Masked thyroid dysfunction among elderly patients with atrial fibrillation

Restoration of sinus rhythm following levothyroxine treatment in a case of primary hypothyroidism presenting with atrial fibrillation and pericardial effusion

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 μIU/ml and total thyroxine (T4) of 5.57 μg/dl). Treatment with levothyroxine led to resolution of symptoms, AF, and pericardial effusion.

Risk index for peri-operative atrial fibrillation in patients undergoing open intracranial neurosurgical procedures

The aim of this prospective study was to determine the prevalence of pre-operative atrial fibrillation and the incidence of postoperative atrial fibrillation in patients undergoing elective or emergency intracranial neurosurgical procedures and the relation to survival and neurological outcome at 6-months follow-up compared to patients with sinus rhythm. A total of 2020 patients were enrolled; 1540 patients underwent elective procedures and 480 underwent emergency procedures. Prevalence of pre-operative atrial fibrillation was 3.7% in elective and 7.2% in emergency procedures (p = 0.0012). In patients undergoing elective cerebral procedures with pre-operative atrial fibrillation, compared to patients with sinus rhythm, 6-month neurological outcome and survival rate are similar. In patients undergoing emergency neurosurgical cerebral procedures, the presence of pre-operative atrial fibrillation is related to an increased risk of poor neurological outcome but with similar survival rate.

Epidemiology, Mechanisms, and Risks

Atrial fibrillation (AF) is one of the most frequent complications of cardiac surgery, affecting more than one third of patients. The mechanism of this arrhythmia is believed to be reentry. The electrophysiologic substrate may be preexisting or may develop due to heterogeneity of refractoriness after surgery. Multiple perioperative factors have been proposed to contribute to the latter, including operative trauma, inflammation, elevations in atrial pressure (including that due to left ventricular diastolic dysfunction), autonomic nervous system imbalance, metabolic and electrolyte imbalances, or myocardial ischemic damage incurred during the operation. Whether ectopic beats originating in the pulmonary veins explain at least some episodes of postoperative AF, as has been shown for nonsurgical patients with the arrhythmia, is of current interest as such sites could easily be isolated at the time of surgery. The development of postoperative AF is associated with a higher risk of operative morbidity, prolonged hospitalization, and increased hospital cost compared with that in patients remaining in sinus rhythm. Many factors have been identified as being associated with postoperative AF, but the most consistent variable across studies is increasing patient age. It is speculated that age-related pathologic changes in the atrium contribute to arrhythmia susceptibility. An important modifiable risk factor for postoperative AF is the failure to resume therapy with beta-adrenergic receptor blockers after surgery. The stratification of patients who are at higher risk for AF would focus preventative strategies on patients who are most likely to benefit from such therapy. Nonetheless, since postoperative AF often develops in patients with comorbidities who are predisposed to other complications and prolonged hospitalization, it is presently unclear whether the prevention of postoperative AF will result in improved patient outcomes, particularly shorter hospitalizations.

Relationship between atrial fibrillation and primary hypothyroidism in the dog

Atrial fibrillation (AF) and primary hypothyroidism are most often diagnosed in middle-aged and older dogs of large and giant breeds. We hypothesized that the frequency of primary hypothyroidism may be higher in dogs with AF than in those without AF. Two groups were investigated. Group 1 (March 1987-June 1990) consisted of 128 dogs with AF. A thyroid-stimulating hormone (TSH) stimulation test was performed in dogs with a low voltage on the ECG and low uptake of pertechnetate on a thyroid scan. Group 2 (July 1990-July 1991) consisted of both dogs with AF (n = 38) and control dogs (n = 235) in which plasma thyroxine (T4) was measured. If T4 was below 15 nmol/l, a TSH stimulation test was performed. The frequencies of primary hypothyroidism in group 1 (8/128) and in the group 2 AF dogs (3/38) were not different, but were higher than in the control animals (3/235) (P < 0.05). The group 1 and the group 2 AF dogs were found to be comparable, and pooling of the data of the two groups enhanced the significance of the frequency of primary hypothyroidism in dogs with AF versus the control animals (11/166 versus 3/235) (P < 0.01). We concluded that the frequency of primary hypothyroidism in dogs with AF is higher than in the group of control dogs without AF. This may be due to the additional cardiovascular changes accompanying primary hypothyroidism in dogs that already have heart disease.

Subclinical thyroid dysfunction in the elderly

Subclinical thyroid dysfunction is more common in older persons. By definition, these disorders are recognized by isolated elevation or suppression of the serum TSH concentration, in association with a normal serum free thyroxine level. Among individuals over 65 years old, subclinical hypothyroidism is found in approximately 10% of women and approximately 3% of men. It is most commonly due to autoimmune thyroiditis or previous treatment for hyperthyroidism. There may be three indications for L-thyroxine therapy: (a) presence of antithyroid antibodies, indicating substantial risk of progression to over hypothyroidism; (b) symptoms consistent with thyroid hormone deficiency; and (c) an elevated serum LDL-cholesterol. Subclinical hyperthyroidism is present in approximately 1%-2% of older persons. The most common cause is excessive thyroid hormone therapy, followed by mild endogenous hyperthyroidism due to Graves' disease or nodular goiter. These can be differentiated from other causes of low serum TSH concentration based on clinical and other laboratory and radionuclide scan criteria. The most serious consequences of subclinical hyperthyroidism are atrial fibrillation and osteoporosis, to which elderly patients are particularly predisposed.

Thyroid disease in the elderly

Thyroid disease in the aged, both hypothyroidism and hyperthyroidism, may be subtle or may be present with no clinical symptoms and signs, and is therefore difficult to diagnose on the basis of clinical evaluation. The help of the laboratory is essential in making the diagnosis of disease of the thyroid. Therapeutic strategies are different in the aged than in the younger adult with thyroid disease. It is essential for geriatricians, and all clinicians who care for the elderly, to have a solid understanding of thyroid function and dysfunctions in this group of patients so that they diagnose diseases of the thyroid correctly and treat them appropriately.

Thyrotoxicosis and the heart

Many patients with thyrotoxicosis have clinical features that reflect the effects of excess thyroid hormone on the cardiovascular system. Thyrotoxicosis can aggravate preexisting cardiac disease and can also lead to atrial fibrillation, congestive heart failure, or worsening of angina pectoris. In elderly patients, these cardiac manifestations may dominate the clinical picture and warrant the measurement of the serum thyrotropin concentration. In the absence of preexisting cardiac disease, treatment of thyrotoxicosis usually results in a return of normal cardiac function.

Thyroid disease in the elderly

As people in our society live longer, it is important for clinicians to know more about problems commonly seen in the elderly. Thyroid problems are especially important to understand because they do occur with rather high frequency, and their mode of presentation is frequently different from those seen in younger patients. The thyroid gland does undergo certain age-related changes in anatomy and physiology, but overall the thyroid is able to produce a normal amount of thyroid hormone throughout the years. Hypothyroidism is frequently difficult to diagnose in the elderly, because many of the symptoms of hypothyroidism can easily be confused with symptoms of aging. When hypothyroidism is looked for in large population studies of elderly patients, the incidence varies from 1% to as high as 17%, with women being more commonly affected than men, and subclinical hypothyroidism being more common than overt hypothyroidism. Virtually all cases of hypothyroidism are due to autoimmune thyroid disease, with most patients having measurable titers of thyroid autoantibodies. The therapy of hypothyroidism is done with extreme caution, as older patients are frequently very sensitive to the effects of excess thyroid hormone. In addition, the metabolism of thyroid hormone slows down with age, making the full replacement dose much less in an older patient than in a younger one. Hyperthyroidism is also quite common, occurring in from 0.5% to 3% of all elderly patients. The presentation is frequently atypical, as patients often lack the hyperdynamic symptomatology and instead have a more sedated, apathetic presentation. Weight loss and cardiac symptoms frequently predominate, and the presence of a goiter is frequently absent, making the diagnosis less obvious than in a younger patient. Therapy is usually radioactive iodine, after an adequate course of antithyroid drugs, to render the patient euthyroid. Thyroid nodules do occur with increasing frequency in the elderly, but most of them are not malignant. Fine-needle aspiration for cytology is very helpful in determining which patients should be referred for surgery. Well-differentiated cancers do predominate, but their course is frequently less predictable than in younger patients. Lymphoma of the thyroid and undifferentiated cancers do occur with increasing frequency in the elderly. Multinodular goiter, usually of longstanding, is frequently seen in elderly patients, and thyroid hormone suppressive therapy not only is not indicated but may contribute to exogenous hyperthyroidism.