No abstract

While cardiac function in the mature heart is dependent on a properly functioning His-Purkinje system, the early embryonic tubular heart efficiently pumps blood without a distinct specialized conduction system. Although His-Purkinje system precursors have been identified using immunohistological techniques in the looped heart, little is known whether these precursors function electrically. To address this question, we used high-resolution optical mapping and fluorescent dyes with two CCD cameras to describe the motion-corrected activation patterns of 76 embryonic chick hearts from tubular stages (stage 10) to mature septated hearts (stage 35). Ventricular activation in the tubular looped heart (stages 10 -17) using both calcium-sensitive fluo-4 and voltage-sensitive di-4-ANEPPS shows sequentially uniform propagation. In late looped hearts (stages 18 -22), domains of the dorsal and lateral ventricle are preferentially activated before spreading to the remaining myocardium and show alternating regions of fast and slow propagation. During stages 22-26, action potentials arise from the dorsal ventricle. By stages 27-29, action potential breakthrough is also observed at the right ventricle apex. By stage 31, activation of the heart proceeds from foci at the apex and dorsal surface of the heart. The breakthrough foci correspond to regions where putative conduction system precursors have been identified immunohistologically. To date, our study represents the most detailed electrophysiological characterization of the embryonic heart between the looped and preseptated stages and suggests that ventricular activation undergoes a gradual transformation from sequential to a mature pattern with right and left epicardial breakthroughs. Our investigation suggests that cardiac conduction system precursors may be electrophysiologically distinct and mature gradually throughout cardiac morphogenesis in the chick.

Screening of applicants for admission to dental school often relies on metrics such as overall undergraduate grade point average (oGPA) and Dental Admission Test (DAT) scores to identify desirable prospective students. The aim of this study was to assess unintended selection bias that may be overlooked or mitigated with holistic review and the inluence of metrics at one U.S. dental school. Descriptive range analysis of oGPA and science GPA (sGPA), DAT scores, and total experience hours was performed for the 2017-18 application cycle for all applicants, those who self-identiied as underrepresented minorities (URM), non-traditional applicants (with postbaccalaureate or master's coursework), and socioeconomically disadvantaged (SED) applicants reporting low parental employment-occupation scores. The results showed that, in screening this school's applicant pool, metrics-based candidate selection would favor those candidates in the 80 th percentile of GPA and DAT Academic Average (AA) scores. Unless mitigated by other screening factors, reliance on these metrics tended to favor majority, traditional, and non-URM SED applicants. These indings suggested that the new admitted class would likely have fewer dental experience and employment hours than in the overall applicant pool. Interestingly, more non-traditional, SED, and URM applicants could be considered if higher general employment and dental experience hours had more impact in the screening process. These results illustrate the importance of deliberately considering non-cognitive metrics and characteristics to admit a more diverse student body.