A permanent pacemaker (PPM) is an electronic device surgically placed in the chest wall in which a lead courses through the subclavian vein into the right heart.
The lead is able to detect the presence of atrial and/or ventricular depolarizations and then deliver a small voltage impulse to cause depolarization if the heart rate decreases below a predetermined threshold, usually 60 beats per minute. This effectively prevents the heart from ever becoming bradycardic.
Sick sinus syndrome (SSS) occurs from sinoatrial node dysfunction is the most common indication for permanent pacemaker implantation. The second most common indication for a permanent pacemaker is atrioventricular (AV) nodal disease such as second degree type II AV block or third degree heart block.
A biventricular pacemaker is used in chronic systolic congestive heart failure with a widened QRS interval on the ECG. It is inserted in the same fashion as a standard pacemaker via the subclavian vein. The major distinguishing feature of a biventricular pacemaker is the insertion of a left ventricular lead which to accomplish left ventricular pacing in addition to the right ventricular lead for right ventricular pacing. The left ventricular lead is inserted through the coronary sinus in the right atrium then fed around posteriorly toward the left ventricle.
The complications of pacemaker implantation include:
- Infection of the pacemaker pocket (treated with IV antibiotics).
- Infection of the pacemaker leads (requires explantation of the device).
- Lead dislodgement/fracture (requires repositioning or replacement of lead).
- Pericardial effusion/tamponade from right ventricular perforation.
- Congestive heart failure (from induced ventricular dyssynchrony from RV pacing).
The ECG of a paced rhythm shows a widened QRS complex since activation occurs from myocyte to myocyte which is slow do conduct in this fashion. Since the pacing lead is in the right ventricle causing this chamber to get activated first, the ECG pattern is that of a left bundle branch block. Below is a 12-lead ECG example of a paced rhythm. Note the large pacemaker spikes prior to each QRS complex from this old device. Newer devices have much smaller spikes.