Smidtaite, R., Z. Navickas, and E. Venskaityte. “ECG Research Using Elements of Matrix Analysis and Phase Planes”. Elektronika Ir Elektrotechnika, vol. 103, no. 7, Aug. 2010, pp. 83-86, https://eejournal.ktu.lt/index.php/elt/article/view/9281.