Signal processing apparatus for use with an electrocardiograph monitoring activity of the human heart is disclosed. The apparatus receives input signals from electrodes attached to the body of a subject whose heart activity is being monitored. These electrodes include chest electrodes positioned...http://www.google.sh/patents/US5711304?utm_source=gb-gplus-sharePatent US5711304 - Signal processing apparatus and method for adding additional chest leads to the 12-lead electrocardiogram without additional electrodes 
