(ECG) An electrocardiogram is a test that records a graph of electrical activity in the heart over time. An electrocardiogram is used in the diagnostic of heart abnormalities, abnormal cardiac rhythms (arrhythmias or dysrhythmias) and heart muscle damage.

Arrhythmia rejection is a method to reject irregular RR intervals (time duration between two consecutive R waves of the electrocardiogram) in cardiac gating during cardiovascular imaging and to improve the image quality, whereby the cardiac frequency is used as the basis of the normal heart rate. The RR interval window determines the percentage variation of the heart rate. Variations of the acquired data outside the window are rejected and not used in the image reconstruction. Also one interval after the arrhythmic beat will be rejected. Arrhythmia rejection may be inappropriate for patients with certain pathologies, because if the RR interval is constant long, short, long, - all intervals would be rejected.

(CCTA) Coronary computed tomography angiography is a diagnostic imaging procedure to visualize the coronary arteries. CCTA is a non-invasive angiogram that allows the assessment of narrowed and clogged arteries that can cause heart attack and stroke.
Coronary CTA is a non-invasive alternative to traditional angiography that offers detailed images of heart function, resulting in faster, more accurate diagnosis. It helps stratify cardiac risk in patients with low to intermediate likelihood of coronary artery disease. For some patients with chest pain, coronary CTA can rule out the need for cardiac catheterization.
Coronary imaging requires a very fast CT scan, because the coronary arteries and other cardiac structures move rapidly during the cardiac cycle. The current 'state of the art' 64 slice multi-detector row CT systems rotate around the patient in less than 500 ms. The data must be acquired monitored by an electrocardiogram, which allows the computer to reconstruct retrospectively slices at different small segments of the cardiac cycle. This cardiac synchronization reduces motion artifacts in the coronary arteries and provides movies of the beating heart and valve motion.
See also Coronary Angiogram, Calcium Score, Cardiac Phase, Cine Mode and Defibrillator.