Overview

History of the Pacemaker:
Paul M. Zoll developed the first pacemaker in conjunction with the Elecrodyne Company in 1952. Early pacemakers where large bulky devices, worn externally, that stimulated the heart using electrodes placed on the chest. However, due to the large impulses required to stimulate the heart externally use of these early pacemakers caused pain and burns. It was not until 1957 that doctors began implanting the electrodes. This was better, but the patient still had to carry around the bulky pulse generator and became more susceptible to infection. Finally in 1959 the first fully implantable pacemaker was developed by engineer Wilson Greatbatch and cardiologist W.M. Chardack. Then in 1965 Greatbatch improved on his original design with a demand pacemaker, which is the basis of all modern pacemakers. Instead of continuously stimulating the heart, the demand pacemaker would only send stimulation when the heart rate dropped below predefined limits.

Medical Background:
The human heart is the strongest muscle in the body, from the day we are born to the day we die it works tirelessly to pump blood through out the body. When the heart begins to fail weather it is due to old age or sickness there are many things that can be done to extend the hearts life. The heart has it’s own internal ‘pacemaker’ responsible for controlling heart rate and efficient pumping. The hearts ‘pacemaker’ is the sinus node and is located at the top of the right atrium. However, when the hearts own internal ‘pacemaker’ fails it may become necessary to implant an artificial pacemaker to insure proper heart function. Modern pacemakers are able to correct a wide variety of heart arrhythmias, such as bradycardia (heartbeat too slow), Tachycardia (heartbeat to fast), and Ventricular Fibrillation, Atrial Fibrillation (erratic heartbeat) or sinus block (no heartbeat).

Pacemaker Basics
The pacemaker consists of three components: the pulse generator, the pacing leads, and the electrode tip. The pulse generator contains the pacemaker’s power source and digital circuitry. A lithium/silver vanadium oxide battery with a 10yr shelf life is the main power source. The digital circuitry is split into two separate components a microcontroller that handles high-level operation and a sequencer to handle routine pacing operation.

Electrical stimulus from the pulse generator move through the pacing leads into the electrode tip. The leads for a pacemaker are used to stimulate the atrium or the ventricle on the right side of the heart.

The electrodes send information about the electrical impulses in the heart muscle back to the pulse generator. The pulse generator senses the hearts own electrical activity and responds accordingly to the way it has been preprogrammed.

Pacemaker controller as a Finite State Machine

In this example we are using a finite state machine to implement a simple demand pacemaker. First we must detect an event, in this case an R-wave. Once the R-wave is detected we set a timer for approximately .83 sec, which will be the time between heartbeats, thus giving us 72 heartbeats/min. Once the timer expires we check to see if a new R-wave was detected. If one was detected we repeat the process of detection and waiting. If one has not been received we need to stimulate the heart and then repeat the process of detection and waiting.

• View simple demand pacemaker state diagram
• View VHDL code for simple demand pacemaker state machine

Research Links

• US Patent No. US 6,442,428 "Implantable Cardiac Stimulation Device Having a Programmable Reconfigurable Sequencer"
• US Patent No. US 4,088,140 "Demand Anti-Arrhythmia Pacemaker"
• US Patent No. US 4,236,522 "Asynchronous/Demand Mode Programmable Digital Cardiac Pacemaker"
• IEEE Virtual Museum "The Pacemaker"