This chapter discusses hemodynamic abnormalities of obstructive and valvular regurgitant lesions of congenital and acquired causes. For convenience, they are divided into the following three groups based on their hemodynamic similarities:
- 1.
Ventricular outflow obstructive lesions (e.g., aortic stenosis [AS], pulmonary stenosis [PS], coarctation of the aorta [COA])
- 2.
Stenosis of atrioventricular (AV) valves (e.g., mitral stenosis [MS], tricuspid stenosis [TS])
- 3.
Valvular regurgitant lesions (e.g., mitral regurgitation [MR], tricuspid regurgitation [TR], aortic regurgitation [AR], pulmonary regurgitation [PR])
Obstruction to Ventricular Output
Common congenital obstructive lesions to ventricular output are AS, PS, and COA. All of these obstructive lesions produce the following three pathophysiologic changes ( Fig. 10-1 ):
- 1.
An ejection systolic murmur (as heard on auscultation)
- 2.
Hypertrophy of the respective ventricle (as seen in the electrocardiographic [ECG] or echocardiography study)
- 3.
Poststenotic dilatation (as seen in chest radiographs or echocardiography images) (this is not seen with subvalvular stenosis)
Aortic and Pulmonary Valve Stenoses
An ejection type of systolic murmur can best be heard when the stethoscope is placed over the area distal to the obstruction. Therefore, the murmur of AS is usually loudest over the ascending aorta (i.e., aortic valve area or upper right sternal border), and the murmur of PS is loudest over the pulmonary artery (i.e., pulmonary valve area or upper left sternal border). However, the actual location of the aortic valve is under the sternum at the level of the third left intercostal space; therefore, the murmur of AS may be quite loud at the third left intercostal space.
In isolated stenosis of the pulmonary or aortic valve, the intensity and duration of the ejection systolic murmur are directly proportional to the severity of the stenosis. In mild stenosis of a semilunar valve, the murmur is of low intensity (grade 1 to 2/6) and occurs early in systole, with the apex of the “diamond” in the first half of systole. With increasing severity of the stenosis, the murmur becomes longer and louder (often with a thrill) with the apex of the murmur moving toward the S2.
With mild pulmonary valve stenosis, the S2 is normal or split widely because of prolonged “hangout time” (see Chapter 2 ). With severe PS, the murmur is long and may continue beyond the A2 and the S2 splits widely, but the intensity of the P2 decreases ( Fig. 10-2 , A ). With severe AS, the S2 becomes single or splits paradoxically because of the delayed closure of the aortic valve (A2) in relation to the P2 ( Fig. 10-2 , B ). In semilunar valve stenosis, an ejection click may be audible. The click is produced by a sudden checking of the valve motion or possibly by the sudden distention of the dilated great arteries.
If the obstruction is severe, the ventricle that has to pump blood against the obstruction will hypertrophy. The left ventricle (LV) hypertrophies in AS and the right ventricle (RV) in PS, which results in left ventricular hypertrophy (LVH) and right ventricular hypertrophy (RVH), respectively, on the ECG. Cardiac output is maintained unless myocardial failure occurs in severe cases; therefore, the heart size remains normal (on chest radiographic films or echo study).
Poststenotic dilatation is the hallmark of a stenosis at the semilunar valve level. The artery distal to the stenotic semilunar valve dilates circumferentially. Poststenotic dilatation is not seen with subvalvular stenosis; it is only mild or not seen at all with supravalvular stenosis. It was once believed that the jet of blood resulting from the stenosis strikes a localized area of the great artery with weakening of that area causing the dilatation. However, there is a circumferential dilatation of the great artery where the jet does not strike. The current understanding is that sustained vibration of the vessel distal to the narrowing causes generalized fatigue of collagen fibers with resulting dilatation, which may add circumferential dilatation. In pulmonary valve stenosis, a prominent PA segment is visible on chest radiographic film (see Fig. 4-7 , A ). In aortic valve stenosis, the dilated aorta may look like a bulge on the right upper mediastinum or a prominence of the aortic knob on the left upper mediastinum on chest films (see Fig. 4-7 , C ). Mild dilatation of the ascending aorta secondary to aortic valve stenosis is usually not visible on plain chest radiographic films because the ascending aorta does not form the cardiac border.
Coarctation of the Aorta
In older children with COA, an ejection-type systolic murmur is present over the descending aorta distal to the site of coarctation (i.e., in the left interscapular area). Because many of these patients also have abnormal aortic valves (most commonly bicuspid aortic valves), a soft AS murmur, ejection click, and occasional AR murmur may be heard. Depending on the severity of the obstruction, the femoral pulses are either weak and delayed or absent. The weak pulse results primarily from a slow upstroke of the arterial pulse in the lower extremity sites. On chest radiographs, poststenotic dilatation of the descending aorta (distal to the coarctation) often produces the figure-of-3 sign on the plain film or an E-shaped indentation on the barium esophagogram (see Fig. 4-10 ). The poststenotic dilatation of the descending aorta distal to the coarctation can be easily imaged by echocardiographic study. The ECG shows LVH because of a pressure overload on the LV. In newborns and small infants, RVH or right bundle branch block (RBBB) is commonly seen, but LVH is not (see later section for the reasons).
The coarctation is almost always juxtaductal (i.e., located opposite the entry of the ductus arteriosus). What are the differences in pathology and pathophysiology between symptomatic infants and asymptomatic children with coarctation of the aorta?
- 1.
Symptomatic newborns with COA
Many patients who become symptomatic early in life have an associated defect such as ventricular septal defect (VSD) or left-sided obstructive lesions. The obstructive lesions may be in the left ventricular outflow tract, the aortic valve, or the proximal aorta (see Fig. 10-3 , A ). These associated defects tend to decrease blood flow to the ascending aorta and to the aortic isthmus (i.e., the segment between the left subclavian artery and the ductus arteriosus) during fetal life. As a result, these structures become relatively hypoplastic.
