Implant technique for the Jarvik 2000 heart

Implant Technique for the Jarvik 2000 Heart Stephen Westaby, PhD, FETCS, O. H. Frazier, MD, David W. Pigott, FRCA, Satoshi Saito, MD, PhD, and Robert K. Jarvik, MD Oxford Heart Centre and The Heart Hospital, London, United Kingdom, Texas Heart Institute, Houston, Texas, and Jarvik Heart Inc, New York, New York

The Jarvik 2000 Heart is a silent compact axial flow impeller pump which is now undergoing clinical trials for both bridge to transplantation and permanent mechanical circulatory support. The pump is implanted into the apex of the failing left ventricle by left thoracotomy. A vascular graft offloads to the descending thoracic aorta

so that only the left pleural cavity is opened. Power supply is through an abdominal drive line or postauricular titanium pedestal according to the treatment strategy. (Ann Thorac Surg 2002;73:1337– 40) © 2002 by The Society of Thoracic Surgeons

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put monitoring system and arterial line are inserted. An infusion of the ino-dilator Milrinone is started. After induction of anesthesia, a left-sided double lumen endotracheal tube is deployed and a transesophageal echocardiography probe deployed. Detailed hemodynamic control is maintained with a combination of nitric oxide gas to reduce pulmonary arterial pressure together with glyceryl trinitrin, esmolol, adrenalin, and dopamine infusions as required. The patient is positioned in the lateral position providing access to the left chest and femoral vessels (Fig 1A). For permanent implants, the left shoulder, neck, and post-auricular scalp are prepared and included in the surgical field (Fig 1B). Surgical procedure begins with exposure of the left femoral artery and vein. In the event of profound hemodynamic deterioration, heparinization, cannulation, and cardiopulmonary bypass are then possible. Intraaortic balloon pump support is continued if present. For permanent implants, a second surgical team undertakes simultaneous implantation of the skull-mounted power system (see later). Left thoracotomy is performed through the sixth intercostal space to provide access to the apex of the left ventricle and the lower one-third of the descending thoracic aorta (Fig 1A). When feasible, the left lung is retracted gently rather than deflated. This reduces the propensity for a rise in pulmonary artery pressure and fall in cardiac output prior to heparinization. An appropriate site is identified for anastomosis of the distal part of the outflow graft. Reference to the thoracic CT scan helps determine the optimum position. We avoid atheromatous plaques or aneurysmal areas and have used the abdominal aorta. Ascending aortic anastomosis is feasible but reqires a longer graft. A side-biting clamp is applied and a 2-cm aortotomy made to accommodate the bevelled edge of a 16-mm Haemashield graft (Boston Scientific, Natick, MA). The oblique anastomosis is per-

he Jarvik 2000 Heart (Jarvik Heart Inc, New York, NY) is a compact axial flow impeller pump which is implanted within the apex of the failing left ventricle [1, 2]. Consequently, alignment and flow characteristics are not altered by changes in left ventricular shape or the cardiac cycle. The device itself is only slightly larger than the inlet cannula of the Heart Mate and Novacor left ventricular assist devices (LVADs) (Thermo Cardiosystems, Inc, Woburn, MA) (2.5 cm ⫻ 5.5 cm, weight 85 g, displacement volume 25 ml). It offloads through a 16-mm Dacron (C. R. Bard, Haverhill, PA) graft to the descending thoracic aorta. The impeller rotates at speeds of 8,000 to 12,000 rpm providing blood flow of up to 8 litres per minute with power consumption less than 12 watts. The Jarvik 2000 Heart is now undergoing clinical trials in end-stage heart failure patients both for bridge to transplantation and permanent mechanical circulatory support [3, 4]. Only the mode of power delivery differs between the two strategies.

Technique Bridge to transplant patients are usually on inotropic and intraaortic balloon pump support. Those currently chosen for permanent support are nontransplant eligible patients with end-stage dilated cardiomyopathy. When feasible, a computed tomographic (CT) scan of the thorax is obtained to assess atheroma or aneurysmal changes in the descending thoracic aorta. Permanent implant patients undergo CT scan of the head to determine skull thickness in the left parietal area. For post-auricular percutaneous power delivery, the site of the titanium pedestal and apical exit site from the chest are identified and marked with an indelible pen. Permanent implant patients are brought to the Intensive Care Unit on the evening before surgery where a continuous cardiac outAccepted for publication Dec 3, 2001. Address reprint requests to Dr Westaby, Oxford Heart Centre, John Radcliffe Hospital, Headley Way, Headington, Oxford OX3 9DU, United Kingdom; e-mail: [email protected].

© 2002 by The Society of Thoracic Surgeons Published by Elsevier Science Inc

Dr Jarvik discloses that he has a financial relationship with Jarvik Heart Inc.

0003-4975/02/$22.00 PII S0003-4975(01)03599-8

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Fig 1. (A) The patient is positioned for left thoracotomy. For permanent implants, access is also required to the shoulder, neck, and scalp. The skin incisions for post-auricular power delivery are shown. (B) The power cable is brought from the apex of the chest through the neck to the site of the titanium pedestal. This conveys a three-pin connector through the skin to the external power cable.

formed with continuous 4-0 polypropylene in such a way as to direct the graft in a gentle curve from the diaphragmatic sulcus to the anastomosis’ site. The graft is then clamped and the aortic side clamp removed, allowing the anastomosis to seal before heparinization. The Jarvik 2000 Heart is brought into the operative field and the power cable tunnelled across the midline below the costal margin to exit through the right hypochondrium. The pump itself is placed in a bowl of saline, the power cable connected to the external controller and battery, and the system tested. The pericardium is then widely opened anterior to the phrenic nerve. The apex of the left ventricle is inspected to determine the implant site in relation to the left anterior descending and diagonal vessels. The site is chosen to avoid the papillary muscles and allow the pump to lie parallel to the septum. At this point, heparin is administered, the intraaortic balloon pump is removed, and cannulation is undertaken for partial cardiopulmonary bypass. A long, thin-walled, venous cannula is advanced from the groin into the right atrium. Normothermic cardiopulmonary bypass is undertaken and the patient tipped into the head down position. The heart is fibrillated to prevent ejection during the coring procedure. Accurate suture placement is easier in the nonbeating heart. A cruciate incision is made through the left ventricular apex at the site for implantation (Fig 2A). The index finger is passed into the ventricle to determine proximity of the papillary muscles. A cylindrical coring knife is used to excise a ring of apical muscle to accom-

modate the Jarvik 2000 Heart. The ventriculotomy is inspected for muscle strands or thrombus which might impinge on the device. Eight to 10 Teflon (Impra Inc, subsidiary of L. R. Bard, Tempe, AZ) buttressed, mattress sutures of 2-0 Tycron are inserted circumferentially through the myocardium in order to anchor the cuff (Fig 2B). We aim to pass each through full-thickness myocardium and endocardium. Care is taken not to overtighten the knots (Fig 2C). Alternatively the cuff can be sewn on before coring and with the heart beating. With this method the pump has been implanted without CPB in a Jehovah’s Witness patient. The Jarvik 2000 Heart is carefully positioned within the cuff with the outflow and Dacron graft orientated inferolaterally. This allows the graft to pass in a gentle curve from the apex around the costophrenic angle to meet the first graft already joined to the descending thoracic aorta (Fig 2D). The pump is secured in the cuff by two integral tapes. The heart is then defibrillated and allowed to fill and dispel air. The pump outflow graft is trimmed to length to join the descending thoracic aortic graft. The graft-to-graft anastomosis is undertaken carefully with continuous 4-0 polypropylene during which the heart begins to eject and evacuate residual air. Transesophageal echocardiography is used to check the system for air bubbles before switching the pump on and weaning from cardiopulmonary bypass. With the circuit filled with blood, pump flow is established at 8,000 rpm and gradually increased to 10,000 rpm. If the left lung has been collapsed to facilitate the

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Fig 2. (A) A cruciate incision is made towards the apex of the failing ventricle and the muscle is cleanly punched out with a cylindrical coring knife. (B) Teflon pledgeted sutures are passed full thickness through the muscle and endocardium. (C) The retaining cuff for the Jarvik 2000 Heart is sewn into position. (D) The device itself is inserted through the cuff parallel to the septum. The two integral restraining tapes are tied to secure the pump in position. The outflow graft is then anastomosed to the descending aortic graft and the system is deaired before switching on the pump.

surgery, ventilation is restored with the addition of nitric oxide gas to reduce pulmonary vascular resistance. Continuous deairing of the graft is used while discontinuing bypass, and the operating table is returned to the horizontal position. Low-dose adrenalin infusion is used as an inotrope for the right ventricle, while preload is optimized to provide a cardiac output between 5 and 6 litres per minute. Protamine sulfate is administered followed by fresh frozen plasma and platelets. During chest closure, cardiac output, radial arterial, pulmonary arterial, and right atrial pressures are monitored continuously. Two intercostal drains and a pacing wire are deployed.

Results The site of power line exit from the chest is posteriorly through the second intercostal space, one hand’s breadth from the midline and 2 cm above the scapula in the sitting position. This old-fashioned approach for the true apical chest drain brings the power line through the trapezius muscle without danger to blood vessels or nerves. A single incision over the trapezius muscle on the posterior aspect of the neck is used to provide a gentle curve between the thoracic exit point and the skull pedestal (Fig 1B). The pedestal is attached to the parietal bone about

5 cm behind and slightly above the ear. A relatively flat area of skull is chosen taking care to avoid the mastoid air cells, the mastoid emissary vein, or the transverse venous sinus. The titanium base is 3 mm in depth, and 8 mm self-tapping screws are employed. A cork bore instrument, the same diameter as the percutaneous stem of the pedestal, is first used to punch out a skin defect through to the periostium at the site chosen. A C-shaped, widely based, full-thickness flap is raised down to the periostium around this defect. The periostium is then elevated and a template used to define the position of the bone screws (Fig 3A). A dental drill is used to penetrate the external table before inserting the self-tapping screws. Incisions are made on the shoulder and neck to convey the three-pin connector and power cable to the skull pedestal site. This process is achieved by inserting the three-pin connector within the end of an intercostal drain. This is withdrawn out through the second intercostal space then via the second neck incision to the prepared cranial site in a gentle curve. The three-pin connector is inserted into the titanium pedestal, which is screwed onto the flat part of the external table with six bone screws. Bone dust from the screw holes is used to promote osseo integration. The skin flap is repositioned with the pedestal stem passed through the punched out defect (Fig 3B). The scalp and skin incisions are then closed securely before heparinization. The external

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Fig 3. Detail of skull pedestal fixation. Before raising the post-auricular flap, a button of scalp is cored clearly to transmit the titanium pedestal. The full thickness flap is then raised down to periosteum. (A) A template is used to tap the screw holes through the outer six fill table. (B) The three-pin connector is passed through the pedestal screwed firmly into place. The scalp is then replaced with the pedestal buttonholed through the previously excised defect.

power cable is joined to the skull pedestal and the power switched on to test the circuit. This process takes between 45 and 60 minutes, during which it is necessary to avoid profound hemodynamic deterioration before heparinization.

Comment In contrast to the pusher plate LVADs, the compact Jarvik 2000 Heart is silent, easily implantable, and apparently imperceptible for the patient. It can be used for all sizes, including older children. Energy requirements are less than those for pusher plate pumps [2, 3].

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The critical design feature is the high rotational speed to promote blood that continuously washes the tiny bearing and prevents thrombus formation. At 8,000 rpm, the pump acts only as a valve preventing functional aortic regurgitation through the Dacron graft. At the maximum speed (12,000 rpm), the left ventricle is completely offloaded with an arterial pulse pressure less than 10 mm Hg. As the pump speed is turned down, the arterial pulse pressure increases progressively, though the aortic valve does not open synchronously until the lower speeds of 8,000 to 10,000 rpm. Mean systemic arterial pressure increases with loss of pulse pressure reflecting increased baro-receptor activity. We employ pump speeds compatible with normal end-organ function preferably with ejection through the aortic valve and a pulse pressure of 10 to 20 mm Hg in the systemic circulation. When the aortic valve remains permanently closed, the brachiocephalic and coronary arteries receive blood only by retrograde aortic flow. Performance of the dilated ventricle often improves early after mechanical offloading, and continued cardiac work may promote left ventricular recovery. In the event of myocardial recovery, the device can be removed by cutting the tapes, withdrawing the pump, and oversewing the apex. The thoracotomy approach enters only one body cavity leaving the sternotomy route for cardiac transplantation or avoiding resternotomy in those who have undergone coronary bypass. Access to the descending aorta is usually easy and only the apex of the left ventricle must be mobilized at the time of transplantation. Surgical trauma is considerably less than experienced during implantation of larger LVADs, and with further experience it is possible that cardiopulmonary bypass may not be required. The smaller transabominal drive line already seems less prone to infection than the larger stiff percutaneous lines of the TCI and Novacor LVADs. Our initial experience with post-auricular power delivery is encouraging with no infection to date. For permanent implants where the patients are discharged into the community, it is an advantage to be able to exchange the external system in the event of damage. Given the encouraging early experience, the Jarvik 2000 Heart may fulfill its promise as a realistic device for widespread use on an outpatient basis.

References 1. Westaby S, Katsumata T, Houel R, Pigott D, Frazier OH, Jarvik RK. Jarvik 2000 Heart; potential for bridge to myocyte recovery. Circulation 1998;98:1568–74. 2. Frazier OH, Myers TJ, Jarvik RK, et al. Research and development of an implantable axial-flow left ventricular device: the Jarvik 2000 Heart. Ann Thorac Surg 2001;71:S125–32. 3. Westaby S, Banning AP, Jarvik R, et al. First permanent implant of the Jarvik 2000 Heart. Lancet 2000;356:900–3. 4. Westaby S, Jarvik R, Freeland A, et al. Post-auricular percutaneous power delivery for permanent mechanical circulatory support. J Thorac Cardiovasc Surg 2002; in press.