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Ann Thorac Surg 1999;68:761-763
© 1999 The Society of Thoracic Surgeons
a Division of Cardiovascular and Thoracic Surgery, The University of Texas, Houston Medical School, and Department of Cardiovascular Surgery, Texas Heart Institute, Houston, Texas, USA
Address reprint requests to Dr Sweeney, 6410 Fannin, Suite 410, Houston, TX 77030
Presented at the Fourth International Conference on Circulatory Support Devices for Severe Cardiac Failure, Houston, TX, Oct 3–5, 1997.
Abstract
Background. The Hemopump (Medtronic, Inc, Minneapolis, MN) was conceived in 1975 and designed in 1982 as a temporary, extracorporeal cardiac assist system. Although it has been used clinically in Europe, it is not currently available in the United States.
Methods. In vitro and in vivo testing of the Hemopump began in 1983. Clinical investigations have included studies of patients in cardiogenic shock, Hemopump-supported coronary artery bypass operations in Sweden, and European studies of percutaneous transluminal coronary angioplasty (PTCA) with Hemopump support.
Results. The Hemopump has demonstrated positive hemodynamic effects in patients. Laboratory and clinical studies have shown that the nonpulsatile axial flow generates flows of up to 4.5 L/min while maintaining adequate perfusion of other organs. In Europe, hemopumps have been used successfully to support coronary bypass and PTCA.
Conclusions. The Hemopump system is simple, inexpensive, and well tolerated by the blood elements. Moreover, its design allows flexibility in supporting patients during cardiopulmonary bypass (in lieu of conventional techniques) and high risk angioplasty, as well as in rescuing patients with low cardiac output.
The Hemopump (Medtronic, Inc, Minneapolis, MN) was conceived by Dr Richard Wampler in 1975 while he worked as a public health consultant in Egypt. It was designed around 1982 while Dr Wampler worked with Nimbus Corporation in Rancho Cordova, California. As a temporary cardiac assist system, it is intended to assume up to 80% of the workload of the resting heart for at least 7 days, thus giving the heart in cardiogenic shock the opportunity to rest and recover.
Hemopump system components
The Hemopump’s extracorporeal power is derived from a standard AC line voltage source (with battery backup for portable operation), which is incorporated into a console. The console is a portable, mobile unit weighing about 20 pounds; it contains not only the power mechanisms but also the control and diagnostic/alarm systems required to operate the pump and supply it with purge fluid. The console is usually attached to a bedside stand, but it can also be mounted on the foot of the patient’s bed or carried by hand.
The pump system is intracorporeal. This rather novel concept in 1975, involves axial blood flow, pumped by a rapidly turning (25,000 RPM) Archimedes screw. About the size of a pencil eraser, the disposable pump assembly is made of stainless steel and is attached to a soft silicone rubber inflow cannula (Fig 1). Although the actual pump is positioned just above the aortic valve, the cannula is positioned across the valve and into the left ventricle, from which blood is entrained and pumped into circulation. Nonpulsatile flow rates of 3.5– 4.5 L/min are readily achieved through either the 24 French (femoral artery insertion) or the 26 French (ascending aortic insertion) cannula.
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In the Hemopump system, electrical power from the console creates pulsing electromagnetic fields in the motor, causing the permanent magnet to rotate. This spinning motion is then imparted to the drive shaft and the pump blades, which turn rapidly and draw a steady stream of oxygenated blood from the left ventricle. Because the pumping action is nonpulsatile and continuous, blood flows through the pump even during diastole when the aortic valve is closed. Moreover, the pump can even be used effectively when the heart is fibrillating.
Contraindications to Hemopump use include significant blood dyscrasias, presence of a prosthetic aortic valve, dissecting thoracic or abdominal aortic aneurysm, severe peripheral vascular disease, severe aortic valve stenosis or insufficiency, left ventricular thrombosis, or end-stage terminal illness.
Comment
After initial development of the Hemopump, a patent was filed in 1983 and the project continued with in vitro and in vivo testing. Numerous experimental studies demonstrated that the system was well tolerated by the blood elements and that normal organ functions were maintained during prolonged periods of support [1–3]. A detailed study from our institution proved the efficacy of the Hemopump on hemodynamics, left ventricular function, myocardial perfusion, and fractional shortening in the face of coronary ischemia or acute left ventricular compromise [4].
In 1988, the Food and Drug Administration (FDA) gave Investigational Device Exemption (IDE) approval to study Hemopump use in patients suffering from cardiogenic shock. In our initial clinical study of 7 patients in cardiogenic shock, we did not find any incidence of infection, thrombosis, or vascular injury while the Hemopump was operating, and 3 of the 7 patients were alive and well 1 year after hospital discharge [5]. Further successes led to a larger, multi-institutional study [6] in which 41 patients were treated, with a 30-day survival rate of 31.7%. Positive hemodynamic effects (decreased pulmonary capillary wedge pressures and increased cardiac indices) without leg ischemia or hemolysis were seen in all patients. Indeed, the device seemed so efficient that practicing clinicians were anxious to apply it in desperate situations (under "compassionate usage" exceptions) in a way that deviated from the original protocol. In 1991, Johnson and Johnson Interventional Systems (JJIS) purchased the Hemopump technology, and the clinical study initiated by Nimbus was discontinued when the FDA determined that the Premarket Approval Application was not feasible. Medtronic, Inc, purchased the Hemopump technology from JJIS in 1995.
Intrigued by the 3.5–4.5 L/min flow rates and good left ventricular decompression, we initiated a series of coronary artery bypass operations in 1991 using the Hemopump for circulatory support and the patient’s own lungs for oxygenation [7]. We added the short-acting beta-blocker esmolol to the system to make the heart more tranquil during this "beating-heart" surgery. Although the FDA’s action made the Hemopump temporarily unavailable to us, Lönn and associates in Linköping, Sweden, carried this concept forward [8, 9]. Their experience includes over 30 patients with an average of 2.8 bypass grafts per patient. No adverse sequelae have been encountered. A randomized, prospective trial of Hemopump-supported aortocoronary bypass operations versus conventional bypass techniques began in Linköping with 16 patients in each group. Lönn and his colleagues found no differences in length of operation, length of postoperative intubation, or length of intensive care unit stay. Significant differences favoring the Hemopump cohort have been noted in the amount of intraoperative bleeding and the requirements for blood transfusion. Ninety-day follow-up angiography showed good flow in all bypass grafts from the Hemopump group.
The Hemopump has been available in Europe as a 14 French percutaneously placed device. This smaller device is usually inserted in the femoral artery and advanced proximally across the aortic valve; it can supply 2.5 L/min of forward flow as well as left ventricular unloading. Studies in France, Germany, and Switzerland targeted patients for support during percutaneous transluminal coronary angioplasty (PTCA) [10–12]. These patients must have unstable angina pectoris, have at least one dilatable coronary stenosis, and have left ventricular ejection fractions of less than 25%. In all, 32 patients were treated, 31 of whom had 2- or 3-vessel disease. Of the 50 lesions that have been treated, 46 have been successfully dilated. Several patients were in cardiogenic shock or ventricular fibrillation during PTCA, but Hemopump support allowed the procedure to be successfully completed, after which the patients were defibrillated or resuscitated. During these episodes, pump support allowed the patients to remain conscious.
Despite thoughtful research and clinical successes, the Hemopump is not yet readily available in the United States. It has been used clinically in Europe and has proved to be an important adjunct in the treatment strategies of patients who have cardiogenic shock, need high-risk angioplasty, or develop postcardiotomy pump failure. In addition, the technology may play an important role in the evolution of new strategies for aortocoronary bypass surgery. In patients with ongoing ischemia or poor preoperative ventricular function who require operation, Hemopump use would ensure that an effective ventricular assist device is already in place if needed. "Myocardial protection" with the Hemopump appears to be at least as good as with most conventional methods. Moreover, the mechanical ventricular decompression reduces acute infarct size. It is reasonable to theorize that the 14 French percutaneous version may supplant the intraaortic balloon pump in certain clinical settings. The Hemopump is a reliable and simple device that is safe and easy to use. Its versatility and low cost should one day make it an important part of the array of therapies for treating patients with sick hearts, even in hospitals that are not major referral centers.
References
This article has been cited by other articles:
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  D. Mancini and D. Burkhoff Mechanical Device-Based Methods of Managing and Treating Heart Failure Circulation, July 19, 2005; 112(3): 438 - 448. [Abstract] [Full Text] [PDF]
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 T. Schmidt, J. Siefker, S. Spiliopoulos, and O. Dapunt New experience with the paracardial right ventricular axial flow micropump impella elect 600 Eur. J. Cardiothorac. Surg., August 1, 2003; 24(2): 307 - 308. [Abstract] [Full Text] [PDF]
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