The current results of aortic valve replacement for acquired aortic stenosis represent a medical triumph. Age-corrected survival after aortic valve replacement is excellent for patients over the age of 65 years and is similar to that of the normal population of that age.1 In the absence of extracardiac co-morbidity and in the absence of coronary artery disease, aortic valve replacement can be performed at a 2% to 3% operative mortality with an 85% age-corrected 10-year survival.1 This excellent outcome can be attributed to a variety of factors including the universal use of intraoperative cardiac protection, the insertion of hemodynamically excellent and durable valve prostheses, and the proper timing of aortic valve replacement.
Currently, timing in most cases is predicated upon the absence or presence of symptoms. In the absence of cardiac symptoms, survival is excellent without surgery.2 3 4 5 Since there is always some risk of operative death and some risk of prosthetic valve–related complications, the risk-benefit ratio does not favor operating on the asymptomatic patient. However, studies that have examined the “natural” history of aortic stenosis in the modern era consistently report a few subjects who progress from the asymptomatic state to the development of symptoms and then to sudden death in a very short period of time.3 4 In two echocardiographic studies of asymptomatic patients in whom aortic stenosis was quantified by Doppler interrogation as at least moderate, 5 of 195 patients with aortic stenosis suffered this rapid and unfortunate progression.3 4 Thus, the guidelines for timing aortic valve replacement are not yet perfect. An obvious question is, “How do we recognize and protect this small at-risk minority of patients with aortic stenosis?” It is clear that prophylactic surgery (surgery before symptoms develop) is not the answer, since the whole population of patients with aortic stenosis would have to be exposed to the risks of surgery and to the complications of a valve prosthesis in order to protect a tiny minority. In fact, in the study by Pellikka et al,4 mortality was slightly higher in the asymptomatic group that received “prophylactic” valve replacement than in patients not operated on until symptoms developed.4
Analogy to the Timing of Surgery in Aortic Regurgitation
In the past 15 years, the surgical outcome for patients with aortic regurgitation has also improved dramatically. As with aortic stenosis, improved surgical techniques and better valve prostheses are in part responsible for this improvement. However, in my view, a major contribution to improved prognosis is the adoption of the “55 rule” for asymptomatic patients with aortic regurgitation.6 7 If the patient with aortic regurgitation has an echocardiographic left ventricular end-systolic dimension of ≥55 mm, symptoms are imminent and long-term survival is reduced. An ejection fraction <55% also confirms a poor prognosis. Thus, there is a persuasive argument to operate on patients with aortic regurgitation even if they are asymptomatic when these thresholds are approached.
Where We Are Headed
If similarly prognostic noninvasive parameters could be developed for aortic stenosis, surgery in asymptomatic patients could be contemplated. The study by Otto and colleagues8 presented in this issue provides data that are a step in this direction. Two findings from this study stand out. First, of 123 patients with an initial average mean gradient of 30 mm Hg followed for 21/2 years, there were no sudden cardiac deaths. Second, of those patients who entered the study with a peak aortic jet velocity >4 m/s, only 21% were alive and free of valve replacement after 2 years of follow-up.
In light of Otto’s study, should we now recommend prophylactic aortic valve replacement for asymptomatic patients with aortic stenosis whose peak outflow velocity exceeds 4 m/s? The argument in support of this position would be that since such patients are likely to become symptomatic within the next 2 years anyway, why not proceed with surgery to avoid the potential risks of further delay, which include unexpected sudden death? The answer to this rhetorical question is yes and no. If every patient could receive a pulmonary autograft (transfer of the native pulmonary valve into aortic position, ie, the Ross procedure) or a durable homograft and the operative risk was ≤1.0%, then the answer would be yes; early surgery in asymptomatic patients predicted to soon become symptomatic (jet velocity >4.0 m/s) would be justified because the complications of prostheses could be avoided at low operative risk. Unfortunately, the Ross procedure is difficult for some to perform and is not universally practiced, and the durability of homografts is not known with certainty. Furthermore, the current study was not designed to answer questions about reducing mortality, so we cannot know whether the prophylactic approach would save lives. Thus, for the most part the answer is no, we are not yet ready for “prophylactic” surgery. Nonetheless, the current data are provocative and point to a time in the future when such surgery might be advisable.
The Dreaded Stress Test
Other important information regarding the timing of surgery comes from Otto et al8 about exercise testing in patients with aortic stenosis. While it was of interest that the patients with an end point (surgery or death) had a smaller increase in valve area during exercise, this factor was not useful as a multivariate predictor of outcome. More important in my opinion is the fact that a large number of patients with relatively severe but asymptomatic aortic stenosis underwent exercise testing without incident. While a large experience in Europe is similar to that of the current study,9 the general practice in the United States has been not to exercise patients with aortic stenosis for fear that such patients were at high risk for complications during the test.10 While indeed, it is unwise to stress the patient with aortic stenosis who has any of the classic aortic stenosis symptoms (angina, syncope, or heart failure), exercise testing in asymptomatic patients or patients with vague symptoms appears to be safe and useful. Safety is probably predicated in part on the fact that physicians testing such patients avoid the extremes of exercise tolerance in a prudent effort to avoid complications. During exercise testing, the unexpected precipitation of typical symptoms at a low workload support prompt surgery, in my view. On the other hand, it would be difficult to recommend aortic valve replacement in an asymptomatic patient who achieved greater than age-predicted exercise tolerance, even if aortic jet velocity exceeded 4 m/s.
What Is ‘Critical’ Aortic Stenosis, and How Does Valve Area Help Time Surgery?
My definition of critical aortic stenosis is that valve area small enough to cause the symptoms of aortic stenosis that often presage sudden death: a “critical” situation indicating aortic valve replacement. The current study amplifies the concept that no discrete value for critical valve area exists, but varies from patient to patient. Different cardiac output demands from the valves of different patients, together with problems inherent in the calculation of valve area, cause patients to become symptomatic in a range of valve areas between 0.6 and 0.8 cm2.8 11 12 13 14 Areas of 0.8 to 1.0 cm2 constitute a gray zone into which some cases of critical stenosis also fall. These are usually cases in which the patient is large or in which the cardiac output is high.
For patients with valve areas >1.0 cm2, another source for symptoms should be sought, especially if the mean transvalvular gradient is ≤30 mm Hg. For the patient with clear symptoms whose valve area is <0.8 cm2 and possibly <1.0 cm2, aortic valve replacement is indicated.
Current Timing of Aortic Valve Replacement for Aortic Stenosis
The data from the current study taken with previous investigations suggest a reasonable plan for the timing of aortic valve replacement aortic stenosis as follows.
Asymptomatic patients with aortic stenosis whose initial peak jet velocity is <3 m/s should be followed medically at yearly intervals with written instructions in layman’s terms, which indicate that upon the onset of angina, syncope, or the symptoms of heart failure, the patient should alert his or her physician immediately. Echocardiography should probably be repeated during the yearly visit to assess the rate of progression of the disease, a potentially useful datum in following the patient according to the present study. However, a strong recommendation regarding the need for additional echocardiograms cannot be made conclusively since the exact influence of this information on management is not clear.
For asymptomatic patients with a jet velocity >3 m/s, follow-up at 6-month intervals, again with written instructions regarding the onset of symptoms, is recommended. Repeat echocardiography in patients with an initial jet of velocity of ≥4.0 m/s is probably unnecessary until symptoms develop since such patients have already been identified as at high risk for rapid progression to aortic valve replacement.
Patients With Vague Symptoms
Patients with symptoms that cannot be directly attributed to aortic stenosis should have an initial workup that includes a history, physical examination, and Doppler interrogation of the aortic valve. If the peak jet velocity exceeds 3.0 m/s, an exercise test should be performed to assess exercise tolerance and to investigate objectively for the presence of symptoms more typical of aortic stenosis. If these symptoms are present, or if exercise tolerance is subnormal, further workup for aortic valve replacement is recommended. A cardiac catheterization to obtain additional data in this murky situation is warranted in my opinion.
If exercise tolerance is normal and exercise does not elicit symptoms, continued medical follow-up is indicated. It should be noted that ST-segment shifts during exercise do not constitute a positive test in this group of patients with left ventricular hypertrophy.
For symptomatic patients whose symptoms are unquestionably attributable to severe aortic stenosis, prompt surgery is indicated. As Otto and colleagues point out, there is not an exact definition of what constitutes a critical valve area. Patients who are symptomatic but have a valve area >1.0 cm2 probably have symptoms based on another extravalvular problem. Patients with a valve area of <0.8 cm2 who have typical symptoms almost certainly have them on the basis of aortic valve stenosis, and surgery is indicated. Patients with areas ranging from 0.8 to 1.0 cm2 are in the gray zone in which a variety of clinical factors must be taken into account. In such patients, additional hemodynamic data obtained during cardiac catheterization are likely to be helpful in establishing a course of action.
The opinions expressed in this editorial are not necessarily those of the editors or of the American Heart Association.
- Copyright © 1997 by American Heart Association
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