Age: 47 years
Gender: Female
Occupation: Elementary school teacher
Working diagnosis: Subaortic stenosis
HISTORY
The patient was noted to have a heart murmur at age 5. She was referred to a cardiologist at age 26 when she was contemplating pregnancy. The diagnosis of bicuspid aortic valve was made, based on the cardiac examination. She had two successful uneventful pregnancies at age 28 and age 32. She did well until a year ago (46 years old) when she started noticing dyspnea on exertion and exercise intolerance. At that time an echocardiogram revealed severe subaortic stenosis with LV hypertrophy, a tricuspid aortic valve associated with moderate aortic regurgitation, and a possible small ASD with left-to-right shunt. Based on these findings she was referred to the adult congenital heart disease clinic.
Comments: Fibromuscular subvalvular aortic stenosis accounts for 15% to 20% of all types of congenital LVOT obstruction, and commonly presents in adulthood. The fibromuscular obstruction typically is localized and extends in the shape of a ring around the outflow tract while inserting into the anterior mitral valve leaflet and the anteroseptum. It is more common than the tunnel-like subaortic stenosis that extends over several centimeters in the outflow tract. Although congenital aortic valve stenosis is much more common in males, this male prevalence is less in fixed subaortic stenosis. Familial occurrence of subaortic stenosis has been reported.
Subaortic stenosis is thought to be an acquired anomaly caused by altered shear stress in the LVOT. The alterations in shear stress are created by a combination of congenital abnormalities of LVOT morphometry including a steeper aortoseptal angle, a longer mitral-aortic separation, and an exaggerated aortic override. These abnormalities could alter the angle of ejection of blood and cause abnormal in utero accumulation of embryonic cells that eventually differentiate into fibroelastic tissue and a membrane that is often not noted at birth. Therefore, in contrast to a bicuspid aortic valve, a systolic murmur is rarely present at birth but appears later in life.
The associated symptoms depend on the severity of the stenosis. They may be entirely absent until physical stress results in an inadequate increment in cardiac output and an increase in the left ventricular diastolic pressure, initially causing exertional dyspnea, lightheadedness, and/or easy fatigability. Chest pain, exertional syncope, and congestive heart failure occur later as the left ventricular obstruction worsens, similar to a patient with valvular aortic stenosis.
CURRENT SYMPTOMS
The patient complained of exertional dyspnea and fatigue not allowing her to perform as well on her treadmill. Prior to the onset of her symptoms, she used to exercise regularly on a treadmill at a speed of 3 miles an hour, 5 to 7 days a week for a period of 1 hour.
She had no dyspnea, orthopnea, or paroxysmal nocturnal dyspnea. She complained of nonpleuritic, nonradiating chest pain occurring at rest, lasting for few seconds to a few minutes and resolving spontaneously. She also reported short episodes of rapid palpitations without dizziness or syncope.
NYHA class: II
Comments: Dyspnea on exertion occurs as a result of an inadequate incremental rise in cardiac output due to the fixed LV outflow obstruction. This leads to an increase in LV diastolic pressure and pulmonary congestion. As with aortic valve stenosis, the risk of developing congestive heart failure increases as the severity of the obstruction increases.
Angina pectoris can occur either as a result of acquired coronary atherosclerosis in the adult age group or secondary to the LV hypertrophy leading to subendocardial ischemia.
Exertional syncope can occur in patients with severe subaortic stenosis possibly because of an exaggerated fall in systemic vascular resistance during exercise, and a reflex bradycardia mediated by LV baroreceptors. Sudden death has been reported in patients with this condition.
PHYSICAL EXAMINATION
BP 120/65 mm Hg (right arm), 125/65 (left arm), 124 systolic (right leg); HR 84 bpm, oxygen saturation 99% on room air
Height 170 cm, weight 97.9 kg, BSA 2.18 m 2
Neck veins: The neck veins were normal, with a mildly diminished and delayed carotid pulse.
Lungs/chest: The lungs were clear to auscultation with no wheezes, rales, or rhonchi.
Heart: There was a right upper sternal thrill, but no parasternal lift. The rhythm was regular. The first and second heart sounds were soft. No extra heart sounds or clicks were appreciated. There was a grade 4/6 late-peaking systolic murmur noted at the left sternal border radiating to the base of the neck and into the carotids. There was also a grade 2/6 diastolic blowing murmur appreciated best at the mid-left sternal border.
Abdomen: Soft and nontender, with no hepatomegaly or splenomegaly, and no masses felt. There was no abdominal bruit.
Extremities: The peripheral pulses were normal with no brachial-femoral delay. There was no edema, cyanosis, or clubbing.
Comments: The JVP can be normal in the absence of secondary pulmonary hypertension. However, significant septal hypertrophy may result in reduced distensibility of the RV, causing the RA to contract with greater force and resulting in a higher amplitude jugular venous A-wave.
As with aortic valve stenosis, the carotid pulse is often reduced and delayed as the severity of LV obstruction increases. The pulse volume, however, can be elevated in the presence of significant aortic regurgitation.
A sustained and strong LV impulse or heave can be found in patients with severe obstruction and ventricular hypertrophy. The first heart sound is often normal whereas the aortic component of the second heart sound can be normal, delayed, diminished, or even absent, depending on the severity of the subaortic stenosis. Ejection clicks are not a feature of fixed subaortic stenosis.
A systolic crescendo-decrescendo murmur and associated thrill, if severe stenosis, can be noted at the left sternal border and apex. This radiates into the second right intercostal space, and often into the suprasternal notch, and both carotid and subclavian arteries.
The configuration, length, and loudness of the murmur are similar to that of aortic valve stenosis.
A blowing decrescendo murmur of aortic regurgitation is heard in 50% of patients with fixed subaortic stenosis. A fourth heart sound is a sign of hemodynamically significant stenosis causing an increase in atrial contraction and contribution to ventricular filling.
LABORATORY DATA
| Hemoglobin | 12.6 g/dL (11.5–15.0) |
| Hematocrit/PCV | 37.1% (36–46) |
| MCV | 89.5 fL (83–99) |
| Platelet count | 224 × 10 9 /L (150–400) |
| Sodium | 139 mmol/L (134–145) |
| Potassium | 4.3 mmol/L (3.5–5.2) |
| Creatinine | 1.0 mg/dL (0.6–1.2) |
| Blood urea nitrogen | 16 mmol/L (2.5–6.5) |
OTHER RELEVANT LAB RESULTS
| TSH | 3.3 mIU/L (0.30–5.0) |
| Cholesterol | 157 mg/dL (<200) |
| Triglyceride | 102 mg/dL (<150) |
| HDL | 71 mg/dL (>40) |
| LDL | 66 mg/dL (<130) |
Comments: Laboratory tests are usually normal in patients with subaortic stenosis.
ELECTROCARDIOGRAM
FINDINGS
Heart rate: 55 bpm
PR interval: 204 msec
QRS axis: −4°
QRS duration: 92 msec
Sinus bradycardia with borderline first-degree AV block, poor R-wave progression, and nonspecific lateral ST-T abnormalities
Comments: Electrocardiographic criteria do not distinguish valvular from subvalvular or supravalvular stenosis, nor do they reliably reflect the severity of aortic stenosis.
Left-axis deviation occurs more in adults than in children with severe stenosis; however, the QRS axis can be normal even in the presence of severe stenosis. Signs of LVH with and without ST-T abnormalities may be seen in 60% to 85% of patients, including 50% of patients with mild stenosis, and therefore cannot predict the severity of subaortic stenosis. On the other hand, severe subaortic stenosis has been associated at times with a normal ECG.
CHEST X-RAY
FINDINGS
Cardiothoracic ratio: 50%
The cardiac silhouette was normal with no rib notching. There was no pulmonary venous congestion. The CXR was normal.
Comments: The cardiac silhouette in patients with subaortic stenosis can be normal or show signs of left ventricular enlargement leading to downward and posterior displacement of the heart. These can be evident by the appearance of an elongated heart on the posteroanterior view and a more convex ventricular shadow on the lateral view. Significant LV enlargement often suggests significant aortic regurgitation.
There may be LA enlargement related to chronically increased LA pressure. Pulmonary venous congestion occurs only in the presence of severe stenosis leading to elevated filling pressure and at times pulmonary hypertension.
Dilatation of the aorta is not a feature of subaortic stenosis, which helps distinguish it from congenital bicuspid or unicuspid aortic valvular stenosis.
FINDINGS
Normal lateral CXR.
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