Dissection, Aortic

Introduction

Aortic dissection is defined as separation of the layers within the aortic wall. Tears in the intimal layer result in the propagation of dissection (proximally or distally) secondary to blood entering the intima-media space.

This disease was first described long ago (>200 y), but new challenges have arisen since the advent of advanced diagnostic and therapeutic modalities. The clinical manifestations are diverse, making the diagnosis difficult and requiring a high clinical index of suspicion.1,2,3

Aortic dissection can be diagnosed premortem or postmortem because many patients die before presentation to the emergency department (ED) or before diagnosis is made in the ED.

Aortic dissection is more common in males than in females, with a male-to-female ratio of 2:1. The condition commonly occurs in persons in the sixth and seventh decades of life.3 Patients with Marfan syndrome present earlier, usually in the third and fourth decades of life.


Aortic dissection. CT scan showing a flap (right side of image).



Aortic dissection. CT scan showing a flap (center of image).


Aortic dissection. CT scan showing a flap (center of image).

For more examples of aortic dissection visible on CT scans, see the Multimedia section.


History of the Procedure

Morgagni first described aortic dissection more than 200 years ago. The condition was associated with a high mortality rate before the introduction of the cardiopulmonary bypass in the 1950s, which led to aortic arch repair and construction.

Recent advancements in the field of stent placements and percutaneous aortic fenestrations have further reduced mortality rates. However, despite recent advancements, the mortality rate associated with aortic dissection remains high.1,3
Problem

An aortic dissection is a split or partition in the media of the aorta; this split is frequently horizontal or diagonal. An intimal tear connects the media with the aortic lumen, and an exit tear creates a true lumen and a false lumen. The true lumen is lined by intima, and the false lumen is within the media.


Aortic dissection. True lumen and false lumen separated by an intimal flap.


Typically, flow in the false lumen is slower than in the true lumen, and the false lumen often becomes aneurysmal when subjected to systemic pressure. The dissection usually stops at an aortic branch vessel or at the level of an atherosclerotic plaque.

An acute aortic dissection (<2 wk) is associated with high morbidity and mortality rates (highest mortality in the first 7 d) compared with chronic aortic dissection (>2 wk), which has a better prognosis.

Frequency

In the United States, aortic dissection is an uncommon disease. The true prevalence of aortic dissection is difficult to estimate, and most estimates are based on autopsy studies. Evidence of aortic dissection is found in 1-3% of all autopsies (1 in 350 cadavers). The incidence of aortic dissection is estimated to be 5-30 cases per 1 million people per year. Aortic dissection occurs once per 10,000 patients admitted to the hospital; approximately 2,000 new cases are reported each year in the United States.4
Etiology
Arterial hypertension:3 Of patients with aortic dissection, 70% have elevated blood pressure.
Aortic dilatation and wall thinning: Aortic aneurysm is defined as a pathologic dilatation of a segment of a blood vessel. A true aneurysm involves all 3 layers of the aortic wall.
Iatrogenic: Aortic dissection can be caused by cardiac surgery, including aortic and mitral valve replacements, coronary artery bypass graft surgery, or percutaneous catheter placement (eg, cardiac catheterization, percutaneous transluminal coronary angioplasty). Aortic dissection occurs when the layers are split in the process of cannulation or aortotomy.
Aortic atherosclerosis: Factors include cystic medial necrosis and aortic medial disease.
Congenital aortic valve anomalies: These may include unicommissural or bicuspid aortic valves or aortic coarctation.
Marfan syndrome
Advanced age
Pregnancy
Ehlers-Danlos syndrome
Syphilitic aortitis
Deceleration injury possibly with related chest trauma
Aortic arch hypoplasia
Cocaine use
Pathophysiology

The aortic wall is continuous and is exposed to high pulsatile pressure and shear stress (the steep slope of the pressure curve, ie, the water hammer effect), making the aorta particularly prone to injury and disease from mechanical trauma. The aorta is more prone to rupture than any other vessel, especially with the development of aneurysmal dilatation, because its wall tension, as governed by the Laplace law (proportional to the product of pressure and radius), is intrinsically high.

An intimal tear connects the media with the aortic lumen, and an exit tear creates a true lumen and a false lumen. The true lumen is lined by intima, and the false lumen is lined by media. The true lumen is frequently smaller than the false lumen, but not invariably. The false lumen is indeed within the media, but suggesting that it is "lined" with it is misleading; if the aortic dissection becomes chronic, the lining becomes a serosal pseudointima. Typically, flow in the false lumen is slower than flow in the true lumen, and the false lumen often becomes aneurysmal when subjected to systemic pressure.


Aortic dissection. True lumen versus false lumen in an intimal flap.



The dissection usually stops at an aortic branch vessel or at the level of an atherosclerotic plaque. Most classic aortic dissections begin at 1 of 3 distinct anatomic locations, including (1) the aortic arch, (2) approximately 2.2 cm above the aortic root, or (3) distal to the left subclavian artery.

Ascending aortic involvement may result in death from wall rupture, hemopericardium and tamponade, occlusion of the coronary ostia with myocardial infarction, or severe aortic insufficiency. The nervi vascularis (ie, bundles of nerve fibers found in the aortic adventitia) are involved in the production of pain.

DeBakey and coworkers classify aortic dissection into 3 types, as follows:
Type I: The intimal tear occurs in the ascending aorta, but the descending aorta is also involved.
Type II: Only the ascending aorta is involved.
Type III: Only the descending aorta is involved.
Type IIIA involves the descending aorta that originates distal to the left subclavian artery and extends as far as the diaphragm.
Type IIIB involves the descending aorta below the diaphragm.

The Stanford classification has 2 types, as follows:
Type A: The ascending aorta is involved (DeBakey types I and II).
Type B: The descending aorta is involved (DeBakey type III).

This system also helps delineate treatment. Type A dissections usually require surgery, whereas type B dissections are managed medically under most conditions.5


Image A represents a Stanford A or a DeBakey type 1 dissection. Image B represents a Stanford A or DeBakey type II dissection. Image C represents a Stanford type B or a DeBakey type III dissection. Image D is classified in a manner similar to A but contains an additional entry tear in the descending thoracic aorta. Note that a primary arch dissection does not fit neatly into either classification.


Presentation

Patients with acute aortic dissection present with the sudden onset of severe and tearing chest pain, although this description is not universal. Some patients present with only mild pain, often mistaken for a symptom of musculoskeletal conditions located in the thorax, groin, or back. Some patients present with no pain.6

Consider thoracic aortic dissection in the differential diagnosis of all patients presenting with chest pain. The pain is usually localized to the front or back of the chest, often the interscapular region, and typically migrates with propagation of the dissection.

The pain of aortic dissection is typically distinguished from the pain of acute myocardial infarction by its abrupt onset, although the presentations of the two conditions overlap to some degree and are easily confused. Aortic dissection can be presumed in patients with symptoms and signs suggestive of myocardial infarction but without classic ECG findings.

Presenting signs and symptoms in acute thoracic aortic dissection include the following:

Anterior chest pain is a manifestation of ascending aortic dissection. Neck or jaw pain is a manifestation of aortic arch dissection. Interscapular tearing or ripping pain is a manifestation of descending aortic dissection.

Neurologic deficits are a presenting sign in up to 20% of cases. Syncope is part of the early course of aortic dissection in approximately 5% of patients and may be the result of increased vagal tone, hypovolemia, or dysrhythmia.6 Cerebrovascular accident (CVA) symptoms include hemianesthesia and hemiparesis or hemiplegia.6 Altered mental status is also reported. Other causes of syncope or altered mental status include (1) CVA from compromised blood flow to the brain or spinal cord or (2) ischemia from interruption of blood flow to the spinal arteries.

Patients with peripheral nerve ischemia can present with numbness and tingling in the extremities, limb paresthesias, pain, or weakness.

Horner syndrome is caused by interruption in the cervical sympathetic ganglia and manifests as ptosis, miosis, and anhidrosis.

Hoarseness from recurrent laryngeal nerve compression has also been described.

Cardiovascular manifestations involve symptoms and signs suggestive of congestive heart failure6 secondary to acute severe aortic regurgitation or dyspnea, orthopnea, bibasilar crackles, or elevated jugular venous pressure. Signs of aortic regurgitation include bounding pulses, wide pulse pressure, and diastolic murmurs. Hypertension may result from a catecholamine surge or underlying essential hypertension.7,6 Hypotension is an ominous finding and may be the result of excessive vagal tone, cardiac tamponade, or hypovolemia from rupture of the dissection.

Other cardiovascular manifestations include findings suggestive of cardiac tamponade (eg, muffled heart sounds, hypotension, pulsus paradoxus, jugular venous distension); these may be present and must be recognized quickly. Superior vena cava syndrome can result from compression of the superior vena cava from a large, distorted aorta. Wide pulse pressure and pulse deficit or asymmetry of peripheral pulses is reported. Patients with right coronary artery ostial dissection may present with acute myocardial infarction, commonly inferior myocardial infarction. Pericardial friction rub may occur secondary to pericarditis.

Respiratory symptoms can include dyspnea and hemoptysis if dissection ruptures into the pleura or if tracheal or bronchial obstruction has occurred. Physical findings of a hemothorax may be found if the dissection ruptures into the pleura.

GI symptoms include dysphagia, flank pain, and/or abdominal pain. Dysphagia may occur from compression of the esophagus. Flank pain may be present if the renal artery is involved. Abdominal pain may be present if the dissection involves the abdominal aorta.

Other nonspecific clinical presentations include fever or anxiety and premonitions of death.8

Indications

Emergent surgical correction is the preferred treatment for the following classifications of aortic dissection:

Stanford type A (DeBakey type I and II) ascending aortic dissection
Complicated Stanford type B (DeBakey type III) aortic dissections with clinical or radiological evidence of the following conditions:
Propagation (increasing aortic diameter)
Increasing size of hematoma
Compromise of major branches of the aorta
Impending rupture
Persistent pain despite adequate pain management
Bleeding into the pleural cavity
Development of saccular aneurysm
Relevant Anatomy

From outside to inside, the aorta is composed of the intima, media, and adventitia. The intima, the innermost layer, is thin, delicate, lined by endothelium, and easily traumatized.

The media is responsible for imparting strength to the aorta and is composed of laminated but intertwining sheets of elastic tissue. The arrangement of these sheets in a spiral provides the aorta with its maximum allowable tensile strength. The aortic media contains very little smooth muscle and collagen between the elastic layers and thus has increased distensibility, elasticity, and tensile strength. This contrasts with peripheral arteries, which, in comparison, have more smooth muscle and collagen between the elastic layers.

The outermost layer of the aorta is adventitia. This largely consists of collagen. The vasa vasorum, which supplies blood to the outer half of the aortic wall, lies within the adventitia. The aorta does not have a serosal layer.

The aorta plays an integral role in the forward circulation of the blood in diastole. During left ventricular contraction, the aorta is distended by blood flowing from the left ventricle, and kinetic energy from the ventricle is transformed into potential energy stored in the aortic wall. During recoil of the aortic wall, this potential energy is converted to kinetic energy, propelling aortic lumen blood into the periphery.

The volume of blood ejected into the aorta, the compliance of the aorta, and resistance to blood flow are responsible for the systolic pressures within the aorta. Resistance is mainly due to the tone of the peripheral vessels, although the inertia exerted by the column of blood during ventricular systole also plays a small part.

The aorta has thoracic and abdominal regions. The thoracic aorta is divided into the ascending, arch, and descending segments; the abdominal aorta is divided into suprarenal and infrarenal segments.

The ascending aorta is the anterior tubular portion of the thoracic aorta from the aortic root proximally to the innominate artery distally. The ascending aorta is 5 cm long and is made up of the aortic root and an upper tubular segment. The aortic root consists of the aortic valve, sinuses of Valsalva, and left and right coronary arteries. The aortic root extends from the aortic valve to the sinotubular junction. The aortic root supports the base of the aortic leaflets and allows the 3 sinuses of Valsalva to bulge outward, facilitating the full excursion of the leaflets in systole. The left and right coronary arteries arise from these sinuses.

The upper tubular segment of the ascending aorta starts at the sinotubular junction and ends at the beginning of the aortic arch. The ascending aorta lies slightly to the right of the midline, with its proximal portion in the pericardial cavity. Structures around the aorta include the pulmonary artery anteriorly; the left atrium, right pulmonary artery, and right mainstem bronchus posteriorly; and the right atrium and superior vena cava to the right.

The arch of the aorta curves upward between the ascending and descending aorta. The brachiocephalic arteries originate from the aortic arch. Arteries that arise from the aortic arch carry blood to the brain via the left common carotid, innominate, and left subclavian arteries. Initially, the aortic arch lies slightly left and in front of the trachea and ends posteriorly to the left of the trachea and esophagus. Inferior to the arch is the pulmonary artery bifurcation, the right pulmonary artery, and the left lung. The recurrent laryngeal nerve passes beneath the distal arch, and the phrenic and vagus nerves lie to the left. The junction between the aortic arch and the descending aorta is called the aortic isthmus. The isthmus is a common site for coarctations and trauma.

The descending aorta extends from distal to the left subclavian artery to the 12th intercostal space. Initially, the descending aorta lies in the posterior mediastinum to the left of the course of the vertebral column. It passes in front of the vertebral column in its descent and ends behind the esophagus before passing through the diaphragm at the level of the 12th thoracic vertebra. The abdominal aorta extends from the descending aorta at the level of the 12th thoracic vertebra to the level of bifurcation at the fourth lumbar vertebra. The splanchnic arteries branch from the abdominal aorta. The thoracoabdominal aorta is the combination of the descending thoracic and abdominal aorta.

With increasing age, the elasticity and distensibility of the aorta decline, thus inducing the increase in pulse pressure observed in elderly individuals. The progression of this process is exacerbated in patients with hypertension, coronary artery disease, or hypercholesterolemia. The loss of physiologic distensibility is observed anatomically by fragmentation of elastin and the resultant increase in collagen. This results in an increased collagen-to-elastin ratio. This, along with impairment in flow in the vasa vasorum, may be responsible for the age-related changes. These factors cumulatively lead to increased left ventricular systolic pressure and wall tension with associated increases in end-diastolic pressure and volume.

Contraindications

Cautions and relative contraindications to surgery include the following:

Cerebrovascular accident
Severe left ventricular dysfunction
Coagulopathy
Pregnancy
Postmyocardial infarction ( <6 mo)
Significant arrhythmias
Advanced age
Severe valvular disease

http://emedicine.medscape.com/article/425118-overview

Aortic Stenosis

Introduction
Background


Aortic stenosis is a narrowing or obstruction of the aortic valve. With the aging of the United States population, diseases in the elderly are a major interest among health care professionals. Valvular aortic stenosis (AS) is no exception; senile degenerative aortic stenosis is now the leading indication for aortic valve replacement (AVR). The favorable long-term outcome following aortic valve surgery and the relatively low operative risk emphasize the importance of an accurate and timely diagnosis.


Stenotic aortic valve (macroscopic appearance).

Pathophysiology

The pathophysiologic mechanisms responsible for symptoms (ie, angina, syncope, congestive heart failure) in patients with aortic stenosis include an increase in left ventricular (LV) afterload, progressive LV hypertrophy, and a decrease in systemic and coronary flow as consequences of valve obstruction.

In adults with aortic stenosis, LV outflow obstruction increases gradually over a long period of time, during which time the patient is asymptomatic. This progressive outflow obstruction results in increased LV mass by parallel replication of sarcomeres producing concentric hypertrophy, which is a compensatory mechanism to normalize LV wall stress. Inadequate development of hypertrophy, depression of myocardial contractility, or a combination of these factors may lead to impairment of LV performance (so-called afterload mismatch) and congestive heart failure (CHF) symptoms. Indeed, wall thickness appears to be a critical determinant of ventricular performance in patients with aortic stenosis. If afterload mismatch occurs, the LV ejection fraction, cardiac output, stroke volume, and transvalvular pressure gradient decline.

In most patients with aortic stenosis, LV systolic function is preserved and cardiac output is maintained for many years despite an elevated LV systolic pressure. Despite the fact that cardiac output at rest is normal, it often fails to increase appropriately during exercise, which may result in exercise-induced syncope or near syncope.

In the patient with aortic stenosis, diastolic dysfunction may occur as a consequence of impaired LV relaxation and/or decreased LV compliance, as a result of increased afterload, LV hypertrophy, or myocardial ischemia. LV hypertrophy often regresses following relief of valvular obstruction. However, in some individuals, extensive myocardial fibrosis develops, which may not disappear despite regression of hypertrophy.

In patients with severe aortic stenosis, atrial contraction plays a particularly important role in diastolic filling of the LV. Thus, development of atrial fibrillation in aortic stenosis is often catastrophic to the maintenance of normal forward stroke volume.

Increased LV mass, increased LV systolic pressure, and prolongation of the systolic ejection phase all elevate the myocardial oxygen requirement, especially in the subendocardial region. Coronary blood flow at rest is increased but normal when corrected for LV mass; however, coronary flow reserve is often reduced. Myocardial perfusion is also compromised by the relative decline in myocardial capillary density and by a reduced diastolic transmyocardial (coronary) perfusion gradient due to elevated LV diastolic pressure. Therefore, the subendocardium is susceptible to underperfusion, which results in myocardial ischemia.

Frequency
United States

Aortic sclerosis (considered a precursor of calcific degenerative aortic stenosis) increases in incidence with age and is present in 29% of individuals older than 65 years and in 37% of individuals older than 75 years. In elderly persons, the prevalence of aortic stenosis is between 2% and 9%.
Mortality/Morbidity

Patients with severe aortic stenosis may be asymptomatic for many years despite the presence of severe LV outflow tract obstruction. Such patients have a survival similar to those without aortic stenosis. With the appearance of symptoms, however, their survival is reduced; onset of angina is associated with an average survival of 5 years, syncope with an average survival of 2-3 years, and congestive heart failure with an average survival of 1.5-2 years.

Among symptomatic patients with medically treated moderate-to-severe aortic stenosis, mortality rates from the onset of symptoms are approximately 25% at 1 year and 50% at 2 years. More than 50% of deaths are sudden.
Asymptomatic patients, even with critical aortic stenosis, have an excellent prognosis regarding survival, with an expected death rate of less than 1% per year; only 4% of sudden cardiac deaths in severe aortic stenosis occur in asymptomatic patients.
Although the obstruction tends to progress more rapidly in patients with degenerative calcific aortic valve disease than in those with congenital or rheumatic disease, predicting the rate of progression in individual patients is not possible. Therefore, careful clinical follow-up is mandatory in all patients with moderate-to-severe aortic stenosis. Catheterization and echocardiographic studies suggest that, on average, the valve area declines 0.1-0.3 cm2 per year; the systolic pressure gradient across the valve can increase by as much as 10-15 mm Hg per year. A more rapid rate of progression is observed in elderly patients with coronary artery disease (CAD) and chronic renal insufficiency.

Race

No racial predilection is associated with congenital or acquired aortic stenosis.
Age

Severe aortic stenosis is rare in infancy, occurring in 0.33% of live births and is due to a unicuspid or bicuspid valve. Most patients with a congenitally bicuspid aortic valve who develop symptoms do not do so until middle age or later. Patients with rheumatic aortic stenosis typically present with symptoms after the sixth decade of life, and those with senile degenerative aortic stenosis may not manifest symptoms until their mid 70s to early 80s.
Clinical
History

In aortic stenosis, a long latent period exists during which time the LV outflow obstruction and the pressure load on the myocardium gradually increase while patients remain asymptomatic.

The classic symptom triad of aortic stenosis includes angina pectoris, syncope, and heart failure, which most commonly manifest after the sixth decade of life.
Some patients remain asymptomatic, but others develop exertional chest pain, effort dizziness or lightheadedness, easy fatigueability, and progressive inability to exercise.
Exertional dyspnea is the most common initial complaint, even with normal LV systolic function, and it often relates to abnormal LV diastolic function.
Angina pectoris occurs in approximately two thirds of patients with critical aortic stenosis, of which 50% have significant coronary artery disease. Because angina commonly is precipitated by exertion and relieved by rest, it simulates symptoms of coronary artery disease. Angina results from a concomitant increased oxygen requirement by the hypertrophic myocardium and diminished oxygen delivery secondary to diminished coronary flow reserve, decreased diastolic perfusion pressure and relative subendocardial myocardial ischemia. Of course, angina also can result from coexistent coronary artery disease.
The cause of syncope is multifactorial. It often occurs upon exertion when systemic vasodilatation causes the arterial systolic blood pressure to decline in the presence of a fixed forward stroke volume. It also may be caused by atrial or ventricular tachyarrhythmias.
Syncope at rest may be due to transient ventricular tachycardia, atrial fibrillation, or atrioventricular block, with the latter due to extension of the calcification of the valve into the conduction system. Another cause of syncope is abnormal vasodepressor reflexes caused by increased LV intracavitary pressure (vasodepressor syncope).
Congestive heart failure symptoms (ie, paroxysmal nocturnal dyspnea, orthopnea, dyspnea on exertion, and shortness of breath) may be due to systolic dysfunction from afterload mismatch, ischemia, or a separate cardiomyopathic process. Alternatively, diastolic dysfunction from LV hypertrophy or ischemia may also result in congestive heart failure symptoms.
In patients in whom the aortic valve obstruction remains unrelieved, the onset of symptoms predicts a poor outcome with medical therapy; the approximate time interval from the onset of symptoms to death is 2 years for congestive heart failure, 3 years for syncope, and 5 years for angina.
Gastrointestinal bleeding due to angiodysplasia or other vascular malformations is present at a higher than expected frequency in patients with calcific aortic stenosis; it usually resolves following aortic valve surgery.
The risk of infective endocarditis is higher in younger patients with mild valvular deformity than in older patients with degenerated calcified aortic valves, but it can occur in either. It can occur at any age with hospital-acquired Staphylococcus aureus bacteremia, which frequently results in aortic valve replacement.
Calcific aortic stenosis rarely may cause emboli of calcium to various organs, including the heart, kidney, and brain.
Sudden cardiac death is rare and usually occurs in symptomatic patients.

Physical

In severe aortic stenosis, the carotid arterial pulse is typically diminished and rises slowly (pulsus parvus et tardus); however, in elderly individuals with rigid carotid vessels, this may not be present. A lag time may be present between the apical impulse and the carotid impulse. Systolic hypertension can coexist with aortic stenosis, but a systolic blood pressure higher than 200 mm Hg is rare in patients with critical aortic stenosis.
Pulsus alternans can occur with the onset of LV dysfunction. The jugular venous pulse may show prominent a waves reflecting reduced RV compliance consequent to hypertrophy of the interventricular septum.
At the apex, a precordial a wave often is visible and palpable. A hyperdynamic LV is unusual and suggests concomitant aortic regurgitation or mitral regurgitation. A systolic "thrill" may be present at the second right intercostal space or at the suprasternal notch. The thrill is best felt while the patient is leaning forward. On occasion, it can be transmitted to the carotids.
S1 is usually normal or soft.
The aortic component of the second heart sound, A2, is usually diminished or absent because the aortic valve is calcified and immobile and/or aortic ejection is prolonged and it is obscured by the prolonged systolic ejection murmur. The presence of a normal or A2 speaks against the presence of severe aortic stenosis. Paradoxical splitting of the S2 also occurs because of late closure of A2. P2 may also be accentuated when LV failure leads to secondary pulmonary hypertension.
The presence of an ejection sound (eg, ejection click) is dependent on the mobility of the valve cusps and disappears when they become immobile and severely calcified. Thus, an ejection click is common in children and young adults with congenital aortic stenosis but rare in elderly individuals with acquired calcific aortic stenosis. This sound occurs approximately 40-60 milliseconds after the onset of S1 and is frequently heard best along the mid to lower left sternal border; it is often well transmitted to the apex and may be confused with a split S1.
A prominent S4 is usually present due to forceful atrial contraction into a hypertrophied left ventricle. The presence of an S4 in a young patient with aortic stenosis indicates significant aortic stenosis, but with aortic stenosis in an elderly person, this is not necessarily true.
The classic crescendo-decrescendo systolic murmur of aortic stenosis is best heard at the second intercostal space in the right upper sternal border; it is harsh at the base and radiates to one or both carotid arteries. However, it may be more prominent at the apex in elderly persons with calcific aortic stenosis due to radiation of the high-frequency components of the murmur to the apex (Gallavardin phenomenon) leading to its misinterpretation as a murmur of mitral regurgitation. Accentuation of the aortic stenosis murmur following a long R-R interval (as in atrial fibrillation or following a premature beat) distinguishes it from the mitral regurgitation murmur, which usually does not change.
The intensity of the systolic murmur does not correspond to the severity of aortic stenosis, rather, the timing of the peak and the length or duration of the murmur corresponds to the severity of aortic stenosis. The more severe the stenosis, the longer the duration of the murmur and the more likely it peaks at mid-to-late systole.
The murmur of valvular aortic stenosis is augmented upon squatting or following a premature beat; the murmur intensity is reduced during Valsalva strain, which is contrary to what occurs with hypertrophic obstructive cardiomyopathy where a Valsalva maneuver increases the intensity of the murmur.
When the left ventricle fails and cardiac output falls, the aortic stenosis murmur becomes softer and may be barely audible. Atrial fibrillation with short R-R intervals can also decrease the murmur intensity or make it appear absent.
Rarely, RV failure with systemic venous congestion, hepatomegaly, and edema precede LV failure. This is probably due to the bulging of the interventricular septum into the right ventricle, with impedance in filling, elevated jugular venous pressure, and a prominent a wave (Bernheim effect).

Causes

Most cases of aortic stenosis are due to the obstruction at the valvular level. Common causes are summarized in Table 1. Valvular aortic stenosis can be either congenital or acquired.
Congenital valvular aortic stenosis
Congenitally unicuspid, bicuspid, tricuspid, or even quadricuspid valves may be the cause of aortic stenosis. In neonates and infants younger than 1 year, a unicuspid valve can produce severe obstruction and is the most common anomaly in infants with fatal valvular aortic stenosis.
In patients younger than 15 years, unicuspid valves are most frequent in cases of symptomatic aortic stenosis.
In adults, congenital aortic stenosis is usually due to a bicuspid valve. It does not cause significant narrowing of the aortic orifice during childhood. The altered architecture of the bicuspid aortic valve induces turbulent flow with continuous trauma to the leaflets, ultimately resulting in fibrosis, increased rigidity and calcification of the leaflets, and narrowing of the aortic orifice in adulthood.
Congenitally malformed tricuspid aortic valves with unequally sized cusps and commissural fusion can also cause turbulent flow leading to fibrosis and, ultimately, to calcification and stenosis. Clinical manifestations of congenital aortic stenosis in adults usually occur after the fourth decade of life.
Acquired valvular aortic stenosis
The main causes of acquired aortic stenosis include rheumatic heart disease and senile degenerative calcification.
In rheumatic aortic stenosis, the underlying process includes progressive fibrosis of the valve leaflets with varying degrees of commissural fusion, often with retraction of the leaflet edges and, in certain cases, calcification. As a consequence, the rheumatic valve often is regurgitant and stenotic. Coexistent mitral valve disease is common.
Degenerative (senile) calcific aortic stenosis involves progressive calcification of the leaflet bodies resulting in limitation of the normal cusp opening during systole. This represents a consequence of long-standing hemodynamic stress on the valve and is currently the most frequent cause of aortic stenosis requiring aortic valve replacement. It usually occurs in individuals older than 75 years. Cellular aging and degeneration have been implicated. Diabetes mellitus and hypercholesterolemia are risk factors for the development of this lesion. The calcification may also involve the mitral annulus or extend into the conduction system, resulting in atrioventricular or intraventricular conduction defects.
The available data suggest that the development and progression of calcific aortic stenosis are due to an active disease process at the cellular and molecular level that shows many similarities with atherosclerosis, ranging from endothelial dysfunction to, ultimately, calcification.
Calcific aortic valve disease is associated with older age, male sex, serum LDL and Lp(a) levels, systemic arterial hypertension, diabetes mellitus, and smoking.
Other infrequent causes of aortic stenosis include obstructive vegetations, homozygous type II hypercholesterolemia, Paget disease, Fabry disease, ochronosis, and irradiation.
Table 1. Common Reasons of Aortic Stenosis Requiring Surgery


Open table in new windowAge <70 years (n=324)
Bicuspid AV (50%)
Postinflammatory (25%)
Degenerative (18%)
Unicommissural (3%)
Hypoplastic (2%)
Indeterminate (2%)

Age >70 years (n=322)
Degenerative (48%)
Bicuspid (27%)
Postinflammatory (23%)
Hypoplastic (2%)

http://emedicine.medscape.com/article/150638-overview

Aortic Regurgitation

Introduction
Background

Aortic regurgitation (AR) results from reverse flow through the aortic valve during diastole as a result of any of a number of potential causes, including intrinsic valvular abnormalities (infection, congenital, inflammation, rupture/tear, fistula, fibrosis, myxomatous degeneration, connective tissue disease) and extra-valvular abnormalities (aortic dissection, dilitation, inflammation, aneurysm, cardiac enlargement).

Primary disease of the aortic valve leaflets, the wall of the aortic root, or both may cause aortic regurgitation (AR). With the decline in the incidence of syphilitic aortitis and rheumatic valvulitis in the second half of the 20th century, various aortic root disorders such as Marfan disease and degeneration of bicuspid aortic valves have become the most common causes of AR.
Pathophysiology

Chronic AR produces left ventricular (LV) volume overload that leads to a series of compensatory changes, including LV enlargement and eccentric hypertrophy. The enlarged ventricle is more compliant and is well suited to deliver a large stroke volume. This occurs through rearrangement of myocardial fibers with the addition of new sarcomeres in series, causing the individual myocardial fibers to become longer. The dilated left ventricle can accommodate increased end-diastolic volume and deliver a larger stroke volume to compensate for the regurgitant aortic flow.

Wall thickness must increase to compensate for the increased ventricular dimensions. These compensatory changes are necessary to minimize or normalize wall stress according to the Laplace law (ie, wall tension/stress is related to the product of intraventricular pressure and radius divided by wall thickness). Increased wall thickness results from increased fiber diameter achieved by an increased number of sarcomeres in parallel. This type of hypertrophy observed in a volume-overload state usually is eccentric, as opposed to concentric hypertrophy observed in a pressure-overload state (ie, aortic stenosis). The increased myocardial mass in a hypertrophic heart enables individual sarcomeres to shorten to a normal degree.

As long as LV wall stress is maintained in the normal range, the LV preload reserve, contractility, and ejection fraction (EF) remain within the normal range. This is the chronic compensated stage. During this phase of the disease, most patients remain asymptomatic for decades because chronic AR generally is a slow and insidious disease with very low morbidity during a long asymptomatic phase.

With time, transition from a compensated to a decompensated state marks the progression of the disease. Progressive LV enlargement beyond that required by the valvular regurgitation occurs and is associated with a change of the left ventricle from an elliptical shape to a spherical shape.

The cause of this pathologic dilatation is not well understood, but loss of the collagen support system that acts as a skeleton for the heart may play a substantial role. These maladaptive changes in the interstitium of the heart are an intricate part of the LV hypertrophy process. In addition, diminished coronary flow reserve in this hypertrophied ventricle is thought to result in chronic subendocardial ischemia, even in the absence of epicardial coronary artery disease (CAD). Eventually, subendocardial necrosis and fibrosis occur, along with disruption of the collagen support system, with loss of LV systolic function. The neurohormonal response complicates the disease state further by its excessive growth stimuli, which are thought to be partially responsible for apoptosis (programmed cell death) of the remaining functional myocytes.

The vicious cycle continues until the decompensated stage develops over many years. Progressive LV enlargement, spherical LV shape, increased wall stress, decline in the contractility and EF, increased afterload, and decreased diastolic compliance with a rise in end-diastolic pressure characterize this stage. Frequently, development of congestive symptoms heralds this stage, but an insidious deterioration of ventricular function may occur without overt clinical signs.

In acute AR, the normal-sized left ventricle poorly tolerates the sudden large volume imposed on it. The left ventricle poorly accommodates the abrupt increase in end-diastolic volume, and diastolic filling pressure increases rapidly and dramatically. This leads to an acute decrease in forward stroke volume, and, although tachycardia develops as a compensatory mechanism to maintain cardiac output, this often is insufficient. The rise in LV filling pressure is transmitted to the left atrium, pulmonary veins, and pulmonary capillaries, leading to pulmonary edema and congestion. Acute AR usually is severe and rapidly leads to LV decompensation and/or failure and cardiogenic shock.

Frequency
United States

With the advent of Doppler echocardiogram studies, many cases of mild AR have been identified in the general population. In some studies, up to 8.5% of women and 13% of men were found to have some degree of AR. In surgical literature, up to 20% of all aortic valve surgeries are performed because of pure AR; however, aortic stenosis remains the most frequent indication for aortic valve replacement (AVR). Multiple logistic regression analysis revealed age and male gender to be predictors of AR.
Mortality/Morbidity

A long asymptomatic period with a relatively rapid downhill course after the onset of cardiac symptoms characterizes the natural history of chronic AR. Data from several studies concerning the natural history of chronic severe AR with normal LV function found the rate of progression to symptoms and/or LV dysfunction (LV ejection fraction [LVEF] <0.50) to be approximately 4.5% per year. The incidence rate of sudden cardiac death was very low, at less than 0.2% per year. Sudden cardiac death has generally not been considered an important risk for patients with AR who are asymptomatic and have normal LV function at rest. AVR can be postponed safely until the appearance of cardiac symptoms and/or LV dysfunction (LVEF <0.50) at rest.

The prognosis of severe AR in asymptomatic patients with normal LV function remains excellent, but extra vigilance is required in monitoring these patients to ensure that the optimal time for surgical intervention is not overlooked.

The risks associated with chronic severe AR are as follows:
In asymptomatic patients with normal LV systolic function, the rate of progression to symptoms and/or LV dysfunction is less than 5% per year, the rate of progression to asymptomatic LV dysfunction is less than 2% per year, and the rate of sudden death is less than 0.2% per year.
For asymptomatic patients with LV systolic dysfunction, the rate of progression to cardiac symptoms is higher than 25% per year. In symptomatic patients, the mortality rate associated with angina is higher than 10% per year and, with congestive heart failure (CHF), is higher than 20% per year.
The rates of death, symptoms, or LV dysfunction in patients with LV end-systolic dimension (LVESD) greater than 55 mm is 19% per year, in patients with an LVESD of 40-49 mm is 6% per year, and in patients with LVESD less than 40 mm is 0% per year.
Because angina and dyspnea have long been considered an indication for surgery in this patient population, no large-scale recent studies exist of the natural history of symptomatic AR. These patients remain at high risk and mortality rates are estimated between 10% and 20%. For these reasons, the Guidelines for the Management of Patients with Valvular Heart Disease presented by the American College of Cardiology (ACC) and American Heart Association (AHA) recommend AVR for patients with class II-IV symptoms of angina or dyspnea and chronic severe AR.
Race

Incidence of AR is similar across various racial populations.
Sex

AR affects males and females equally.
Age

Significant AR can be found in patients of any age; however, the age at which AR becomes clinically significant varies based on etiology. Patients with Marfan disease and those with bicuspid aortic valve problems tend to present earlier in life and generally are free of disability from LV dysfunction at the time of presentation. If left untreated, significant cardiac symptoms commonly appear in the fifth decade of life and beyond, usually after considerable cardiomegaly and myocardial dysfunction have occurred.
Clinical
History

The natural history of AR is a slow and insidious disease process, with many patients remaining asymptomatic for decades. In asymptomatic patients, a cardiac murmur found during a routine medical examination often leads to diagnosis; however, once cardiac symptoms develop, clinical deterioration may progress rapidly.

The principal symptoms associated with severe AR are exertional dyspnea, orthopnea, and paroxysmal nocturnal dyspnea. These symptoms appear when pulmonary venous pressure is elevated in association with significant cardiomegaly and myocardial dysfunction. These changes occur late in the natural history of the disease.
Angina pectoris may occur without CAD because coronary perfusion is inadequate to meet the demands of the enlarged and hypertrophic left ventricle. Less commonly, aortitis can involve the origin of the coronary arteries, leading to angina.
Palpitations are a common complaint associated with a hyperdynamic and tachycardic left ventricle in significant AR. Palpitations also may be due to frequent premature ventricular contractions.
Syncope is an uncommon symptom associated with AR.
Sudden cardiac deaths have been relatively rare in asymptomatic patients with normal LV function (<0.2% per year).
In contrast to chronic AR, symptoms of acute AR (commonly from infective endocarditis, aortic dissection, or trauma) develop rapidly and are very poorly tolerated. In acute AR, the normal-sized ventricle is unable to adapt to the sudden increase in regurgitant volume, in addition to the normal left atrial inflow. Thus, patients develop pulmonary congestion associated with LV failure and, possibly, cardiogenic shock.

Physical
Hemodynamically severe AR causes a widened pulse pressure, often greater than 100 mm Hg, associated with a low diastolic pressure, often less than 60 mm Hg.
The de Musset sign is when patients' heads frequently bob with each heartbeat.
The Corrigan pulse is when patients' pulses are of the water-hammer or collapsing type, with abrupt distention and quick collapse.
The Quincke sign is when light transmitted through the patient's fingertip shows capillary pulsations.
The Hill sign is when popliteal cuff systolic pressure exceeds brachial cuff pressure by more than 40 mm Hg.
The Duroziez sign is when a systolic murmur is heard over the femoral artery when compressed proximally and when a diastolic murmur is heard when the femoral artery is compressed distally.
The Müller sign is systolic pulsations of the uvula.
The Traube sign (also called pistol-shot sounds) refers to booming systolic and diastolic sounds heard over the femoral artery.
The apical impulse in chronic AR is diffuse, hyperdynamic, and displaced inferiorly and leftward.
S3 gallop correlates with development of LV dysfunction.
The typical diastolic murmur of AR has a decrescendo shape. A high-frequency early diastolic murmur often occurs in mild AR, whereas a rough holodiastolic or decrescendo diastolic murmur occurs more commonly in severe AR. The volume and velocity of blood across the incompetent aortic valve tapers off in mid-to-last diastole as the aortic and LV pressures equilibrate. The diastolic murmur of AR is usually best heard adjacent to the sternum in the second to fourth left intercostal space. A concomitant systolic ejection murmur is common in moderate-to-severe AR due to the increased volume of blood flowing across the aortic valve.
The murmur associated with acute AR may not be impressive. If cardiac decompensation is present, the diastolic murmur of acute AR may be very soft and surprisingly short.
Antegrade flow across a partially closed mitral valve is thought to cause an Austin Flint murmur, which is a mid- and late-diastolic apical low-frequency murmur or rumble. The rumble occurs during premature closure of the mitral valve, which occurs when LV diastolic pressure is rising rapidly because of severe aortic reflux. Its presence indicates severe AR.
Causes
Acute aortic regurgitation
Infective endocarditis may lead to destruction or perforation of the aortic valve leaflet. The vegetation can also interfere with proper coaptation of the valve leaflets and can sometimes lead to frank prolapse or flail of a leaflet.
In acute ascending aortic dissection (type A), the retrograde proximal dissection undermines the suspensions of the aortic valve leaflets. Varying levels of aortic valve malcoaptation and prolapse occur.
Prosthetic valve malfunction can lead to AR.
Chest trauma may lead to a tear in the ascending aorta and disruption of the aortic valve support apparatus.
Chronic aortic regurgitation
While a congenital bicuspid aortic valve often leads to progressive aortic stenosis, incomplete closure or prolapse can also lead to significant regurgitant flow across the valve. This common congenial lesion remains the most common cause of isolated AR requiring aortic valve surgery. Histologic abnormalities of the bicuspid root frequently lead to proximal aortic dilatation and further exacerbation of AR.
Connective tissue disorders syndrome, including Marfan syndrome, Ehlers-Danlos syndrome, floppy aortic valve, aortic valve prolapse, sinus of Valsalva aneurysm, and aortic annular fistula can all lead to significant chronic AR.
The use of diet drugs such as fenfluramine and dexfenfluramine (commonly referred to as Phen-Fen) may lead to chronic AR.
Rheumatic fever was a common cause of AR in the first half of the 20th century. The cusps become thickened with fibrous tissues and retract, which causes central valvular regurgitation. Most commonly, some fusion of the cusps occurs, resulting in some degree of aortic stenosis and regurgitation. Associated rheumatic mitral valve disease is always present.
Syphilitic aortitis leads to dilatation of the ascending aorta. The aortic annulus becomes dilated, and coaptation of the cusps is lost.
Takayasu arteritis involves the aorta and its major branches. AR may complicate type I and type III of this disease.
Ankylosing spondylitis leads to shortening and thickening of the aortic valve cusps and dilatation of the aortic root.
Reiter syndrome presents similarly to ankylosing spondylitis. Dilatation of the aortic root and associated AR occurs. Reiter syndrome may involve the coronary ostium rarely, producing angina.
Rheumatoid arthritis can produce granulomata involving the valve leaflets and rings. The central portion of the leaflets is usually involved, with sparing of the peripheral portions.
Systemic lupus erythematosus (SLE) is associated with Libman-Sacks endocarditis (noninfectious), and these verrucous vegetations can produce mitral and aortic regurgitation. Distinct from endocarditis, SLE can produce valvulitis, leading to thickened, calcific, and dysfunctional valves.
Behcet disease is a diffuse aortitis, often leading to proximal aortic dilatation and severe AR.
Whipple disease is a gastrointestinal condition in which aortic root dilatation and aortic valve insufficiency may be present.

http://emedicine.medscape.com/article/150490-overview