the presence of aortic pathology (von Kodolitsch et al. 2004; Hiratzka et al. 2010). Although changes in the ascending aorta often cannot be recognized in the mediastinal shadow, larger aneurysms in the descending thoracic aorta are often surprisingly well demonstrated (Hiratzka et al. 2010). On a sagittal noncontrast image, an isthmus stenosis may be demarcated as a notch-like dent in the aorta at the junction of the aortic arch and descending aorta, known as the “3 sign” of aortic isthmus stenosis. When one is assessing aortic isthmus stenosis radiographically, it should be borne in mind that the characteristic defects from the third to eighth ribs (notching on the underside of the ribs) usually appear only after the age of 8. These defects arise as a result of dilated intercostal arteries (known as Dock’s sign; Fig. 2.1-28). In general, a chest x-ray only has very limited diagnostic reliability, with a sensitivity of < 20% for detecting re-stenoses after correction of an aortic isthmus stenosis (Therrien et al. 2000).
Fig. 2.1–28a, b Posteroanterior (a) and lateral (b) radiographs in a 37-year-old patient with aortic isthmus stenosis. Rib defects can be seen as typical radiographic signs of aortic isthmus stenosis, as well as a notch in the descending aorta. Left ventricular hypertrophy is present as a secondary sign. A localized luminal constriction in the aorta can be seen in the area of the aortic isthmus on the lateral image.
Echocardiography: The aortic valve, ascending aorta and aortic arch with the origins of the supra-aortic branches can usually be well assessed with transthoracic echocardiography. It is important to carry out the examination from a suprasternal direction, which allows Doppler echocardiographic assessment of the gradient across the aortic isthmus stenosis (Warnes et al. 2008). Both Doppler echocardiography and invasive measurement of pressure gradients may underestimate the severity of an isthmus stenosis when there is good collateral flow (Warnes et al. 2008). Echocardiography has a sensitivity of 87% and a specificity of 78% for diagnosing recurrent stenoses of the aortic isthmus, while its sensitivity and specificity for diagnosing aneurysms in adults after correction of an aortic isthmus stenosis are only 29% and 98%, respectively (Therrien et al. 2000). It is important to carry out a search for malformations typically associated with aortic isthmus stenosis during the echocardiographic examination (Table 2.1-8) (Warnes et al. 2008). Transesophageal echocardiography is rarely used to identify an aortic isthmus stenosis.
Magnetic resonance imaging (MRI) or computed tomography (CT) with three-dimensional reconstruction: According to the current guidelines, all adults with aortic isthmus stenosis should undergo an initial examination with demonstration of the entire aorta and intracranial vessels (Warnes et al. 2008). MRI produces high-quality, high-resolution images that show the anatomy very well and it can also be used to quantify the flow in collateral vessels (Fig. 2.1-29) (Warnes et al. 2008). It provides all the information required for surgical correction, and it is also used for follow-up imaging examinations in patients who have undergone surgery for aortic isthmus stenosis. Several studies have confirmed that MRI can also be used in infants and neonates.
Fig. 2.1–29 Aortic isthmus stenosis on magnetic resonance imaging, with marked collateral formation and development of an aneurysm in the ascending aorta. Sagittal image with gadolinium contrast.
Fig. 2.1–30a, b Angiographic imaging of an aortic isthmus stenosis before (a) and after balloon angioplasty with successful stent placement (b, arrows).
Intracardiac catheter examination: Invasive diagnosis is by today’s standards only indicated in the context of interventional therapy for the aortic isthmus stenosis or to clarify complex cardiac defects, or in adults for preoperative exclusion of coronary heart disease (Fig. 2.1-30) (Warnes et al. 2008; Marek et al. 1995).
2.1.10.5 Treatment
Conservative treatment and general principles
Official recommendations are only available for control of arterial hypertension with medications. β-Blockers, angiotensin-converting enzyme (ACE) inhibitors and sartanes are the agents of choice (Warnes et al. 2008). In patients with aneurysm formation, β-blockers and vasodilators are particularly recommended (Warnes et al. 2008). The effect of statins is currently being tested for reducing atherosclerotic complications in adult patients with congenital heart defects (Krieger and Stout 2010). In accordance with the recommendations of the 36th Bethesda Conference, patients with significant re-stenosis or untreated isthmus stenosis, associated bicuspid aortic valve with aortic stenosis and those with dilation of the aortic root are advised not to take part in contact sports, isometric exercise, weightlifting, or sports involving abrupt starting and stopping (Graham et al. 2005). There has often been critical discussion of pregnancy in women with aortic isthmus stenosis. However, the published data suggest that relatively few complications occur and in particular that the risk of aortic dissection only appears to be slightly increased (Warnes et al. 2008; Pourmoghadam et al. 2002). According to the current guidelines, endocarditis prophylaxis is only indicated if surgical correction or stent placement has taken place during the previous 6 months, while uncomplicated and untreated aortic isthmus stenoses and uncomplicated re-stenoses do not require endocarditis prophylaxis (Warnes et al. 2008).
Correction of aortic isthmus stenosis
An indication for correction is basically established at the first diagnosis of aortic isthmus stenosis. In adults with previously undiagnosed aortic isthmus stenosis, an intervention is indicated according to the current guidelines if the peak-to-peak gradient over the isthmus stenosis on invasive measurement is ≥ 20 mmHg, or with smaller gradients if there is evidence on noninvasive imaging of severe isthmus stenosis with clear collateral formation (Warnes et al. 2008). If the noninvasively measured gradient already shows clear evidence of high-grade aortic isthmus stenosis, invasive measurement is not absolutely necessary.
