Rate-dependent left bundle-branch block in a child with propionic aciduria.

In most cases, a left bundle-branch block pattern on an electrocardiogram is a postoperative phenomenon. Under rare circumstances, it can be found in patients after myocardial infarction or in patients with hypertrophic cardiomyopathy, or it can be exercised induced. We describe a pediatric patient with propionic aciduria, dilated cardiomyopathy, and rate-dependent left bundle-branch block on her electrocardiogram.