The ECG model is based on the work of McSharry et al. and is available on the 'Physionet' website as 'ECGSYN'. According to these authors:
" ECGSYN generates a synthesized ECG signal with user-settable mean heart rate, number of beats, sampling frequency, waveform morphology (P, Q, R, S, and T timing, amplitude,and duration), standard deviation of the RR interval, and LF/HF ratio (a measure of the relative contributions of the low and high frequency components of the RR time series to total heart rate variability). Using a model based on three coupled ordinary differential equations, ECGSYN reproduces many of the features of the human ECG, including beat-to-beat variation in morphology and timing, respiratory sinus arrhythmia, QT dependence on heart rate, and R-peak amplitude modulation. The output of ECGSYN may be employed to assess biomedical signal processing techniques which are used to compute clinical statistics from the ECG."
By default, the available ECG patterns are:
McSharry PE, Clifford GD, Tarassenko L, Smith LA.A dynamical model for generating synthetic electrocardiogram signals. IEEE Trans Biomed Eng. 2003 Mar;50(3):289-94.