SUN-497 - Pheochromocytoma Presenting as Complete Heart Block: A Rare Cause of Bradyarrhythmia

Introduction: Pheochromocytoma is a rare catecholamine-secreting tumor that is typically associated with tachyarrhythmias and hypertension. Bradyarrhythmia and atrioventricular conduction disturbances are uncommon manifestations.

Case: A 71-year-old woman with hypertension initially presented with severe substernal chest pain and right arm numbness and weakness. There was concern for a ST-elevation myocardial infarction, and the patient was taken for cardiac catheterization which showed normal coronary arteries. Immediately afterwards, she developed a hypertensive crisis requiring intravenous antihypertensives and transfer to the intensive care unit. However, a day later she developed right arm and right leg weakness, and stroke workup revealed multifocal embolic infarctions on brain MRI. CT angiography of her neck revealed no carotid artery stenosis; however, CT angiography of the abdomen showed a 9 cm heterogeneously enhancing mass in the left renal fossa. The patient had multiple episodes of syncope and brief episodes of atrial tachycardia and heart block with sinus pauses, requiring transcutaneous pacing. She had complete heart block on electrocardiography, and she underwent placement of a permanent pacemaker. Laboratory studies demonstrated markedly elevated plasma free metanephrines of 36 nmol/L (normal less than 0.5 nmol/L) and free normetanephrine level of 72 nmol/L (normal less than 0.9 nmol/L), consistent with a pheochromocytoma. She was managed pre-operatively with phentolamine and then phenoxybenzamine. She successfully underwent left adrenalectomy. Pathology confirmed the diagnosis of a 7.1 cm pheochromocytoma with features correlating with aggressive behavior (Pheochromocytoma of the Adrenal gland Scaled Score of 9) and a Ki-67 5-10 %. The patient’s heart block resolved as the pacemaker interrogation revealed no arrhythmias.

Conclusion: This case highlights an atypical presentation of pheochromocytoma with complete heart block. While excess catecholamines typically induce tachyarrhythmias, paradoxical bradyarrhythmia and complete heart block may rarely occur due catecholamine-induced myocardial injury. Although most patients present with tachyarrhythmia, about 10% of patients with pheochromocytoma can debut with bradycardia due an unusual reflex to catecholamine surge. Elevated catecholamine levels lead to a decrease in cardiac β1-adrenergic receptor levels and functional activity, resulting in notable desensitization of the heart to inotropic β-adrenergic stimulation. Recognition of pheochromocytoma as a reversible cause of conduction disease is critical, as timely diagnosis and treatment may obviate the need for permanent pacing. In this case, the patient achieved resolution of the heart block and did not require pacing after treatment of her pheochromocytoma.

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