I understand that the voltage will be positive as measured by the ECG but I was wondering why the voltage reaches a maximum exactly at the midpoint. Is there a physiological reason (like sodium channels closing or something else) that causes the wave to increase, reach a maximum then decrease?
Picture source: Harvard Medical School. Pathophysiology of Heart Disease : A Collaborative Project of Medical Students and Faculty. Edited by Leonard S Lilly, Edition 6 ed., Wolters Kluwer, 2016.