Aortic stenosis (SA)
What is aortic stenosis?
With the term aortic stenosis it indicates a narrowing of the aortic valve orifice which represents a bridge between the left ventricle and the aorta, the arterial trunk that carries blood throughout the body.
Aortic stenosis (AS) is the most common valve disease in the senile generation leading to surgery or catheterization in Europe and North America.
With the increase of the average age this pathology has seen a progressive increase over the years.
Anatomy of the aortic valve
The heart has 4 valves necessary to regulate the passage of blood between the two heart chambers (atria and ventricles) and between the heart and the body during each cardiac cycle. So two valves are predisposed to the passage of blood between atria and ventricles and are the tricuspid valve and the mitral valve, while two other valves allow the blood to reach either into the pulmonary circulation or into the rest of the body, respectively: pulmonary valve and aortic valve, called semilunar valves.
In particular the aortic valve is formed between 3 semilunar cusps (right coronary, left coronary and posterior or non-coronary) which prevent reflux of blood into the left ventricle at the end of a cardiac cycle. These cusps at their closure form three hemispherical swellings with concavity facing upwards called breasts of Valsalva, from which the coronary arteries originate, the main arterial branches of the heart and whose occlusion represents one of the causes of myocardial infarction.
Causes of aortic stenosis and predisposing factors
Main causes of aortic stenosis
- Degenerative, valvular calcification: calcium deposition on the aortic side of the valve cusps is common after 65 years of age. High blood pressure can be a predisposing factor.
Aortic sclerosis represents the initial stage of valve calcification
- Congenital, the valve may be monocuspid or bicuspid, the most common cause in young adults.
Subvalvular stenosis (ventricular obstruction due to the presence of labrum or membrane) or supravalvular (uniformly narrow aortic vessel, which represents an obstacle to the passage of blood) stenosis are also of congenital origin.
- Rheumatic fever, less common than in the past, is an acute inflammatory disease caused by a bacterium (Streptococcus type A).
In particular, it affects the commissures, the lines of approach of the valve flaps, thus preventing their correct closure
Epidemiology of aortic stenosis
There aortic stenosis it is a very common pathology in old age, epidemiological studies report a prevalence of 2-7% in patients over 65 years. On the other hand, bicuspidia of the aortic valve represents the most frequent heart disease in the young adult population.
Diagnosis and classification of the types of aortic stenosis
The key examination for the diagnosis of aortic stenosis is the echocardiogram (2D, 3D, Doppler), which using ultrasound energy can confirm the presence of stenosis by assessing the degree of calcification of the valve, any repercussions on the ventricular wall left, the presence of other concomitant valve pathologies. Doppler echocardiography is the best technique for defining the severity of stenosis by evaluating changes in flow through the valve.
Based on specific echocardiographic parameters such as AVA (Aortic valve area, normal value between 3-4 cm ^ 2), the flow velocity through the valve (vn 1-2.5 m / s) and MPG (mean gradient, vn <5 mmHg ) the SA can be divided into:
- Mild: when the valve area is greater than 1.5 cm², the velocity is less than 3 m / s and the average gradient is less than 25 mmHg;
- Moderate: when the valve area is between 1 and 1.5 cm², the speed is between 3 and 4 m / s and the average gradient between 25 and 40 mmHg;
- Strict: when the valve area is less than or equal to 1 cm², the velocity greater than 4 m / s and the mean gradient greater than 40 mmHg.
Other first-line diagnostic tests that allow you to complete the picture are:
- L'electrocardiogram with signs of left ventricular hypertrophy.
- laboratory measurement of natriuretic peptides such as BNP, NTproBNP whose increase predicts the appearance of symptoms and adverse events (in an advanced phase);
- chest x-ray which can show the presence of calcifications or in case of decompensation a dilated left ventricle.
The exams of second line to be performed in case of inconclusive echocardiography are:
- Cardiac MRI (cardiac magnetic resonance or cardio-MRI),
- Cardiac catheterization (cardiac catheterization) insertion through arm or leg of a catheter which under X-ray guide is brought up to the heart.
Symptoms of aortic stenosis
The main symptoms of aortic stenosis are due to a discrepancy that arises under stress between the heart's need for oxygen and the actual availability of blood flow, obstructed by the stenotic valve.
The most important symptoms of stenosis of the aortic valve they can be summarized with the acronym SAD ("sad" in English):
- S.incope, transient loss of consciousness, from reduced blood flow to the brain. It usually appears after exertion. A feeling of lightheadedness may be felt prior to syncope.
- TOngina, stab-like chest pain due to a discrepancy when stressed between the heart muscle's oxygen requirement and available coronary flow. In the absence of medical treatment, the poor prognosis is 5 years.
- D.wheezing, difficulty breathing from left ventricular decompensation. In the absence of medical therapy, the poor prognosis is 2 years.
The clinical examination performed by the doctor shows:
- Pulsus parvus et tardus, a weak pulse (therefore the heartbeat transmitted through arterial vessels, eg the one heard on the carotids) that is slower and with reduced intensity compared to normal and delayed with respect to the closing of the valve.
- Harsh proto-mesosystolic murmur in crescendo and decrescendo (Gallavardin murmur) on the aortic focus (II right intercostal space on the parasternal) with irradiation to the neck and carotids, due to a turbulent flow of blood that is abruptly expelled through a valve that does not open correctly.
- Splitting of the second tone in severe aortic stenosis.
Complications of aortic stenosis
- Systemic embolisms (calcium microembolias),
- Endocarditis: infectious process affecting the valve,
- Sudden death (in 3-7% of cases as the first manifestation of the disease since the subject becomes symptomatic only in an advanced stage),
- the left branch block,
- dissection of the aorta (in association with bicuspidia which also affects the ascending aorta)
Treatment of aortic stenosis
There is still no optimal medical therapy that has been shown to improve patient prognosis.
The onset of symptoms that usually occurs when the disease is already in an advanced state is an indication to perform the surgery; therefore, drug therapy with Ace inhibitors or diuretics (standard heart failure therapy) should only be seen as a bridge to surgery for patients who are not yet eligible for surgery. Coexisting hypertension should also be treated.
It is important to avoid arrhythmias by maintaining a sinus rhythm, through the use of beta blockers or calcium antagonists.
In accordance with the latest guidelines of the ESC 2017 (European Society of Cardiology) in severe aortic stenosis, if patients are asymptomatic, the Ejection Fraction of the left ventricle is evaluated (Eco parameter to understand cardiac function, vn 60 %): if not is below 50%, the patient is not physically active and there are no correlated risk factors reevaluate at 6 months or upon the onset of symptoms; if there were any risk factors then there is an indication to SAVR (Surgical Aortic Valve Replacement). If, on the other hand, the patient is physically active and is subjected to an exercise test, if during the latter the patient is not symptomatic, there is no marked pressure drop and has no particular risk factors, then an indication is made for follow-up. up to 6 months or at the onset of symptoms. In the event that it is symptomatic to the stress test then the SAVR is indicated.
If the left ventricular ejection fraction is reduced below 50%, SAVR is performed.
Patients who are symptomatic due to the high risk of sudden death, on the other hand, are all indicated for surgery and can undergo either SAVR or TAVI.
There SAVR is a more invasive surgical technique, under general anesthesia, open heart, with extracorporeal circulation, which involves a median sternotomy and the replacement of its valve with a biological one if the patient is older than 65 years, mechanical (which will require the life-long anticoagulant therapy) in younger patients.
An alternative to the SAVR is represented by the TAVI , i.e. a transcatheter aortic valve replacement, a minimally invasive surgery technique performed under local anesthesia, thanks to which the new aortic valve can be implanted through a catheter percutaneously or transapically.
The decision whether to use one technique rather than another rests with the heart surgery and cardiology team.