Left Ventricular outflow tract obstruction can occur due to various aortic valvular, subvalvular and supra valvular lesions (Table ).
Rheumatic aortic stenosis is often seen in young and middle aged individuals and is almost always associated with rheumatic involvement of mitral valve; Fibrocalcific degenerative changes of aortic valve is another important cause of aortic stenosis often seen in the elderly. Such changes occur more rapidly if the underlying valve is bicuspid or if atherosclerotic risk factors are present. Hypercholesterolemia typically hastens the degenerative changes of aortic valve and homozygous patients may present with aortic stenosis in younger age. Similarly hypertension,smoking and male sex also predispose to aortic valve degeneration leading to aortic stenosis.
Pathology
Rheumatic aortic stenosis is often seen in young and middle aged individuals and is almost always associated with rheumatic involvement of mitral valve; Fibrocalcific degenerative changes of aortic valve is another important cause of aortic stenosis often seen in the elderly. Such changes occur more rapidly if the underlying valve is bicuspid or if atherosclerotic risk factors are present. Hypercholesterolemia typically hastens the degenerative changes of aortic valve and homozygous patients may present with aortic stenosis in younger age. Similarly hypertension,smoking and male sex also predispose to aortic valve degeneration leading to aortic stenosis.
Pathology
Congenital abnormalities of aortic valve may lead to unicuspid aortic valve. This may be dome shaped with central stenotic orifice. Unicuspid appearance may also be due to fusion of two commissures with an eccentric opening. Usually these patients become symptomatic in childhood or by early adulthood.Congenital bicuspid aortic valve is one of the common congenital cardiac abnormalities (about 2 per cent) and it has higher prevalence in males. There seems to be certain genetic transmission and it may be associated with other left sided obstructive lesions like coarctation of aorta seen in about 10 per cent of patients. In some patients this may be part of generalized connective tissue disorder associated with cystic medial necrosis and focal apoptosis in aortic media leading to aortic root dilatation. Ascending aortic dissection occurs nine times more frequently in patients with bicuspid aortic valve compared to those with tricuspid valve. Due to altered flow pattern across bicuspid aortic valve, turbulence is generated leading to abnormal hemodynamic stress on the cusps. This results in micro thrombi formation, fibrosis and calcification resulting in aortic stenosis in majority of patients.
Rheumatic aortic valve stenosis is characterized by fusion of one or more commissures with variable cusp fibrosis and calcification. Mitral valve involvement is almost always present.Commissural fusion and edge calcification distinguish rheumatic etiology from degenerative etiology.
Degenerative aortic valve disease that is seen increasingly in elderly shares common pathogenesis with atherosclerosis. Primarily there is lipid accumulation, migration of inflammatory cells and dystrophic calcification in valve cusps. Same atherosclerotic risk factors like age, male sex,diabetes, hypertension and smoking and hyperlipidemia hasten valve degeneration and calcification. Early stages of fibrosis and mild calcification not leading to a significant hemodynamic abnormality are called aortic sclerosis. Extensive distortion due to fibrosis and calcification results in significant hemodynamic abnormality that results in aortic stenosis. While atherosclerosis vascular disease and valvular aortic stenosis seem to have similar etiopathogenesis — it should be noted that majority of patients with extensive coronary artery disease have normal aortic valves and only 50 per cent of patients with degenerative aortic valve disease have significant associated coronary artery disease.
Certain metabolic conditions like hyper cholesterolemia, Fabry’s disease and alkaptaneuria lead to valvular stenosis due to metabolite deposition. SLE with associated anticardiolipin antibodies and radiation may also lead to aortic valve stenosis.
Pathophysiology
Patient is often asymptomatic till the orifice size decreases from normal 3 – 4 cm2 to 1.5 cm2.Usually valve area < 1.0 cm2 is considered severe, 1 – 1.5 cm2 moderate and >1.5 cm2 is considered mild aortic stenosis. As the area decreases left ventricle to aorta gradient increases.With a severe AS, in the presence of normal cardiac output, mean gradient across aortic valve increases to more than 50 mm Hg. To generate more intracavitary pressure left ventricle undergoes concentric type hypertrophy, i.e., chamber size remains same or decreased but wall thickness increases. As per Laplace law increased wall thickness in the presence of normal or decreased cavity size maintains wall stress. As the severity of LVOT obstruction increases, afterload mismatch sets in, i.e., wall stress cannot keep pace with increasing left ventricular pressure. Left ventricular end systolic volume increases and left ventricular failure occurs. In addition to afterload mismatch some patients have decreased contractile function due to patchy fibrosis due to chronic myocardial ischaemia. While failure due to afterload mismatch responds well to relief of obstruction, failure due to decreased contractile function may not.The degree of left ventricular hypertrophy varies between individuals. Elderly women tend to have small reduced left ventricular chambers with very thick left ventricular wall.While left ventricular systolic function is maintained till late in the natural history of disease diastolic dysfunction sets in early. Patients have elevated left ventricular end diastolic pressure due to altered chamber compliance and this leads to prominent atrial contraction (atrial kick).Loss of atrial boost to diastolic filling due to any cause like in atrial fibrillation or complete heart block may suddenly precipitate heart failure.
Compensatory hypertrophy increases the capillary myocardial distance. Left ventricular hypertrophy that would squeeze coronary arteries during prolonged systole and elevated left ventricular diastolic pressure – both lead to demand supply mismatch and ischaemia. Prolonged and repeated ischaemic episodes cause angina, arrhythmias and myocardial necrosis with fibrosis and there by loss of systolic function.
Natural History
There is a prolonged latent period of few decades followed by rapid deterioration. Average survival is 2 – 3 years after the onset of symptom of angina, syncope and heart failure. The rate of progression of stenosis is variable but is consistent for an individual. On an average, in a patient with degenerative aortic valve stenosis valve area decreases by 0.12 cm2 per year. Rise in trans valvular gradient varies between 10 – 15 mmHg. and in some patients it may increase in the range of 15 – 20 mm Hg. Rate of progression in an individual patient may not be accurate and close clinical follow-up is indicated. Sudden death rarely occurs in asymptomatic patients at an estimated frequency of 0.4 per cent per annum.
Clinical Features
Patients with congenital aortic stenosis usually present in childhood or adolescence. Those with rheumatic heart disease present during 30–50 years and with bicuspid valve between 40–60 years.Degenerative aortic valve disease patients present late in elderly age group. There is no direct correlationship with severity of disease and presence or absence of symptoms. However, those with mean transaortic gradient of more than 60 mmHg are often symptomatic. Symptoms include dizziness or syncope, angina and those of heart failure. Dizziness or syncope may be due to arrhythmias or LV dysfunction but more often due to inappropriate baroreceptor function that results in vasodilatation in the presence of fixed cardiac output.
Angina is noted in approximately 50–60 per cent of patients and in about 50 per cent of these patients it is due to associated CAD. Onset of heart failure symptoms usually portends poor prognosis. The life span is usually considered to be 5, 3 and 2 years after the onset of symptoms of angina, heart failure and syncope respectively.While infective endocarditis may affect non calcified valves, it is uncommon to affect calcific valves. However, micro emboli from calcific valves may occur. Lower G.I. bleeding due to angiodysplasia of ascending colon is a known association of severe valvular aortic stenosis.
Physical Signs
Typically the carotid pulse in severe aortic stenosis is delayed (pulsus tardus). It is also decreased in amplitude (pulses parvus) when cardiac decompensation occurs. This pulse is fairly specific for severe aortic stenosis. However, patients with low cardiac output and mild stenosis will have a low volume pulse that is normal in timing.
In patients with atherosclerotic vessels carotid upstroke may be brisk even in severe aortic stenosis. A detectable time gap between the apical pulse and carotid pulse suggests prolonged ejection time of severe aortic stenosis. Wide pulse pressure in the presence of other findings of severe aortic stenosis suggests associated aortic regurgitation. Also wide pulse pressure with normal diastolic pressure is fairly common in elderly patients with concomitant hypertensive vascular disease.
Typically apical impulse is forcible and sustained and with decompensation of left ventricle it is displaced. A palpable S 4 is common in severe aortic stenosis. Absence of a valvular ejectionclick in children should make one suspect the diagnosis of non valvular aortic stenosis. Usually S 2 is single due to muffled A 2 . If the valve is pliable with less extent of calcification, it may
produce paradoxical split in a patient with severe valvular aortic stenosis.
Typically the murmur of valvular aortic stenosis starts after S 1 , is crescendo decrescendo ejection systolic murmur with maximum intensity at second right inter costal space and radiates to carotids. A grade I murmur in the absence of decompensation suggests mild lesion while the same in a patient with severe decompensation should not make one eliminate aortic stenosis as a cause of decompensation.
A grade IV murmur almost always suggests severe aortic stenosis. In children and elderly selective conduction of high frequency sounds to apical area may give risk to cooing murmur at apex (Gallavardin phenomenon). However, the intensity of murmur may vary with cardiac output, chest valve thickness, emphysema and direction of turbulent jet. A late peaking loud grade IV murmur is very specific to severe aortic stenosis.
Electrocardiogram
Typically left ventricular hypertrophy with strain pattern is seen in severe aortic stenosis. Total QRS amplitude in mm. tends to correlate and equals trans aortic gradient in pure aortic stenosis.A normal ECG though suggestive of mild aortic stenosis does not totally eliminate severe aortic stenosis. Left atrial enlargement, left axis deviation and various kinds of conduction abnormalities including left bundle branch block, 1° heart block or even complete heart block may occur.Though atrial fibrillation may occur in an advanced aortic stenosis with decompensation–one should eliminate concomitant mitral valve disease.
Roentgenogram
Cardiac enlargement does not occur in pure compensated aortic stenosis. Post stenotic dilatation of aorta may be seen. Fluoroscopy may reveal calcified aortic valve and often concomitant mitral annular calcium. Decompensated aortic stenosis may present with signs of left ventricular dilatation and pulmonary venous hypertension. Gross left atrial dilatation on roentgenogram should suggest associated mitral valve disease. Absence of ascending aortic dilatation gives a clue that valve may not be the site of stenosis.
Echo Cardiography
2D and M-mode Echo cardiography visualize thickened, often calcific aortic cusps with doming motion. In M-mode Echo cardiography relative sizes of aorta, left atrium, left ventricular dimensions and extent of left ventricular hypertrophy and function can be measured. 2D Echo cardiogram shows the number of cusps. But presence of raphae and distorted anatomy due to calcification may make if difficult to assess. Localization of stenosis to sub-valvular or supravalvular or valvular location can easily be done. Ascending aorta may be disproportionately dilated in some patients with bicuspid aortic valve with a tendency for aortic dissection.
Hemodynamic severity of aortic stenosis can be measured by Doppler echocardiography. Peak and mean trans valvular aortic gradients, aortic valve area and ratio of LVOT and aortic valve time velocity integral (VTI) are important measurements. Meticulous search using all transducer positions should be made to obtain maximal aortic velocity. In patients with normal LV function and cardiac output, aortic stenosis is considered severe when peak aortic velocity is more than or equal to 4.5 m/sec; mean pressure gradient equal to or more than 50 mmHg, aortic valve area less than or equal to 0.75 cm 2 or LVOT/Aortic valve VTI ratio less than or equal to 0.25. It should be noted that in-patients with left ventricular dysfunction and/or low cardiac output, transvalvular pressure gradients will be under estimated while in situations with increased flow across aortic valve like aortic regurgitation and/or anemia transvalvular gradient will be over estimated. Since in both these situation LVOT and Aortic valve VTI move in the same direction and value area as measured by continuity equation makes use of ratio of these two, valve area measurements tends to be more accurate. Also valve resistance which takes into account valve area and flow across the valve is a more reliable index. Further while following a patient serially with echocardiography combined use of transvalvular gradients, left ventricular function and valve area calculation are more useful. Otto and his colleagues have shown that in asymptomatic patients, peak aortic jet velocities increase by 0.32 ± 0.34 m/sec per year, mean gradient by 7± 7mmHg and valve area decrease by 0.12 ± 0.19 cm per year. Beyond a peak velocity of 4.0 m/sec most of the patients become symptomatic within 2 years. Aortic valve area is d” 0.75 cm 2 when peak aortic velocity is > 4.5 m/sec and mean gradient is e” 50 mm Hg. However, half of patients with aortic valve area d” 0.75 cm 2 have lower peak velocities and mean gradients due to lower cardiac output.
Ratio of LVOT/Aortic valve VTI is another good index in measuring aortic valve area. A ratio of LVOT/AV VTI is < 0.25 correlates well with a aortic valve area of < 0.75 m 2 .In a patient with low out put and low aortic valve gradients dobutamine echo (upto dose of 20 mcg/KG/mt) is useful in differentiating between true aortic stenosis and pseudo or functional aortic stenosis. With dobutamine infusion, in a patient with true aortic stenosis, LVOT velocity and aortic velocity increase proportionately but the ratio between both remains same or less than 0.25. Conversely in a patient with functional or pseudo aortic stenosis with severe left ventricular dysfunction–aortic velocity does not increase in proportion to LVOT velocity because aortic valve area increases with increased stroke value. This results in higher LVOT to aortic valve VTI ratio. It becomes more than 0.25 ruling out any significant aortic stenosis.During echocardiography we should be careful in measuring trans aortic flow than mitral or tricuspid regurgitation jets. Aortic annulus measurement is important for the surgeon to plan aortic valve replacement.
Trans esophageal echocardiography (TEE) is an important complement to transthoracic window.It helps in assessing the severity of mitral regurgitation and pathology of mitral valve if any.Number of cusps can be confidently measured. Planimetry measurement of aortic valve area can also be done in TEE short axis view. Pre-operative TEE is helpful in assessing associated mitral
regurgitation.A well done echocardiographic assessment precludes the need for invasive hemodynamic measurement.
Exercise Testing
Exercise testing is relatively contraindicated in patients with aortic stenosis. Its diagnostic accuracy to pick up additional coronary artery disease is limited in view of baseline ECG changes and left ventricular hypertrophy. Exercise testing should not be performed in symptomatic patients. It is safe to do in asymptomatic patients provided it is supervised by an experienced physician and ECG and blood pressure are closely monitored. While prognostic information of exercise induced ECG changes is uncertain—it can provide data about patient’s exercise capacity and exercise induced hypotension. Limited exercise tolerance and/or exercise induced hypotension is an indication for aortic valve replacement in a patient with moderate to severe aortic stenosis.
Cardiac Catheterization
The indications are to confirm hemodynamics when the non-invasive tests are not conclusive or there is a discrepancy between clinical evaluation and echocardiographic findings. It is also done pre-operatively to obtain coronary angiography if associated CAD needs to be ruled out. During cardiac catheterization right and left heart pressures and all necessary gradients should be measured in a meticulous manner. Transvalvular gradients, cardiac out put should be measured to calculate aortic valve area. Crossing a calcified degenerated aortic valve should be avoided unless it is clearly indicated. If entering left ventricle is not possible by retrograde approach transeptal puncture may be done to assess left ventricle to aorta gradient. When clinical impression correlates well with non-invasive evaluation–invasive hemodynamic evaluation with all its complications can be avoided.
Rheumatic aortic valve stenosis is characterized by fusion of one or more commissures with variable cusp fibrosis and calcification. Mitral valve involvement is almost always present.Commissural fusion and edge calcification distinguish rheumatic etiology from degenerative etiology.
Degenerative aortic valve disease that is seen increasingly in elderly shares common pathogenesis with atherosclerosis. Primarily there is lipid accumulation, migration of inflammatory cells and dystrophic calcification in valve cusps. Same atherosclerotic risk factors like age, male sex,diabetes, hypertension and smoking and hyperlipidemia hasten valve degeneration and calcification. Early stages of fibrosis and mild calcification not leading to a significant hemodynamic abnormality are called aortic sclerosis. Extensive distortion due to fibrosis and calcification results in significant hemodynamic abnormality that results in aortic stenosis. While atherosclerosis vascular disease and valvular aortic stenosis seem to have similar etiopathogenesis — it should be noted that majority of patients with extensive coronary artery disease have normal aortic valves and only 50 per cent of patients with degenerative aortic valve disease have significant associated coronary artery disease.
Certain metabolic conditions like hyper cholesterolemia, Fabry’s disease and alkaptaneuria lead to valvular stenosis due to metabolite deposition. SLE with associated anticardiolipin antibodies and radiation may also lead to aortic valve stenosis.
Pathophysiology
Patient is often asymptomatic till the orifice size decreases from normal 3 – 4 cm2 to 1.5 cm2.Usually valve area < 1.0 cm2 is considered severe, 1 – 1.5 cm2 moderate and >1.5 cm2 is considered mild aortic stenosis. As the area decreases left ventricle to aorta gradient increases.With a severe AS, in the presence of normal cardiac output, mean gradient across aortic valve increases to more than 50 mm Hg. To generate more intracavitary pressure left ventricle undergoes concentric type hypertrophy, i.e., chamber size remains same or decreased but wall thickness increases. As per Laplace law increased wall thickness in the presence of normal or decreased cavity size maintains wall stress. As the severity of LVOT obstruction increases, afterload mismatch sets in, i.e., wall stress cannot keep pace with increasing left ventricular pressure. Left ventricular end systolic volume increases and left ventricular failure occurs. In addition to afterload mismatch some patients have decreased contractile function due to patchy fibrosis due to chronic myocardial ischaemia. While failure due to afterload mismatch responds well to relief of obstruction, failure due to decreased contractile function may not.The degree of left ventricular hypertrophy varies between individuals. Elderly women tend to have small reduced left ventricular chambers with very thick left ventricular wall.While left ventricular systolic function is maintained till late in the natural history of disease diastolic dysfunction sets in early. Patients have elevated left ventricular end diastolic pressure due to altered chamber compliance and this leads to prominent atrial contraction (atrial kick).Loss of atrial boost to diastolic filling due to any cause like in atrial fibrillation or complete heart block may suddenly precipitate heart failure.
Compensatory hypertrophy increases the capillary myocardial distance. Left ventricular hypertrophy that would squeeze coronary arteries during prolonged systole and elevated left ventricular diastolic pressure – both lead to demand supply mismatch and ischaemia. Prolonged and repeated ischaemic episodes cause angina, arrhythmias and myocardial necrosis with fibrosis and there by loss of systolic function.
Natural History
There is a prolonged latent period of few decades followed by rapid deterioration. Average survival is 2 – 3 years after the onset of symptom of angina, syncope and heart failure. The rate of progression of stenosis is variable but is consistent for an individual. On an average, in a patient with degenerative aortic valve stenosis valve area decreases by 0.12 cm2 per year. Rise in trans valvular gradient varies between 10 – 15 mmHg. and in some patients it may increase in the range of 15 – 20 mm Hg. Rate of progression in an individual patient may not be accurate and close clinical follow-up is indicated. Sudden death rarely occurs in asymptomatic patients at an estimated frequency of 0.4 per cent per annum.
Clinical Features
Patients with congenital aortic stenosis usually present in childhood or adolescence. Those with rheumatic heart disease present during 30–50 years and with bicuspid valve between 40–60 years.Degenerative aortic valve disease patients present late in elderly age group. There is no direct correlationship with severity of disease and presence or absence of symptoms. However, those with mean transaortic gradient of more than 60 mmHg are often symptomatic. Symptoms include dizziness or syncope, angina and those of heart failure. Dizziness or syncope may be due to arrhythmias or LV dysfunction but more often due to inappropriate baroreceptor function that results in vasodilatation in the presence of fixed cardiac output.
Angina is noted in approximately 50–60 per cent of patients and in about 50 per cent of these patients it is due to associated CAD. Onset of heart failure symptoms usually portends poor prognosis. The life span is usually considered to be 5, 3 and 2 years after the onset of symptoms of angina, heart failure and syncope respectively.While infective endocarditis may affect non calcified valves, it is uncommon to affect calcific valves. However, micro emboli from calcific valves may occur. Lower G.I. bleeding due to angiodysplasia of ascending colon is a known association of severe valvular aortic stenosis.
Physical Signs
Typically the carotid pulse in severe aortic stenosis is delayed (pulsus tardus). It is also decreased in amplitude (pulses parvus) when cardiac decompensation occurs. This pulse is fairly specific for severe aortic stenosis. However, patients with low cardiac output and mild stenosis will have a low volume pulse that is normal in timing.
In patients with atherosclerotic vessels carotid upstroke may be brisk even in severe aortic stenosis. A detectable time gap between the apical pulse and carotid pulse suggests prolonged ejection time of severe aortic stenosis. Wide pulse pressure in the presence of other findings of severe aortic stenosis suggests associated aortic regurgitation. Also wide pulse pressure with normal diastolic pressure is fairly common in elderly patients with concomitant hypertensive vascular disease.
Typically apical impulse is forcible and sustained and with decompensation of left ventricle it is displaced. A palpable S 4 is common in severe aortic stenosis. Absence of a valvular ejectionclick in children should make one suspect the diagnosis of non valvular aortic stenosis. Usually S 2 is single due to muffled A 2 . If the valve is pliable with less extent of calcification, it may
produce paradoxical split in a patient with severe valvular aortic stenosis.
Typically the murmur of valvular aortic stenosis starts after S 1 , is crescendo decrescendo ejection systolic murmur with maximum intensity at second right inter costal space and radiates to carotids. A grade I murmur in the absence of decompensation suggests mild lesion while the same in a patient with severe decompensation should not make one eliminate aortic stenosis as a cause of decompensation.
A grade IV murmur almost always suggests severe aortic stenosis. In children and elderly selective conduction of high frequency sounds to apical area may give risk to cooing murmur at apex (Gallavardin phenomenon). However, the intensity of murmur may vary with cardiac output, chest valve thickness, emphysema and direction of turbulent jet. A late peaking loud grade IV murmur is very specific to severe aortic stenosis.
Electrocardiogram
Typically left ventricular hypertrophy with strain pattern is seen in severe aortic stenosis. Total QRS amplitude in mm. tends to correlate and equals trans aortic gradient in pure aortic stenosis.A normal ECG though suggestive of mild aortic stenosis does not totally eliminate severe aortic stenosis. Left atrial enlargement, left axis deviation and various kinds of conduction abnormalities including left bundle branch block, 1° heart block or even complete heart block may occur.Though atrial fibrillation may occur in an advanced aortic stenosis with decompensation–one should eliminate concomitant mitral valve disease.
Roentgenogram
Cardiac enlargement does not occur in pure compensated aortic stenosis. Post stenotic dilatation of aorta may be seen. Fluoroscopy may reveal calcified aortic valve and often concomitant mitral annular calcium. Decompensated aortic stenosis may present with signs of left ventricular dilatation and pulmonary venous hypertension. Gross left atrial dilatation on roentgenogram should suggest associated mitral valve disease. Absence of ascending aortic dilatation gives a clue that valve may not be the site of stenosis.
Echo Cardiography
2D and M-mode Echo cardiography visualize thickened, often calcific aortic cusps with doming motion. In M-mode Echo cardiography relative sizes of aorta, left atrium, left ventricular dimensions and extent of left ventricular hypertrophy and function can be measured. 2D Echo cardiogram shows the number of cusps. But presence of raphae and distorted anatomy due to calcification may make if difficult to assess. Localization of stenosis to sub-valvular or supravalvular or valvular location can easily be done. Ascending aorta may be disproportionately dilated in some patients with bicuspid aortic valve with a tendency for aortic dissection.
Hemodynamic severity of aortic stenosis can be measured by Doppler echocardiography. Peak and mean trans valvular aortic gradients, aortic valve area and ratio of LVOT and aortic valve time velocity integral (VTI) are important measurements. Meticulous search using all transducer positions should be made to obtain maximal aortic velocity. In patients with normal LV function and cardiac output, aortic stenosis is considered severe when peak aortic velocity is more than or equal to 4.5 m/sec; mean pressure gradient equal to or more than 50 mmHg, aortic valve area less than or equal to 0.75 cm 2 or LVOT/Aortic valve VTI ratio less than or equal to 0.25. It should be noted that in-patients with left ventricular dysfunction and/or low cardiac output, transvalvular pressure gradients will be under estimated while in situations with increased flow across aortic valve like aortic regurgitation and/or anemia transvalvular gradient will be over estimated. Since in both these situation LVOT and Aortic valve VTI move in the same direction and value area as measured by continuity equation makes use of ratio of these two, valve area measurements tends to be more accurate. Also valve resistance which takes into account valve area and flow across the valve is a more reliable index. Further while following a patient serially with echocardiography combined use of transvalvular gradients, left ventricular function and valve area calculation are more useful. Otto and his colleagues have shown that in asymptomatic patients, peak aortic jet velocities increase by 0.32 ± 0.34 m/sec per year, mean gradient by 7± 7mmHg and valve area decrease by 0.12 ± 0.19 cm per year. Beyond a peak velocity of 4.0 m/sec most of the patients become symptomatic within 2 years. Aortic valve area is d” 0.75 cm 2 when peak aortic velocity is > 4.5 m/sec and mean gradient is e” 50 mm Hg. However, half of patients with aortic valve area d” 0.75 cm 2 have lower peak velocities and mean gradients due to lower cardiac output.
Ratio of LVOT/Aortic valve VTI is another good index in measuring aortic valve area. A ratio of LVOT/AV VTI is < 0.25 correlates well with a aortic valve area of < 0.75 m 2 .In a patient with low out put and low aortic valve gradients dobutamine echo (upto dose of 20 mcg/KG/mt) is useful in differentiating between true aortic stenosis and pseudo or functional aortic stenosis. With dobutamine infusion, in a patient with true aortic stenosis, LVOT velocity and aortic velocity increase proportionately but the ratio between both remains same or less than 0.25. Conversely in a patient with functional or pseudo aortic stenosis with severe left ventricular dysfunction–aortic velocity does not increase in proportion to LVOT velocity because aortic valve area increases with increased stroke value. This results in higher LVOT to aortic valve VTI ratio. It becomes more than 0.25 ruling out any significant aortic stenosis.During echocardiography we should be careful in measuring trans aortic flow than mitral or tricuspid regurgitation jets. Aortic annulus measurement is important for the surgeon to plan aortic valve replacement.
Trans esophageal echocardiography (TEE) is an important complement to transthoracic window.It helps in assessing the severity of mitral regurgitation and pathology of mitral valve if any.Number of cusps can be confidently measured. Planimetry measurement of aortic valve area can also be done in TEE short axis view. Pre-operative TEE is helpful in assessing associated mitral
regurgitation.A well done echocardiographic assessment precludes the need for invasive hemodynamic measurement.
Exercise Testing
Exercise testing is relatively contraindicated in patients with aortic stenosis. Its diagnostic accuracy to pick up additional coronary artery disease is limited in view of baseline ECG changes and left ventricular hypertrophy. Exercise testing should not be performed in symptomatic patients. It is safe to do in asymptomatic patients provided it is supervised by an experienced physician and ECG and blood pressure are closely monitored. While prognostic information of exercise induced ECG changes is uncertain—it can provide data about patient’s exercise capacity and exercise induced hypotension. Limited exercise tolerance and/or exercise induced hypotension is an indication for aortic valve replacement in a patient with moderate to severe aortic stenosis.
Cardiac Catheterization
The indications are to confirm hemodynamics when the non-invasive tests are not conclusive or there is a discrepancy between clinical evaluation and echocardiographic findings. It is also done pre-operatively to obtain coronary angiography if associated CAD needs to be ruled out. During cardiac catheterization right and left heart pressures and all necessary gradients should be measured in a meticulous manner. Transvalvular gradients, cardiac out put should be measured to calculate aortic valve area. Crossing a calcified degenerated aortic valve should be avoided unless it is clearly indicated. If entering left ventricle is not possible by retrograde approach transeptal puncture may be done to assess left ventricle to aorta gradient. When clinical impression correlates well with non-invasive evaluation–invasive hemodynamic evaluation with all its complications can be avoided.
Management of Asymptomatic Patient
The most common cause of death in a truly asymptomatic patient with severe aortic stenosis is aortic valve replacement (AVR). While expected incidence of sudden death in those patients is 0.4 per cent per annum, direct surgical mortality and post-operative complications are more in operated patients. However, patients with severe aortic stenosis may undergo aortic valve replacement if they are undergoing coronary artery bypass surgery, other valvular or aortic root surgery. Similarly, AVR may be done even for moderate aortic stenosis in some situations. AVR may also be considered in patients with asymptomatic severe “AS” if it is documented that they have left ventricular dysfunction or hypotensive response to exercise. It may also be considered for patients with very severe AS or excessive hypertrophy.
Follow-up
Asymptomatic severe aortic stenosis patient needs to be followed once in a year or even more frequently. Patients with moderate aortic stenosis need follow up once in two years and those with mild aortic stenosis over a five years provided they do not have any new symptoms or clinical worsening. Echo cardiogram should also be performed whenever there is change in symptoms on signs. In obese individuals or patients with poor echo window serial follow-up withmagnetic resonance imaging (MRI) is a good alternative. Patients should be advised to come for prompt follow-up, if they developed any exercise related symptoms.
Management of Symptomatic Patients
All symptomatic patients with severe aortic stenosis or even moderately severe aortic stenosis should undergo aortic valve replacement and they do well after surgery. Even patients with severe LV dysfunction should be offered aortic valve replacement, if they have severe aortic stenosis.However, if the cause for patient’s left ventricular dysfunction is decreased myocardial function rather than afterload mismatch or if they do not have severe aortic stenosis they may not do well after aortic valve replacement.
The most common cause of death in a truly asymptomatic patient with severe aortic stenosis is aortic valve replacement (AVR). While expected incidence of sudden death in those patients is 0.4 per cent per annum, direct surgical mortality and post-operative complications are more in operated patients. However, patients with severe aortic stenosis may undergo aortic valve replacement if they are undergoing coronary artery bypass surgery, other valvular or aortic root surgery. Similarly, AVR may be done even for moderate aortic stenosis in some situations. AVR may also be considered in patients with asymptomatic severe “AS” if it is documented that they have left ventricular dysfunction or hypotensive response to exercise. It may also be considered for patients with very severe AS or excessive hypertrophy.
Follow-up
Asymptomatic severe aortic stenosis patient needs to be followed once in a year or even more frequently. Patients with moderate aortic stenosis need follow up once in two years and those with mild aortic stenosis over a five years provided they do not have any new symptoms or clinical worsening. Echo cardiogram should also be performed whenever there is change in symptoms on signs. In obese individuals or patients with poor echo window serial follow-up withmagnetic resonance imaging (MRI) is a good alternative. Patients should be advised to come for prompt follow-up, if they developed any exercise related symptoms.
Management of Symptomatic Patients
All symptomatic patients with severe aortic stenosis or even moderately severe aortic stenosis should undergo aortic valve replacement and they do well after surgery. Even patients with severe LV dysfunction should be offered aortic valve replacement, if they have severe aortic stenosis.However, if the cause for patient’s left ventricular dysfunction is decreased myocardial function rather than afterload mismatch or if they do not have severe aortic stenosis they may not do well after aortic valve replacement.
Aortic valve replacement may not be indicated if the patient is very elderly, debilitated and has associated severe co morbid conditions like cancer, stroke etc. Patients with extreme degree of left ventricular hypertrophy also have increased surgical complications. In elderly patients age alone should not influence the decision regarding surgery.
Balloon Aortic Valvuloplasty
This is the procedure of choice in children and young individuals where the valve is not calcified.In elderly patients with calcified valves results are suboptimal. Peri procedural complications may be seen in upto 10 per cent of patients. Restenosis rates requiring repeat intervention are very high. In elderly patients this should be done only as a bridge to surgery as in the patients with cardiogenic shock or pulmonary edema. This may also be considered as an emergency procedure in patients who require non cardiac surgery or have serious comorbid conditions.Percutaneous aortic valve replacement is newer modality of treatment that has to be established.
Medical Therapy
Definitive therapy for aortic stenosis is surgical and medical therapy is only palliative. Infective endocarditis and rheumatic fever proplylaxis should be given as indicated. In patients who are not being considered for aortic valve replacement digoxine and diuretics can give symptom relief.In decompensated heart failure ACE inhibitors may be tried cautiously. Sinus rhythm should be maintained with amiodarone. Beta blockers or other drugs with negative inotropic effect should be used very cautiously or not at all. Nitrates may be given cautiously. Patients with moderate to severe aortic stenosis, even when asymptomatic, should be advised against any kind of vigorous exercise or physical activity. In degenerative valvular AS statin therapy retards the progression of the disease.
Low Gradient Aortic Stenosis
One may come across patients who have severe left ventricular dysfunction and modest gradients across aortic valve. This situation may be due to afterload mismatch in a patient with severe valvular aortic stenosis and left ventricular dysfunction or this situation can also be due to moderate aortic stenosis in a patient with intrinsically severe left ventricular muscle dysfunction.Valve area calculation or valve resistance calculations are not particularly useful in this situation with low cardiac output. Dobutamine stress echo cardiography is helpful in this situation. In a patient with intrinsic myocardial dysfunction, cardiac output, trans aortic gradient and calculated valve area — all increase. In a patient with severe aortic stenosis with afterload mismatch also dobutamine infusion would increase calculated valve area but it will still be in the range severe aortic stenosis. The latter patient may benefit from aortic replacement while the former would not.
Balloon Aortic Valvuloplasty
This is the procedure of choice in children and young individuals where the valve is not calcified.In elderly patients with calcified valves results are suboptimal. Peri procedural complications may be seen in upto 10 per cent of patients. Restenosis rates requiring repeat intervention are very high. In elderly patients this should be done only as a bridge to surgery as in the patients with cardiogenic shock or pulmonary edema. This may also be considered as an emergency procedure in patients who require non cardiac surgery or have serious comorbid conditions.Percutaneous aortic valve replacement is newer modality of treatment that has to be established.
Medical Therapy
Definitive therapy for aortic stenosis is surgical and medical therapy is only palliative. Infective endocarditis and rheumatic fever proplylaxis should be given as indicated. In patients who are not being considered for aortic valve replacement digoxine and diuretics can give symptom relief.In decompensated heart failure ACE inhibitors may be tried cautiously. Sinus rhythm should be maintained with amiodarone. Beta blockers or other drugs with negative inotropic effect should be used very cautiously or not at all. Nitrates may be given cautiously. Patients with moderate to severe aortic stenosis, even when asymptomatic, should be advised against any kind of vigorous exercise or physical activity. In degenerative valvular AS statin therapy retards the progression of the disease.
Low Gradient Aortic Stenosis
One may come across patients who have severe left ventricular dysfunction and modest gradients across aortic valve. This situation may be due to afterload mismatch in a patient with severe valvular aortic stenosis and left ventricular dysfunction or this situation can also be due to moderate aortic stenosis in a patient with intrinsically severe left ventricular muscle dysfunction.Valve area calculation or valve resistance calculations are not particularly useful in this situation with low cardiac output. Dobutamine stress echo cardiography is helpful in this situation. In a patient with intrinsic myocardial dysfunction, cardiac output, trans aortic gradient and calculated valve area — all increase. In a patient with severe aortic stenosis with afterload mismatch also dobutamine infusion would increase calculated valve area but it will still be in the range severe aortic stenosis. The latter patient may benefit from aortic replacement while the former would not.
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