Aortic Stenosis

 

INTRODUCTION

Background: Aortic stenosis (AS) is the obstruction of blood flow across the aortic valve. AS has several etiologies: congenital unicuspid or bicuspid valve, rheumatic fever, and degenerative calcific changes of the valve.

Pathophysiology: When the aortic valve becomes stenotic, resistance to systolic ejection occurs and a systolic pressure gradient develops between the left ventricle and the aorta. Stenotic aortic valves have a decreased aperture that leads to a progressive increase in left ventricular systolic pressure. This leads to pressure overload in the left ventricle, which, over time, causes an increase in ventricular wall thickness (ie, concentric hypertrophy). At this stage, the chamber is not dilated and ventricular function is preserved, although diastolic compliance may be affected.

Eventually, however, the left ventricle dilates. This, coupled with a decrease in compliance, is associated with an increase in left ventricular end-diastolic pressure, which is increased further by a rise in atrial systolic pressure. A sustained pressure overload eventually leads to myocardial decompensation. The contractility of the myocardium diminishes, which leads to a decrease in cardiac output. The elevated left ventricular end-diastolic pressure causes a corresponding increase in pulmonary capillary arterial pressures and a decrease in ejection fraction and cardiac output. Ultimately, congestive heart failure (CHF) develops.

Frequency:

  • In the US: This is a relatively common congenital cardiac defect. Incidence is 4 in 1000 live births.

Mortality/Morbidity: Sudden cardiac death occurs in 3-5% of patients with AS. Adults with AS have a 9% mortality rate per year. Once symptoms develop, the incidence of sudden death increases to 15-20%, with average survival duration of less than 5 years. Patients with exertional angina or syncope survive an average of 3 years. After the development of left ventricular failure, life expectancy is slightly greater than 1 year.

Sex: Among children, 75% of cases of AS are in males.

Age: AS usually is not detected until individuals are school aged. AS exists in up to 2% of those who are younger than 70 years. The etiology of AS in those aged 30-70 years can be rheumatic disease or calcification of a congenital bicuspid valve. In those older than 70 years, degenerative calcification is the primary cause of AS. Among people older than 75 years, 3% have critical AS.


CLINICAL

History: AS usually has an asymptomatic latent period of 10-20 years. Symptoms develop gradually. Ultimately, patients experience the classic triad of chest pain, heart failure, and syncope. Typical symptoms include the following:

  • Palpitations
  • Fatigue (may be an early symptom among children)
  • Visual disturbances
  • Gradual decrease in physical activity with insidious progression of fatigue and dyspnea on exertion
  • Angina pectoris (30-40%)
    • Patients may have a higher incidence of nitroglycerin-induced syncope than the general population.
    • Always consider AS as a possible etiology for a patient in the ED with particular hemodynamic sensitivity to nitrates.
  • Syncope during exertion: Proposed mechanisms include arrhythmias and left ventricular failure with an abrupt decline in cardiac output.
  • Symptoms of left ventricular failure (eg, dyspnea on exertion, nocturnal cough, orthopnea, paroxysmal nocturnal dyspnea, hemoptysis) may occur. This is due to an elevation of the pulmonary capillary pressure from left ventricular dilation and reduced compliance.

Physical:

  • Palpation reveals a laterally displaced apex reflecting the presence of left ventricular hypertrophy.
  • A systolic thrill may be palpable at the base of the heart, in the jugular notch, and along the carotid arteries.
  • Crescendo-decrescendo systolic ejection murmur begins shortly after the first heart sound. The intensity increases toward midsystole, then decreases, and the murmur ends just before the second heart sound. It is generally a rough, low-pitched sound that is loudest at the base of the heart and most commonly is appreciated in the second right intercostal space. An ejection click may be auscultated. This is associated with bicuspid valves.
  • An audible fourth heart sound indicates the presence of left ventricular hypertrophy in severe AS. Once the left ventricle dilates and fails, a third heart sound may be audible.
  • Pulsus parvus et tardus: This is an arterial pulse with a delayed and plateaued peak, decreased amplitude, and gradual downslope. A high-pitched, diastolic blowing murmur may be present if the patient has associated aortic regurgitation.

Causes: The ventricular pressure required to deliver a certain cardiac output at the required perfusion pressure is the pressure gradient across the valve in systole. This pressure gradient defines the degree of aortic valve obstruction.

  • Newborns with significant AS develop CHF within the first week of life. The left ventricle is often too small to be compatible with life. The newborn heart develops left-to-right shunting through the patent foramen ovale, which leads to worsening CHF.
  • Congenital AS caused by a congenital unicuspid or bicuspid aortic valve is usually asymptomatic in the otherwise healthy developing child. It often is diagnosed on routine physical examination, although a child may present with angina pectoris with exercise.
  • As rheumatic fever decreases in frequency, so does rheumatic fever–induced AS. These patients have a fibrous contracture with shortening of the cusps due to recurrent inflammation from rheumatic carditis. Adjacent cusps tend to fuse at the commissures. This causes a form of acquired unicuspid or bicuspid aortic valve. Calcifications may develop, but the primary cause of stenosis is the adhesions that fuse the cusps. In patients older than 70 years, the most common cause of AS is degenerative calcification of the valve. Mönckeberg senile calcific AS occurs in elderly patients in whom all 3 cusps are highly calcified.
  • Calcific AS also occurs in older patients with congenital or acquired bicuspid valves. Congenital bicuspid valves cause calcific AS 4 times more frequently than acquired forms do.


DIFFERENTIALS

Acute Coronary Syndrome
Aortic Stenosis
Mitral Regurgitation
Mitral Stenosis
Mitral Valve Prolapse
Myocardial Infarction
Shock, Hypovolemic


 

WORKUP

Imaging Studies:

  • Chest x-ray
    • Chest radiographs may show cardiac enlargement. Minimal enlargement and more subtle signs of concentric hypertrophy without dilatation are present, including mildly enlarged heart size, rounding at the cardiac apex, and slight backward displacement of the heart as seen in lateral view.
    • In later, more severe stages of AS, roentgenographic signs of left atrial enlargement, pulmonary artery enlargement, right-sided enlargement, and pulmonary congestion are evident.
  • Echocardiograph
    • Two-dimensional transthoracic echocardiography can confirm the clinical diagnosis of AS and provide specific data on left ventricular function. It can show the structure and function of the other valves as well.
    • The following 3 significant findings can help define the severity of the disease and describe the current hemodynamic significance:

      • An echo-dense aortic valve with no cusp motion is indicative of severe AS. This may be unreliable in congenital or rheumatic valvular stenosis.

      • A decrease in the maximal aortic cusp separation (<8 mm in the adult) is also indicative of severe AS.

      • The presence of otherwise unexplained left ventricular hypertrophy implies significant AS.
    • Utilizing echo-Doppler techniques, the systolic pressure gradient across the aortic valve can be assessed. Doppler techniques also can help visualize any mitral or aortic regurgitation that might be present.

Other Tests:

  • Electrocardiogram
    • Generally, ECG is not a reliable test because of the wide variations seen in AS and other cardiac conditions.
    • An ECG of a patient with significant AS most likely shows evidence of left ventricular hypertrophy with or without a strain pattern.
    • While the degree of severity of ECG changes does not correlate well with the degree of hemodynamic instability, the ECG, if performed as a serial study, is valuable in demonstrating the progression of the disease.
    • Approximately 25% of patients with significant AS may not show clear ECG evidence of ventricular hypertrophy. This population includes the elderly who have significant myocardial fibrosis and adolescents who may experience ST-segment changes before QRS changes.
    • Of patients with significant AS, 13% have conduction defects seen on ECG. These can include first-degree heart block, left bundle-branch block, and any other conduction defects.
    • The presence of left atrial enlargement suggests an associated mitral valve process.
  • Cardiac catheterization and coronary arteriography
    • Perform cardiac catheterization and coronary arteriography on patients who may have surgery, are suspected of having coronary artery disease, or are older than 40 years (even without significant symptoms).

    • These patients have a 50% incidence of underlying coronary artery disease. This is a significant consideration if the patient may have surgical intervention.
  • Other considerations in the complete workup of AS include radionuclide studies to evaluate myocardial perfusion at rest and during exertion and exercise studies. Perform these tests cautiously on symptomatic patients. Surgery is recommended routinely in patients with a valve cross-sectional area of 0.8-1.9 cm. However, with improvements in aortic valve replacement, this parameter is becoming more liberal.

TREATMENT

Emergency Department Care:

  • Prehospital and ED management is focused on acute exacerbations of the symptoms of AS.
    • As always, assess and address airway, breathing, and circulation.
    • If the patient is in cardiopulmonary arrest, perform resuscitation according to the recommendations of the American Heart Association in their Advanced Cardiac Life Support guidelines.
    • A patient presenting with uncontrolled CHF should be treated supportively with oxygen, cardiac and oximetry monitoring, intravenous access, loop diuretics, nitrates (remembering the potential nitrate sensitivity of patients with AS), morphine (as needed and tolerated), and noninvasive or invasive ventilatory support (as indicated).
  • Diagnostic studies in the ED should include ECG, chest radiograph, serum electrolytes, cardiac enzymes, CBC, and arterial blood gases (if hypoxemia or a mixed respiratory disease state is suspected). Emergency formal ultrasound may be useful in centers that have this capability.
  • Vasodilators should be used judiciously in patients with AS, as they may cause a significant drop in blood pressure.
  • Patients with heart failure due to AS that is resistant to medical management should be considered for emergent surgery.
  • A patient presenting with angina pectoris requires monitoring and studies as listed above. Measures should be taken to relieve the chest discomfort. This may include administration of nitrates, oxygen, and morphine.

  • Nitroglycerin-induced syncope occurs more often in patients with AS than in those without AS. This information should be obtained through the history at presentation.
  • Syncope in the face of AS should be assessed and treated as in any patient presenting with a syncopal episode.

  • A patient with AS may present initially with one or more of the above complaints. A thorough history and physical should be obtained in addition to baseline laboratory studies, a chest radiograph, and an ECG. Hospital admission, telemetry/intensive care unit admission, and cardiology consultation all should be considered. If available, an echocardiogram may be indicated in the ED.
  • Atrial fibrillation in the setting of AS is considered a medical emergency and should be converted urgently in patients who are hemodynamically unstable. Associated symptoms also should be treated urgently.

Consultations:

  • Cardiology
  • Cardiothoracic surgery

MISCELLANEOUS

Medical/Legal Pitfalls:

  • The main issue to recognize with AS is that the possible symptoms (chest pain or syncope) often are attributed to other disease processes. This is a diagnosis often missed in the ED and only discovered during a more extensive workup.