Basic Pacemakers

When the electrical system of the heart fails to work properly, we can assist the heart by implanting electrical leads into regions of the heart to provide the necessary electrical stimulus for muscle contraction. These electrical stimuli must go through the muscle itself and as such the pattern displayed on the electrocardiogram resembles that seen with bundle branch block morphology. You will notice that the conventionally placed ventricular lead is in the right ventricle. This means - as you should remember from the prior books on reading electrocardiograms - the morphology will appear as a left bundle as the electrical stimulus will begin in the right ventricle and then travel through the walls of the left ventricle. Initially these electrical leads were powered by external sources and vacuum tubes (aka the Fleming valve) invented by Professor John Ambrose Fleming in 1904. Today these leads are powered by implantable sources that are closely monitored and replaced every 3-7 years depending upon what is required from the battery sources. In this brief tutorial we will look at the nomenclature of pacemakers and what is seen on the electrocardiogram. I dedicate this book to my friend and teacher, Dr. Denton Arthur Cooley with whom I had the privilege of sharing patient care.