Rajasekhar, K. “A Prospective Study of ECG and Echocardiographic Changes in Chronic Obstructive Pulmonary Disease Patients in a Tertiary Care Hospital”. International Journal of Health and Clinical Research, vol. 3, no. 12, Dec. 2020, pp. 40-42, https://ijhcr.com/index.php/ijhcr/article/view/554.