1. A method for detecting cardiac rhythm abnormality, comprising the steps of: providing a plurality of electrodes at a tip of a cardiac lead, which are electrically separated from each other; placing said tip of said cardiac lead in contact with cardiac tissue so that all of said electrodes are simultaneously in substantially fixed contact with said cardiac tissue; obtaining individual unipolar electrical signals from said cardiac tissue respectively via said electrodes, said unipolar signals exhibiting a time relationship relative to each other; and analyzing said time relationship to obtain an analysis result and generating a signal indicating a cardiac rhythm abnormality dependent on said analysis result.