Electrocardiogram-gated Kilohertz Visualisation (EKV) Ultrasound Allows Assessment of Neonatal Cardiac Structural and Functional Maturation and Longitudinal Evaluation of Regeneration After Injury

The small size and high heart rate of the neonatal mouse heart makes structural and functional characterisation particularly challenging. Here, we describe application of electrocardiogram-gated kilohertz visualisation (EKV) ultrasound imaging with high spatio-temporal resolution to non-invasively characterise the post-natal mouse heart during normal growth and regeneration after injury. The 2-D images of the left ventricle (LV) acquired across the cardiac cycle from post-natal day 1 (P1) to P42 revealed significant changes in LV mass from P8 that coincided with a switch from hyperplastic to hypertrophic growth and correlated with ex vivo LV weight. Remodelling of the LV was indicated between P8 and P21 when LV mass and cardiomyocyte size increased with no accompanying change in LV wall thickness. Whereas Doppler imaging showed the expected switch from LV filling driven by atrial contraction to filling by LV relaxation during post-natal week 1, systolic function was retained at the same level from P1 to P42. EKV ultrasound imaging also revealed loss of systolic function after induction of myocardial infarction at P1 and regain of function associated with regeneration of the myocardium by P21. EKV ultrasound imaging thus offers a rapid and convenient method for routine non-invasive characterisation of the neonatal mouse heart.

Small-Group Activity to Reinforce the Impact of Valvular Defects and Heart Failure on Cardiac Pressure-Volume Relationships

INTRODUCTION

An important topic in cardiac physiology is the relationship between changes in intracardiac pressures and volumes during the cardiac cycle. This topic lends itself well to utilizing active learning principles to facilitate student understanding of pressure and volume changes in normal cardiac physiology and in the pathophysiology of valve disease and heart failure. We describe an active learning exercise regarding this topic that engages and facilitates student learning in a small-group setting.

METHODS

Following an overview lecture on the normal cardiac physiology, small groups of students under the guidance of a facilitator were provided with a worksheet consisting of questions related to background knowledge of cardiac physiology. Additional questions related to five valve disease and heart failure cases were also provided to promote the application of basic physiology principles to clinically relevant problems. The facilitator was provided with a guide to help facilitate the student interactions. Following the group worksheet activity, an animated slide presentation was shown to further engage student learning through active discussion of their worksheet answers.

RESULTS

Students were assessed by written examination, and were found to have a higher performance on the subset of questions related to this learning activity compared to the overall exam. Of the 175 students completing the exercise, 23 voluntarily provided feedback via a survey. Student surveys provided overwhelmingly positive feedback on the benefits of this active learning exercise.

DISCUSSION

Small group, active learning exercises benefited student learning by providing a framework for analysis, synthesis, and application of clinically relevant cardiac physiology concepts.