Characterizing the true incidence of CHD in the United States also has proven difficult because of variations in the definitions and methods used to detect lesions across the multiple studies that have looked at this matter.The estimated incidence of CHD, grouped according to severity, is 2.5 to 3 per 1000 live births for severe CHD, and from 3 to 13 per 1000 live births for moderately severe forms.9 When all forms are considered, including minor CHD (which includes tiny muscular ventricular septal defect [VSDs] present at birth and other trivial lesions), the total incidence of CHD rises to 75 per 1000 live births.9 CHD is one of the most common chronic illnesses in young adults with special health care needs.
Complications in Adulthood
The ACHD population represents a diverse population in terms of severity of CHD, history of surgical/catheter-based interventions, and socioeconomic status. However, a unifying clinical concern for these patients is their increased risk for morbidity and mortality in the young adult years. Despite the tremendous advances in the field over previous decades, mortality in this population in adulthood is estimated to be up to 7 times higher compared to age-matched peers.10,11 For many patients, palliative CHD interventions result in a significant drop in early morbidity and mortality but frequently lead to delayed morbidity from secondary multi-organ complications as these patients transition from pediatric to adult care. For example, due to the chronic low flow and low cardiac output state created by Fontan palliations, patients are at risk for diastolic dysfunction, arrhythmias, thrombotic events, protein-losing enteropathy, and cirrhosis/congestive hepatopathy, among other chronic conditions. These patients require frequent follow up and management by a multidisciplinary team including a primary care provider and various specialty groups.
Cardiac Disease
The most common causes of death in ACHD patients are heart failure (27%) and sudden cardiac death (19%), which occur at mean ages of 48 years and 39 years, respectively.10 The form of heart failure in ACHD patients is related to subsystemic right ventricle (RV) dysfunction, coronary under-perfusion, residual shunts, and residual progressive valve regurgitation. One of the more common examples of this is seen in palliated Tetralogy of Fallot patients who have undergone a transannular patch as a neonate. These patients are frequently left with significant pulmonary regurgitation leading to RV dilation, RV failure, and subsequent left ventricle (LV) failure. Another common example is the patient with dextro-transposition of the great arteries (DTGA) status post atrial switch who has a subsystemic morphologic RV. These patients will often develop significant RV dysfunction related to the chronic high pressures associated with systemic circulation.
Arrhythmias are a major contributor to morbidity and mortality in this population and are the most common reason patients present back into care. Difficult to control, multifocal intra-atrial re-entrant tachycardia is extremely common in ACHD, with an estimated 50% of all patients developing atrial arrhythmia by age 55. A recent study determined that the risk of atrial fibrillation in individuals with CHD was 22 times higher than that in age-matched controls, with the highest risk being seen in patients with conotruncal defects. Furthermore 10% of these patients develop heart failure.12 The risk for, incidence of, and type of arrhythmia is associated with the severity of the congenital heart lesions, as well as the type and timing of surgical interventions. Later age of repair has been associated with an increased likelihood of arrhythmias.13 Tetralogy of Fallot is an example of a moderately complex congenital heart lesion and is the most common cyanotic congenital heart lesion. In these individuals, the risk for atrial tachycardias, ventricular tachycardias, and need for a pacemaker is much higher than in age-matched peers.14 This includes an increased risk of sudden cardiac death, with many of these patients requiring placement of an implantable cardioverter defibrillator.
Pulmonary Disease
There is a 44% to 56% prevalence of restrictive pulmonary disease in the ACHD population, compared to 9% in the general non-CHD adult population. The incidence of pulmonary hypertension is also significantly higher in the ACHD population. The etiology for development of pulmonary hypertension is multifactorial, including chronic thromboembolic disease, left-sided heart disease, longstanding left to right shunts, and obstructive sleep apnea. These conditions have a significant impact on survival, as moderate/severe lung function impairment is an independent predictor of survival. Patients with shunt lesions are at risk of developing pulmonary arterial hypertension later in life,1 which quadruples the risk of all-cause mortality and more than triples the risk of cardiovascular mortality.7
Liver Disease
Hepatic morbidity associated with palliated CHD is often related to prior surgical interventions. The most common morbidities include chronic hepatitis C and liver failure from chronic under-perfusion and passive congestion, especially following Fontan palliation. Long term, these complications can lead to cirrhosis and hepatocellular carcinoma.15-18 Unfortunately, hepatic morbidity often precludes patients from having a surgical intervention, complicating the management of a population with baseline significantly increased need for surgical re-intervention.
Renal Disease
Approximately 50% of the ACHD population has some degree of renal dysfunction, with a higher incidence in cyanotic CHD.19 The American College of Cardiology/American Heart Association (ACC/AHA) recommends routine assessment of renal function in all adults with moderate and severe CHD due to its association with a poor prognosis in the ACHD population.1 In the immediate cardiac postoperative period, acute kidney injury leads to an eightfold increase in mortality.20 Over the longer term, there is a fivefold increase in mortality with moderate to severe renal impairment and a twofold increase with mild renal impairment compared to those with normal renal function.21
