Asian Cardiovasc Thorac Ann 2006;14:418-421
© 2006 Asia Publishing EXchange Ltd
Treatment of Right Heart Failure with a New Microaxial Blood Pump
Stefan Christiansen, MD,
Guido Dohmen, MD,
Rüdiger Autschbach, MD
Department of Cardiothoracic Surgery, University of Aachen, Aachen, Germany
For reprint information contact: Stefan Christiansen, MD Tel: 49 241 808 9221 Fax: 49 241 808 2454 Email: schristiansen{at}ukaachen.de, Department of Cardiothoracic Surgery, University of Aachen, Pauwelsstr. 30, 52074 Aachen, Germany.
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ABSTRACT
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Isolated postcardiotomy right ventricular failure is rare but associated with a high mortality. Therefore, new developments reducing this mortality are necessary. We report our first successful clinical use of a new paracardiac right ventricular microaxial blood pump which was developed for postcardiotomy right heart failure.
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INTRODUCTION
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Isolated postcardiotomy right ventricular failure is rare but associated with a high mortality.1 Only 15–35% of these patients survive to discharge from hospital.1,2 In most cases centrifugal pumps or paracorporeal right ventricular assist devices are used for right ventricular support due to the lack of alternative devices.1 The microaxial blood pump technique was developed at the Institute for Biomedical Engineering of the University of Aachen and primarily used for cardiac support during beating heart coronary surgery. Using this technology, a paracardiac right ventricular microaxial blood pump (Recover 600, Impella Cardiotechnik, Aachen, Germany) was developed for postcardiotomy right heart failure (approved by the MEDCERT Zertifizierungs- und Prüfungsgesellschaft für die Medizin GmbH, Hamburg, Germany, Process No.: PP-10752, Certificate No.: 10752GB41 1020523). Therefore, we report our first successful clinical use of this pump.
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DEVICE DESCRIPTION
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The microaxial paracardiac right ventricular assist device is a miniaturized rotary blood pump with a diameter of 6.4 mm and a weight of 11 g. The pump consists of a rotor driven by an incorporated brushless DC motor, the housing of the rotor, the inflow cage, the outflow cannula and the driveline. The inner volume of the pump is limited to 12 mL (avoiding the necessity to prime the pump), the inner artificial, blood contacting surface to 65 cm2. At the maximal speed of 32,500 rates·min–1, a flow of 6 L·min–1 may be delivered under physiological pressure difference conditions. A pressure sensor is placed in front of the rotor measuring the pressure difference between the outflow and the inflow of the pump. Using the pressure difference and the rotational speed of the rotor, pump flow is calculated online. All these values are displayed on the driving console continuously, which also allows the management of the pump by varying the rotational speed. A purge fluid is used to prevent blood from entering into the motor unit. Figure 1
demonstrates an intraoperative setting of the microaxial blood pump for right ventricular support. The overall cost of this pump is 3500 Euro.
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Figure 1. The microaxial blood pump implanted into the right atrium via the right atrial appendage for right ventricular support; the top of the pump is at the left lower corner and the Goretex outflow graft is connected to the main pulmonary artery at the right upper corner.
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CASE REPORT
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A 57-year-old patient was referred for emergency cardiac surgery because he sufferecd from an acute myocardial infarction of the anterior wall of the left ventricle complicated by a left ventricular wall rupture. He also suffered from an isolated occlusion of the left anterior descending coronary artery (LAD). The other coronary arteries did not demonstrate any stenoses. Therefore, an off-pump procedure with revascularization of the LAD and closure of the left ventricular wall rupture was planned to minimize operative trauma.
Unfortunately, there was a significant drop of blood pressure during displacement of the heart, so that it was necessary to institute extracorporeal circulation and cardioplegic arrest. Subsequently, the perforation of the left ventricular lateral wall was sutured with interrupted stitches and the left internal mammary artery was anastomosed to the LAD. Weaning from extracorporeal circulation was possible with catecholamines. Two days later, the patient demonstrated serious hemodynamic instabilities with prolonged periods of low blood pressures despite continuously enhanced catecholamines. The pulmonary artery pressures as well as the pulmonary capillary wedge pressure and the cardiac output were diminished whereas the central venous pressure was significantly enhanced (measured by a Swan-Ganz catheter). The echocardiographic study demonstrated a dilated, non-contractile right ventricle and a well-contracting, small left ventricle. Therefore, the diagnosis of a predominant right heart failure was made despite conservative therapy with inhaled NO and phosphodiesterase inhibitors. Additionally, there was no history relevant to the development of pulmonary hypertonus. Therefore, it was decided to implant the paracardiac microaxial blood pump for right ventricular support. After resternotomy, the inflow cage was inserted into the right atrium via the right atrial appendage using a purse-string suture and the outflow graft was anastomosed to the main pulmonary artery with a running suture. After de-airing of the pump via the pulmonary artery anastomosis, pump flow was adjusted to 3.5–4 L·min–1 to unload the right ventricle. Anticoagulation was achieved by intravenous administration of heparin adjusting the activated coagulation time to 160–200 seconds. During the proceeding days, the pump flow was reduced, controlling right ventricular function by echocardiographic studies (measurement of pulmonary artery pressures and so on were not possible due to artifacts produced by the pump).
After three days, pump flow was reduced to 1 L·min–1 and right ventricular function completely recovered. Therefore, the microaxial blood pump was explanted. The patient recovered well and was extubated on the 7th postoperative day. The overall drainage loss was 1850 mL. Altogether, 4 units of packed red blood cells and 6 units of fresh frozen plasma were administered. Unfortunately, he subsequently developed renal failure requiring a prolonged postoperative hospital stay. After 35 days, the patient was discharged home in a well overall condition.
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DISCUSSION
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Right ventricular failure has a multifactorial etiology with prolonged extracorporeal circulation, right ventricular ischemia, pulmonary hypertension, transfusion of numerous blood products, and use of vasopressors being the most frequent causes in patients suffering from ischemic cardiomyopathy.3 Although rare, right ventricular failure accounts for a mortality greater than 50% after circulatory support with an extracorporeal membrane oxygenation for postcardiotomy failure.2 Early application of circulatory support, and proper selection of support type may be key criteria in influencing mortality and non-weaning from circulatory support.2 Development of new right ventricular support devices appears to be necessary considering the poor results with currently used extracorporeal membrane oxygenation and paracorporeal right ventricular assist devices. This becomes more and more true considering the substantial number of complications with these right ventricular support devices.1–3
Other devices which are currently used for RV support are the ABIOMED BVS 5000 and the Biomedicus pump. Samuels et al4 reported their experiences with the ABIOMED BVS 5000 in 45 patients (25 left heart support, 10 RV support and 10 biventricular assist devices) for postcardiotomy shock in 36 patients (80%) and precardiotomy shock in 9 patients (20%) for a mean of 8.3 days. A total of 22 patients (49%) were weaned, however only 14 (31%) were discharged from hospital. The most common complications included bleeding (78%) and adverse neurologic events (22%). Transient neurologic events occurred with increasing frequency as the duration of support was extended beyond the first week. Similar results are reported by Noon et al5 for the Biomedicus pump: the pump was implanted in 141 patients for postcardiotomy failure for a mean of 3.8 days, in 110 patients for left ventricular assistance, in 8 patients for right ventricular assistance, and in 23 patients for biventricular assistance. Altogether, 54% of all patients were weaned from cardiac support but only 22% were discharged. For isolated RV support these figures are 12.5% and 0%. Bleeding was described as a frequently occurring complication requiring re-exploration for removal of excessive blood clots or relief of cardiac tamponade.
If more reliable right ventricular support devices with a significantly lower frequency of complications were available, the more liberal use of right ventricular mechanical support, as proposed by Moazami et al1, may become reality. Especially for patients with acute right ventricular failure secondary to myocardial infarction, early identification and aggressive management including right ventricular assist devices is necessary, since the dysfunctional right ventricle cannot accommodate the acute volume overload.6 Indications for right ventricular assist device implantation are cardiac index < 2.0L·min–1·m–2, aortic pressure < 90 mm Hg, central venous pressure > 20 mm Hg, and secondary organ dysfunction (usually renal failure).7
In addition to evident virtues of the new blood pumps, the safety and highly accepted standards of currently used devices must be met. Important aspects of blood pumps are device lifetime, cost, adaptability to diverse applications and patient requirements, rapid and easy deployment, thrombogenicity, flow characteristics and blood damage.8 The major advantages of the paracardiac right ventricular microaxial blood pump are its small size (inner volume: 12 mL, inner surface: 65 cm2), the simple design, the low energy requirements, and the avoidance of a priming volume. These figures lead to a reliable pump function without technical failures, and may result in a reduced number of transfusion requirements which is reported to be excessively high in patients with extracorporeal membrane oxygenation support.8 Up to 87.3% of patients undergoing extracorporeal membrane oxygenation support require blood transfusions with an average number of transfused units of red blood cells, fresh frozen plasma, and platelets of 29 ± 2, 19 ± 2, and 36 ± 4 units respectively. For the same reasons Chen et al3 tried to minimize the use of heparin in isolated right ventricular support patients since exogenous blood products themselves carry an attendant risk of worsening right-sided cardiac failure by increasing pulmonary vascular resistance. This strategy may help to reduce the transfusion requirements but also results in an enhanced number of thrombotic and/or thromboembolic complications.
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CONCLUSION
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This newly developed right ventricular microaxial blood pump is a promising right ventricular assist device which may be used more frequently if this initial positive experience is confirmed in the future.
Supported by: Bundesministerium für Bildung und Forschung, Germany
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REFERENCES
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- Moazami N, Pasque MK, Moon MR et al: Mechanical support for isolated RV failure in post-cardiotomy patients. J Heart Lung Transplant, 22, 2003, S206–7.
- Kitamura M, Aomi S, Hachida M, Nishida H, Endo M, Koyanagi H, et al. Current strategy of temporary circulatory support for severe cardiac failure after operation. Ann Thorac Surg 1999;68:662–5.[Abstract/Free Full Text]
- Chen JM, Levin HR, Rose EA, Addonizio LJ, Landry DW, Sistino JJ, et al. Experience with right ventricular assist devices for perioperative right-sided circulatory failure. Ann Thorac Surg 1996;61:305–10.[Abstract/Free Full Text]
- Samuels LE, Holmes EC, Thomas MP, Entwistle JC 3rd, Morris RJ, Narula J, et al. Management of acute cardiac failure with mechanical assist: experience with the ABIOMED BVS 5000. Ann Thorac Surg 2001;71:S67–72.[Abstract/Free Full Text]
- Noon GP, Lafuente JA, Irwin S. Acute and temporary ventricular support with BioMedicus centrifugal pump. Ann Thorac Surg 1999;68:650–4.[Abstract/Free Full Text]
- Moazami N, Hill L. Right ventricular dysfunction in patients with acute inferior MI: role of RV mechanical support. Thorac Cardiovasc Surg 2003;51:290–2.[Medline]
- Schmid C, Radovancevic B. When should we consider right ventricular support? Thorac Cardiovasc Surg 2002;50:204–7.[Medline]
- Magovern GJ Jr, Simpson KA. Extracorporeal membrane oxygenation for adult cardiac support: the Allegheny experience. Ann Thorac Surg 1999;68:655–61.[Abstract/Free Full Text]
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ABSTRACT
INTRODUCTION
