The effect of serum calcium level on the success of diltiazem treatment: A retrospective cohort study

Diltiazem is an antiarrhythmic drug widely used in the treatment of atrial fibrillation (AFib) with rapid ventricular response (RVR). It reveals its effect by blocking L-type calcium channels. Thus, it inhibits the extracellular calcium influx into the cytosol. The relationship between serum calcium level and the efficacy of intravenous (IV) diltiazem used in the treatment of AFib with RVR has not been investigated in vivo. The aim of this study is to investigate the mentioned relationship. This study was planned as a single-center retrospective study. The data of 349 patients who presented to the emergency department with AFib with RVR and treated with diltiazem were retrospectively analyzed. A patient was considered to have responded to diltiazem treatment if the existing heart rhythm returned to sinus rhythm, or the heart rate decreased below 100 beats/min, or the heart rate decreased >20% provided that it was below 120 beats/min. The ionized calcium levels were recorded. The relationship between serum calcium level and the success of diltiazem treatment was examined. Fifty five percent of the patients were female. The median age was 75 years. The rate of response to diltiazem treatment was 67.3%. The median of ionized calcium levels in the group which responded to diltiazem treatment (n = 235) was 1.14 mmol/L (IQR: 0.12), and the group which did not respond to diltiazem treatment (n = 114) was 1.11 mmol/L (IQR: 0.12) (p = 0.322). The patients were divided into three groups as low, normal, and high calcium levels according to the calcium reference levels determined by the hospital laboratory. The rate of response to diltiazem treatment was 61.4% in patients with low ionized calcium levels, 76.1% in patients with normal ionized calcium levels, and 40.0% in patients with high ionized calcium levels. The rate of response to diltiazem treatment was higher in patients with normal ionized calcium levels compared to patients with low or high ionized calcium levels (p = 0.004, p = 0.003). The success rate of diltiazem used in the treatment of AFib with RVR was highest in physiological calcium levels. The current study may provide the clinician with awareness about the consideration of serum ionized calcium levels when choosing drugs in patients with AFib with RVR.