MIRIAM JENNINGS, 78, visits her primary care provider complaining of shortness of breath, inability to sleep lying down, and increasing fatigue. After a physical exam, she's referred to a cardiologist, who performs a comprehensive workup and diagnoses aortic stenosis. Ms. Jennings isn't a good candidate for conventional aortic valve replacement due to multiple comorbidities, including a history of heavy smoking, chronic kidney disease, and heart failure. She's referred to a cardiac surgical team to be evaluated for a transapical valve placement.
The newest, most innovative procedure available for treating heart disease, the transapical valve is a compressed heart valve that can be positioned directly into the diseased aortic valve through a transfemoral or transapical approach. This valve provides an alternative treatment option for the highest-risk older adults with valve disease. Although this type of heart valve initially received mixed reviews, recent research appears to show improved results for patients. The device is now being studied in high-risk, symptomatic patients with severe aortic stenosis.
More than 99,000 heart valve repair or replacement surgeries are performed each year for stenosis, insufficiency, and related congenital valve disorders.1 The causes of valvular disease may be congenital or acquired. Valve disease may develop acutely, but usually is a chronic process. Because of the higher pressures involving the mitral and aortic valves, valvular disease is more common on the left side of the heart.
In developed countries, the most common causes of valvular heart disease are now myocardial infarction (MI), birth defects, severe lung disease, age-related calcification of valves, and cardiomyopathies with valve damage due to chamber distortion.2 Congenital valvular disease occurs in 4 to 50 of 1,000 people in the general population.3 More patients with congenital heart disease are surviving to old age, resulting in the need for valve repair or replacement via less-invasive techniques that are associated with a reduced mortality.2
Recognizing trouble
Initially, a patient developing chronic valve disease may be asymptomatic, and depending on the type of valvular defect, the symptoms may vary. Mild symptoms such as fatigue, heart palpitations, chest pain, or changes in BP might be confused with other conditions. If undiagnosed or untreated, the patient may develop heart failure with shortness of breath, edema of the extremities, general weight gain, and unexplained cough.
Diagnosis of valvular disease is based on a comprehensive physical exam that should include:
* an ECG, to determine cardiac rate and rhythm, and identify dysrhythmias (atrial fibrillation [AF] is common in patients with valvular disease)
* a chest X-ray, to indicate the size and shape of the heart and provide information about its general condition.
* an echocardiogram, to visualize cardiac function including the ejection fraction.
Cardiac catheterization is the gold standard for evaluating valve disease.4 This test analyzes cardiac function through an analysis of chamber pressures and ejection fraction. The cardiologist will determine whether the patient has coronary artery disease as well as examine the function of the heart valves.
Treatment goals
Treatment of valvular heart disease depends on the type and severity of the disease. The age and the general health of the patient also must be considered, as well as the patient's ability to adhere to treatment.
The primary goals of therapy are to minimize the risk of death, control bleeding, improve tissue oxygenation, improve perfusion to end organs, achieve hemodynamic stability, treat dysrhythmias, and prevent complications such as stroke or pulmonary embolism. In general, there are two options for treatment of valve disease: pharmacologic therapy or surgery.
Pharmacologic therapy for valvular disease may be prescribed when the disease is in the early stages, or for patients who may not survive valvular surgery, and should follow the American College of Cardiologists (ACC)/American Heart Association (AHA) guidelines for the management of patients with valvular heart disease.4 Valvular heart disease usually responds well to medications depending on the patient's symptoms.
For patients with dysrhythmias, such as AF, drugs may be prescribed to help control the ventricular rate and maintain a regular heart rhythm. Anticoagulants may be administered to prevent left atrial thrombi secondary to the irregular rhythm. Cardiotonics may also be given to increase the force of the cardiac contraction and decrease stasis of blood in the ventricles.
Surgical intervention
If pharmacologic therapy is no longer effective or the patient's condition deteriorates, surgery may be required. Several procedures can be done in the cath lab. Treatment options may include:
* Percutaneous balloon valvuloplasty performed in the cath lab. A catheter is inserted into a stenotic valve to open it.
* Valvulotomy, a cardiac surgery procedure, used to repair a damaged valve.
* Minimally invasive heart valve surgery performed through a small incision in the patient's chest. This technique can be used to repair a damaged heart valve, depending on the severity of disease and if the patient is a candidate for this type of surgery. Complications from a minimally invasive approach are comparable to conventional procedures. Length of stay may be slightly shorter, but patient age, complications, and type of procedure will usually affect the patient outcome.
* Conventional valve replacement surgery, in which the diseased valve is replaced with either a mechanical or a biological valve. Surgical valve replacement is still considered the gold standard for treating valvular disease. Current treatment for valve disease involves excision of the old valve or repair of the damaged valve root. This open-heart procedure is performed under anesthesia with the assistance of cardiopulmonary bypass. In the most traditional types of valve repair or replacement procedures, the heart is stopped with cardioplegia and blood is diverted from the surgical field to the cardiopulmonary bypass machine. These are relatively common procedures in cardiac surgery, but pose great risks to older patients.
The most common valve replacement for young patients is a mechanical valve. Older patients will often receive a biological or tissue valve such as a cadaver, bovine, or porcine valve. A small percentage of patients will receive a human donor valve.
* Percutaneous valve replacement, done in the cath lab or OR, in which a special valve is inserted using a transfemoral or transapical approach.
In 2000, Bonhoeffer implanted the first catheter-based stent valve into a 12-year-old boy with severe pulmonary valve stenosis.5 This innovative procedure used a bovine jugular vein valve sutured onto a platinum stent that was placed percutaneously into the boy's heart via the femoral vein. Two types of valves are available in the United States for implantation at present.6
Determining the correct procedure for the appropriate patient isn't an easy decision. The ACC and AHA have developed guidelines to assist with the decision-making process.4 Aortic balloon valvulotomy is indicated if the patient has symptomatic disease without aortic calcification or aortic regurgitation. The presence of calcification on the valve poses significant risk for stroke and other related complications, especially in older patients. Valvulotomy should be considered carefully if the patient's valve has significant calcification.
Because valve surgery is frequently performed on older adults, it may be associated with an even higher mortality due to comorbidities. Published estimates for mortality associated with conventional valve replacement have indicated a rate between 12% and 50%.7 This discrepancy demonstrates a significant variance in mortality and reflects the varying degree of illness for this population of cardiac patients. Originally, percutaneous valve replacement was developed for the sickest classification patients who might not survive conventional valve replacement.
Typically, the average length of stay in the hospital for conventional valve replacement is 5 to 7 days, of which 2 to 3 days may be spent in the CCU. The cost of the average valve replacement surgery can vary greatly because of the less-predictable postoperative course of valve replacement patients. Comparatively, there's little published evidence about the length of stay or cost of percutaneous valve replacement procedures.
Recent research
The early studies on percutaneous valves cited a higher-than-expected mortality, and the transfemoral approach had better results than the transapical.8 In Germany, transapical placement had much better results in the early phase of the investigation. Problems with the transapical valve have been attributed to patient selection, correct placement of the valve, and comorbidities. These few studies also noted that tremendous skill was required for the operator to successfully implant this type of valve.8 Studies also indicated the importance of appropriate patient selection for percutaneous valve implantation.
In a study of 50 patients, aortic valves were implanted transapically via minimally invasive technique and without cardiopulmonary bypass.8 Although these were high-risk patients, the overall success was positive. Evaluation of long-term effectiveness of percutaneous valve implantation and the complications associated with the valve have yet to be adequately studied.
Placing a valve via the transfemoral approach can be done in the cardiac catheterization lab with local anesthesia or moderate sedation and analgesia with fluoroscopy guidance. An open-chest procedure isn't required, as with the transapical approach. Patients must be prepared in standard fashion for the cath lab including chest X-ray, routine labs, echocardiogram, and ECG. Using a femoral approach, the catheter is advanced into position with the valve crimped onto the catheter. The catheter has a unique mechanism that facilitates placement of the valve into the proper position. The new prosthetic valve is usually inserted over the calcified valve leaflets. The native valve may be left in place. In some cases, a valvuloplasty may be performed before the deployment of the new valve to dilate the annulus so it can accommodate the new valve. After the valve is successfully deployed into the annulus, the catheter is withdrawn. Complications of this procedure include stroke, bleeding from the femoral site, and dysrhythmias.3 Recovery usually occurs in the cardiac surgery ICU and requires standard protocols for care.
Transapical valve placement may be used as treatment for either valvular stenosis or regurgitation. This approach is performed in the OR under anesthesia. The patient is prepped in the same manner as for any cardiac or thoracic surgery procedure. The surgeon makes an incision through the chest wall and another incision into the apex of the heart. The valve is crimped onto a catheter that is passed through the incision in the chest wall and again through the apex of the heart. The valve is deployed into the annulus of the damaged valve, in the same manner as in the cath lab procedure. The apex of the heart is closed with a purse-string suture. The patient is transported to the cardiac surgery ICU where recovery is achieved through standard protocols for postoperative cardiac surgery procedures.
Problems with the transapical valve have been attributed to patient selection, correct placement of the valve, and comorbidities. Several cardiac interventionalists have been very outspoken about the high transapical valve mortality and have voiced concern that the initial poor outcomes could prevent the adoption of transapical valves in the United States.8 Surgeons involved in the early studies feel that the procedure is rapidly improving and should become a viable option for patients. No randomized studies have compared transfemoral, transapical, and conventional aortic valve replacement, so it's difficult to discern which procedure is the best procedure for a particular population of patients.
Who can and can't have percutaneous valve replacement
Percutaneous valve replacement is indicated for patients who are predicted to have more than 15% chance of death because of associated comorbidities, aortic valve stenosis with a mean gradient higher than 40 mm Hg, and a New York Heart Association functional class of II or higher.
Patients who may be excluded from receiving a percutaneous valve replacement include those who had evidence of an acute MI within the last month; a congenital valve, which doesn't permit placement of this type of valve due to severe structural abnormality; presence of both stenosis and regurgitative states; presence of a preexisting prosthetic heart valve in any position or prosthetic ring; disorders of blood coagulation; coronary artery disease requiring revasculation; hemodynamic instability requiring inotropic support; hypertrophic cardiomyopathy; severe ventricular dysfunction with an ejection fraction of less than 20%; presence of intracardiac mass; or relative aortic annulus size that's too small or too large.2 Additional exclusion criteria include patients who've had a previous stroke; renal insufficiency or failure; iliofemoral disease, which prevents cannulation; and patients who aren't expected to survive for 1 year because of other conditions.
Surgeons have been interested in finding alternative methods to provide therapies for the sickest cardiac patients, who wouldn't survive conventional surgery. The higher mortality seen in the initial percutaneous valve replacement procedures has been attributed to advanced patient age and extreme infirmity. More recently, the procedure has been directed at a slightly younger and healthier population with improved results.
What's next?
In addition to a comparison study of patient outcomes among transapical, transfemoral, and conventional valve surgery procedures, several other areas hold research potential, including postprocedure complications. Little research has been reported about the long-term effects of these types of valves. Perhaps the most important consideration is the proper selection criteria for patients who can benefit from a percutaneous valve. Lastly, developing evidence-based protocols for percutaneous valve placement should be undertaken to provide the highest level of care for these patients, who are often the sickest patients requiring valve procedures.
References