System and Cardiac Anatomy

2 The right atrial lead of a dual chamber ICD. limitations. 

Should a left ventricular lead be desired to allow for biventricular pacing, it can be placed either within the left ventricular venous anatomy through the coronary sinus (CS)  

The CS drains venous blood from the heart into the right atrium. Many branches from the LV flow into the CS, including those from the lateral and posterior LV. Currently, it is there that a left ventricular pacing lead is optimally placed. This maybe best visualized under fluoroscopy from a left anterior oblique (LAO) perspective. Many patients who are candidates to receive a CS left ventricular lead, however, have had myocardial infarctions that may limit the ability to pace from these sites. Stimulation of the left phrenic nerve during ventricular pacing may occur, and can preclude placement there (the left phrenic nerve travels in close proximity to this cardiac region on its way to the left hemi-diaphragm). 

the cardiac venous anatomy is extremely variable between individuals. Some may not have venous branches large enough to accept a pacemaker lead. 

5 The anatomy of the cardiac venous system is extremely between 

---