Aortic Stenosis Flashcards
Summarise aortic stenosis
Obstruction of blood flow across the aortic valve due to aortic calcification.
Presentation includes shortness of breath with exertion, angina, or syncope.
Characteristic murmur is systolic, mid-to-late peaking with a crescendo-decrescendo pattern, and radiates to the carotids.
Doppler echo is essential to the diagnosis and will show a pressure gradient across the stenotic aortic valve.
Surgical aortic valve replacement was the only effective therapy for aortic stenosis for over 50 years. However, with the advent of transcatheter valve therapies, patients and physicians have more options.
Following valve replacement, patients are subject to the complications of prosthetic valves.
Define aortic stenosis
Aortic stenosis (AS) represents obstruction of blood flow across the aortic valve due to pathological narrowing. It is a progressive disease that presents after a long subclinical period with symptoms of decreased exercise capacity, exertional chest pain (angina), syncope, and heart failure.
Describe the epidemiology of aortic stenosis
AS is the most common valvular disease in the US and Europe and is the second most frequent cause for cardiac surgery. It is largely a disease of older people, and patients typically present in the seventh or eighth decade of life. Although the prevalence of AS is only 0.2% in adults aged 50 to 59 years, estimates increase to 1.3% in patients aged 60 to 69 years, and up to 9.8% in patients aged 80 to 89 years.[1] Overall, AS is present in 2.6% of adults older than 75 years of age.[2] It is preceded by aortic sclerosis (defined as aortic valve thickening without flow limitation), often suspected by the presence of an early-peaking, systolic ejection murmur, and confirmed by echocardiography. Nearly 25% of people ≥65 years have aortic sclerosis, and nearly 17% of people with aortic sclerosis will progress to AS in their lifetime.[3] The average time from diagnosis of aortic sclerosis to the development of moderate and severe AS is 6 and 8 years, respectively
Which patients are at a particular risk of developing aortic stenosis at an earlier age
Patients with bicuspid valves and AS present two decades earlier on average than patients with trileaflet valves.[4] Congenital bicuspid aortic valves affect 0.9% to 1.36% of the general population with a 2:1 male:female predominance.[5] Overall, about half of all aortic valve replacements are performed for congenitally malformed valves. A study of a large series of patients undergoing aortic valve replacement for AS found that in patients <50 years old, one third had unicuspid valves, and two-thirds had bicuspid valves. Among patients aged 50 to 70 years, two-thirds had bicuspid valves and one third had trileaflet valves. For patients >70 years old, 60% had trileaflet valves, and 40% had bicuspid valves
Describe the aetiology of aortic stenosis
Calcification of normal trileaflet valves is the most common cause of AS in adults and accounts for as many as 80% of cases in the US and Europe.[7] Calcific aortic disease represents a spectrum ranging from aortic sclerosis (defined as leaflet thickening without obstruction) to severe AS. Several risk factors have been associated with aortic sclerosis including smoking, hypertension, diabetes, low-density lipoprotein (LDL)-cholesterol, and elevated C-reactive protein. Retrospective studies have shown that high LDL-cholesterol levels and smoking are associated with progression to AS, but causality has not been confirmed
Congenitally bicuspid valves account for the majority of the remainder of cases. Patients with coarctation of the aorta and Turner’s syndrome have a higher incidence of bicuspid valves.
Rheumatic heart disease has historically been an important cause of AS, but due to improvements in treatment, it is now uncommon in industrialised countries. Rheumatic heart disease remains prevalent in developing nations.
Other circumstances including connective tissue diseases, radiotherapy, and hyperlipoproteinaemia syndromes can cause AS, but these are unusual consequences of rare conditions.
Chronic kidney disease is associated with abnormal calcium homeostasis, and it has been shown that AS progresses faster in patients with this condition.
Describe the process of aortic calcification
Aortic calcification is no longer thought to reflect age-related wear and tear, and is recognised to be an active process. The valvular endocardium is damaged as the result of abnormal blood flow across the valve. Endocardial injury initiates an inflammatory process similar to atherosclerosis and ultimately leads to deposition of calcium on the valve. Calcification occurs slowly and is subclinical until the disease is fairly advanced. Progressive calcium deposition limits aortic leaflet mobility and eventually produces stenosis.
Unicuspid and bicuspid valves experience abnormal shear and mechanical stresses from birth. Therefore, the pathological processes and resultant stenosis occur earlier than in trileaflet valves.
What causes the calcification in rheumatic disease
In rheumatic disease, an autoimmune inflammatory reaction is triggered by prior Streptococcus infection that targets the valvular endothelium, leading to inflammation and eventually calcification
Describe LV remodelling in response to the aortic stenosis
Long-standing pressure overload leads to the development of left ventricular hypertrophy (LVH). This adaptive response permits the ventricle to maintain a normal wall stress (afterload) despite the pressure overload produced by stenosis. As the stenosis worsens, the adaptive mechanism fails and left ventricular wall stress increases. Systolic function declines as wall stress increases, and eventually the heart fails.
LVH is a contributing factor to many of the symptoms seen in AS. The consequence of concentric LVH is a smaller, less compliant chamber. Thus, left ventricle end-diastolic pressure is increased, especially during periods of increased cardiac output (e.g., exercise), leading to the sensation of dyspnoea. Furthermore, in LVH, myocardial oxygen demand is greater due to increased left ventricular mass, while coronary blood flow may be reduced through a variety of mechanisms. Thus, even patients who lack coronary atherosclerotic disease may develop symptoms of anginal chest pain.
Describe a typical case history of aortic stenosis
A 78-year-old man presents to his primary care physician complaining of 2 months of progressive shortness of breath on exertion. He first recognises having to catch his breath while gardening and is now unable to walk up the stairs in his house without stopping. Previously he was healthy and active without similar complaints. On physical examination there is a loud systolic murmur at the right upper sternal border radiating to the carotid vessels.
Describe some other presentations of aortic stenosis
Other presentations
AS is a progressive disease that presents after a long subclinical period with symptoms of chest pain, syncope, and heart failure. While the most common complaint is dyspnoea with exertion, patients also frequently note syncope or chest pain that may be identical to that caused by coronary artery disease. Many cases of AS are diagnosed during the subclinical phase while a murmur noted on physical examination is being investigated. Even with severe AS, patients may be truly asymptomatic. A careful history is important to determine if the patient has altered his or her habits in response to slowly worsening stenosis.
Summarise the clinical evaluation of aortic stenosis
Many cases of AS are diagnosed during the subclinical phase while a murmur, noted on physical examination, is being investigated. Even patients with severe AS may be truly asymptomatic. A careful history is important to determine if the patient has altered his or her habits in response to slowly worsening stenosis.
Complaints of decreased exercise tolerance, shortness of breath on exertion, exertional chest pain (angina), syncope, or near syncope, and heart failure symptoms should prompt consideration of AS. Patients have an increased risk of bleeding and may complain of epistaxis or bruising. They are also more likely to develop chronic gastrointestinal bleeding that is associated with angiodysplasia. This may be due to turbulent flow across the stenotic valve producing an acquired von Willebrand deficiency.
The physical examination is the most important screening tool for valvular heart disease. A complete cardiac examination including precordial palpation, auscultation with attention to murmurs and the aortic closure sound, and evaluation of arterial and venous pulsation is essential in generating clinical suspicion for AS.
Describe the general grading of murmurs
Murmurs are generally graded on a scale of 1 to 6:
Grade 1: murmur is faint and heard only with effort
Grade 2: murmur is faint but easily detected
Grade 3: murmur is loud
Grade 4: murmur is very loud and associated with a palpable thrill
Grade 5: murmur is so loud that it can be heard with only the edge of the stethoscope
Grade 6: murmur is extremely loud and heard even when the stethoscope is no longer in contact with the patient.
Describe the murmur in aortic stenosis
The typical murmur of AS is a systolic murmur ≥3/6, with a diamond-shaped crescendo-decrescendo pattern that peaks in mid-systole and radiates to the carotid arteries. The murmur is generally loudest at the right upper sternal border and terminates with S2 and the end of systole. As the severity of stenosis worsens, the murmur peaks later in systole and may be accompanied by a palpable thrill. The aortic heart sound (A2) is delayed as the systolic ejection period becomes prolonged. In severe stenosis, paradoxical splitting of the second heart sound may be noted such that in expiration, the pulmonic sound (P2) is heard before A2. The intensity of the second heart sound tends to be diminished as the severity of stenosis increases and leaflet mobility is reduced.
Describe some uncommon murmur characteristics in aortic stenosis
Uncommon findings include the presence of a holosystolic murmur at the apex (Gallavardin’s phenomenon), mimicking the murmur of mitral regurgitation.
A delayed and diminished carotid upstroke (carotid parvus et tardus) may occur with severe AS, although this finding is often difficult to distinguish in older patients. In these circumstances, palpation of the brachial artery may reveal this finding.
Describe the ECG in aortic stenosis
An ECG is indicated in the initial work-up of all patients and is abnormal in >90% of patients with AS, with the most common abnormality being left ventricular hypertrophy (LVH) due to pressure overload.[19] Evidence of LVH and absent Q waves helps distinguish AS from other conditions such as aortic sclerosis with ischaemic heart disease. Patients with AS often have conduction disease manifesting as atrioventricular (AV) block, hemiblock, or bundle branch block.
Describe the use of echocardiography
Echocardiography is the test of choice in the evaluation of suspected AS and for the evaluation of murmurs detected on physical examination. The American College of Cardiology/American Heart Association (ACC/AHA) recommends transthoracic echocardiography (TTE) when there is an unexplained systolic murmur, a single second heart sound, a history of a bicuspid aortic valve, or symptoms that might be due to AS.[20]
Although murmur intensity does not correlate well with the haemodynamic significance of the associated lesion, grade 3 murmurs are generally thought to reflect more significant lesions and thus warrant further evaluation with TTE. In practice, most patients with suspected cardiac disease and a murmur on examination should have an echocardiogram.
Describe Doppler transthoracicechocardiogram
Doppler TTE can reliably and accurately detect the presence of a pressure gradient across the aortic valve. It can also assess left ventricle function and the presence of hypertrophy. It is essential for the diagnosis of AS and for serial evaluation once the diagnosis has been established. Measurements taken during echo examination are used to grade the severity of AS
Describe trans oesophageal echocardiography
Transoesophageal echocardiography (TEE) provides alternative detailed views of the aortic valve apparatus, and is frequently used in patients undergoing valve surgery or transcatheter aortic valve replacement (TAVR). However, the test is invasive and is not recommended in the routine evaluation of AS given the efficacy and safety of Doppler TTE.
