Interpolation Technique for Extracting Features from ECG Signals Sampled at Low Sampling Rates

The occurrence of the R peak (tR), and the area of the QRS complex (AQRS) are among the features estimated from each ECG wave. To estimate these parameters ECG is traditionally sampled at a high sampling rate (250-500Hz). However, since tR and AQRS are identified by the selective analysis of the QRS complex and since the QRS maximal frequency component is about 25 Hz, we propose a new procedure to identify tR and AQRS from ECG sampled at the relatively low rate dictated by the frequency content of the QRS complex. The procedure identifies each QRS complex from the sampled ECG, and estimates tR and AQRS after interpolation of the QRS complex. The interpolation is obtained as the Inverse Discrete Fourier Transform (IDFT) of the zero-padded DFT of the QRS. The technique was tested on a public database of ECG. Results showed that by this technique tR and AQRS can be accurately derived from ECG sampled at frequency as low as 70 Hz.