Cardiovascular disorders

II./4.2.: Aortic stenosis (AS)

II./4.2.1.: Etiology

Aortic stenosis has three forms, i.e. valvular (obstruction developing at the level of the valve), supravalvular and subvalvular forms. Its supravalvular form is caused most frequently by a rigid fibromuscular plate, and the cause of subvalvular form may consist of a similar “fixed” subaortic membrane or a hypertrophic septum in hypertrophic cardiomyopathy causing a dynamical obstruction (Drawing 2). Valvular stenoses are much more frequent (Drawing 3).

Drawing 2: Longitudinal axis imaging of the aortic valve. A supravalvular stenosis is located above the plane of the valvular cusps, in the ascending aorta. A subvalvular stenosis is below the plane of the valve in the outflow tract of the left ventricle.

Drawing 3: Semilunar valve: normal, membranous, tricuspid aortic valve at closed and open valve position. (1) Valva semilunaris ( zart ); (2) Valva semilunaris ( nyitott ); (3) Lunula; (4) Nodulus; (5) Arteria coronaria sinistra; (6) Arteria coronaria dextra

Among 40- to 60-year-old patients an isolated AS is usually due to a bicuspid aortic valve that is the commonest heart defect in adult age because of the fusion of two cusps in the fetal life and then fibrotic degeneration and sclerosis of the cusps in adult age. In patients over 60 years atherosclerotic and senile calcification of the valve is to be considered primarily. Valvulitis due to rheumatic fever may cause commissural fusion and consequent stenosis; usually associated with an insufficiency and a mitral defect as well.

II./4.2.2.: Pathophysiology, symptomatology

Valvular stenosis is termed severe when the area of its opening decreases below 0.75 cm². The left ventricle can assure blood flow through the narrowing only by increasing the intraventricular systolic pressure; measurement of the pressure gradient that developed through the valve is a base of diagnostics (a mean gradient exceeding 50 mmHg is significant). Initially the ventricular myocardium undergoes a compensating hypertrophy, and then as it weakens, dilatation of the ventricle also develops. The significant tension of the wall and the intraventricular pressure may cause ischemia of the subendocardial myocardium and lead to the appearance of typical angina pectoris. At the beginning dyspnea is triggered only by exertion, however later orthopnea and paroxysmal nocturnal dyspnea may also occur. As increasing the cardiac output through the narrowing is hindered, as a typical symptom, syncope may occur upon an effort.

II./4.2.3.: Course

The disease may be asymptomatic for long; the time of the symptoms’ appearance is unpredictable. As symptoms occur, the patient’s life expectancy rapidly deteriorates without a surgical solution; the average survival is estimated to be between 1 and 5 years, and the patient’s death is caused by a sudden cardiac death due to a malignant arrhythmia, or by a progressive heart failure. Statistically a decrease of the valvular area by 0.1 cm² per year is to be counted with; therefore also the non-significant symptomatic patients should be followed up and kept under care.

II./4.2.4.: Diagnostics

If clinical suspicion emerges, already the physical examination and the findings of auscultation may help the orientation. An accentuated apical impulse, a palpable systolic vibration on the thoracic wall, a low-pressure, slowly elevating pulsation, as well as a coarse, scraping ejection type systolic murmur that starts with the ejection sound in the aortic area and is conveyed towards the cervical vessels are characteristic in patients with AS. In patients with senile calcification no ejection sound is heard, and as the disease becomes more severe, the second cardiac sound is more and more fading. The murmur of dynamic subaortic stenosis increases towards the end of the systole, and it fades upon a reduction of left ventricular preload (e.g. by Valsalva maneuver). The ECG characteristically shows signs of left ventricular hypertrophy and left ventricular strain as the muscular mass of the left ventricle increases. Left anterior hemiblock is common, and the calcification of the aortic anulus leads to the development of left bundle branch block or Grade 3 AV block.

On a thoracic X-ray picture our attention may be called to this heart defect by an “aortic configuration” that can be observed due to the left ventricular hypertrophy; a calcification seen in the projection of the valve, and the post-stenotic dilation of the ascending aorta. Currently a measurement of valvular gradient and calculation of an area by an invasive way, with cardiac catheterization is already rare because of the exact, well reproducible parameters provided by echocardiography. Difficulties of differential diagnosis rarely occur in patients with aortic stenosis; however the assessment of the defect’s severity may present a challenge, particularly in patients with concomitant valvular and subvalvular obstruction, or in relation to an abnormally decreasing pump function. In patients with a left ventricular dysfunction the elevation of the gradient is of lesser extent, and the inaccuracies of calculating the valvular area make the assessment even more difficult; therefore a pharmacologic (dobutamine) stress echocardiography may be required.

II./4.2.5.: Therapy

Patients with asymptomatic significant aortic stenosis should be followed up in every six months. There is no known specific medicinal therapy; the use of a beta blocker may be beneficial due to a reduction of the heart rate and increasing the duration of systole. If the maximal flow velocity over the valve exceeds 4 m/sec, most of the patients become asymptomatic within 2 years. Progressive calcification and a decreasing area suggest a poor prognosis. In symptomatic patients or in those with a deteriorating left ventricular function, surgical replacement of the valve is indicated. In elderly patients biologic artificial valves are implanted, which have a shorter lifetime, but require no long-term oral anticoagulation therapy. If the patient’s life expectancy exceeds 15 years, usually a mechanical metal artificial valve is chosen by the surgeon. In modern types two plates (occluders) ensure the unidirectional blood flow; and due to the thrombogenic propriety of these metal components, continuous anticoagulation is required.

The perioperative risk is very much increased by the elderly age, impaired pulmonary, hepatic and renal functions, as well as the left ventricular dysfunction. In these patients transcatheter aortic valve implantation (TAVI) may be beneficial. After a balloon predilation of the stenotic valve a biologic artificial valve applied on a self-expanding metal grid is positioned in the aortic anulus through a transarterial or transapical way; this presses the degenerated, calcified native cusps to the wall of the aortic radix. The intervention is not without dangers, but as its technique is developed further and its long-term effectiveness is fully demonstrated, the range of its indication will broaden continuously.