Method: We prospectively screened patients hospitalized for newly diagnosed and otherwise unexplainable LVSD (ejection fraction, EF, <50%) and coinciding tachyarrhythmia. Coronary angiography and cardiac magnetic resonance imaging were performed to exclude other causes for LVSD. During the initial stay, patients underwent a rhythm control strategy in accordance to the locally implemented clinical pathways. LVEF was assessed by echocardiography at presentation, before discharge and at follow-up (FU) visits after 2, 4, and 6 months. Patients, who lost sinus rhythm during FU, were excluded from our analysis. Patients with any increase of ≥15% in absolute EF or an EF ≥50% with an absolute improvement of ≥10% after 6 months of FU were assigned to the AIC-group, which is a common definition of AIC. All others were assigned to an idiopathic DCM-group as final comparator.

Results: 63 patients were eligible, 13 of them presented with recurrent arrhythmia and were excluded for this analysis. Thus, our sample consists of a total of 50 patients. 39 of 50 patients have completed all FU visits so far and their results are reported in this interim analysis. At presentation, mean±SD heart rate (HR) was 121±17/min. After rhythm therapy, HR was normalized to 66.7±10/min. The development of EF in AIC and DCM patients can be seen in Fig. 1. Surprisingly, only 6 patients did not fulfill the AIC-criteria in this specific collective resulting in a prevalence of 84.6% (95%-CI: 69.5% – 94.1%). This high prevalence of AIC clearly underlines the importance of the disease. Two and 4 months after rhythm intervention, 57.5% and 72.5% of patients fullfilled AIC-criteria (see Fig. 2). The sensitivity for detection of AIC via echocardiographic measurement of EF at months 2 and 4 of FU was 65.0% and 85.7% with a specificity of 100%, emphasizing that a FU of 6 months is necessary to certainly distinguish between AIC and idiopathic DCM.

Conclusion: In this prospective trial we demonstrate, that the prevalence of AIC in the clinically relevant patient collective with newly diagnosed and otherwise unexplainable LVSD with concomitant tachycardia is higher than expected. Analysis of the time course of AIC clearly suggests that diagnosis cannot be established before 6 months of follow-up after successful rhythm restoration. These results may help to improve diagnosis of AIC in daily clinical practice.