The average battery life is 10 years. The leads are threaded through the subclavian vein to the heart. Each lead is a catheter with one or two electrodes at the tip of the catheter. The negative electrode contacts the myocardium and delivers the electrical impulse.
Bipolar pacemakers have two electrodes at the catheter tip.
The negative electrode touches the myocardium and the positive electrode is just above it. Bipolar pacemakers create a much smaller pacemaker spike on ECG paper, sometimes making it difficult to identify a paced beat.