Is it possible for an arrhythmia to be missed even after doing multiple tests?

Arrhythmia: Arrhthmias can show up infrequently and be missed on multiple tests. When a high level of suspicion exists of a dangerous rhythm disturbance we sometimes implant a device under the skin that can monitor the heart for very long period to minimize the chance of missing an arrhythmia. This is invasive however and only done when absolutely indicated.