Coarctation of the Aorta P. Syamasundar Rao, MD Address the media and superimposed neointimal tissue. The local- Division of Pediatric Cardiology, The University of Texas/Houston ized constriction may form a shelf-like structure with an Medical School, 6431 Fannin, MSB 3.130, Houston, TX 77030, USA. eccentric opening or it may be a membranous curtain-like E-mail: [email protected] structure with a central or eccentric opening. The coarcta- Current Cardiology Reports 2005, 7:425–434 tion may be discrete, or a long segment of the aorta may be Current Science Inc. ISSN 1523-3782 Copyright © 2005 by Current Science Inc. narrowed; the former is more common. In the past, AC has been described as preductal (or infantile) type and post- ductal (or adult) type, depending upon whether the coarc- Coarctation of the aorta is an important, treatable cause of tation segment is proximal or distal to the ductus secondary hypertension. Its prevalence varies from 5% to arteriosus, respectively. However, a detailed review of the 8% of all congenital heart defects. This condition is most anatomy suggests that all coarctations are juxtaductal. often detected because of a murmur or hypertension found Dilatation of the descending aorta immediately distal on routine examination. Delayed or absent femoral pulses to the coarctation segment, poststenotic dilatation, is usu- and an arm/leg systolic blood pressure difference of 20 mm ally present. Varying degrees of hypoplasia of the isthmus Hg or more in favor of the arms may be considered as evi- of the aorta (the portion of the aorta between the origin of dence for aortic coarctation. The coarctation may be dem- the left subclavian artery and ductus arteriosus) and trans- onstrated on a suprasternal notch two-dimensional verse aortic arch (the portion of the aorta between the ori- echocardiographic view along with increased Doppler flow gins of left common carotid and left subclavian artery) are velocities across the coarctation site. Cardiac catheteriza- present in the majority of patients with thoracic coarcta- tion reveals significant systolic pressure gradient (> 20 mm tion. Collateral vessels that connect arteries from the Hg) across the coarctation and angiography demonstrates upper part of the body to the vessels below the level of the degree and type of aortic narrowing. Aortic obstruc- coarctation may be seen; these may be present as early as a tion may be relieved by surgery or by transcatheter tech- few weeks of life. niques; the latter include balloon angioplasty and stent implantation. In the past, surgery has been used exclusively, but because of morbidity and complications associated with Prevalence surgery, catheter techniques are increasingly used in the The prevalence of AC was found to vary between 5% to 8% management of aortic coarctation. Balloon angioplasty in of all congenital heart defects [1,2]. Slight male preponder- children and stents in adolescents and adults are becoming ance has been observed in older patients, although it is initial therapeutic options for management of coarctation. minimal in infants. Studies evaluating long-term follow-up results of the inter- ventional techniques are needed. Associated Defects Bicuspid aortic valve may be seen in nearly two thirds of Introduction infants with AC, whereas only 30% of older children may Coarctation of the aorta is an important cause of secondary have such an anomaly. Mitral valve anomalies, although less hypertension and consequently, inclusion of this entity frequent than those of the aortic valve, are also seen with when discussing secondary hypertension is appropriate. In AC. Some patients with AC may have cerebral aneurysms, this review, definition, pathology, prevalence, pathogenesis, predisposing them to development of cerebrovascular acci- pathophysiology, clinical features, noninvasive and invasive dents with severe hypertension later in life. AC is the most evaluation, treatment, and prognosis of aortic coarctation common cardiac defect seen in Turner’s syndrome. (AC) in children, adolescents, and adults is discussed. Pathogenesis Definition and Pathology The exact mechanism by which AC is produced is not Coarctation of the aorta is defined as a congenital cardiac clearly understood [3]. Two hypotheses are most com- anomaly consisting of a constricted aortic segment com- monly invoked: hemodynamic and ectopic ductal tissue. In prising localized medial thickening with some infolding of the first hypothesis, an abnormal preductal flow or abnor- 426 Hypertension mal angle between the ductus and coarctation are invoked. Palpation of the brachial and femoral artery pulses simulta- Spontaneous postnatal closure of the ductus arteriosus neously will reveal decreased and delayed or absent femoral completes the development of aortic obstruction. A high pulses. Blood pressure in both arms and one leg must be incidence of AC in congenital heart defect patients with determined; a pressure difference of more than 20 mm Hg in decreased antegrade aortic flow in utero and virtual absence favor of the arms may be considered evidence for AC. of AC in patients with right heart obstructions would lend The LV impulse may be increased. A thrill is usually felt credence to the hemodynamic hypothesis. Abnormal exten- in the suprasternal notch. The first and second heart sion of ductal tissue into the aorta (ectopic ductal tissue) sounds are usually normal in isolated aortic coarctation. has been postulated to create coarctation shelf, and with Because of the large percentage (up to 60%) of patients ductal closure, development of aortic coarctation. This the- with AC have associated bicuspid aortic valve, an ejection ory, however, does not explain the variable degrees of isth- systolic click may be heard at the apex and left mid and mic and aortic arch hypoplasia seen with AC. right upper sternal borders; this click is constant and does not change with respiration. An ejection systolic murmur may be heard best at the left or right upper sternal borders, Pathophysiology but is usually heard best over the back in the left interscap- In children, adolescents, and adults, the mode of presenta- ular region. Sometimes, a faint continuous murmur may tion is hypertension or systolic murmur. The aortic be heard in the left interscapular region, secondary to con- obstruction is deemed to have developed slowly with evi- tinuous flow in the coarcted segment or on the back (sec- dence for development of left ventricular hypertrophy ondary to flow in the collateral vessels). (LVH) and collateral circulation. The mechanism for devel- opment of hypertension is not clearly understood; mechanical obstruction and rennin-angiotensin–medi- Noninvasive Assessment ated humoral mechanisms have been postulated [3]. Chest radiograph Mechanical obstruction theory explains the increased Chest roentgenogram may show significant cardiomegaly blood pressure by postulating that a higher blood pressure or the heart size may be normal. Rib-notching secondary is required to maintain flow through the coarcted segment to collateral vessels may also be seen. Other roentgeno- and collateral vessels. The stroke volume, ejected into the graphic features include a “3” sign on a highly penetrated limited aortic receptacle, produces a higher pressure proxi- chest radiograph (frontal view) or inverted “3” sign of the mal to coarctation. However, this theory does not explain barium-filled esophagus. 1) the lack of relationship between the degree of elevation of blood pressure and the magnitude of obstruction, 2) Electrocardiogram increased peripheral vascular resistance distal to the site of The electrocardiogram may be normal or it may show LVH. obstruction, and 3) delayed or lack of reduction of blood Sometimes the LVH may be manifested by increased S pressure following relief of obstruction. waves in leads V5 and V6, the so-called posterobasal LVH. Humoral theory postulates activation of the rennin- angiotensin system secondary to reduction of renal blood Echocardiography-Doppler studies flow and appears to explain most of the clinical features. Echocardiographic imaging usually reveals the coarctation However, measurement of plasma rennin activity both in in suprasternal notch, two-dimensional echocardiographic animal models and human subjects did not show consis- views. Increased Doppler flow velocity in the descending tently elevated plasma rennin levels. The reason for the aorta by continuous wave Doppler and a demonstrable inability to demonstrate elevation of rennin levels may be jump in velocity at the coarcted segment by pulsed-Dop- related to lack of inadequate accounting for salt intake, pos- pler technique are usually present. Instantaneous peak ture, extracellular fluid volume, and sympathetic influences pressure gradients across the AC can be calculated by on rennin release. More recent studies did demonstrate employing a modified Bernoulli equation [6]: abnormalities in rennin-angiotensin-aldosterone systems. ∆ ()2 2 In addition, activation of central sympathetic nervous sys- P = 4V2 – V1 tem may also be responsible for hypertension of AC. where ⌬ P is peak instantaneous gradient and V2 and V1 are peak flow velocities in the descending aorta distal to Clinical Features coarctation (continuous-wave Doppler) and proximal to Most often, the coarctation is identified because of a murmur the coarctation (pulsed Doppler), respectively. or hypertension detected on routine examination. The AC is not frequently recognized by the primary care physician