Arrhythmia recognition is based on basic electrocardiography. It is impossible to really understand and work with arrhythmias without having at least some rudimentary information on basic electrocardiogram (ECG) interpretation. This is a fact that eludes many authors and educators, and is probably one of the major reasons why people can understand the principles of arrhythmias but constantly miss the diagnoses on actual strips.
In this chapter, we will give you a basic tour of electrocardiography. We will primarily focus on relevant information that is going to affect your ability to recognize and interpret arrhythmias. These topics include the three-dimensional picture of the heart, the electrical axes of the heart (including the P-wave axis), and left and right bundle branch blocks.
We will cover the three-dimensional capabilities of electrocardiography because it will become increasingly important to you to isolate the pathologies involved in the various arrhythmias. We will cover the electrical axes because the waves we see on the ECG are graphical representations of the individual axes for those waves: the P-wave we see on the strip is a graphical representation of the P-wave axis; the QRS complex is a graphical representation of the main ventricular axis. Finally, why study the bundle branch block morphologies? Because they are representative of the way ectopic ventricular pacemakers cause aberrant morphology on the ECG and rhythm strip. If you understand how the bundle branch blocks are formed, it will be much easier for you to understand how ventricular complexes are formed and how aberrancy develops and affects morphology.
At the end of this chapter, you will not be able to interpret ECGs, but you will have a working knowledge of these points, and more importantly, you will know how to apply that knowledge clinically in your everyday practice. As you proceed through this book, you will notice that the information in this chapter will continually strengthen your ability to interpret arrhythmias and make their individual pathologic processes a little clearer.