Leads posterior, placement

The left anterolateral thoracotomy also offers excellent exposure of the heart and left ventricle. An incision is created in the fifth intercostal space (Fig. 4.44). This approach is ideal for extrapericardial placement of a large patch electrode over the posterior surface of the left ventricle as well as a smaller patch anteriorly between the sternum and pericardium. This approach is associated with considerable postoperative pain and is its major drawback. This pain frequently results in atelectasis and transient pleural effusions. Today, a more lateral approach has been adopted that eliminates pain associated with division of the latissimus dorsi. Once again, the leads are tunneled to an abdominal pocket by use of a small chest tube or hemostat... 

Proper electrode placement is the single most important fector for determining whether transcutaneous pacing will be effective. The proper position of the cathode (negative) electrode is directly over the cardiac apex or over the position of ECG chest leads V3 (Fig. 7.1). The anode (positive) electrode is placed either posteriorly (recommended) on the back between the spine and the lower half of the left or right scapulae, or, alternatively, if the back is inaccessible, over the right upper chest centered approximately 6-10 cm above the... 

In the radiograph shown in Fig. 18.11, ventricular lead placement could be compatible with apical lead placement. However, the lateral view shows a nonapical position, and the lead is in fact positioned in a tributary of the posterior cardiac vein. 

Anatomic variations can alter the placement of the pacing system and therefore the radiographic appearance. It is not possible to discuss all potential anatomic variations. However, one anatomic variation does merit discussion - a persistent left superior vena cava. A permanent pacing system can be implanted via a persistent left superior vena cava (Fig.18.21). (If this anatomic variation is noted before pacemaker implantation, it is easier to implant the system via the right side if the patient has a normal right superior vena cava.) If pacing leads are implanted through a persistent left superior vena cava, the lead in the PA projection descends within the left side of the cardiac shadow and enters the atrium and then the ventricle by communication of the left superior vena cava and the coronary sinus. On the lateral projection, the ventricular lead is seen on the posterior cardiac wall within the coronary sinus. 

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). 

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