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Delayed pericarditis and cardiac tamponade associated with active-fixation lead pacemaker in the presence of mitochondrial myopathy and Ockham's razor.

A 23-year-old male patient, with a diagnosed mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes, was referred for recurrent fainting. Long sinus pauses were documented, and an atrial pacemaker with an active-fixation lead was implanted. He was admitted again 4 months later because of chest pain and diffuse ST segment changes. On the basis of these, pericarditis was diagnosed, corticosteroid therapy and the adjunct of salicylates were started, which in few hours enabled the relief of symptoms and the reduction of ECG abnormalities. However, 24 h later, the patient suddenly experienced severe hypotension and tachycardia, and an emergency echocardiogram showed pericardial tamponade. The differential diagnoses with atrial free-wall perforation and Dressler-like syndrome were discussed, along with the difficulties in management. By a 'wait and see' strategy, the active-fixation atrial lead was eventually changed into a passive-fixation one, while continuing corticosteroids and salicylates. The patient quickly improved and is now, after 1 year, symptom free. For the explanation of any phenomenon, it is important that as few assumptions as possible are considered, eliminating those that make no difference in the observable predictions of the explanatory hypothesis or theory, according to the concept of Ockham's razor.