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Corresponding author: Sandra Lauck, RN, MSN, CCN (C), The Heart Centre, St. Paul’s Hospital, 1081 Burrard St, Vancouver, BC V6Y 1Z5, Canada (e-mail: slauck{at}providencehealth.bc.ca).
Aortic stenosis has been documented in 2% to 4% of patients more than 65 years old; the incidence is higher in men than in women.4 Increasing evidence4–6 indicates that the disease is accelerated by the same factors that affect coronary artery disease, including smoking, hypercholesterolemia, hypertension, and diabetes. Until now, surgical valve replacement, pioneered in the 1960s with mechanical or tissue prostheses, was the only effective treatment available to alleviate signs and symptoms and prolong life in patients with severe aortic stenosis.4,7 Surgical aortic valve replacement improves quality of life and prognosis,8 but the procedure is a high-risk one for patients of advanced age who have multisystem dysfunction and calcific aortic stenosis.9
Interventional cardiology is rapidly evolving to include innovative approaches to manage valvular heart disease. In 2002, Cribier et al10 reported the first successful human percutaneous aortic valve implantation done via an antegrade transvenous approach. This procedure was technically complex; the implant valve was guided through an interventricular transseptal puncture, across the mitral valve, and then placed in the native aortic annulus. Complications associated with difficulties in steering and stabilizing the equipment, as well as risks of mitral valve damage and pericardial tamponade, prompted development of the arterial retrograde approach. The cardiac catheterization team at the Heart Centre at St. Paul’s Hospital in Vancouver, British Columbia, under the medical leadership of John Webb, MD, has been involved in the development and early evaluation of a percutaneous heart valve replacement program. Initial findings have been reported,9 and, to date, more than 100 procedures have been successfully performed at St. Paul’s Hospital.
Such innovations in clinical practice challenge critical care nurses to adapt rapidly, take a leadership role to guide program development, define the care of patients undergoing new procedures, and meet the learning needs of patients and staff. In this article, we review the pathophysiology and clinical features of aortic stenosis, describe the emerging option of percutaneous aortic valve replacement, and discuss implications for critical care nurses.
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Aortic Stenosis |
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The restricted opening of the valve leaflets in aortic stenosis is due to progressive calcific changes of either a normal trileaflet or a congenitally bicuspid valve, or to the effects of rheumatic heart disease.4 Until recently, calcific aortic stenosis was considered a degenerative disease of the elderly. However, new evidence11 suggests that aortic stenosis and coronary artery disease have common features; aortic stenosis is now thought to be an active disease involving deposition of lipoproteins, chronic inflammation, and active calcification of the leaflets.12 For example, recent histopathological studies have shown plaquelike lesions on the leaflets of stenotic valves and evidence of accumulation of low-density lipoproteins, oxidation, inflammatory cell infiltrates, and microscopic calcification. These findings are consistent with the pathophysiology and disease progression of atherosclerosis.12
As calcium deposits accumulate, the mobility of the aortic leaflets depends on the capacity of the left ventricle to force open the valve during systole.6 Thickening of valve leaflets and the progressive obstruction of left ventricular outflow impair aortic valve hemodynamics and increase left ventricular afterload, resulting in increased thickness of the wall of the left ventricle, diastolic dysfunction, and, less commonly, decreased systolic performance.4 Even in instances of severe aortic stenosis, the left ventricle can initially maintain normal contractility and adequate stroke volume at rest.4 Progressive pressure overload on the left ventricle leads to concentric hypertrophy. This increased muscle mass is an adaptive response to chronic high left ventricular pressure, enabling the left ventricle to generate enough force to propel blood past the stenotic valve. Such cardiac remodeling also has the deleterious effect of decreasing coronary blood flow reserve, causing both diastolic and systolic left ventricular dysfunction and producing the signs and symptoms of congestive heart failure.11
Hemodynamically, disturbances become evident only after the valve area has been reduced from the normal area of 3 to 4 cm2 to less than 2 cm2. The additional reduction from half its normal size to 1 cm2 produces severe obstruction to ejection of stroke volume and contributes to progressive pressure on the left ventricle. The increasing pressure gradient between the left ventricle and the aorta and the reduced cross-sectional area of valve opening indicate worsening disease severity11 (Table 1
). Figure 1 shows hemodynamic tracings associated with measurement of the pressure gradient in normal cardiac function and in severe aortic stenosis.
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Clinical Manifestations |
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shows the relationship between the onset of signs and symptoms and mortality in treated and untreated severe aortic stenosis.
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Diagnosis |
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Cardiac catheterization may be used to supplement the diagnostic information provided by echocardiography by providing measurements of pressure gradient and valve area. In addition, coronary angiography is routinely performed because of the high prevalence of coronary artery disease among patients who have aortic stenosis.4 High-resolution computed tomography and cardiac magnetic resonance imaging may be future options for the diagnosis of aortic stenosis.4,6 Because of the hemodynamic implications of severe aortic stenosis, exercise stress testing is unwarranted and dangerous, although it may have a role in diagnosis of milder forms of the disease.11
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Percutaneous Aortic Valve Implantation |
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). The objective of the care map is to improve the quality of care, reduce risks, increase patients’ satisfaction, and optimize resource utilization.15
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| CASE STUDY Mr R is an 82-year-old man with severe aortic stenosis and New York Heart Association functional class III heart failure. He also has chronic stable angina (Canadian Cardiovascular Society class II). His medical history includes coronary artery bypass grafting 15 years ago and repeat bypass surgery 6 years ago for occluded grafts. A year ago, he underwent percutaneous coronary intervention of the native right coronary artery to relieve signs and symptoms and improve quality of life. Mr R’s risk factors for coronary heart disease include hypertension, hypercholesterolemia, and a 30-pack year history of smoking. In addition, his renal function is impaired: serum level of creatinine, 180 µmol/L and serum level of urea nitrogen, 13.5 mmoL. Mr R has worsening chest pain, shortness of breath at rest, and difficulty sleeping. As part of the evaluation of his exacerbated heart failure, he undergoes cardiac echocardiography, which reveals left ventricular hypertrophy, ejection fraction 40%, aortic valve orifice 0.7 cm2, and mean transvalvular gradient 55 mm Hg. The cardiac surgery team evaluates Mr R for aortic valve replacement and concludes that his risks for complications and death is extremely high because of his age, surgical history, and comorbid conditions. Because of his poor quality of life and ongoing signs and symptoms, Mr R is referred for consideration for percutaneous aortic valve replacement.
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Care Before Implantation
Before PHV implantation, patients undergo rigorous diagnostic testing to evaluate their suitability for the procedure, including ileofemoral contrast vascular angiography to assess arterial vascular access size and patency and coronary angiography with percutaneous coronary intervention, if appropriate, to optimize cardiac perfusion. Renal function is evaluated (serum levels of urea and creatinine, glomerular filtration rate), and coagulation studies are performed, especially if patients are receiving oral anticoagulants.
Because of the advanced age of patients undergoing PHV implantation, anticipating, assessing, and managing clinical issues are especially challenging. A careful review of each patient’s functional status, comorbid conditions, family and community support, and quality of life is essential to meet the patient’s needs during hospitalization and to facilitate the discharge process.
The day before admission, patients are seen in the preassessment clinic. Patients are assessed by a nurse practitioner to establish baseline findings and begin discharge planning. Patients must also be assessed by the anesthesia service, because they will require general anesthesia during the implant procedure.
Coordination of cardiac echocardiography and vascular surgery services is needed to facilitate transesophageal echocardiography during the procedure and closure of the vascular access site after the procedure. Immediately before the procedure, a nurse administers aspirin, clopidogrel, and a prophylactic intravenous antibiotic.
Implant Procedure
Percutaneous heart valve implantation is performed either in a cardiac catheterization laboratory or in an operating room that has the capacity for hemodynamic monitoring and fluoroscopy imaging. In preparation for a procedure that may take up to 3 hours, patients are positioned carefully and appropriately, according to perioperative nursing standards, including use of padding materials under all bony prominences, tucking techniques to ensure the patients’ safety, and warming equipment to prevent heat loss during the procedure.16 A urinary catheter is inserted to track urine output. Standard equipment is used to monitor heart rate and rhythm, respiratory rate and oxygen saturation, and arterial blood pressure.
Patients undergo parenteral induction for general anesthesia, which is then maintained with inhaled agents for the duration of the procedure. Because patients with aortic stenosis usually have vasoconstriction before induction and can easily become hypotensive with the administration of anesthetics, aggressive treatment of hypotension may be started with an 
-adrenergic agonist such as phenylephrine. Early intervention decreases the risks of decreased coronary perfusion, myocardial perfusion, ventricular dysfunction, and cardiovascular collapse associated with sudden hypotension in patients with severe aortic stenosis.13
Although the actual valve deployment takes less than 20 seconds, the PHV procedure requires careful preparation of the access site, steering of catheters, and placement of the valve apparatus with the aid of fluoroscopic and echocardiographic imaging. The following events occur during the procedure:
Our experience has been with the Cribier-Edwards valve (Edwards LifeSciences, Irvine, California), which consists of a large tubular stainless steel stent with an attached bovine pericardial trileaflet valve. The stent-valve is available with a diameter of 23 or 26 mm with a height of 14.5 or 16 mm, respectively (Figures 3 and 4). A deflectable guiding catheter (Edwards LifeSciences) and a valvuloplasty delivery balloon catheter onto which the stent-valve is crimped, are used to steer and deploy the device.
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When the position of the stent-valve within the native aortic annulus is confirmed, the device is ready for deployment. Short-term, rapid, right ventricular pacing, which reduces cardiac wall motion, left ventricular blood ejection, and transaortic flow, is used to prevent the stent-valve from slipping from its correct position during balloon inflation. A temporary pacing lead is placed in the right ventricle via the femoral vein and is connected to a temporary pacemaker pulse generator.
Coordination and clear communication between the interventional cardiologist and the critical care nurse responsible for initiating and terminating pacing are essential during the rapid sequence of pacing and stent deployment (see Along Side). The cardiologist observes the fluoroscopic image, maintains valve position, and coordinates balloon inflation and stent deployment; the circulating nurse initiates pacing when requested, at a rate of 200 to 220 impulses per minute, and observes for reliable pacemaker capture and desired reduction in arterial pressure (Figure 5). Initiation of pacing resulting in adequately decreased cardiac output is promptly followed by rapid inflation and deflation of the stent-deployment valvuloplasty balloon and termination of pacing with return of normal rhythm and cardiac output. Figures 6 and 7 show placement and deployment of the stent-valve.
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). Angiography of the right and left coronary arteries is performed to assess coronary blood flow, because any degree of blockage by the newly implanted valve could cause decreased coronary perfusion, leading to myocardial ischemia and impaired cardiac output.
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| ALONG SIDE Pacing Script Initiating and terminating pacing are pivotal to the success of percutaneous heart valve replacement and require clear communication between members of the implant team. A clear "script" can be used to facilitate consistent practice :
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Vascular Closure
In the immediate period after implantation, the focus is on repairing the femoral artery and achieving hemostasis. The removal of a 22F (8 mm) to 24F (9 mm) sheath in an elderly patient with peripheral vascular disease and calcification cannot be safely accomplished with standard techniques for sheath removal. Our protocol calls for a vascular surgeon to join the procedure team after valve deployment. In addition, nurses from the cardiac catheterization laboratory who have additional expertise and education in vascular operating room technique assist with the surgical closure of the site. This approach has resulted in improved patient safety and outcomes, accelerated healing and recovery, and early ambulation and discharge. Early investigation indicates promise for the development of a vascular closure device to replace surgical repair.
Care Immediately After the Procedure
After the procedure, patients are transferred to a critical care area staffed by personnel familiar with the management of cardiac patients, where the focus is safe recovery from general anesthesia, maintenance of adequate circulation, and assessment of the vascular repair site. Besides standard airway and breathing assessment, attention is focused on ensuring neurological recovery. Alterations in pupil size or reaction, motor movement, or verbal response could indicate an embolic cerebrovascular event. Manipulation of a calcified valve, diseased aortic arch, and arterial system may result in atheroembolism.4 Because elderly patients often experience alterations in level of consciousness after general anesthesia, it is crucial that nurses conduct vigilant and thorough neurological assessments to detect early complications and intervene as appropriate.
Cardiac monitoring is supplemented by invasive hemodynamic monitoring of arterial and central venous pressure to allow early detection of cardiac complications or fluid imbalances. PHV patients are subject to multiple risks for myocardial ischemia, including the proximity of the device to the coronary ostia, a high incidence of concomitant coronary artery disease, and the potential for alterations in cardiac output due to the implant procedure. Continuous ST-segment monitoring and 12-lead electrocardiography after the procedure allow for early detection of myocardial ischemia. Circulation may also be impaired by procedure-induced aortic insufficiency and regurgitation due to perivalvular leak. If the stent-valve is not fully deployed or does not fit the native annulus perfectly, blood may regurgitate from the aorta into the left ventricle through the small areas of leakage. In acute aortic insufficiency, the left ventricle cannot remodel to accommodate fluid overload, causing a sharp increase in left atrial and ventricular pressures, acute congestive heart failure, and pulmonary edema.17,18
To monitor for vascular access complications, including hemorrhage and limb ischemia, caregivers check the femoral site and dressing and the color, warmth, movement, and sensation in the legs every 15 minutes in the first hour after admission to the recovery area and then hourly for the subsequent 4 hours. The affected limb must be kept straight, and the head of the bed should be elevated no more than 30° for 8 hours after hemostasis, with bed rest maintained for 12 to 24 hours after the procedure. Potential complications include a tear in the arterial repair, retroperitoneal hemorrhage, and embolization. Vascular ultrasound or computed tomography may be required if hemorrhage or limb ischemia are suspected.
Pain management measures are started after the procedure to provide comfort and minimize risks associated with pain, including increased myocardial demand and anxiety. Because intravenous narcotics can cause confusion in elderly patients, we favor subcutaneous hydromorphone and early addition of nonsteroidal analgesics.
The large amount of contrast medium required for a long fluoroscopic procedure is potentially nephrotoxic, especially in patients with preexisting impaired renal function. At our center, if a patient’s glomerular filtration rate is less than 50 mL/min, a protocol to prevent contrast-induced nephropathy is started; normal saline is administered at a rate of 0.5 mL/kg per hour for 24 hours starting the morning of the procedure. Serum levels of creatinine and urea and glomerular filtration rate are measured daily for the next 2 days and at the time of discharge.
| Case Study, Update 1 Mr R is extubated in the cardiac catheterization laboratory after vascular repair and hemostasis. His vital signs have remained stable since his new valve was implanted, and he has been weaned from vasoactive medications that were used briefly during the procedure. Although he has a hematoma at the vascular access site, the hematoma is not expanding, the dressing is stained with a moderate amount of dark sanguineous discharge, and vascular parameters are within normal limits. His vital signs are normal and his neurological status has returned to its preprocedure state. On the evening of the procedure, he resumes a normal cardiac diet. Because Mr R had multiple risk factors for surgical valve replacement, this recovery is a stark contrast to the potentially challenging recovery from cardiopulmonary bypass, sternotomy, and extended intubation and ventilation.
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Transfer and Discharge Planning
In order to promote early mobilization and return to normal function and to minimize elderly patients’ risks for disturbance in sleep pattern, delirium, and alterations in nutrition and bowel and urinary function associated with extended admissions to a critical care area,19,20 every effort should be made to rapidly transfer PHV patients to an acute care, step-down, or telemetry unit the day after the procedure. Striving to rapidly normalize care while continuing vigilant assessment for potential complications is key to facilitate discharge and return home. Cardiac and invasive hemodynamic monitoring and urinary catheterization are discontinued before patients are transferred from the coronary care unit to facilitate transfer and mobilization. Patients must walk as early as possible, preferably the day after the procedure, to prevent respiratory, embolic, and cognitive complications.21
Administration of all regular medications, including cardiac and antithrombotic agents, is resumed, because pharmacological adjustments are not required in the short term and should ideally be implemented by the patient’s primary care provider. An antiplatelet agent such as clopidogrel is usually prescribed for a minimum 1-month course to prevent platelet aggregation within the stent valve. Early consultation with physiotherapy, occupational therapy, social work, or home care nursing services may provide additional resources for discharge planning.
Before discharge, patients also undergo transthoracic echocardiography and prosthesis fluoroscopy to assess and document valve function. These noninvasive diagnostic tests are well tolerated and do not require special preparation. Serum levels of hemoglobin and electrolytes and renal profile are monitored during the week after the implant procedure.
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Experience to Date and Implications for Cardiac Programs |
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Beyond meeting the learning needs of the critical care nurses working in interventional cardiology, educational and clinical support has also been directed at all nurses in the cardiac program. The essentials of PHV implantation, its innovative and investigational nature, and guidelines designed to ensure continuity of care between the different clinical areas have formed the educational program. As our experience grows in the care of PHV patients, whose advanced age and comorbid conditions put them at high risk for complications, nurses are becoming increasingly competent in anticipating challenges and complications and in intervening to optimize outcomes.
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Conclusion |
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. The lack of research, experience, and published clinical guidelines have necessitated reliance on critical care and cardiac nursing expertise and a commitment to sharing information, interdisciplinary communication, and collaborative practice. PHV implantation, although still an immature technology, offers patients with aortic stenosis the hope of decreasing their signs and symptoms, thus providing improved quality of life in the more advanced years of life. In the words of MN, a patient who wrote to us in January 2007:
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On October 6, 2006, you and your team performed a percutaneous heart valve implant for me. I wish to thank you from the bottom of my heart. I feel like a new person and my quality of life has improved 100%. Prior to your fabulous procedure, I had trouble breathing, walking, and had little energy. Today, I am resuming my exercises with our Healthy Heart group and feel that I am now functioning normally for my age. Thanks for prolonging my life. Just celebrated my 89th birthday. Interventional cardiology is
rapidly expanding to offer new approaches to valvular heart disease, especially for the aging population. Critical care nurses are well positioned to rise to the opportunities and challenges of such new treatment options for patients.
| Case Study, Update 2 Four days after his percutaneous aortic valve replacement, Mr R is discharged home. Discharge instructions include schedule of medical follow-up with his primary care provider, follow-up blood tests and echocardiography, and self-care of the vascular repair site.
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PRIME POINTS |
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Acknowledgment |
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References |
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
