Plasma Thyroid Hormone Profiles Immediately Following Out-of-Hospital Cardiac Arrest

Abstract

Previous studies have shown abnormal thyroid hormone profiles during cardiac arrest. We explored this association further by characterizing plasma thyroid hormone profiles in 473 patients with out-of-hospital cardiac arrest and correlating them with clinical outcomes. Paramedics collected blood at the end of attempted resuscitation regardless of success. Bloods were collected and processed in a similar manner from 18 control subjects randomly selected from the community. Total thyroxine and total triiodothyronine were lower and reverse triiodothyronine and thyrotropin were higher in cardiac arrest patients than control subjects (all p < 0.001). Except for reverse triiodothyronine, findings were similar for a subgroup of cardiac arrest patients considered to be previously healthy (n = 30). Being discharged alive was associated with total thyroxine, total triiodothyronine and reverse triiodothyronine concentrations closer to the control range and thyrotropin concentrations farther from it, namely higher. In a multivariate stepwise model, only total triiodothyronine and thyrotropin were significantly associated with outcome. Whether these profoundly abnormal profiles represent a pre-existing state or a sudden change of thyroid hormone concentrations cannot be answered with this retrospective study. These observations suggest that thyroid hormones may play a role in the etiology of cardiac arrest, its prognosis, or both.

The role of thyroid hormones in acute coronary syndromes: Prognostic value of alterations in thyroid hormones

“…However, it has been linked to worse prognosis and increased mortality in patients with septic shock or acute stroke . Acute cardiac diseases also have been associated with low serum T3 levels . It has been reported that THs alterations constitute a powerful independent marker of the severity of illness and mortality in patients after resuscitated cardiac arrest .…”

Clinical investigation: thyroid function test abnormalities in cardiac arrest associated with acute coronary syndrome

“…Iervasi and coworkers [23] reported low serum T 3 levels as an independent predictor of mortality in patients with cardiovascular disease. Alterations in TFTs are more marked in seriously ill patients [24-27]. In the present study the TFT findings in those who died within the first 2 months deteriorated more than did those in survivors.…”

“…Regardless of resuscitation success, Longstreth and coworkers [24] observed low T 3 and T 4 levels and high TSH levels in patients with out-of-hospital cardiac arrest. They stated that these alterations in thyroid hormones may play a role in cardiac arrest aetiology and prognosis.…”

“…Low T 3 concentrations are known to be major independent indicators of mortality in patients hospitalized for cardiac causes [23]. Previous studies [24-27] reported critical impairments in thyroid homeostasis during the acute stage of cardiac arrest. However, it is not certain how, for how long and in which patient population this critical condition occurs.…”

Sick Euthyroid Syndrome

“…Although Tj and thyroid hormone analogs have been studied as adjuncts to the treatment of heart failure [93][94][95], the rationale for use of these hormones has been for their potential ionotropic properties and interactions with the adrenergic system rather than to correct abnormal serum thyroid hormone concentrations. Serum T 4 and Tjlevels decrease acutely following myocardial infaction [96] and cardiac arrest [97][98][99], raising a question as to what role, if any, thyroid hormones have in acute cardiac injury. Similar alterations in thyroid hormone parameters are observed following cardiopulmonary bypass [100-106), and it is in this setting that Tj administration has been extensively studied.…”