Cardiac Pacemakers

Abstract

Ever since the introduction of the first artificial pacemaker in 1932, pacemaker technology has advanced rapidly. The early pacemakers could not sense the electrogram. They were brainless devices which only paced the ventricles asynchronously. Subsequent advanced devices called demand mode pacemakers contained a sense amplifier. This amplifier measured the cardiac activity of the patient to evade competition of the actual rhythms of the heart with paced rhythms. Furthermore, single-, dual-, and biventricular pacemakers were launched. Single-chamber pacemakers (one lead) were used to set the pace of only chamber of the heart; this single chamber was usually the left ventricle. Dual-chamber pacemakers (two leads) could set the pace of two chambers of the heart. Biventricular pacemakers used three leads. One lead was placed in the right atrium. The other two leads lay inside the ventricles, one lead per ventricle. Another noteworthy feature is that the early devices were an assembly of discrete resistors, transistors, and capacitors wired together on printed circuit boards, whereas the new devices are highly complex and integrated microprocessor-based systems. They are essentially extremely small computers equipped with RAM and ROM facilities. The topical topologies of pacemakers are tremendously complicated. They include two parts: the analog part and the digital part. The analog portion comprises the sense amplifier and an output stage which performs the pacing. The digital portion consists of sections containing the microcontroller with associated circuitry and the storage memory with accessories. The pacemakers are capable of implementing diagnostic scrutiny of the received electrograms. They provide device programmability. Also, they offer adaptive rate pacing, i.e., they are able to change the paced rate in proportion to metabolic workloads using an accelerometer.