11.3: Coarctation of the Aorta

Case report

Introduction

Coarctation of the aorta is a narrowing of the thoracic aorta, typically located in the region of the obliterated ductus arteriosum. (Figure 11.3.1) The relation to the position of the left subclavian artery differs, in most patients the left subclavian artery is located anterior of the coarctation. Aortic coarctation is frequently associated with diffuse hypoplasia of the aortic arch and isthmus.

Figure 11.3.1: Schematic drawing of the anatomy prenatal (left) and postnatal (right) in coarctation of the aorta. In the normal situation (without coarctation) only 10 percent of the fetal cardiac output flows through the descending aorta. Therefore there are no hemodynamic consequences prenatal of coarctation of the aorta. In the postnatal situation, after closure of the ductus arteriosus, around 75% of cardiac output needs to pass the coarctation, leading to obstruction.

The incidence of coarctation of the aorta is 4 in 10.000 live births, accounting for 5–9% of the children with congenital heart defects, occurring two to five times more frequently in males than females.

Coarctation of the aorta can be an isolated congenital heart defect, however usually it coincides with other congenital defects. Associated heart defects are patent ductus arteriosus, ventricular septal defect, mitral valve stenosis and valvular and subvalvular aortic stenosis. Furthermore around 75% of all patients with a coarctation of the aorta have a bicuspid aortic valve.

The development of coarctation aorta depends on genetic as well on non-genetic factors. Parents with coarctation aorta have a 2% (male) or 4% (female) chance of passing this defect to their child.

Pathophysiology

Coarctation aorta has no hemodynamic consequences in utero, because only 10% of the total cardiac output crosses from the ascending to the descending aorta. However after birth the ductus arteriosus and foramen ovale close, leading the whole cardiac output through the narrowed aortic segment. This leads to an increase in resistance in the left ventricular outflow tract, resulting in an elevated systolic pressure in the left ventricle and upper extremities. When coping with the elevated pressures, the left ventricle will become hypertrophic.

If the coarctation is severe or in the acute phase (after birth when the ductus is closed), systolic dysfunction of the left ventricle and heart failure can occur.

Most adult patients are asymptomatic unless severe hypertension is present leading to headache, epistaxis, heart failure, or aortic dissection. In addition, claudication may occur due to reduced flow to the lower extremities.

Evaluation

Coarctation of the aorta is easily diagnosed without invasive methods, by means of physical examination, echocardiography or MRI. The combination of weak or absent femoral arterial pulses and upper body hypertension in physical examination points into the direction of coarctation of the aorta. Nevertheless, studies have shown that the diagnosis in hypertensive patients is often missed by the referring doctor. As a consequence, a significant number of asymptomatic subjects with aortic coarctation are probably not detected until adult life, so their incidence at birth is likely to be underestimated. Late detection of subjects with aortic coarctation can have detrimental effects on survival. For, without correction, the mean life expectancy of patients with aortic coarctation is 35 years and 90% of those patients die before reaching the age of 50 years.

Chest radiograph varies with age and severity of the coarctation. In infants with heart failure, the chest radiograph shows generalized cardiomegaly with increased pulmonary vascular markings due to pulmonary venous congestion. In older children and adults, the heart size may be normal but notching of the posterior one-third of the third to eighth ribs due to erosion by the large collateral arteries might be present.

Transthoracic echocardiography, including suprasternal notch views, is useful for initial imaging and hemodynamic evaluation in suspected aortic coarctation. Echocardiographic evaluation should also include measurement of the dimensions of the aortic annulus, aortic sinuses, sinotubular ridge, and ascending aorta; identification of aortic valve anatomy; determination of left ventricular size and function; and identification of any potential associated lesions such as ventricular septal defect, subvalvular aortic stenosis and mitral valve deformity.

Treatment and outcome

Since surgical repair of aortic coarctation became available in 1944, survival of patients with aortic coarctation has dramatically improved and the number of patients who were operated on and reach adulthood is steadily increasing. However, life expectancy is still not as normal as in unaffected peers. Survival of patients operated at a median age of 16 years was 91% at 10 years, 84% at 20 years and 72% at 30 years after operation. Survival of post-coarctectomy patients is significantly affected by age at operation and nowadays early repair is advocated. Even after early repair—before the age of 5 years—the estimated survival is still reduced, with 91% of the operated patients alive at 20 years and 80% at 40 to 50 years after surgery. However, repair of aortic coarctation is still recommended in patients at older age when diagnosis is delayed, because it improves blood pressure regulation and is probably associated with a lower risk of cardiovascular events in later years and improved survival.

There are several surgical techniques used for correction of the aortic coarctation. (Figures 11.3.2 & 11.3.3) Resection of the narrowed aortic segment with end-to-end anastomosis is the most commonly used technique. The subclavian flap aortoplasty and dilatation with a patch are not in use anymore due to a decreased blood flow in the left arm and a high rate of aneurysmatic deformation of the vessel respectively. When end-to-end anastomosis is not feasible, an interposition graft might be used instead. Sometimes a complete resection of the stenosis is not possible, for example when the carotid arteries are part of the coarctation, then an extended aortic arch repair or extra-anatomic bypass might be an appropriate choice.

Figure 11.3.2: Schematic drawing showing surgical procedures for repair of coarctation of the aorta. Left: resection with end-to-end anastomosis. Middle: dilating technique using a patch; this technique is used in coarctations involving a long segment of the aorta. Right: the subclavian flap aortoplasty, using the left subclavian artery.

Figure 11.3.3: Schematic drawing showing surgical procedures for repair of a coarctation of the aorta. Left: an interposition graft. Middle: the extended aortic arch repair. Right: the extra-anatomical bypass.

Transcatheter interventions for native aortic coarctation have been used for over 20 years. Transcatheter treatment for native aortic coarctation has been shown to be feasible, relatively safe and effective at short term and intermediate follow-up and is rapidly becoming the treatment of choice. Older age, however, seems to be a risk factor for suboptimal outcome after balloon angioplasty possibly due to a more fibrotic and rigid aorta. Especially in the full grown patient, stent placement seems a particularly attractive option, resulting in an almost complete relief of the gradient in 95% of the patients. Another benefit of stent placement is the ability to address longer segment coarctations, which typically have a poorer outcome after balloon angioplasty alone. Long-term results, however, are to be awaited. Concern after surgery or catheter intervention falls chiefly in seven categories: recoarctation, aortic aneurysm formation or aortic dissection, coexisting bicuspid aortic valve, endocarditis, premature coronary atherosclerosis, cerebrovascular accidents and systemic hypertension.