By this point, we’ve had a couple of discussions about vectors and how they affect the morphologic appearance of the strip or ECG pattern for each beat. We’ve seen that every myofibril forms an individual vector based on shape, size, orientation, and the time it takes to form. These individual vectors mathematically sum up to create bigger vectors until we finally arrive at the vector for each zone. Those vectors give rise to what we see as a final vector group for each complex.
As a beginner, I always assumed that most hearts were the same. In reality, however, they vary from each other in weight, size of the walls, size of the valves, changes due to variations in preload and afterload, different size atria, septal walls, interventricular walls, and the angles they sit at in the human body. On top of that, age and pathologic processes alter the morphology of each heart. Your ECG at age 18 years is not the same as it is at age 65. Bottom line is that hearts, like fingerprints, are unique. Each will have its own set of vectors and morphologic presentation on the ECG strip.
As a beginner, most people do not give normal sinus rhythm a second look; even advanced practitioners are guilty of this mistake. But how can you tell what is abnormal if you don’t understand what normal looks like?
Though I may stand accused of insensitivity, I will relate the following story anyway because of the underlying truths involved, and I wholeheartedly apologize to any readers who I may offend. My dad loves to recount a story of when he was a medical student. A strange-looking young man presented to the clinic one day with a large rectangular head, close-set eyes, and large ears. The medical residents asked the students to identify the genetic malformation involved. A long discussion ensued and no one was clear about the answer. The residents didn’t have a clue either, by the way. Suddenly, the door opened and the attending walked in with the mother, who had the exact same general appearance. When asked later, the attending said there was no genetic defect. The patient was just an FLK. What is an FLK? A funny-looking kid. The patient simply resembled his parents.
In electrocardiography, we encounter many presentations, ranging anywhere from obviously normal to pathologic. We also encounter FLGs, funny-looking grams. These are just hearts that have some variations that make the ECG or strip look funny but are not a sign of serious pathology. As a beginner, this is a lesson you need to learn right now. Not everything is perfect. You need to spend the time to understand what makes an ECG normal. Is the P wave upright in II, III, and aVF? Are the intervals correct? Is the PR interval elevated or depressed, and by how much? What does the QRS look like? Are there any abnormally large or small waves? Is there too much ST depression or elevation? If so, in what leads? Are there any T-wave abnormalities? Was the strip obtained at the right paper speed? Was the gain altered (as can happen on rhythm strips)? And, to finish it all off, what are the measurements of all the intervals in the complex? Remember, there are confidence intervals that describe “normal”; the intervals need to fall within those ranges.
Think of a rhythm strip as a video clip of a transient period of what is occurring rhythmically in the heart. You have no idea what happened 2 seconds before or 2 seconds after you took the strip. Therefore, it is critical that you look at the patient as a whole. If you have old charts with old ECGs, you need to look at them and establish what is normal for that patient.
People often say that things are either black or white, but there are very few things that are so cut and dried in real life. In actuality, there is only one shade of black and one shade of white, and everything else is a gradient of infinite grays. Use any tool available to you to verify that what you are seeing is normal sinus rhythm and you’ll save yourself a lot of work.
A final point for this section is to always look closely at the start and end of any arrhythmia, if you can capture it. That point where normal sinus rhythm transforms into an arrhythmia will provide valuable clues as to the source of the new rhythm and the underlying pathology involved. It usually takes a pebble to set off an avalanche. Of course, the avalanche is the thing that will kill your patient, but by seeing the pebble, it can provide valuable information that can lead your treatment down the right path.
Take-home messages:
—Daniel J. Garcia