Final answer:
The priority test for a patient with significant electrical burns is a 12-lead electrocardiogram to monitor for potentially life-threatening cardiac issues.
Step-by-step explanation:
In the case of a patient with 50% total body surface area electrical burns, the priority test would be a 12-lead electrocardiogram (ECG or EKG). Electrical burns can cause significant cardiac issues due to the electrical current passing through the body, potentially leading to arrhythmias or other cardiac dysfunctions. A 12-lead ECG is crucial as it provides a comprehensive view of the heart's electrical activity from multiple angles, allowing for the detection of any abnormalities that could be life-threatening. While chest X-rays, bronchoscopy, and CT scans are important in assessing various other injuries or complications, monitoring heart function should take precedence in the immediate aftermath of an electrical burn injury.