Low voltage electrocardiogram with tachycardia in hypothyroidism--a warning sign of cardiac tamponade.

Pericardial tamponade is a rare complication of pericardial effusion associated with hypothyroidism. In myxedematous patients with pericardial effusion, the occurrence of paradoxical tachycardia may be a clue that pericardial tamponade is impending or has occurred. This should lead to urgent investigations, particularly echocardiography, to confirm the diagnosis so as to allow prompt treatment. Two patients who presented with cardiac tamponade from severe hypothyroidism are described. There was a paradoxical association of a low voltage QRS complex on the electrocardiogram with a fast ventricular rate in both patients. This may be a useful warning sign in patients with impending cardiac tamponade in hypothyroidism if confirmed by further cases.