As we discussed in the Foreword, we are using these beginner’s perspective blocks to introduce concepts that will help a practitioner from beginner to intermediate level or higher. These are established concepts in clinical medicine, but ones beginners are typically not exposed to during training. One of the most important concepts is that of the differential diagnosis.
As we have mentioned before, very few things are black or white, or as we say in clinical medicine, very few things are pathognomonic (a specific characteristic finding) for a disease or syndrome. Most fall within the gray zone. Gray zones, by definition, are not 100% of either color, so there is always room for error. In clinical medicine, we should always strive to decrease our margin of error, because errors lead to an increase in the morbidity or mortality of our patients.
To combat this inherent error, we need to come up with lists of differential diagnoses. Basically, the process goes something like this: The evaluation starts with the facts about the case (e.g., the history, physical, lab values, ancillary tests). Then you need to list all of the possible diseases or syndromes that present with similar clinical pictures (your list of differential diagnoses). Now comes the hard part: taking that list and evaluating everything to tease out the correct diagnosis and separating it away from the runner-ups.
Take for example a sore throat. When someone presents with a sore throat, most of us immediately think of a cold or virus. However, if that were our only thought, we would have a lot of dead patients. The list of differential diagnoses for a sore throat is very long, due to its nonspecific nature, so we’ll consider only a few of them. Some possible differentials include tonsillitis, strep throat, infectious mononucleosis, gonorrhea, foreign bodies, opportunistic infections (thrush), pharyngeal abscesses, and cancer, to name a few. Once you think of a list of potential differentials, it is up to you to narrow that list down by reanalyzing the history and physical examination and ordering additional appropriate tests that can help you decide among the possibilities.
One of the most important tools in your arsenal is a thorough history and physical. List the main findings you obtained and write or mentally note the differential diagnosis of each complaint or abnormality. Once that is done, step back and look at all the lists. The findings that are most common to all of the lists are the major potential culprits. Eventually, you can narrow this down to one, which is usually the one you are searching for. Try applying this technique to the strips in this chapter to help you sort out the underlying rhythm or events.
Using this method of narrowing the differential diagnoses is tailor-made for arrhythmia recognition. The greater the amount of attention you apply to this method, the higher your chances are of making the correct diagnosis and minimizing mistakes of omission or recognition. Remember, use all the tools available to you, including prior strips, ECGs, past medical history, family history, and basically anything else you can think of. Remember that if you haven’t thought about it, you will never diagnose it!
—Daniel J. Garcia