Transcatheter and Transapical Aortic Valve Replacement

The authors discuss the minimally invasive AVR and review the nursing care of patients who have AVR.Aortic valve replacement (AVR) is a common cardiac surgical procedure. An estimated 106 000 cardiac valve operations were performed in the United States in 2005 (the most recent year for which procedure numbers are available).1 AVR is the most widely performed valve replacement.2,3 Aortic stenosis affects from 2% to 7% of persons more than 65 years old in the United States and is likely to increase in prevalence as the population ages. The current American Heart Association guidelines4 for valvular heart disease recommend AVR to improve signs and symptoms and survival rates in patients with symptomatic aortic stenosis or in asymptomatic patients with an ejection fraction less than 50%. In a retrospective cohort study, Pai et al5 found that asymptomatic patients with severe aortic stenosis had a significant survival improvement with AVR. Therefore, the need for AVR will most likely increase over time, and with people living longer, AVR will be increasingly needed in elderly patients or patients with significant comorbid diseases.Many larger, experienced centers have an operative mortality of less than 1% for AVR.6 Mortality data from several large databases are presented in Table 1. Operative mortality depends on many factors such as the patient’s age, ventricular function, and associated cardiac and noncardiac diseases. Figure 1 illustrates the effect of age on mortality. Postoperative complication rates may also be affected by the patient’s age. Edwards and Taylor9 reported that 77% of patients more than 90 years of age experienced postoperative complications. Although researchers in other studies did not report overall complication rates by age group, rates of specific complications in the Society of Thoracic Surgeons database from more than 400 000 valve operations between 1994 and 2003 were as follows: atrial fibrillation, 27%; prolonged ventilation, 19%; renal failure, 7.1%; reoperation for bleeding, 5.5%; heart block, 5.2%; pneumonia, 4.5%; gastrointestinal problems, 43%; cardiac arrest, 3.3%; stroke, 2.8%; sepsis, 2.5%; and cardiac tamponade, 1.4%.3 Less-invasive AVR may be more desirable in higher risk groups of patients such as elderly patients because it may reduce complications.In this article, we discuss the development of minimally invasive AVR and focus on the differences between conventional AVR, transcatheter AVR, and transapical AVR. We review the nursing care of patients who have transcatheter and transapical AVR, and to emphasize the key points, we present a case study of a woman with severe aortic stenosis who underwent transapical AVR.Many factors have promoted the development of less-invasive valve procedures. AVR that does not require full sternotomy may be more cosmetically attractive to patients. Being able to perform AVR in patients with severe aortic atherosclerosis or calcification without the risk of stroke from cross-clamping a calcified aorta is not only beneficial in terms of improved outcomes for patients but also might reduce hospital stays due to complications such as stroke. Conventional AVR must be done with cardiopulmonary bypass with the attendant risks of elevating creatinine level (particularly in patients with renal disease), bleeding, and impaired lung function due to deflation of the lungs during bypass. The avoidance of the use of cardiopulmonary bypass could prevent some of these complications in high-risk patients. In addition, AVR could be extended to patients with conditions previously considered inoperable if the avoidance of cardiopulmonary bypass and sternotomy improved outcomes.Until recently, transcatheter aortic valve interventions have been limited to balloon aortic valvuloplasty, in which a balloon is placed across the stenotic aortic valve and inflated to reduce aortic stenosis. Balloon aortic valvuloplasty has been useful in treating children with aortic stenosis, but it is recommended solely for younger adults without valve calcification. The 2006 American College of Cardiology/American Heart Association (ACC/AHA) guidelines for valvular disease management4 recommend balloon aortic valvuloplasty in adults solely as a bridge to surgery in patients with aortic stenosis who have unstable hemodynamic status and are at high risk for AVR or for patients with aortic stenosis in whom AVR cannot be performed because of serious comorbid conditions. The ACC/AHA recommendations were based on a review of the literature that cited greater than 10% frequency of serious complications and the fact that restenosis and clinical deterioration typically occur within 6 to 12 months of balloon aortic valvuloplasty. However, the studies cited in the ACC/AHA recommendations are dated, and some technical improvements have occurred since the studies were done that may lead to further study of balloon aortic valvuloplasty,10 especially in nonagenarians.11In 2000, the first valve replacement that became available by catheter delivery was the pulmonary valve replacement (PVR) performed by Bonhoeffer’s group with a bovine jugular vein valve that was intended for use inside surgically placed conduits from the right ventricle to the pulmonary artery.12 The results of the first North American trial of transcatheter PVR were recently reported13; no significant complications or urgent surgical intervention occurred. Transcatheter PVR is intended for patients with congenital heart disease in whom reoperation could be delayed until a future date by the implantation of one of these valves.Andersen et al14 reported the first transcatheter AVR in 1992 in pigs. The first transcatheter AVR in humans was reported by Cribier et al15 in 2002. Transcatheter and transapical AVR are currently in clinical trials in a few centers in Canada, the United States, and Europe.In a position paper,16 the Society of Thoracic Surgeons, the American Association for Thoracic Surgery, and the Society for Cardiovascular Angiography and Interventions recommended that the initial patients to undergo percutaneous AVR strategies should be at extremely high operative risk (generally >20% operative mortality) as indicated by an established risk scoring system such as the logistic EuroSCORE17 or the Society of Thoracic Surgeons risk calculator.18 The guidelines reported by Vassiliades et al16 state that use of such devices is not acceptable for patients who simply refuse open heart surgery on the basis of personal preference. It was also recommended that initial feasibility studies be conducted in a small number of high-volume cardiology and cardiac surgery programs (minimum 100–150 valve operations per year with each surgeon performing a minimum of 40–50 valve repairs or replacements annually). Some of the indications and contraindications for minimally invasive AVR are indicated in Tables 2 and 3, respectively.Traditional heart valves consist of homografts from another human being, bioprosthetics (valves constructed from bovine pericardium or porcine valves mounted in a metallic stent to preserve their shape or prepared as stentless valves), or mechanical valves mounted in a fabric sewing ring. The valves are sutured into the heart after the diseased valve is excised. Traditional bioprosthetic valves last a mean of 10 to 15 years, and mechanical valves could potentially last a lifetime. In contrast to traditional heart valves, implantation of the transcatheter valve does not require removal of the native heart valve. The transcatheter valves are bioprosthetic valves that are crimped or loaded onto a stent or frame. Once in place, the stent or frame containing the valve is expanded to anchor the valve in the aortic annulus. The transcatheter valves are sutureless and are held in place by the stent or frame. The valves currently in clinical trials are the Edwards SAPIEN transcatheter heart valve (Edwards Lifesciences, Irvine, California), also referred to as the Cribier-Edwards valve (Figure 2), and the CoreValve (CoreValve Inc, Irvine, California; Figure 3). A number of other valves are in development.6,25The Edwards SAPIEN transcatheter heart valve was an equine and is now a bovine trileaflet pericardial valve on a balloon-expandable stainless steel stent. It is currently available in 23- and 26-mm sizes and can be used for transcatheter and transapical AVR. A sewn fabric cuff covers the left ventricular part of the prosthesis. The valve is approximately 14 mm in height with cloth covering the proximal 6 mm of the valve. The cloth-covered part of the valve must sit in the annulus to prevent regurgitation though the stent into the left ventricle.26 In order to use the Edwards valve, a balloon valvuloplasty must be undertaken first to dilate the native valve and allow placement of the new valve.The CoreValve ReValving System consists of a porcine pericardial valve on a multilevel self-expanding nitinol frame in an hourglass shape (expands with blood temperature), a delivery catheter, and a disposable loading system. The current generation catheter is 18F. The shape of the frame allows secure positioning within the aortic annulus while the valve functions in the supraannular position. Two valve sizes are available for use in aortic annuli between 20 and 27 mm. To date, more than 1800 patients have been treated with the CoreValve device. This system is neither commercially nor investigationally available in the United States at the present time (Rob Michiels, CoreValve Inc, written communication, September 25, 2007).Transcatheter AVR is performed with either local or spinal anesthesia with sedation or with general anesthesia in a cardiac catheterization laboratory or an operating room equipped with fluoroscopy and transesophageal echocardiography. Transcatheter AVR may require surgical cutdown and may require placement of femoral grafts in order to insert the large transcatheter delivery systems. The large size of the delivery catheters limits the transcatheter approach to patients with vessels large enough to accommodate the catheters. An angiogram or a computed tomographic angiogram (and probably femoral Doppler imaging) is required before transcatheter AVR to ensure that the femoral and iliac vessels are not tortuous and are large enough to accommodate the valve delivery catheters.Two approaches have been described for deployment in transcatheter AVR. In the antegrade, transeptal approach, access is via the femoral vein; the catheter is passed into the right ventricle and then punctures the septum to be placed ante-grade across the aortic valve. This approach is technically difficult and may cause mitral valve damage, including acute mitral regurgitation, if not carefully performed.23,26,27 In the retrograde approach, a femoral artery puncture is used. The catheter is advanced retrograde through the aorta to cross the aortic valve. Limitations of the retrograde approach include the small size of the femoral artery compared with the femoral vein, a situation that makes the approach difficult to use in older patients with peripheral vascular disease or small patients whose vessels cannot accommodate the 18F to 24F sheath sizes. With the retrograde technique, atherosclerotic material can be embolized from the aorta into the distal circulation.26 Gupta et al28 compared 52 antegrade vs 111 retrograde AVRs and found no difference in outcomes except that antegrade deployment avoided vascular complications (7% in retrograde vs 0% in antegrade approach, P<.05).Contrast medium is used to ensure correct positioning of the catheter valve across the aortic annulus. Transcatheter AVR with the Edwards valve requires rapid pacing of the heart (rate, 150–220/min) to decrease cardiac output to place the valve. Failure to stop the cardiac output with pacing while the valve is placed could result in ejection of the valve into the aorta. The alternative would be brief femoral-femoral cardiopulmonary bypass to place the valve. In some centers, the femoral vessels are cannulated for possible emergent cardiopulmonary bypass in case of problems such as valve embolization into the aorta. Great care must be used in positioning the valve to ensure that the coronary ostia are not blocked or that a bulky native aortic valve leaflet does not block the ostia when pushed back by the stent.24The CoreValve ReValving system uses a suture-mediated closure device (Prostar, Abbot Vascular Devices, Redwood City, California) for femoral percutaneous closure (Rob Michiels, CoreValve Inc, written communication, September 25, 2007). The Edwards SAPIEN transcatheter heart valve system uses a femoral graft closure.Because of the possible vascular complications of transfemoral catheter approaches, the transapical approach has been developed. The transapical approach can be used in persons who have small or tortuous femoral or iliac vessels or severe peripheral vascular disease such as persons with previous aortobifemoral grafting. It would be a preferential approach if a porcelain (heavily calcified) aorta prevented cannulation for cardiopulmonary bypass or aortic cross-clamping or if aortic atheroma was marked. The transapical approach is quicker and less technically difficult than the transcatheter technique.27 The transapical approach could be a problem, however, if a left ventricular apical thrombus, a left ventricular aneurysm, or apical scarring from previous surgery or chest radiation was present.The transapical AVR is placed via a 5- to 8-cm anterolateral left thoracotomy usually in the sixth intercostal space (Figure 4). The pericardium is opened, and a small transapical stab incision of the left ventricle is made to accommodate the delivery catheter.23 A total of 1 bipolar or 2 unipolar epicardial pacing wires are placed on the left ventricle to pace the heart during valve placement. A balloon aortic valvuloplasty is performed to dilate the native aortic valve before placement of the new valve. The new valve is then placed on a catheter across the native aortic valve (Figure 5) and uncrimped by balloon expansion of the stent (Figure 6). Cardiac output must be momentarily stopped by the use of high-rate pacing of the heart (rate, 150–220/min) until the valve is positioned. Transapical placement of an AVR requires a collaborative team approach between cardiology and cardiovascular surgery to ensure that imaging and pacing capabilities merge to allow the surgeon to place the valve precisely and at exactly the appropriate time to prevent valve embolization. At the end of the procedure, the pacing wires are removed, the pericardium is closed to prevent herniation of the heart through the pericardium, and the minithoracotomy is closed, with a chest tube left in situ for overnight drainage. An example of a stented aortic valve placed via a transapical approach is seen on a chest radiograph in Figure 7.Valves used for transcatheter and transapical AVR must be oversized to ensure stability within the aortic valve annulus without perivalvular regurgitation. Paravalvular insufficiency can be caused by undersizing or inadequate dilatation of the valve stent.23 Therefore, the aortic annulus is measured, and a valve size is selected that is slightly larger than the patient’s own annulus. Because of the current limitation in sizes available in these new valves, patients with larger annuli cannot currently receive the valve. Lichtenstein et al23 stated that an unusually bulky coronary leaflet could be displaced by the valve stent or frame and would therefore be a contraindication.Anomalous coronary ostia might be a contraindication to the use of these valves. The valve stent or frame may interfere with introducing catheters into the coronary arteries.23 Such interference could be an issue if catheterization or stenting of coronary arteries should be required at a later date. Therefore, before these valves are placed surgeons must ensure that patients have no marked coronary disease. Open bypass grafts would provide a safety margin in the situation of a short distance between the annulus and the coronary ostia.21If the valve is placed via the femoral vessels, the vessels must not have a tortuous course or be severely calcified. The catheters used to deliver the valves are relatively stiff and large. Therefore, vessel rupture, dissection, formation of a pseudoaneurysm, bleeding, and thrombus formation can be problems,29 as can myocardial perforation and cardiac tamponade.23 Embolization of calcified material could also occur during the balloon valvuloplasty,22 or atheromatous material in the aorta could be embolized during retrograde valve placement.Early outcomes for humans after transcatheter and transapical AVR have been reported by a number of investigators (Table 4). In general, valve implantation is successful in most patients, who have symptomatic improvement after the implant. Because these valves are secured in place by the valve stent or frame, perivalvular regurgitation may occur. Morbidity and mortality are currently higher than with conventional valve implantation and will most likely decrease as experience with transcatheter valves increases and design is improved. Long-term follow-up is limited with these newer valves.Long-term follow-up is needed to determine the durability of transcatheter valves and to assess what other problems may arise. For those who had SAPIEN equine valves, equine valves have not been tested for durability beyond a few years in humans.32 It is not clear if crimping the valve for delivery will affect long-term function of the valve.21A number of long-term problems have been reported with percutaneous PVR, and it is unclear whether these problems will occur with the newer AVR techniques.Stent fractures occurred in 19.5% of the series of 123 percutaneous PVRs reported by Nordmeyer et al33 from 8 to 843 days after insertion of the valve. A total of 4 patients required insertion of a second percutaneous PVR, and 1 required surgical explantation. Endocarditis and hemolysis have also been documented with percutaneous PVR,33 and it is unclear what the incidence of these problems will be with transcatheter and transapical AVR.Other outcomes that should be monitored include death, stroke, myocardial infarction, paravalvular leaks, device migration, changes in signs and symptoms after implantation of the device, angiographic gradients, and rehospitalization.16 Until it can be determined that the newer AVR technologies are as durable as conventional AVR, it would be unethical to offer this new technology to patients who are at low surgical risk for conventional AVR. For most patients, conventional AVR will remain the gold standard of treatment for the foreseeable future. As more experience is gained with less-invasive valve technology, outcomes most likely will improve.Removal and ablation of the native aortic valve in situ might be possible in the future with lasers to facilitate positioning of a new valve. This procedure would need a filtering mechanism to prevent embolization of valve remnants.34 Tissue-engineered heart valves may be placed by transcatheter or transapical routes in the future. These grafts consist of a scaffold seeded with host cells that eventually cover the scaffold. The valve can then be conditioned to function under normal intracardiac pressures before implantation.Table 5 presents the nursing care required by patients undergoing transcatheter and transapical AVR. Because multiple comorbid diseases may have made a patient a candidate for transcatheter and transapical AVR, much of the focus of nursing care is on preventing complications due to these comorbid conditions. The case study highlights key concepts of the nursing care.Transcatheter and transapical AVR are new technologies that could benefit many patients who are considered high-risk candidates for traditional surgical AVR. Although experiences with transcatheter and transapical AVR are limited, preliminary results indicate that these techniques are feasible in selected high-risk patients and have satisfactory short-term outcomes. Long-term follow-up in a larger population of patients is needed to determine if transcatheter and transapical AVR reduce surgical risk, lower complication rates, and produce satisfactory longer term outcomes.