Figure 39-1 The pulse generator and lead of a typical pacemaking unit.
© Jones & Bartlett Learning.
In this chapter, we present a quick look at the specifics of the rhythms that are created artificially by either temporary or permanent artificial cardiac pacemakers. This quick look is only intended to give us the ability to recognize the presence of a paced rhythm, and not to provide an in-depth discussion of the diagnostic issues that can develop in these patients. The complexity of the problem-solving or diagnostic issues associated with pacemakers can be daunting and are well above the scope of an intermediate text on arrhythmias. In addition to the general diagnostic problems involved, there are many individual variations between the individual pacemaker manufacturers and indeed, the individual models themselves, which further complicate the issues.
An internal pacemaker typically has two components (Figure 39-1): the pulse generator and the leads. The pulse generator is basically a mini-computer that includes a power source (usually a lithium iodide battery), wave or voltage amplifiers (which include analyzing function), a transmitter system to send data to clinicians, a receiver to allow programmability or changing rates, an internal clock, and, of course, sensors. The pulse generator is the heart and soul of the pacemaker.
Figure 39-1 The pulse generator and lead of a typical pacemaking unit.
© Jones & Bartlett Learning.
The leads are the electrical “wires” used to transmit the electrical data back and forth from the heart to the pulse generator. The wires can be either unipolar or bipolar in nature. Unipolar leads are composed of a single wire that transmits the impulse from the pulse generator to the heart. Since electricity has to work along circuits, the electricity must return to the pulse generator through the body tissues in order to complete the circuit. Bipolar leads have two internal wires. One of the wires terminates at the end of the lead and is used to transmit the impulse to the heart. The other wire, which usually has its end about 1 cm from the end of the lead, is meant to transmit the impulse back to the pulse generator and complete the circuit. Note that the circuit formed with bipolar leads is only about 1 cm wide. This short circuit is more than enough to cause a depolarization wave because, as we have seen, a single ectopic cell can be enough.