Median sternotomy is the standard approach used for ventricular assist device (VAD) implantation. It provides a good operative view, easy accessibility to cardiac structures, and a readiness for instituting cardiopulmonary bypass. However, it must be taken into consideration that most patients have undergone a previous sternotomy or will require a repeated sternotomy later for heart transplantation or device removal.1,2 In cases of repeated sternotomy, adhesion of the retrosternal space and fibrosis surrounding the grafts make it difficult to perform the anatomical dissections; thus, injury to major cardiovascular structures may occur.3,4 It also increases the risk of postoperative bleeding and subsequent complications.1,5,6 To avoid the complications related to repeated sternotomy, alternative methods might be preferred in patients with previous sternotomy, mediastinal infections, those in whom sternotomy should be reserved for either corrective cardiac surgery or transplantation at a later date, or for those in whom, for any technical reasons, a sternal approach should be avoided.
Because the surgical technique for VAD implantation consists mainly of cannulation procedures, we hypothesized that each of the four cardiac structures for VAD cannulation might be approached from the right side of the heart. The purpose of this study was to establish a surgical technique with the use of a right thoracotomy for VAD implantation.
Materials and Methods
From 1999 to 2004, 20 cases of Korean bi-ventricular assist device (BVAD) (AnyHeart™, BiomedLab Co., Seoul, Korea) implantation, with the use of a right thoracotomy technique without cardiopulmonary bypass, were performed on various animals weighing 51 to 148 kg. The animals included calves (n = 15), dogs (n = 3), and sheep (n = 2). The types of devices used for implantation were the BVAD (n = 17) and the left ventricular assist device (LVAD, n = 3), using AnyHeart. Of the 20 cases, the implantable type was used in 15 cases and the wearable type in 5.
AnyHeart is an electrically driven, implantable/wearable single-piece unit, having a bi-ventricular pulsatile pump. The measurements are width, 145.7 mm; length, 166.8 mm; height, 71.8 mm; and weight, 800 g. It has a total volume of 600 cc, and maximum stroke volume is 75 cc. At first, AnyHeart was developed as an implantable BVAD. However, with mechanical progression, it has become available as a wearable BVAD, implantable/wearable LVAD, and as an implantable/wearable right VAD (RVAD).
Under general anesthesia, the animals were placed in the left lateral decubitus position, and a right anterior-lateral thoracotomy was made. The incision was deepened into the chest cavity through the fourth intercostal space or the fifth periosteal bed after partial resection of the fifth rib. The pericardium was incised longitudinally approximately 1 to 2 cm anterior to the right phrenic nerve. The right side of the heart was carefully explored from both outside and inside the pericardium. The main pulmonary artery was approached first. To ensure good exposure, the main pulmonary artery was gently lifted up with a silicone catheter passed through the transverse sinus (Figure 1). After placing a side-biting clamp on the main pulmonary artery, a longitudinal incision was made. A 12- to 14-mm Dacron vascular graft (Gelsoft, Vascutek Ltd., Renfrewshire, Scotland) attached to an outflow cannula was anastomosed end-to-side to the main pulmonary artery, using running sutures of 4/0 monofilament polypropylene (Prolene, Ethicon, Edinburgh, U.K.) (Figure 2). During the procedure, care was taken to avoid fluctuations in blood pressure. A 28F36F inflow cannula (Venous cannula, Edwards Life Sciences, Irvine, CA, USA) was inserted into the left atrium through the interatrial groove (Figure 3). Two sets of 4/0 monofilament polypropylene purse string sutures were enough to secure the cannula in position. Procedures for the ascending aorta and the right atrium were similarly performed without any difficulty (Figures 2 and 3). All four cannulae were passed through the intercostal space and carried down to the wearable or implantable BVAD located at the right flank and then were connected to the BVAD, with careful avoidance of air entry. Blood flow at the left and right outflow cannulae was measured directly with a flowmeter (Transonic Flowmeter T106, Transonic Systems Inc., Ithaca, NY, USA). The operative wound was closed in standard fashion after placing two chest tubes in the right thoracic cavity with full expansion of the right lung. During the postoperative period, anticoagulation was maintained. An intravenous infusion of heparin (maintaining the activated clotting time at 1.5 to 2 times the preoperative level) or subcutaneous injection of low-molecular-weight heparin was used during the immediate postoperative period. Long-term anticoagulation was maintained with the use of oral coumadin and ticlopidine (1000 mg/d). The prothrombin time was maintained at 1.5 to 2 times the preoperative level.
All animals received humane care as described in the Guide for the Care and Use of Laboratory Animals at Korea University Medical College, and perioperative care including anesthesia was supervised by cardiac anesthesiologists, veterinarians, and animal husbandry personnel. At the end of each experiment, the animals were killed under an anesthetic state, according to the guidelines. A necropsy was performed to identify the status of the inflow and outflow cannulae.
Preclinical Cadaver Fitting Tests
Between 2000 and 2004, preclinical fitting tests were performed, with the permission of the Anatomical Research Committee of Korea University Medical College, to observe the anatomical feasibility of a right thoracotomy method in 7 human cadavers. The right side of the heart was explored, and cannulation sites for 4 cardiac structures were identified. We took special care with the intracardiac or intraluminal positioning of each cannula tip and the way it was connected from the cannulae to the pumps, as described in our previous report.7
A 62-year-old man with cardiogenic shock was admitted after acute myocardial infarction. Coronary angiography showed total obstruction of the proximal left anterior descending coronary artery. Percutaneous coronary artery angioplasty was tried but failed because of cardiac arrest. After resuscitation, the patient was supported with an intra-aortic balloon pump, and a mechanical ventilator was connected after tracheostomy. His heart failure worsened even with a high dose of inotropics, and he was referred to us for mechanical circulatory support. Before surgery, the chest radiograph showed severe pulmonary congestion with bilateral pleural effusions. The arterial oxygen tension was 96 mm Hg, with mechanical ventilation (Fio2 0.8 in volume control mode ventilation). The vital signs were heart rate, 120 to 130/min; systolic blood pressure, 75 to 90 mm Hg; systolic pulmonary artery pressure, 45 to 65 mm Hg; pulmonary capillary wedge pressure, 22 to 28 mm Hg; and, cardiac index, 2.1 l/min per m2. An echocardiogram demonstrated an ejection fraction of 10% to 15%, a left ventricular end-diastolic dimension of 52 mm, and a visible thrombus in the left ventricular chamber. Despite intensive medical treatment, including multiple inotropic agents (dopamine, 10 μg/kg per minute; dobutamine, 15 μg/kg per minute' Primacor, 5 μg /kg per minute) and Lasix 15 mg/h), his condition worsened. In addition, renal insufficiency, hepatic dysfunction, and mental drowsiness developed. With the completely informed consent of the patient's family members, a Korean external LVAD (Hemopulsa™, BiomedLab Co., Seoul, Korea) was implanted. We decided to use a right thoracotomy technique because of the presence of a tracheostomy as well as the possibility for needing a sternotomy for later heart transplantation or device removal after recovery. A 36F inflow cannula (Venous cannula, Edwards Life Sciences, Irvine, CA, USA) was inserted into the left atrium through the interatrial groove, and an outflow cannula with a 12-mm graft (Gelsoft, Vascutek Ltd, Renfrewshire, Scotland) was anastomosed to the ascending aorta. Both cannulae were externalized to the right flank and connected to the LVAD.
We dismissed the first five animal cases as an acute fitting test to establish the operative technique (one sheep, two dogs, and two calves). After the first five animals, all except one were able to stand 6 to 12 hours after the operation and were without any problems in feeding or growing. Paralysis of the right anterior leg developed in one calf after BVAD implantation (Table 1). BVAD pump flow measured from 2.6 to 6.5 L/min, depending on the size of the animal or the inflow cannulae. The right side pump flow tended to be slightly higher than that of the left side. The longest surviving period for a calf was 37 days. After a term of observation, the animals were euthanized. All underwent necropsy, and we confirmed the freely located cannula tips in both right and left atria (Figure 4). The anastomosed sites of vascular grafts to the ascending aorta and the main pulmonary artery were also maintained in good condition. There were no respiratory complications, such as severe compression of the lung, pneumonia, or diaphragmatic injury in the necropsy findings.
In the preclinical cadaveric right thoracotomy fitting test, the optimal sites for outflow cannulation were identified as the ascending aorta for the left side of the BVAD and the main pulmonary artery and the right pulmonary artery for the right side of the BVAD. When approaching the right pulmonary artery, either a Seldinger technique or direct anastomosis of the vascular graft was applicable. For inflow cannulation, we determined that the right atrium for the right side of the BVAD and the interatrial groove for the left side of the BVAD were appropriate (Table 2). The optimal routes for approaching the artery with the cannulae were along the interlobar fissure for the right pulmonary artery cannula and along the right antero-lateral heart border for the main pulmonary artery cannula. The other three cannulae were placed along the pericardial border.
In our clinical case, the patient's general condition and hemodynamic status demonstrated a rapid recovery with minimal pharmacological support soon after the start of LVAD. Under LVAD, support of 2.5 3.0 L/min, the ejection fraction was 25% to 30%, the systolic blood pressure 90 to 130 mm Hg, pulmonary capillary wedge pressure 8 to 12 mm Hg, and the cardiac index 3.0 to 4.0 L/min/m2. Heart function was tolerable, and his hemodynamic values were stable with low-dose inotropics (dopamine, 3 μg /kg per minute; dobutamine, 5 μg/kg per minute) and Lasix, 3 mg/h. On the 21st postoperative day, after weaning from the LVAD, the device and the cannulae were successfully removed through a repeat thoracotomy. Postoperative wound healing was uneventful, and the patient underwent an uneventful recovery.
Heart transplantation is the fundamental treatment for patients with end-stage heart disease who have become unresponsive to pharmacologic agents. Unfortunately, a lack of supply is lengthening the waiting time for a donor heart, thus, use of a VAD has become an alternative proposal.8,9 Its use can improve symptoms and quality of life for such patients, and furthermore, save lives. However, VAD implantation still has complications that must be addressed, such as hemorrhage, thrombosis, and infection.8 Therefore, firm efforts should be devoted to minimizing these complications.
A median sternotomy has been regarded as a standard method in VAD implantation because of its advantages, such as providing a wide operative field and easy access to the great vessels.2,6 However, most candidates for VAD implantation require repeated sternotomy, since they already have had a median sternotomy for previous cardiac surgery.6 In addition, repeated sternotomy would be required for the removal of a VAD after recovery of cardiac function or for heart transplantation.2 Patients who need a repeated sternotomy are exposed to additional complications, such as hemorrhage and wound infection.1,5,6,10–13,14 In addition, they must be placed on anticoagulants.6 Follis et al.10 reported that hemorrhage leading to death occurred in 1% of patients with repeated sternotomy and that the patients with a dilated right ventricle or atrium are at high risk for fatality when having a repeated sternotomy. Dobell et al.11 reported an incidence of catastrophic hemorrhage of 2% to 6% during repeated sternotomy. Sternal wound infection remains a serious complication after cardiac surgery, with rates ranging from 1% to 10%.12 Borger et al.13 also reported the repeated sternotomy as one of the risk factors for deep sternal wound infections.
In contrast, VAD implantation with the use of a thoracotomy can possibly decrease the risk of fatal hemorrhage and infection by avoiding a surgical approach at the site of a previous incision. Furthermore, when subsequently performing a median sternotomy for heart transplantation or removal of the device in the future, there is the advantage that inserted cannulae and devices can be removed only with a median sternotomy without need for an extra thoracotomy. Samuels et al.6 reported several situations in which the trans-sternal approach is undesirable but the thoracic approach appealing. Such circumstances may include patients with one or more previous sternotomies, those in whom the sternotomy should be reserved for either corrective cardiac surgery or transplantation at a later date, those in whom the additional cannulae would allow for sternal closure, and those with mediastinal infections.
Appropriate maintenance of blood flow after the implantation of a VAD is very important to prevent thrombus-related complications. To maintain sufficient blood circulation, it is important to perform an insertion technique that places the cannula tips within the heart chambers in the best position, to have an adequate caliber of the cannulae, and to maintain the pump's operating capability. The optimal dosage of anticoagulant is also essential. Among these several factors, we believe that the most important is placing the cannula tips within the heart chambers in an appropriate position within the operative fields. For this purpose, many routes for inserting the cannulae have been reported.6,14–17 The left side of the heart can be approached through the interatrial groove, the left atrial appendage, the left ventricular apex, the dome of the left atrium, or right superior pulmonary vein. Samuels et al.6 reported various cannula insertion sites to the heart chamber with sternotomy and thoracotomy for VAD implantation. Minami et al.15 noted that the cannula to the right pulmonary artery could be inserted by using the Seldinger technique between the superior vena cava and the ascending aorta.
In our study, the optimal sites for outflow cannulation were identified as the ascending aorta for the left side of the BVAD, and the main pulmonary artery and the right pulmonary artery for the right side of the BVAD. When approaching the right pulmonary artery, either the Seldinger technique or direct anastomosis of the vascular graft was applicable. For inflow cannulation, we found that the right atrium for the right side of the BVAD and the interatrial groove for the left side of the BVAD were appropriate. We also tried various cannulation methods in our preclinical cadaver fitting tests with the same results.7 In our animal experiments and one clinical application, this approach supplied a sufficient amount of blood from the heart to the VAD by using a right thoracotomy.
During the right thoracotomy procedure, the most difficult site to approach was the main pulmonary artery because it was located deep inside. To make this approach easier when implanting the BVAD, we pulled up the main pulmonary artery by using a silicone catheter, which lifted the main pulmonary artery through the transverse sinus. We noted that with this method, when the main pulmonary artery was anastomosed, there was a decrease in blood pressure in the experimental animals. This phenomenon develops when the main pulmonary artery is compressed by lifting the silicone catheter too strongly, resulting in a decrease in pulmonary blood flow. This problem is avoidable by carefully maintaining the pulling direction and tension of the silicone catheter. There were no additional procedure-related difficulties.
VAD implantation with the use of a right thoracotomy can be an alternative method to the standard median sternotomy for patients who have already had sternotomy for cardiac surgery and for those with mediastinal infections. It can also be used for patients in whom further sternotomy should be reserved for either corrective cardiac surgery or transplantation at a later date and for those who need to avoid the sternal approach for technical reasons. Such an approach can reduce repeated sternotomy-related morbidity and mortality.
This study was supported by a grant from the Korea Health 21 R&D Project, Ministry of Health and Welfare (grant 02-PJ3-PG6-EV09-0001) and the Brain Korea 21 Project of the Ministry of Education and Human Resources Development, Republic of Korea.
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