hyperthyroidism is commonly associated with atrial fibrillation ( af ) , particularly in the elderly .
we hereby report a case of patient with primary hypothyroidism presenting with af and pericardial effusion which resolved with levothyroxine therapy .
he complained of chest pain which was substernal , nonradiating , and throbbing in nature .
he smoked 10 cigarettes per day for past 25 years , and denied use of alcohol , caffeine , or drugs .
physical examination was unremarkable except for the irregular heart rate ( approximately 130 beats per min ) and muffled heart sounds on auscultation .
electrocardiogram [ figure 1 ] confirmed af with rapid ventricular rate , which responded to initial treatment with metoprolol [ figure 2 ] .
af with rapid ventricular rate normalization of af with metoprolol thyroid function tests revealed a sensitive thyroid stimulating hormone ( tsh ) concentration of 34.70 iu / ml ( normal : 0.40 - 4.70 iu / ml ) , and thyroxine ( t4 ) of 5.57 g / dl ( normal : 8 - 12 g / dl ) confirming primary hypothyroidism .
transthoracic echocardiography showed normal left ventricular systolic function ( ejection fraction of 63% ) , decreased left ventricular diastolic compliance , and massive pericardial effusion ( posterior 17 mm , anterior 13 mm ) .
right atrial and right ventricle showed 30% collapse during diastole , mild left ventricular hypertrophy was present with no regional wall motion abnormalities .
patient was treated with levothyroxine which lead to resolution of symptoms and restoration of normal sinus rhythm .
repeat echocardiography showed no collapse of right atrium and right ventricle during diastole ) and mild pericardial effusion ( 11 mm circumferential ) .
the most common cardiovascular signs and symptoms of hypothyroidism include bradycardia , mild hypertension ( diastolic ) , narrow pulse pressure , cold intolerance , pericardial effusion , cardiomyopathy and fatigue .
hypothyroidism is often associated with electrocardiographic changes like bradycardia , right bundle branch block , flat or inverted t wave , qrs prolongation , qt prolongation , and infrequently ventricular arrhythmia , torsades de pointes .
treatment of hypothyroidism is well - documented to cause af due to inadvertent overdosing of levothyroxine .
although atrial arrhythmias are common and ventricular ectopy is rare in patients with hyperthyroidism , it is rarely associated with hypothyroidism .
af is seen in 5 - 15% patients of hyperthyroidism and may be the presenting feature . increased chronotrophic activity
due to increased thyroid hormones and increased sympathetic tone are the proposed underlying mechanisms . the physiological chronotropic response and normal tension of the heart muscle in
diastolic phase depend on the action of triiodothyronine in the heart cells and its stimulating influence on na - k atpase and ca atpase in endoplasmic reticulum .
normal contractility is also related to triiodothyronine stimulated transcription of the myosin heavy - chain alpha gene and inhibition of the heavy - chain beta gene .
moreover , triiodothyronine acts on the cardiac muscle affects the number of beta adrenergic receptors and their sensitivity to catecholamines .
few case reports have demonstrated that hypothyroidism may cause a prolongation of the qt interval which predisposes the patient to ventricular irritability .
the canadian registry of atrial fibrillation investigators reported that 1.5% of 726 patients with af had hypothyroidism over a period of 1.7 years .
studies have also reported that up to 8% of patients with atrial fibrillation were hypothyroid .
hypothyroidism is known to cause nodal defects , but the mechanism of af in hypothyroidism is not known .
it is also not clear whether its presence is causally related or is a mere manifestation of an underlying unrecognized structural heart disease .
however in our case , reversal of af with levothyroxine treatment negates underlying structural damage of the heart nans suggests causal relationship .
previous case reports have shown association of af with hypothyroidism but pericardial effusion was absent in those cases .
this is possibly the first reported case of af and pericardial effusion in a case of hypothyroidism .
young patients with no evidence of organic heart disease may be started on a full replacement dose of thyroxine .
older patients or those with known or suspected ischemic heart disease , should initially be given about 25% of the anticipated replacement dose , and the dose should be increased gradually at 6 - 8 week intervals .
 a 72-year - old man presented with palpitation , dyspnea , and chest discomfort . 
 initial investigations revealed atrial fibrillation ( af ) and pericardial effusion , further investigations unraveled primary hypothyroidism ( thyroid stimulating hormone ) of 34.7 iu / ml and total thyroxine ( t4 ) of 5.57 g / dl ) . 
 treatment with levothyroxine led to resolution of symptoms , af , and pericardial effusion . 