2.2. ECG Data

This study was based on ambulatory ECG data from the RATe control in Atrial Fibrillation (RATAF) study, which is approved by the regional ethics committee and the Norwegian medicines agency and was conducted in accordance with the Helsinki Declaration (Ulimoen et al., 2013). The RATAF study contains 24-h Holter recordings of 60 patients under baseline and during treatment with four different rate reducing drugs. All patients had permanent AF, no heart failure or symptomatic ischemic heart disease, an age of 71±9 (mean ± std), and 70% were men. To evaluate the presented model, we selected 15 min ECG segments, one for each of five patients, obtained under baseline conditions between 1:00 and 3:00 pm. These five patients were selected to be representative for the whole data set, with varying RR interval series characteristics and an average heart rate ranging between 63 and 140 bpm. In addition, corresponding ECG data obtained during treatment with Diltiazem was also used for one of the five patients.

The RR interval series were extracted from the ECG signals by first detecting the R peaks, before removing RR intervals preceding and following ectopic beats identified based on heartbeat morphology (Lagerholm et al., 2000). Along with this, the mean arrival rate of the atrium-to-atrium (AA) intervals was estimated from the f-waves in the ECG by first extracting the atrial activity from the ECG using spatiotemporal QRST cancellation (Stridh and Sornmo, 2001), before tracking the atrial fibrillatory rate (AFR) using a method based on a hidden Markov model (Sandberg et al., 2008). Finally, correction of the atrial fibrillatory rate by taking the atrial depolarization time into account was used to obtain an estimate of the arrival rate. Here, we denote the true mean arrival rate λ, and the estimated mean arrival rate λ^. One value of λ^ was obtained for each ECG segment (Corino et al., 2013).