Single chamber pacemakers may be (right) atrial or (right) ventricular. Dual chamber pacemakers utilise leads in both the right atrium and ventricle. Biventricular pacemakers also pace the left ventricle through placement in one of the coronary veins via the coronary sinus which drains into the right atrium. The advantage of biventricular pacemakers is synchrony of ventricular contraction. Lead position can be inferred from the ECG (LBBB is normally seen, but RBBB may be seen if perforation of the septum occurs and the lead lies in the left ventricle). Assessment of lead position is also assessed using chest radiography.
Remember the right ventricle is the most anterior chamber of the heart. The right ventricular lead should enter the right atrium via the SVC and curve leftwards across the heat. The tip should face downwards and proximal to the tip there should be evidence of some slack in the lead. The atrial lead should project into the right atrium and curve upwards into the atrial appendage. Both these leads ought to point anteriorly when seen on the lateral chest radiograph. The left ventricular lead should enter the right atrium and then pass leftwards through the coronary sinus where it will often curve anterosuperiorly and then anteroinferiorly as it passes into the anterior interventricular vein.
ICDs (implantable cardioverter defibrillators) may act as pacemakers, but also assume functions as indicated by their name. These can be identified by the thicker coils (identified by a thickened part of the lead) used to deliver the shocks. The distal coil will lie within the RV and the proximal coil will lie in the SVC and brachiocephalic vein.
Potential problems with the leads or with pacemaker insertion are:
1. Lead misplacement
2. Ventricular or septal perforation
5. Lead migration (twiddler’s)
6. Lead fracture