Microcardia is encountered less frequently than cardiomegaly. Radiographically, microcardia has been observed as a shrinking cardiac silhouette on serial chest radiographs . A small heart on chest radiographs may be considered to be of little clinical significance, as this may be a normal finding in slender patients. Additionally, a heart may appear small if the patient inspired deeply with exaggerated depression of the diaphragm and marked increased intrathoracic pressure causing elongation of the mediastinum.
However, microcardia may occur in concert with cardiac atrophy as seen in conditions such as chronic wasting disease, or malnutrition [1, 2]. The most commonly cited medical condition causing cardiac atrophy is Addisonâ€™s disease . This is postulated to be secondary to chronic hypotension and lowered blood volume, that over time require the heart to perform less work, and as a result disuse atrophy results . Malnutrition is also implicated as a cause of microcardia, which is usually seen as the result of severe starvation, or as a result of malignant neoplasms, or chronic infection [1, 2]. Additionally, although not reported, patients who are status-post bariatric surgery and fail to adhere to specific dietary recommendations are at increased risk of developing nutritional deficiencies that can result in microcardia.
Microcardia without cardiac atrophy is seen secondarily to a rapid decrease in blood volume associated with severe dehydration or massive hemorrhage . Patients with this type of microcardia, demonstrate signs of dehydration, and potentially may present in shock if severe. Microcardia without cardiac atrophy can present at any age, however, it generally is appreciated more readily in infants and young children secondary to increased susceptibility to rapid fluid shifts .
In either microcardia with or without cardiac atrophy, treating the underlying disease results in normalization of the heart size.