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A 14 month old African American girl with a history of Wolff-Parkinson-White (WPW) syndrome presented to the emergency department apnoeic, cyanotic, and without a pulse. She had suddenly become limp and unarousable. She did not respond to resuscitative efforts and was pronounced dead.
The patient had been diagnosed with WPW when she was 6 months old, after an irregular rhythm was noted in a routine examination. ECG showed normal sinus rhythm with infrequent preventricular contractions, a delta wave, a PR interval of 0.06 seconds, and a QRS interval of 0.096 seconds. QTc and axis were normal. Echocardiography revealed a normal sized heart with no structural abnormalities. She was not treated for WPW because she did not have episodes of arrhythmia on 72 hour Holter monitoring.
Necropsy revealed congestion of the lungs with prominent lymphatic dilatation and cardiomegaly. The right ventricular wall was thin and two subendocardial nodules (fig 1) were identified near the atrioventricular valves. The left atrial nodule measured 0.2 cm and the right atrial nodule measured 0.5 cm.
Microscopically, the myocardium and subendocardial muscle of both ventricles contained bundles of large round myocytes with smooth borders, granular and eosinophilic cytoplasm, and small slightly irregular nuclei (fig 1). Electron microscopy showed increased mitochondria and loss of myofibres in these histiocytoid cells, consistent with the diagnosis of histiocytoid cardiomyopathy.
Histiocytoid cardiomyopathy is a rare myocardial disorder of unknown aetiology which is characterised by increased heart weight, subendocardial nodules, and the presence of histiocytoid cells within the myocardium. Involvement of the valves and conduction system is occasionally seen. The histiocytoid cells have decreased bundles of myofibrils and increased numbers of dilated mitochondria.1
Histiocytoid cardiomyopathy usually affects girls between the ages of 6 months and 2 years. However, cases have been reported as early as 3 days old and as late as 4 years old. Arrhythmias, including ventricular tachycardia, ventricular fibrillation, supraventricular tachycardia, and sudden death are common presentations.2 In the few cases of histiocytoid cardiomyopathy that have been diagnosed ante mortem, one patient benefited from treatment with amiodarone,3 and three others from surgical excision of the abnormal tissue.4
Although not as common as ventricular tachycardia, WPW is frequently found in patients with histiocytoid cardiomyopathy.5 While WPW has a generally favourable prognosis in children, cases of WPW in combination with histiocytoid cardiomyopathy are uniformly fatal, due to the poor prognosis of histiocytoid cardiomyopathy alone.
This research was supported in part by the Robert Wood Johnson Foundation.