Final answer:
The most likely diagnostic test for a patient with suspected acute pericarditis is an echocardiography. It provides detailed images of the heart's structure and function, necessary for diagnosing pericarditis.
Step-by-step explanation:
A patient admitted to the hospital with possible acute pericarditis would most likely undergo an echocardiography as a diagnostic test. Echocardiography, or an "echo," is a sonogram of the heart that can detect inflammation of the pericardium, the fluid-filled sac surrounding the heart, which is indicative of pericarditis. In comparison to the other options, such as blood cultures (more aligned with infectious issues), cardiac catheterization (primarily used for coronary artery assessments), and a 24-hour Holter monitor (which measures electrical activity over a longer period), an echo can provide detailed images of the heart's structure and function, which is essential for diagnosing conditions like pericarditis.