Ambreen, S., H. F. Khan, A. Hayyat, and N. A. Shamsi. “Association of Age and Symptoms With Frequency of Premature Ventricular Contractions on 24 Hours Holter monitoring”. Pakistan Journal of Medical Sciences, Vol. 37, no. 2, Feb. 2021, doi:10.12669/pjms.37.2.2873.