Atrioventicular block in familial amyloidosis; revisiting an old debate.

Familial amyloidosis with polyneuropathy (FAP) is the rarest of the cardiac amyloidoses, with less than 200 cases diagnosed each year. In this disease, cardiac involvement is characterized by extracellular amyloid infiltration throughout the heart, usually resulting in sinoatrial nodal dysfunction, cardiomyopathy, and congestive heart failure. While cardiac conduction disturbances are a common feature of FAP, the mechanism of these disturbances seems to be a point of contention among researchers. We present a case of a 78-year-old man with a history of FAP admitted with the diagnosis of atrial fibrillation/flutter. After failing to convert to normal sinus rhythm despite medical therapy, an electrical cardioversion was performed. Following the procedure, the patient converted to symptomatic Mobitz type two second-degree atrioventricular block and required dual chamber pacemaker placement. Our case emphasizes the potential consequences of cardioversion in this progressive condition and the need for further studies on the pathophysiology of cardiac involvement in FAP.