Subclinical hypothyroidism and its relationship with therapy failure in patients underwent cardiac resynchronization therapy.

OBJECTIVE: Cardiac resynchronization therapy (CRT) is used in patients with heart failure (HF), an important problem in cardiology practice, with reduced left ventricular systolic dysfunctions and left ventricular dyssynchrony to improve morbidity and mortality. Thyroid diseases have undeniable effects on cardiac functions. So, we aimed to evaluate the effect of subclinical hypothyroidism on CRT response in HF patients in this study.

PATIENTS AND METHODS: After the exclusion, 386 consecutive patients who received first-time CRT-defibrillator (CRT-D) or CRT-pacemaker (CRT-P) were retrospectively included. Known overt hypothyroidism or hyperthyroidism patients were excluded. The response of CRT was defined as a relative increase (≥15%) or absolute increase (≥10%) in left ventricular ejection fraction (LVEF) from implantation to one-year after follow-up.

RESULTS: Diabetes mellitus, atrial fibrillation and coronary artery disease ratios were similar between responder vs. non-responder groups. Thyroid stimulating hormone (TSH) levels were higher (p <0.005) in non-responder group. Responder group had higher baseline LVEF (p <0.001), and follow-up LVEF (p <0.001) and longer baseline QRS interval (p =0.004), but similar post-implant QRS interval duration (p >0.005) with non-responder group. Baseline QRS interval (p =0.002), baseline LVEF (p <0.001) and the presence of subclinical hypothyroidism (SCH) (p =0.001) were independent predictors of CRT response. Adding SCH as a risk factor to our baseline risk modelling has an independent prognostic impact to predict non-responder patients (p =0.01).

CONCLUSIONS: Presence of the SCH may be an important predictor of non-response in patients undergoing CRT. Evaluating the risk factors associated with non-response to CRT may be logical in identifying patients who obtain maximum benefit from CRT treatment.