Answer:
Circulatory system
Step-by-step explanation:
EKG, or ECG, stands for electrocardiogram. It is a record of the heart's electrical activity, specifically reflecting the heart's rate and rhythm with each heartbeat usually using 12 leads applied topically to the skin which are then attached to a monitor. The heart is the main organ of the cardiovascular system, which is closely associated with the circulatory system. The cardiovascular system is also closely associated with the respiratory system, however, ECG specifically examines the electrical activity as the heart fill with blood and subsequently pumps it to the rest of the body's tissues.
The skeletal system is tested with x-rays. The gastrointestinal system is observed using magnetic resonance imaging (MRI). The respiratory system can be detected using computed tomography (CT) scans.