Balloon dilation of coarctation at the time of cardiac catheterization has been successful for native (previously unoperated) coarctation and for postoperative restenosis.
In postoperative restenosis, the results of gradient relief are good and the risk of balloon dilation is low, possibly due to the external buttressing of the dilated region by the old operative scar. Reoperation for restenosis carries increased risk compared with balloon dilation, partly because of the operative scarring, which must be dissected to achieve exposure.
Balloon dilation of native coarctation avoids some operative disadvantages but, compared with operative repair, it involves a greater chance of immediate compli- cations such as extravasation and of late complications of aneurysm formation or restenosis. The age and size of the patient at the time of balloon dilation influence the risks and long-term outcomes: younger and smaller patients have higher risk. Implantation of a metallic stent at the time of balloon dilation may lessen the risk of aneurysm formation but in small patients the stents do not allow for growth, hence repeat balloon dilation of the stented region is usually needed.
Natural history
The anastomotic site following coarctation repair may not grow in proportion to aortic diameter growth. Therefore, recoarctation may develop, often necessitating a second operation when the patient is older. This need occurs more frequently among children with a very hypoplastic aorta who were operated upon in infancy. Follow-up of all operated patients includes periodic determination of blood pres- sure in both the upper and lower extremities.
Since half of the patients with coarctation of the aorta have a bicuspid aor- tic valve, they are at some increased risk for development of endocarditis com- pared with persons with a normal aortic valve; however, antibiotic prophylaxis is no longer advised for most patients (see Chapter 12). The long-term course of patients with bicuspid aortic valve is variable as the valve may become slowly regurgitant or stenotic with age, and eventually require valvar surgery.
Following operation, some patients have persistent hypertension in both the arms and the legs. The reasons are not well understood, but it does not seem to be related to elevated levels of renin and angiotensin. Abnormal vascular reactiv- ity has been demonstrated in patients with well-repaired coarctation. After repair, some patients with normal resting blood pressure have an exaggerated hyper- tensive response to exercise. This hypertension requires management. Delay in
diagnosis and corrective surgery until an older age in childhood increases the risk of permanent systemic hypertension.
Summary
Coarctation of the aorta is usually an easily diagnosed condition. In most patients it requires treatment, as it can lead to several problems: congestive cardiac failure, hypertension, and left ventricular dysfunction. In most patients, either operation or balloon dilation is used to relieve the obstruction. Despite the apparent anatomic success of intervention, recoarctation, persistent hypertension, and a coexistent bicuspid aortic valve are long-term problems following successful gradient relief.
A O R T I C S T E N O S I S
Aortic stenosis can occur at one of three anatomic locations (Figure 5.3). Usu- ally, aortic stenosis is caused by a stenotic congenital bicuspid or unicuspid valve. Obstruction to left ventricular outflow may also occur below the aortic valve, either as an isolated fibrous ring (discrete membranous subaortic stenosis) or as septal hypertrophy [idiopathic hypertrophic subaortic stenosis (i.e. hypertrophic cardiomyopathy)] (see Chapter 9). Rarely, aortic stenosis is located in the proximal ascending aorta (supravalvar aortic stenosis).
Regardless of the site of obstruction, the effect upon the left ventricle is similar. Because of the stenosis, the left ventricular systolic pressure rises to maintain a normal cardiac output.
This relationship can be illustrated by the equation used to calculate the severity of valvar aortic stenosis:
AVA= AVF
K√LV− AO,
where AVA is aortic valve area (area of stenotic orifice; cm2), AVF is aortic
valve flow (blood flow occurring during the systolic ejection period; mL/s), LV is mean left ventricular pressure during ejection (mmHg), AO is mean aortic pressure during ejection (mmHg), and K is a constant.
This equation uses data obtained at catheterization, specifically the mean pressure difference between the left ventricle and aorta, essentially to derive velocities.
The aortic valve area may also be calculated by Doppler echocardiography in a more direct fashion, since velocity is directly measured.
The mean velocities both proximal and distal to the aortic valve are measured by integrating the area under the respective Doppler curves (the velocity time integral, or VTI).
By measuring the diameter of the left ventricular outflow tract, the cross-sectional area proximal to the stenosis can be easily calculated.
Volume (V ) (cm3) can be found when the VTI (cm) is multiplied by area
(cm2).
As flow (volume/time) is the same through the normal left ventricular outflow tract as via the stenotic aortic valve, in the same amount of time, one systolic ejection period, the following equation can be derived:
AVA=(𝜋d2∕4) × VTILVOT
VTIAo ,
where AVA is aortic valve area (cm2), d is left ventricular outflow tract
diameter (cm), VTILVOTis velocity time integral of the left ventricular outflow
tract flow, mean velocity (cm), and VTIAois velocity time integral of the aortic
valve flow, mean velocity (cm).
In practice, the Doppler maximum velocities in the left ventricular outflow tract and in the aorta are sometimes substituted for the mean velocities.
In patients with more severe aortic stenosis (smaller aortic valve area) for a given cardiac output (CO), left ventricular systolic pressure is higher. Similarly, when the patient exercises, since the aortic valve area is fixed, as the cardiac output rises, the left ventricular systolic pressure increases as a squared function (Figure 5.4).
The primary effect upon the heart of each type of aortic stenosis is elevation of left ventricular systolic pressure, resulting in left ventricular hypertrophy. Many of the clinical and laboratory features of aortic stenosis are related to the left ven- tricular hypertrophy and its effects. Because of the elevated left ventricular systolic pressure, the myocardial oxygen demands are increased. During exercise, the oxy- gen demands are further increased because both heart rate and left ventricular systolic pressure increase. If these oxygen needs are unmet, myocardial ischemia may occur and lead to syncope, chest pain, or electrocardiogram changes. Recur- rent myocardial ischemic episodes can lead to left ventricular fibrosis, which can ultimately progress to cardiac failure and cardiomegaly.
Other clinical features of aortic stenosis are related to the turbulence of blood flow through the stenotic area, manifested by a systolic ejection murmur, and in valvar aortic stenosis, manifested by poststenotic dilation of the ascending aorta.
Figure 5.3 Aortic stenosis. Composite drawing showing three types of left ventricular outflow obstruction: subvalvar (fibromuscular ridge or membrane), valvar, and supravalvar aortic stenosis.