Aortic stenosis (AS) due primarily to calcification is the most common and debilitating cardiac valvular lesion.1 In current practice, the standard treatment for patients with symptomatic severe AS is surgical aortic valve replacement (AVR) or percutaneous valvuloplasty. Approximately 20000 AVR surgeries were performed in the United States in 2008.2 As the adult population ages, the number of persons requiring interventions for AS is also likely to increase.3 The prevalence of critical aortic valve stenosis increases with age from 2% at age 75 years to near 6% in persons aged 85 years.4
As the severity of AS progresses, individuals will experience debilitating symptoms of angina, exertional dyspnea, and syncope, among others, which acutely decreases their quality of life2 and prompts them to seek medical and surgical treatment. For patients with severe AS who are of advanced age and have multiple comorbid medical conditions, the surgical risk is often too high to undergo traditional AVR surgery.5 The percutaneous valvuloplasty procedure, an alternative treatment to AVR, is less invasive but provides only temporary improvement in aortic valve pressure gradient and relieves symptoms for about 6 months.6 The transcatheter aortic valve implantation (TAVI) device, first used in humans in 2002, was developed to provide another treatment option for elderly patients with an unacceptably high surgical risk.7
Aortic stenosis, or narrowing of the aortic valve opening because of calcified or thickened valve leaflets, is the primary disease process in approximately 25% of patients who develop valvular heart disease. The common risk factors associated with the progression of AS include high levels of low-density lipoprotein cholesterol, smoking, diabetes, chronic kidney disease with metabolic syndrome, and congenital and rheumatic cardiac valvular changes.8
Calcific and degenerative aortic valve disease occurs most commonly in the presence of congenital disease (bicuspid aortic valve), chronic leaflet deterioration, or with previous rheumatic inflammation. Rheumatic disease produces fusion of the valve leaflets that results in a bicuspid appearance and trauma to the leaflets that leads to fibrosis and calcification over time. The process of valve degeneration due to calcification often mimics the features of vascular atherosclerosis with endothelial dysfunction, lipid accumulation, inflammatory cell activation, cytokine release, and upregulation of several signaling pathways.8 These changes allow for the deposition of calcium crystals that lead to valve dysfunction.8 Figure 1 shows a nondiseased aortic valve compared with severely stenotic aortic valves with calcified leaflets.9
The classifications of AS are labeled as mild, moderate, or severe, and the degree of severity of AS is determined by these 3 factors: rate of increase in aortic jet velocity, increase in mean pressure gradient across the aortic valve, and decrease in aortic valve opening area.8 There is usually no significant obstruction to flow through the valve until the valve area decreases by 50%.10 Aortic stenosis is considered severe if the jet velocity through the valve is greater than 4.0 m/s, the pressure gradient across the valve is greater than 40 mm Hg, and the valve opening area is less than 1.0 cm2.10 The decision to undergo surgery or treatment for AS is based more heavily on the development of progressive symptoms that directly impact a patient’s quality of life rather than the specific aortic valve measurements Table 1.
TREATMENT OPTIONS FOR AS
Aortic Valve Replacement
As stated, AVR, using either homografts, bioprosthetics, or mechanical valve types, is the most common valvular heart surgery used to treat calcific and degenerative severe AS.11 Mechanical heart valves are sturdy and could last a lifetime but require daily anticoagulation medication. Because of their longevity and durability, they are preferred for younger patients to avoid myocardial structural deterioration or need for a device replacement surgery later. Bioprosthetic valves last approximately 10 to 15 years and are favored for older patients because no anticoagulation is required for these tissue valves12 and the valve longevity may be longer than the patient’s. The factors of AVR surgery that increase the risk of complications for the patient are the need for a median sternotomy surgical approach, cardiopulmonary bypass, impaired lung function due to deflation of the lungs during bypass, and long-term anticoagulation when the treatment is a mechanical AVR. The current American Heart Association guidelines for valvular heart disease recommend AVR to improve survival rates in patients with symptomatic AS or in asymptomatic patients with an ejection fraction less than 50%.13 Open AVR surgery has an associated perioperative mortality of 4% to 18%, depending on the patient’s comorbidities.1 Consequently, this type of heart surgery is often withheld or not offered to high-risk patients, despite the poor prognosis of symptomatic AS.
One intervention that was developed to treat AS, without AVR and the use of cardiopulmonary bypass, is minimally invasive transcatheter balloon aortic valvuloplasty. With this procedure, a balloon is placed across the stenotic aortic valve and inflated to force open the diseased valve leaflets and thereby reduce AS.3 Balloon valvuloplasty is recommended mostly for younger patients who do not have a calcific valve. Unfortunately, there is a high rate of valvular restenosis and clinical deterioration within 6 to 12 months after balloon aortic valvuloplasty.3
Transcatheter aortic valve implantation, a less invasive valve replacement procedure, was developed specifically for the patient with severe AS who would benefit from valve replacement but is a high-risk candidate for open-heart surgery and cardiopulmonary bypass. Implanting a TAVI device does not require surgical sternotomy or removal of the native heart valve.3 The 2 types of TAVI devices currently in use in the United States are the Medtronic CoreValve (Medtronic Inc, Irvine, California), still in clinical trials, and the Edwards SAPIEN transcatheter heart valve system (Edwards Lifesciences, Irvine, California), which received Food and Drug Administration approval in November 2011 (Figure 2).
The Medtronic CoreValve is constructed of a porcine pericardial valve on a self-expanding hourglass-shaped nitinol frame. Once the protective sleeve is pulled back from the catheter, the multilevel frame self-expands and fills the aortic annulus and the new valve within the frame is positioned just above the native aortic valve annulus. The 2 sizes of the Medtronic CoreValve are 20 and 27 mm.3 The Medtronic CoreValve can be implanted through either femoral or subclavian arterial approaches.
The Edwards SAPIEN valve is the only TAVI device currently approved by the Food and Drug Administration for severe AS patients who are deemed inoperable by a board-certified cardiothoracic surgeon.14 This TAVI device is a bovine trileaflet pericardial valve on a balloon-expandable, stainless steel stent. It is currently available in sizes of 23 and 26 mm and can be placed via a transapical and transfemoral approach. For safe insertion, the Edwards SAPIEN valve requires a minimum 7-mm arterial vessel lumen size to pass the catheter.14 The Edwards SAPIEN valve is wider and shorter than the Medtronic CoreValve. The proximal portion of the valve is cloth covered and sits inside the stent, which is positioned within the aortic valve annulus15 during implantation.
TAVI Insertion Procedures
All TAVI patients receive central line access through which a transvenous pacing lead is threaded into the right ventricle. A small catheter through which radiocontrast dye is injected is then placed in the right femoral artery and threaded up into the descending aortic arch and then through the ascending aortic arch down into the native aortic valve to allow fluoroscopy during the procedure. An interventional valvuloplasty catheter is also passed via the femoral artery along the same pathway into the aortic arch and into the calcified aortic valve. The ventricle is then rapidly paced at 150 to 220 beats/min to decrease the stroke volume and cardiac output and allow balloon valvuloplasty to force open the calcified valve leaflets.3 The balloon catheter is then withdrawn and the device-loaded transcatheter is then also threaded via left femoral artery up into the aortic arch and moved into position within the native aortic valve annulus. Transesophageal echocardiography and fluoroscopy are used to verify the placement of the TAVI device within the aortic valve. Rapid pacing is reinitiated, and the self-expanding Medtronic CoreValve is then released from its protective sleeve and fills the annular space.14 For the Edwards SAPIEN valve, the catheter is moved into position and a balloon expands the stent that contains the new aortic valve to fill the annulus.3 The catheter is then removed and a dressing is applied to the site.
The transapical approach, uniquely used only for the Edwards SAPIEN valve, is an approach selected for patients with poor femoral artery access. The transapical approach, although quicker and considered less technically difficult than the femoral approach, is more invasive and can cause more discomfort for the patient.16 A mini-thoracotomy is made at the fifth or sixth intercostal space and the left ventricle is exposed.14 Two purse-string sutures reinforced with pledgets are placed at the left ventricular apex and the left ventricle is punctured between the sutures with an access needle.17 Fluoroscopy guides the placement of guidewires to allow the balloon valvuloplasty catheter and then the Edwards SAPIEN catheter-sheath delivery system to be threaded through the left ventricular apex of the heart14 and into the aortic valve. As with the femoral artery TAVI approach, temporary transvenous pacing is used at a rapid rate to decrease the stroke volume and cardiac output to allow the balloon valvuloplasty procedure.3 This catheter is exchanged for the transcatheter containing the aortic valve stent device, which is then threaded through the left ventricular apex and into the open native aortic valve where the TAVI device is deployed into the annulus. After the TAVI catheter is removed, the small opening at the apex of the heart is sutured, a chest tube is placed, and the thoracotomy incision is closed (Figure 3).
Procedures for TAVI are performed in a hybrid equipped cardiac surgery operating room (OR) with cardiopulmonary bypass machine capability for emergency open AVR if percutaneous procedural complications arise. Patients receive general anesthesia with endotracheal intubation. The anesthetics administered usually permit extubation before leaving the OR in most cases. At the end of the procedure, patients are transferred to the cardiothoracic intensive care unit (ICU).1
NURSING CONSIDERATIONS FOR POSTOPERATIVE CARE
Patients who undergo TAVI already experience the long-term effects of AS, and their postoperative course is more similar than dissimilar to that of patients undergoing open AVR for AS.17 Much like AVR patients, TAVI patients can experience multiple dysrhythmias and hemodynamic changes that require pacing, antiarrhythmics, vasopressors, vasodilators, and volume loading to optimize cardiac index and decrease afterload. It is critical to remember that even though TAVI patients have undergone a minimally invasive procedure, their comorbid medical conditions make them a potentially ill and unstable group of patients.17
Postprocedure Potential Complications
During the initial postoperative 48 hours when TAVI patients are in the ICU, patients are at risk for bleeding complications from the femoral/subclavian artery or transapical thoracotomy approach access sites, limb ischemia, stroke, and bradycardia or heart blocks.17 The potential for these complications is increased because of the use and manipulation of multiple invasive catheters during this procedure and the valvuloplasty intervention. In addition, patients undergoing the transapical approach for TAVI are also susceptible to new-onset mitral regurgitation from inadvertent manipulation of the mitral valve structures while catheters are being threaded through the left ventricular apex. Other potential complications also include pericardial effusion with possible tamponade, pneumothorax, and late apical rupture.17 Although the complications of the TAVI procedure can be serious, the ability to perform this intervention without cardiopulmonary bypass and open sternotomy decreases the potential for subsequent adverse perfusion effects and shortens physical recovery time and discomfort.
Nurse’s Role in Monitoring and Treating Potential Post-TAVI Complications
The critical care nurse admitting the postoperative TAVI patient must assimilate the physical examination findings with the patient’s hemodynamic status and symptoms and follow the appropriate treatment plan. The development of care protocols is valuable to direct the nurse’s timely response to emergency events. Early recognition of dysrhythmias with efficient use of transvenous pacing, hemodynamic management, detection of subtle neurologic changes, and assessment of surgical site hematomas are all key areas where the nurse will provide first-line care and intervention. Table 2 describes the most common potential complications that can occur during the initial 48-hour postoperative period after insertion of TAVI devices, the current monitoring performed by the nurse, and the recommended treatment plan.3
Patients arriving to the ICU are on oxygen support via mechanical ventilator or, if extubated in the OR, a face mask or nasal cannula. Electrocardiogram and hemodynamic pressure monitoring is initiated, and the transvenous pacing lead is attached to the temporary epicardial pacemaker, if not already attached before the patient leaves the OR. Initial laboratory testing usually includes an anticoagulation profile, cardiac enzymes, electrolytes (including potassium, magnesium, calcium, and phosphorus levels), an arterial blood gas panel, and a hematology profile. If the patient is not being paced, a 12-lead electrocardiogram is also performed. Hand-off communication between the anesthesiologist and ICU nurse regarding the patient’s medical history, procedure, and intraoperative course is essential for the nurse to develop a plan of care.
TAVI patients usually spend between 24 and 48 hours in the ICU because of the need for close monitoring for hemodynamic stability and procedure-related complications predominantly from bradyarrythmias, stroke, bleeding, limb ischemia, and the patient’s preexisting comorbid conditions.17 Nursing care unique to these patients includes frequent physical assessment of femoral/subclavian artery or transapical thoracotomy approach access sites for bleeding complications or evidence of hematoma formation, femoral artery dissection, femoral artery pseudoaneurysm, and retroperitoneal hematoma.17 Frequent neurological and neurovascular checks are also necessary because of the risk of stroke from calcium plaques and lower extremity ischemia from thrombosis. An echocardiogram is performed during the first 24 to 48 hours to verify TAVI device placement within the native aortic valve and proper TAVI device leaflet functioning and to assess for any evidence of perivalvular leakage.17
General ICU nursing care should also focus on the following postoperative goals: improving pulmonary status through ventilator and oxygen support weaning and the use of incentive spirometry, managing incisional pain, reinitiation of nutrition support, and increasing mobility. Once stabilized hemodynamically in the ICU, the patient should expect to stay another 5 to 6 days on an inpatient telemetry floor unit before being discharged.
Oral anticoagulants are started within the first 24 hours after the procedure. It is recommended that TAVI patients be treated for a minimum of 6 months with dual antiplatelet therapy to prevent thromboembolism and ensure that the implanted valve is endothelialized.5 If a patient has an indication for long-term anticoagulation such as chronic atrial fibrillation, oral pharmacologic therapy will be started before discharge.
The advanced age of most patients with severe AS who choose to have the TAVI procedure lends itself to special discharge considerations regarding physical rehabilitation and the specialty recovery care needs of more elderly patients. Plans for having the patient go home with family support versus admission for a short stay at an inpatient skilled nursing facility for rehabilitation therapy should be discussed with the patient and family.
It is imperative that the nurse caring for the TAVI patient have a working knowledge of how the devices are inserted and the potential complications, as well as an understanding of the impact of each patient’s preoperative comorbid medical conditions. Nurses caring for the TAVI patient should receive education on these topics. Although there are many similarities in postoperative care of the TAVI and cardiothoracic surgical patient, the unique procedure and complications require a different nursing skill set to positively impact patient outcome.
Appropriate patient selection for the TAVI procedure will continue to evolve with experience and has the potential to decrease the incidence of postoperative complications. This in turn, will directly impact the nursing care required to transition TAVI patients through the ICU recovery phase. Comorbid conditions of the elderly population, such as diabetes, renal dysfunction, long-term smoking, chronic obstructive pulmonary disease, and coronary artery disease, will remain factors in whether the patient experiences related complications. As more older adult patients undergo TAVI procedures, the continued success of TAVI as a treatment option for severe AS will need to be supported by evidence. The ultimate goal will be to prove that the minimally invasive TAVI procedure can provide the high-risk older adult AS patient with a less complicated surgical recovery and improved quality of life.
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