Options for managing severe aortic stenosis: A case-based review
ABSTRACTThe treatment of calcific aortic stenosis is well established and includes careful monitoring of patients who have no symptoms and surgical aortic valve replacement in the patients who do have symptoms. Patients who cannot undergo open heart surgery can now undergo valve replacement via a minimally invasive transcatheter approach. In this article, we use clinical vignettes to illustrate the management of patients with severe aortic stenosis.
KEY POINTS
- Calcific aortic stenosis is the most common acquired valvular disease, and its prevalence is increasing as the population ages.
- Patients who have symptoms should be referred for aortic valve replacement. Patients who are not candidates for open heart surgery may be eligible for transcatheter aortic valve replacement.
- For high-risk patients with multiple comorbidities, “bridging” therapies such as aortic valvuloplasty are an option.
- In patients with aortic stenosis who present with hemodynamic instability and circulatory collapse, time can be gained with the use of intravenous sodium nitroprusside (in the absence of hypotension) or intra-aortic balloon counterpulsation while more definitive treatment decisions are being made.
CASE 4: ASYMPTOMATIC BUT SEVERE STENOSIS
Mr. D, age 74, has hypertension, hyperlipidemia, and aortic stenosis. He now presents to the outpatient department for his annual echocardiogram to follow his aortic stenosis. He has a sedentary lifestyle but feels well performing activities of daily living. He denies dyspnea on exertion, chest pain, or syncope.
His echocardiogram reveals an effective aortic valve area of 0.7 cm2, peak gradient 90 mm Hg, and mean gradient 70 mm Hg. There is evidence of severe left ventricular hypertrophy, and the valve leaflets show bulky calcification and severe restriction. An echocardiogram performed at the same institution a year earlier revealed gradients of 60 and 40 mm Hg.
Blood is drawn for laboratory tests, including N-terminal pro-brain natriuretic peptide, which is 350 pg/mL (reference range for his age < 125 pg/mL). He is referred for a treadmill stress test, which elicits symptoms at a moderate activity level.
How would you manage his aortic stenosis?
Aortic valve replacement can be considered in patients who have asymptomatic but severe aortic stenosis with preserved left ventricular function (class IIb indication).21
Clinical assessment of asymptomatic aortic stenosis can be challenging, however, as patients may underreport their symptoms or decrease their activity levels to avoid symptoms. Exercise testing in such patients can elicit symptoms, unmask diminished exercise capacity, and help determine if they should be referred for surgery.36,37 Natriuretic peptide levels have been shown to correlate with the severity of aortic stenosis,38,39 and more importantly, to help predict symptom onset, cardiac death, and need for aortic valve replacement.40–42
Some patients with asymptomatic but severe aortic stenosis are at higher risk of morbidity and death. High-risk subsets include patients with rapid progression of aortic stenosis and those with critical aortic stenosis characterized by an aortic valve area less than 0.60 cm2, mean gradient greater than 60 mm Hg, and jet velocity greater than 5.0 m/s. It is reasonable to offer these patients surgery if their expected operative mortality risk is less than 1.0%.21
Mr. D has evidence of rapid progression as defined by an increase in aortic jet velocity of more than 0.3 m/s/year. He is at low surgical risk and was referred for elective aortic valve replacement.
CASE 5: TOO FRAIL FOR SURGERY
Mr. E, age 84, has severe aortic stenosis (valve area 0.6 cm2, peak and mean gradients of 88 and 56 mm Hg), coronary artery disease status post coronary artery bypass grafting, moderate chronic obstructive pulmonary disease (forced expiratory volume in 1 second 0.8 L), chronic kidney disease (serum creatinine 1.9 mg/dL), hypertension, hyperlipidemia, and diabetes mellitus. He has preserved left ventricular function. He presents to the outpatient department with worsening shortness of breath and peripheral edema over the past several months. Your impression is that he is very frail. How would you manage Mr. E’s aortic stenosis?
Advances in surgical techniques and perioperative management over the years have enabled higher-risk patients to undergo surgical aortic valve replacement with excellent out-comes.18–20,43 Yet many patients still cannot undergo surgery because their risk is too high. Patients ineligible for surgery have traditionally been treated medically—with poor out-comes—or with balloon aortic valvuloplasty to palliate symptoms.
Transcatheter aortic valve replacement, approved by the US Food and Drug Administration (FDA) in 2011, now provides another option for these patients. In this procedure, a bioprosthetic valve mounted on a metal frame is implanted over the native stenotic valve.
Currently, the only FDA-approved and commercially available valve in the United States is the Edwards SAPIEN valve, which has bovine pericardial tissue leaflets fixed to a balloon-expandable stainless steel frame (Figure 3). In the Placement of Aortic Transcatheter Valves (PARTNER) trial,15 patients who could not undergo surgery who underwent transcatheter replacement with this valve had a significantly better survival rate than patients treated medically.15,17 Use of this valve has also been compared against conventional surgical aortic valve replacement in high-risk patients and was found to have similar long-term outcomes (Figure 4).16 It was on the basis of this trial that this valve was granted approval for patients who cannot undergo surgery.
The standard of care for high-risk patients remains surgical aortic valve replacement, although it remains to be seen whether transcatheter replacement will be made available as well to patients eligible for surgery in the near future. There are currently no randomized data for transcatheter aortic valve replacement in patients at moderate to low surgical risk, and these patients should not be considered for this procedure.
Although the initial studies are encouraging for patients who cannot undergo surgery and who are at high risk without it, several issues and concerns remain. Importantly, the long-term durability of the transcatheter valve and longer-term outcomes remain unknown. Furthermore, the risk of vascular complications remains high (10% to 15%), dictating the need for careful patient selection. There are also concerns about the risks of stroke and of paravalvular aortic insufficiency. These issues are being investigated and addressed, however, and we hope that with increasing operator experience and improvements in the technique, outcomes will be improved.
Which approach for transcatheter aortic valve replacement?
There are several considerations in determining a patient’s eligibility for transcatheter aortic valve replacement.
Initially, these valves were placed by a transvenous, transseptal approach, but now retrograde placement through the femoral artery has become standard. In this procedure, the device is advanced retrograde from the femoral artery through the aorta and placed across the native aortic valve under fluoroscopic and echocardiographic guidance.
Patients who are not eligible for transfemoral placement because of severe atherosclerosis, tortuosity, or ectasia of the iliofemoral artery or aorta can still undergo percutaneous treatment with a transapical approach. This is a hybrid surgical-transcatheter approach in which the valve is delivered through a sheath placed by left ventricular apical puncture.17,44
A newer approach gaining popularity is the transaortic technique, in which the ascending aorta is accessed directly through a ministernotomy and the delivery sheath is placed with a direct puncture. Other approaches are through the axillary and subclavian arteries.
Other valves are under development
Several other valves are under development and will likely change the landscape of transcatheter aortic valve replacement with improving outcomes. Valves that are available in the United States are shown in Figure 3. The CoreValve, consisting of porcine pericardial leaflets mounted on a self-expanding nitinol stent, is currently being studied in a trial in the United States, and the manufacturer (Medtronic) will seek approval when results are complete in the near future.
Mr. E was initially referred for surgery, but when deemed to be unable to undergo surgery was found to be a good candidate for transcatheter aortic valve replacement.
