]. Several groups were involved in development and experimental studies of VASs for clinical use in Japan [5, 6]. The first clinical trial of VAS by the Tokyo University group was performed on a patient with postcardiotomy cardiac failure in 1980 [7]. In 1982, the National Cardiovascular Center (NCVC)-type VAS was applied to a postcardiotomy patient, which was followed by an expansion of VAS applications using several types of pulsatile blood pump in Japan [8].

Clinical evaluation of two types of VASs, the NCVC type (made by Toyobo Co) and the Tokyo University type (pump made by Zeon, control-drive unit [CDU] by Aishin) was started in 1986 to obtain approval for commercial release under the guidance of the Japanese Ministry of Health and Welfare. Each VAS was applied in more than 60 patients [9–11]. In January 1990, both types of VAS were approved by the Japanese government following the successful results and became commercially available without coverage of medical insurance. From April 1994, both types of VAS were approved to be covered by medical insurance in application for acute cardiogenic shock at selected hospitals by government. In this article we present the VAS experience in Japan with both government-approved VASs: the Toyobo-NCVC-type pump and the Zeon-Tokyo University-type pump.

Material and Methods

Description of the Ventricular Assist Systems Used in Japan
Six types of VASs were used in Japan. Two government-approved VASs, the Toyobo-NCVC type and the Zeon-Tokyo University type, were used in the majority of patients: 124 patients (51.7%) and 95 patients (39.6%), respectively. Two types made by Japanese groups were used for some clinical cases, the Tohoku University type (pneumatic sack type) (3 patients) and the Thomas Giken type (pneumatic diaphragm type) (14 patients). Two other VASs, the Thoratec pump (pneumatic sack type), and Thermo Cardiosystems Inc HeartMate (pneumatic pusher-plate type) also were used in 3 patients and 1 patient, respectively.

Toyobo-National Cardiovascular Center-Type Ventricular Assist System
The Toyobo-NCVC type VAS was developed at the National Cardiovascular Center in Osaka and is manufactured by the Toyobo Co, Ltd, also located in Osaka [12, 13]. Blood pumps for adult and pediatric patients are available; the paracorporeal, pneumatic, and diaphragm-type pumps are made of Toyobo TM series segmented polyether polyurethane without a seam (Fig 1Go). Two Björk-Shiley valves are used in the inlet and outlet ports of the pump, no. 23 for adult-sized pumps and no. 21 for pediatric-sized ones. The effective stroke volumes are 70 and 20 mL, and the maximum outputs are 7.0 and 2.4 L/min, respectively. In animal experiments, no anticoagulant is needed when the bypass flow is maintained at greater than 2.0 L/min in the adult-sized pump and 0.8 L/min in the pediatric one [12–14]. The bypass flow was measured continuously by an electromagnetic flow probe fitted on an outlet conduit. There are two types of CDU: the standard type with two regular and two backup drivers, and the compact one with one regular driver and one backup driver. The main part of the CDU consists of an automatic electrocardiogram synchronization system and an automatic bypass flow control system based on automatic level control of left atrial pressure and flow in which bypass flow can be altered closely following changes in cardiac function [15]. The latest versions of both types of CDU are applicable as an intraaortic balloon pump driver, and the standard type has a composite driving system for left VAS (LVAS) and intraaortic balloon pump [16, 17]. These two new types of CDU are shown in Figure 1Go. Both types permit 30 minutes of pumping by a built-in compressor and vacuum unit with internal batteries.



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  		Fig 1. . The Toyobo-National Cardiovascular Center type ventricular assist system: (A) pediatric (right) and adult (left)-sized blood pumps; (B) standard (left) and compact (right) control-drive units.

 
Zeon-Tokyo University-type Ventricular Assist System
The Zeon-Tokyo University type VAS was developed at Tokyo University and is produced by Nippon Zeon Co Ltd, Tokyo, Japan [18]. The blood pump is paracorporeal, pneumatic, and sack-type (Fig 2Go). The pump and cannulas are made of polyvinyl chloride, and all blood contacting surfaces are coated with Cardiothane. Two no. 19 Björk-Shiley valves are used as inlet and outlet valves, and an electromagnetic flow probe is placed at the outflow conduit to measure pump output continuously. The stroke volume is 40 mL, and the maximum flow is approximately 5 L/min. The CDU is manufactured by Aishin Seiki Co Ltd in Kariya, Aichi, Japan, and is equipped with a compressor and vacuum pump that can drive two pumps at the same time (see Fig 2Go). It is capable of functioning in synchronous or asynchronous mode to the electrocardiogram or aortic pressure. Another feature of this CDU is that it has a back-up driver and internal battery packages that permit 40 minutes of pumping.



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  		Fig 2. . The Zeon-Tokyo University type ventricular assist system: (A) blood pump, (B): control-drive unit.

 
Patient Profiles
The database of this report as of October 20, 1994, consisted of 219 patients treated with two types of VAS, the Toyobo-NCVC type and the Zeon-Tokyo University type, in Japan. These included 151 male patients (68.9%) and 68 female patients (31.1%), whose ages ranged from 9 months to 82 years (mean, 53.6 ± 17.3 years). Adult-sized VASs were applied to 211 patients, whose ages ranged from 12 years to 82 years, and a pediatric-sized one in 8, whose ages ranged from 9 months to 10 years. The indications for application of VAS were divided into three categories: postcardiotomy, cardiogenic shock without surgical procedure, and cardiomyopathy. In postcardiotomy, 144 patients (65.8%) were treated by VAS due to failure to be weaned from cardiopulmonary bypass, and 50 patients (22.8%) were treated due to postoperative low cardiac output syndrome. In 13 patients (5.9%) a VAS was used because of cardiogenic shock without surgical procedure including acute myocardial infarction and acute myocarditis. Recently, a VAS was used in an attempt to bridge to transplantation 12 cardiomyopathy patients who were waiting for heart transplantation.

Results

Types of Device
One hundred twenty-four patients (51.7%) were treated with the Toyobo-NCVC-type VAS, and 95 (39.7%) with the Zeon-Tokyo University-type VAS. Mean assisted duration of Toyobo pump was 14.3 ± 13.2 days and that of Zeon was 6.5 ± 10.3 days. Weaned rates and survival rates of both pumps were similar: 47.6% versus 46.3% and 25.0% versus 25.3%, respectively.

Pump Size and Results
Adult-sized blood pumps were applied to 211 patients: 100 patients (47.4%) were weaned and 55 patients (26.1%) survived. Pediatric-sized blood pumps of the Toyobo-NCVC-type VAS were used in 8 patients: 3 of them (37.5%) were weaned, but none of them survived. The body weight of these patients was between 5.8 and 14 kg.

Distribution by Year and Results
The first clinical application was performed in 1980 (Fig 3Go). One hundred fifty-three clinical trials of the Toyobo-NCVC-type VAS and the Zeon-Tokyo University-type VAS were performed between 1986 and 1988. During these clinical trials, the blood pump set was provided free of charge. After the approval, the number of VAS cases decreased, because the cost of these two types of VAS was not covered by medical insurance. From April 1994, both pumps were approved to be covered by medical insurance in cases of acute cardiogenic shock at selected hospitals. Currently, more than 20 hospitals in Japan are approved to use these VASs under coverage of medical insurance. From 1992, cardiomyopathy became one of the indications for VAS. Three patients with cardiomyopathy are on pumping using Toyobo-NCVC type pumps on October 20, 1994.



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  		Fig 3. . Distribution by year and results through Oct 20, 1994.

 
Distribution by Age and Results
Ages of more than 85% of patients ranged from 40 years to more than 70 years, whereas there were 7 children (3.5%) less than 10 years old (Fig 4Go). Thirty-four patients, or 15.5%, were more than 70 years old, and their results were better than those of the patients between 60 and 70 years old. The patients aged 40 to 50 years had the best clinical results. The mortality of young patients was high.



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  		Fig 4. . Distribution by age and results through Oct 20, 1994.

 
Primary Diagnoses and Results
Of 219 patients, primary diagnoses were ischemic heart disease in 110 (50.2%), valvular heart disease in 54 (24.7%), and ischemic heart disease with valvular heart disease in 12 (5.5%). Other diagnoses have included congenital heart disease in 16 (7.3%), cardiomyopathy in 12 (5.5%), and miscellaneous diseases in 13 (5.9%) (Fig 5Go). Clinical results in patients with congenital heart disease and cardiomyopathy were worse.



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  		Fig 5. . Primary diagnoses and results through Oct 20, 1994. (IHD = ischemic heart disease; VHD = valvular heart disease.)

 
Indications for Ventricular Assist System Application and Results (Excluding Patients With Cardiomyopathy)
Of 207 patients, excluding patients with cardiomyopathy, the patients with failure to be weaned from cardiopulmonary bypass showed better results than those with postoperative low output syndrome (Fig 6Go). This may be related to earlier application of VAS in the former. In cardiogenic shock without a surgical procedure, 4 of 13 patients (30.8%) were weaned from VAS and 3 patients (23.1%) survived.



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  		Fig 6. . Indications and results through Oct 20, 1994. Patients with cardiomyopathy were excluded. (CPB = cardiopulmonary bypass.)

 
Types of Assist and Results (Excluding Patients With Cardiomyopathy)
An LVAS has been used for the majority of patients (169 patients; 81.6%) (Fig 7Go). Another 19 patients (9.2%) received a right VAS, and 19 (9.2%) a biventricular assist system. The results in patients with a right VAS were much better than those in patients with an LVAS. The rate of separation from right VAS and survival rate were excellent. The worst clinical results have been obtained in patients with biventricular assist, which corresponds to the experience in other countries.



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  		Fig 7. . Types of assist and results through Oct 20, 1994. Patients with cardiomyopathy were excluded. (BVAS = biventricular assist system; LVAS = left ventricular assist system; RVAS = right ventricular assist system.)

 
Duration of Circulatory Support (Excluding Patients With Cardiomyopathy)
Of 207 patients excluding patients with cardiomyopathy, 101 patients (48.8%) were successfully weaned from the VAS, and 53 patients (25.4%) were long-term survivors who were alive more than 1 month. The duration of circulatory assist had no relation to the results, as shown in Table 1Go.


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  		Table 1. . Duration of Circulatory Support (Patients With Cardiomyopathy Were Excluded)
 
Assisted Duration and Results (Excluding Patients With Cardiomyopathy)
The assisted duration of VAS and the corresponding clinical results for 207 patients are shown in Figure 8Go. The duration ranged from 1 hour to 70 days, and most patients were on the VAS for less than 14 days. Of the 62 patients on the VAS from 3 to 7 days, 44 (71.0%) were weaned and 27 (43.5%) survived. These results are fairly good. The longest support was 70 days, and the longest support in a patient who survived was 25 days. On those receiving VAS support for less than 1 day, only 4 (11.1%) were weaned and 3 (8.3%) survived. The corresponding figures for patients receiving VAS support for more than 14 days were 13 (48.1%) and 4 (14.8%), respectively.



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  		Fig 8. . Assisted duration and results through Oct 20, 1994. Patients with cardiomyopathy were excluded.

 
Acute Myocardial Infarction With Cardiogenic Shock
Sixty-one patients with cardiogenic shock after an acute myocardial infarction were treated with a VAS. An LVAS was applied to more than 95% of patients. Diagnoses and procedures are summarized in Table 2Go.


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  		Table 2. . Acute Myocardial Infarction With Cardiogenic Shock
 
Causes of Death (Excluding Patients With Cardiomyopathy)
Major causes of death in nonweaned patients were heart failure, multiple organ failure, bleeding, and respiratory failure (Fig 9Go). After removal of the VAS, they included multiorgan failure and recurrent heart failure.



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  		Fig 9. . Causes of death through Oct 20, 1994. Patients with cardiomyopathy were excluded. (MOF = multiorgan failure.)

 
Application of Ventricular Assist System in Cardiomyopathy Patients
In 12 patients an LVAS was applied because of severe cardiac failure due to cardiomyopathy. The duration of assist ranged from 12 days to 192 days (ongoing) (mean 72.4 ± 64.8 days). One patient received a transplant at the Texas Heart Institute after 119 days of support, after transportation from Japan to the United States by air [19]. One patient was successfully weaned from the LVAS after 90 days pumping and was discharged in good condition 2 months after removal. Six patients died on an LVAS due to multiorgan failure in 4, biventricular failure in 1, liver failure in 1, and cerebral embolism in 1. Assisted duration ranged from 13 to 190 days (mean, 54.1 ± 63.1 days). Three other patients were on LVAS awaiting a heart transplant for 16, 77, and 192 days, respectively.

Comment

Two types of VAS, the Toyobo-NCVC type and the Zeon-Tokyo University type, were approved by the Japanese government for commercial release in January 1990 and for coverage by medical insurance in cases of acute cardiac failure at selected hospitals. From the clinical trials, the Toyobo-NCVC-type VAS showed the capacity of substituting for 100% of cardiac function [9]. Mean bypass flow of the Zeon-Tokyo University-type VAS was 2.3 ± 0.6 L/min, and the reported limiting factor was the volume to return to the pump [11, 13].

To improve the results of VAS application, early application or decrease in the duration of low cardiac output is most important [9, 10]. The results were also affected by the damage of the native heart before VAS application [20–22]. For unrecoverable heart failure, heart transplantation should have been carried out [23]. Ventricular assist system application without delay, before major organs including the heart itself are irreversibly damaged, is most important to improve the result of VAS application in any indication.

Thrombus formation is a big concern in application of any type of VAS. In most clinical trials (92 patients), the inside of the Toyobo-NCVC pump was clean except for macroscopic ring-shaped thrombus formation in the groove around the valve in 8 patients (8.7%) and macroscopic thrombus formation inside the pump in 8, in which cases incorrect pumping driving mode might have caused delamination of the absorbed protein layer, resulting in the formation of surface thrombi [14]. Also, spotted white thrombi were noted in the case of sepsis. However, pump-originated serious complications, such as thromboembolism, were not seen. In clinical trials of Zeon-Tokyo University-type VAS (77 cases), 13 pumps were found to have macroscopic thrombus formation [24, 25]. These clinical trials were performed in postcardiotomy patients. In recent years, VAS application expanded to patients with cardiomyopathy attempting a bridge to heart transplantation. Toyobo-NCVC pumps have been used in 12 patients. In this situation, the durability and antithrombogenicity require reevaluation. Regarding durability, more than 190 days of support in 2 cases has been reported [26], and further careful management should be performed.

Acknowledgments

We greatly appreciate the contributions of the investigational hospitals and those in the industry who provided the data in this report.

Footnotes

Presented at The Third International Conference on Circulatory Support Devices for Severe Cardiac Failure, Pittsburgh, PA, Oct 28-30, 1994.

Address reprint requests to Dr Takano, Department of Artificial Organs, National Cardiovascular Center, Research Institute, 5-7-1, Fujishiro-dai, Suita, Osaka 565, Japan.

References

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