Electrophysiological studies take place in the catheterization laboratory, with the patient draped, sedated, lying on the X-ray table. Catheters are introduced via the right femoral (subclavian) vein, and placed in the: (i) high right atrium; (ii) alongside the atrioventricular (AV) node/bundle of His; (iii) right ventricle (RV) apex (sometimes RV outflow tract); (iv) coronary sinus. A roving catheter may also be used. Electricity detected by these catheters passes to an ECG machine, which records the signals and prints out high speed/gain paper traces. Electrophysiological catheters detect electricity from multiple sites in and around their tip. The aim is to introduce sufficient catheters to accurately determine when different parts of the heart are activated, both in normal sinus rhythm and during an arrhythmia. Many abnormal pathways that sustain arrhythmias generate electricity during sinus rhythm and can be mapped.