Conventional electrocardiographic monitoring techniques depend on human observation of an oscilloscopic display for detection of transient rhythm disturbances such as premature ventricular contractions (PVCs). It is not surprising that such events are often missed. We have found that transient events are regularly identified only when they occur with a frequency exceeding one per minute. Rhythm disturbances such as coupled PVCs or PVCs in which R waves interrupt the preceding T wave ("R on T"), which constitute indications for antiarrhythmic therapy, may go undetected if they occur less frequently than this.
(JAMA 232:51-53, 1975)
Lindsay J, Bruckner NV. Conventional Coronary Care Unit MonitoringNondetection of Transient Rhythm Disturbances. JAMA. 1975;232(1):51–53. doi:10.1001/jama.1975.03250010033021