McCrary, Andrew W., et al. “The Fourth Heart Sound Revisited: Assessing Cardiographics Associated With Late Diastolic Propagating Events Using High Frame Rate Echocardiography”. Cardiology and Cardiovascular Medicine, vol. 9, no. 3, May 2025, pp. 173-6, https://fortunejournals.org/ojs/index.php/ccm/article/view/16600.