Bi-chamber cardiac pacing system employing unipolar left heart chamber lead in combination with bipolar right chamber lead

Reference is hereby made to the following, commonly assigned, co-pending, U.S. Patent Applications which disclose common subject matter: Ser. No. 09/067,729 filed Apr. 28, 1998 for MULTIPLE CHANNEL, SEQUENTIAL, CARDIAC PACING SYSTEMS filed in the names of C. Struble et al.; Serial No. 09/439,244 filed on event date herewith for MULTI-SITE CARDIAC PACING SYSTEM HAVING CONDITIONAL REFRACTORY PERIOD filed in the names of K. Kleckner et al.; Serial No. 09/439,078 filed on even date herewith for MULTI-SITE CARDIAC PACING SYSTEM HAVING TRIGGER PACE WINDOW in the names of C. Juran et al.; Serial No. 09/439,569 filed on even date herewith for CARDIAC PACING SYSTEM DELIVERING MULTI-SITE PACING IN A PREDETERMINED SEQUENCE TRIGGERED BY A SENSE EVENT in the names of C. Yerich et al.; Serial No. 09/439,568 filed on even date herewith for RECHARGE CIRCUITRY FOR MULTI-SITE STIMULATION OF BODY TISSUE filed in the names of B. Blow et al.; and Serial No. 09/439,243 filed on even date herewith for AV SYNCHRONOUS CARDIAC PACING SYSTEM DELIVERING MULTI-SITE VENTRICULAR PACING TRIGGERED BY A VENTRICULAR SENSE EVENT DURING THE AV DELAY in the names of C. Yerich et al. In a bi-ventricular pacing system, an implantable pulse generator optionally having an IPG indifferent electrode is coupled to a small diameter, unipolar, left ventricular (LV) lead and a bipolar right ventricular (RV) lead. The LV lead is advanced through the superior vena cava, the right atrium, the ostium of the coronary sinus (CS), the CS, and into a coronary vein descending from the CS to locate the LV active pace/sense electrode at a desired LV pace/sense site. An LV lead placed on an epicardial surface can substitute. The RV lead in a preferred embodiment is advanced into the RV chamber to locate RV active and indifferent pace/sense electrodes therein. Sensing of RV spontaneous cardiac depolarizations to provide a RV sense event signal and delivery of RV pacing pulses is conducted across the RV active pace/sense electrode and one of the RV or IPG indifferent pace/sense electrodes. Sensing of LV spontaneous cardiac depolarizations to provide a LV sense event signal is conducted across the LV active pace/sense electrode and one of the RV active or indifferent pace/sense electrodes or the IPG indifferent pace/sense electrodes. Delivery of LV pacing pulses is conducted across the LV active pace/sense electrode and the RV indifferent pace/sense electrode. A similar arrangement is disclosed for left atrial (LA) an