Aortic valve stenosis
Patients with (predominant) aortic stenosis fall into one of four categories of severity:
- valve area > 1.2 cm2??????????.mild
- valve area 1.0 to 1.2 cm2????????.moderate
- valve area 0.7 to 1.0 cm2????????.severe
- valve area < 0.7 cm2??????????.critical
Asymptomatic patients with mild to moderate aortic stenosis should have medical follow-up with regular inquiry as to changes in exercise tolerance or other symptoms. Serial echocardiographic examination should be based on an understanding of the natural history of the lesion, as outlined below. Patients should avoid strenuous activity, and particularly avoid post-prandial exertion. Infective endocarditis precautions following American Heart Association guidelines must be emphasized at each visit.
Hypertension occurs in about 20% to 30% of patients with mild to moderate aortic stenosis and should be managed with angiotensin-converting enzyme inhibitors or angiotensin receptor blockers titrated slowly. Selected patients may be given modest doses of concomitant beta-blockers.
A supervised exercise tolerance test may provide helpful objective assessment in patients with echocardiographic evidence of moderate aortic stenosis who report atypical symptoms, who minimize complaints, or who are sedentary and therefore might not experience exercise intolerance. Functional limitation with inability to exercise to levels greater than 6 metabolic equivalents (METs) may, in some cases, be viewed as a "symptom." Stress testing is not advocated for patients with very severe left ventricular outflow obstruction.
2. Valve replacement
Symptomatic patients, ie, those with angina, syncope, dyspnea, with moderate, severe, or critical aortic stenosis should undergo valve replacement. Indications for aortic valve surgery include moderate aortic stenosis in patients requiring coronary bypass grafting and/or any other cardiac surgery, exercise-induced hypotension, and asymptomatic severe aortic stenosis with evidence of left ventricular dysfunction. Smoking cessation and diabetic control are mandatory after the replacement. Dental care should be completed with antibiotic prophylaxis before surgery.
The advantages and drawbacks of mechanical versus bioprosthetic valves should be discussed with the patient and his or her family. Often the choice of prosthesis is straightforward, but younger patients in particular may have special needs, which should be addressed Bioprosthetic valves offer the advantage of not requiring long-term oral anticoagulation, but have the drawback of relatively limited durability. In contrast, mechanical valves offer long-term durability, but require lifelong warfarin therapy. The generally accepted risk of serious bleeding with warfarin is on the order of 3% per year. Childbearing in women and vigorous sports activities in men are contra-indications to chronic oral anticoagulation with warfarin, and may figure importantly in the choice of valves. In general, bioprosthetic valves are preferred in patients over the age of 60 years and mechanical valves under the age of 50. Homograft aortic valve replacement with a cryopreserved cadaveric valve may offer specific advantages in patients with infective endocarditis or with disease of the aortic root. If significant narrowing of the coronary arteries is found, coronary artery bypass graft surgery (CABG) can be performed during aortic valve replacement surgery.
3. Balloon valvuloplasty
Balloon valvuloplasty is a technique that lowers the pressure across the valve by slightly enlarging the opening. This is usually done when someone is not stable enough for corrective surgery.
Current evidence indicates that calcific aortic stenosis progresses, on the average, at a rate of about 0.1 cm2 per year decline in valve area. To date, no medical therapy exists for the treatment of degenerative aortic stenosis. The possible impact of 'secondary prevention' measures, particularly lipid lowering with HMG-CoA reductase inhibitors (statins), on the progression of aortic stenosis is under investigation.
Successful replacement of the valve restores normal blood flow. The long-term outcome is usually very good. Artificial valves wear out over a period of years. Their function is monitored, and the valves are replaced as necessary. A prosthetic heart valve commits a patient to continued infective endocarditis prophylaxis, regular cardiac follow-up, and often to continued medical therapy, including anticoagulation with warfarin for those with mechanical prostheses. Re-operation may be required for malfunction of the prosthetic valve. In addition, a small but not insignificant subset of patients may require implantation of a permanent pacemaker after valve surgery.
Prognosis and survival
Serious long-term effects of aortic stenosis without timely treatment include:
- congestive heart failure
- coronary heart disease
- enlargement of the left ventricle
- pulmonary edema
- sudden death (occurs in less than 1%)
With surgery, the patient can expect to live a normal life with necessary precautions as explained above.
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