Final answer:
High levels of calcium ions (hypercalcemia) can cause a shortened QT interval and a widened T wave in an EKG.
Step-by-step explanation:
High levels of calcium ions, known as hypercalcemia, have been linked to shortened QT interval and a widened T wave in an EKG. The QT interval represents the time from ventricular depolarization to repolarization, while the T wave represents ventricular repolarization. It's important to note that extremely high levels of calcium can induce cardiac arrest.