Wheezes are coarse whistling sounds generated by vibration of a narrowed airway from turbulent airflow. Wheezing often is equated with asthma, reactive airways disease, bronchiolitis, or other respiratory disease. Wheezing, however, is also a common finding in infants and children with congestive heart failure. Cardiac asthma may be defined as the clinical syndrome induced by acute passive congestion and edema of the lungs. The classic explanation for wheezing during pulmonary edema is that bronchial wall edema and intraluminal edema fluid cause narrowing of the small airways, but bronchial hyperresponsiveness also plays a part. This bronchoconstriction is mediated by unmyelinated C-fiber nerve endings in bronchi, pulmonary vasculature, and lung parenchyma (J or juxtacapillary receptors). In animal studies, these receptors, which are carried in the vagus nerve, have increased their activity fivefold as a result of pulmonary edema.

In infants, heart failure may be difficult to identify. Infants whose bronchioles are proportionately narrow as compared to adults will not typically have crackles with pulmonary edema but rather wheezes. Consequently, the signs of cardiac-induced pulmonary congestion may be indistinguishable from bronchiolitis or asthma. A history of feeding disturbance, slow weight gain, diaphoresis should raise the suspicion of cardiac disease. Further confounding the diagnosis, pneumonitis with or without atelectasis, especially in the right middle and lower lobes is common in children with heart disease due to bronchial compression by the enlarged heart. Physical exam findings can help distinguish heart failure from respiratory disease. Hepatomegaly is a common finding in infants and children with heart failure. The cardiac exam will show increased precordial activity. Auscultation may reveal a gallop or murmur. The presence of these features should prompt further workup with an electrocardiogram and chest x-ray. Cardiomegaly is very frequent in children with significant heart disease.

When presented with the older child with a first episode of acute wheezing, assessment for heart disease is equally important. Myocarditis or dilated
cardiomyopathy can present similarly as RAD. Consideration of heart disease is especially important in children who do not seem to respond to bronchodilator therapy. A history of exercise intolerance, weight loss or gain, or a negative family history of asthma or allergies raises the suspicion of heart disease. Again, the clinician should make note of the presence or absence of hepatomegaly or jugular venous distention.