The difference between a cardiac stimulator (Pacemaker)
and a cardiac defibrillator

A Cardiostimulator
An artificial cardiostimulator is contained within a titanium device, a type of metal that is well tolerated by the human body. Inside this device is a battery and an electronic module. It is connected to the heart by one or more electrical leads.

The electrical component insures a monitoring of the natural impulses of the heart. When a heart beat is not correct, the stimulator transmits an electrical impulse, generated from the battery, and transmits it via the electrical lead to the cardiac muscle where a heartbeat will be stimulated. The stimulator will not work if the natural heart rhythm is less than a previously set frequency threshold.

Due to advanced technology, cardiostimulators can communicate with the programmer using a special type of programming device, called a wand. This wand is placed over the skin, outside of the body, just above the cardiostimulator. It communicates with the stimulator through electromagnetic waves and allows us to regulate and modify the stimulator in relation to the specific needs of each patient.

Since electrical conduction systems of the heart may have varying degrees of problems, several types of cardiostimulators have been developed to better correct the different situations. Aside from a single chamber system, there exists a double chamber system. This system is equipped with a second electrical lead that is placed in the right atrium. This lead maintains the function of the atrium either by stimulating it prior to the ventricle or by detecting its activity through the natural pacemaker (the sinus node) to eventually stimulate the ventricle in case the natural pacemaker fails.

Sensor driven pacemakers contain a mechanism capable of detecting the level of a patients physical activity and accelerating the stimulation frequency and therefore the heartrate in accordance with the patients activity.

The Cardiostimulator (Pacemaker) and the Cardiac Defibrillator
This said, we still need to differentiate between a pacemaker and a defibrillator: Bradycardia (excessive slowing of the hear rate) is treated by a pacemaker which revives cardiac activity by producing an electrical impulse.

The same device does not treat tachycardia, instead, this condition is treated using a defibrillator. The defibrillator, for example, can resynchronise a ventricle that starts beating out of control and contracting in a chaotic fashion . In this case it is said that the heart is in ventricular tachycardia or fibrillation. The defibrillator will give a shock that will defibrillate the heart, recoordinating it and therefore returning it into sinus rhythm. 

One important thing to note is that a defibrillator also is equipped with a pacemaker function. This means that a patient who has a defibrillator is also protected against bradycardia (the slowing of the heart rate), the two functions are incorporated into the one device. On the other hand a patient who has just a pacemaker does not have the defibrillator function incorporated into his/her device.

Ann Allard
Gérante de territoire Sénior
Guidant Canada