Engelmann and his laddergram.
Thomas Lewis is alliteratively credited with devising the laddergram. Engelmann, or perhaps Chauveau, truly deserves the honor. Mackenzie and Wenckebach popularized the schema in their books.
D001145:Arrhythmias, Cardiac / Q000266:history; D004562:Electrocardiography / Q000266:history*; D005858:Germany; D049672:History, 19th Century; D049673:History, 20th Century; D006801:Humans