The subclinical hypothyroid state might predict 30-day readmission in patients admitted with acute heart failure syndrome and reduced left ventricular ejection fraction.

Introduction: Thyroid hormone (TH) has an essential role on the functional capability of cardiac muscle with its gene modulation and induction of vasodilatory effects. There is considerable evidence to suggest the role of TH in patients with acute coronary syndrome, but less is known about its prognostic role in heart failure (HF) patients. We aim to evaluate the association between subclinical hypothyroid state (SCHS) and event rates including 30-day all-cause and HF readmission in patients with an index hospitalization for acute HF syndrome (AHFS).

Methodology: A retrospective chart review analysis of 2335 patients admitted with the diagnosis of AHFS between 1 January 2007 and 31 December 2017 was conducted. SCHS was defined as thyroid-stimulating hormone (TSH) level >4.50 mIU/L with a normal thyroxine (T₄) level. Patients with pre-existing thyroid disease or receiving thyroid replacement therapy were excluded. HF with preserved ejection fraction (HFpEF) was defined as left ventricular ejection fraction (LVEF) >40% and HF with reduced ejection fraction (HFrEF) was defined as having LVEF ⩽40%. Percentage of 30-day, 3-month and 6-month all-cause readmission and mortality rates were calculated in both cohorts of AHFS (HFpEF and HFrEF) with and without SCHS.

Results: The mean age of the 2335 AHFS population was 65 (±14.8) years. Of the 2335 patients admitted with AHFS, 1228 (52.6%) patients were found to have HFrEF and 1107 (47.4%) with HFpEF. There were 170 (7.3%) patients with AHFS found to have SCHS. There were more males than females (54% versus 46%). The percentage of hospital readmission within 30 days was higher for patients with SCHS compared with those without SCHS in the HFrEF group (42% versus 30%, p = 0.001). Hospital readmission within 30 days for patients with SCHS compared with those without SCHS in the HFpEF group did not differ (36.5% versus 31%, p = 0.47). Additionally, all-cause mortality was higher among patients with SCHS compared with patients without SCHS in the HFrEF group (18.7% versus 7.0%, p < 0.001). All-cause mortality was found similar in both arms of the HFpEF group (9.5% versus 7.7%, p = 0.73).

Conclusion: During an index hospital admission for AHFS, SCHS was an independent predictor of readmission in 30 days in patients with HFrEF but not in patients with HFpEF. Additionally, it was related to adverse outcome such as all-cause mortality in HFrEF patients but not in HFpEF patients. Further studies regarding the concept of tissue thyroid and the potential for a therapeutic target are warranted.