1 The Romans also used a 12 hour clock. 2  The 12 hour dial became popular with mechanical clocks during the 15th and 16th centuries and this has continued to this day.  The abbreviations for am and pm are often also written as a.m. and p.m. or AM and PM.
Stress Testing/Stress Echocardiogram. A stress echocardiogram is a non-invasive test that combines two tests--a treadmill stress test (TST) and an echocardiogram (ECHO). This test is used to see how the heart muscle contracts during rest and during exercise. A stress echo is made up of three parts: a resting echo study, a stress test, and a repeat echo while the heart is beating fast. (See also Drug Induced Stress Test or Nuclear Stress Test--below)
These imaging stress tests can show how well blood is flowing in your heart and how well your heart pumps blood when it beats. One type of imaging stress test involves echocardiography (echo). This test uses sound waves to create a moving picture of your heart. An exercise stress echo can show how well your heart's chambers and valves are working when your heart is under stress.