A12-year-old presents with an injury of his left arm and leg. he states that he felt dizziness during the 2nd mile of the long distance run organized by the school. he fell and lost the consciousness for several seconds, but after that he felt "normal". his father has been diagnosed with emery-dreifuss muscular dystrophy type 1. on examination, you find a few superficial excoriations; there is also symmetric humero-peroneal weakness involving the biceps, triceps, and peroneal muscles. there is also atrophy and contractures of achilles-heel, elbows, and posterior neck. after taking care of his injuries, what test should you order? a ckb ldhc ekgd eege ct