Ask the Clinical Instructor

Heart Blocks: Understanding Which is Which

Todd Ginapp, EMT-P, RCIS, FSICP. Todd is the Cardiology Manager for Memorial Hermann Southeast in Houston, Texas. He also teaches an online RCIS Review course for Spokane Community College, in Spokane, Washington, and regularly presents with RCIS Review Courses.
Todd Ginapp, EMT-P, RCIS, FSICP. Todd is the Cardiology Manager for Memorial Hermann Southeast in Houston, Texas. He also teaches an online RCIS Review course for Spokane Community College, in Spokane, Washington, and regularly presents with RCIS Review Courses.
“HELP! I am new to the cath lab. When I took the ECG class that my hospital required, I was very confused about heart blocks and understanding which one is which. I have 5 people giving me their opinions about the best way to learn and memorize these. Any suggestions?” – Cath lab employee, Mississippi I can certainly appreciate your situation. As I was undertaking my paramedic training 29 years ago, I had the same difficulty. Nothing really sunk in and I had a hard time getting it. I obtained my training at Mary Greeley Medical Center in Ames, IA. One of my preceptors (unfortunately, I no longer recall his name) sat me down and made a drawing for me, and it immediately made sense. I still use this process today when I need to quickly identify a heart block while in the procedure room. Of course, this is only one way to remember such rhythms, and may not work for everyone. You should always rely on the experienced staff and educators to help you with ways to learn and memorize important items. I have included in this article a chart I have long since memorized (Figure 1). In this article, I will also assume that the reader knows the components of a normal ECG. Other than cases of unusual atrioventricular (AV) dissociations, this chart has worked for me for nearly 30 years. I hope that it will work for you as well. If it does, share it with anyone you know that might also need some help. STEP ONE You need to be able to see a section of the ECG (on paper, or on the monitor) that is free from artifact. Look for whether there are more ‘P’ waves than ‘QRS’ complexes. If you have more than 1 P wave compared to QRS complexes, then you have an AV (atrioventricular) block (AVB) of some kind. That being said, some common sense needs to be applied. If the cause of more ‘P’ waves is atrial flutter or atrial fibrillation, this chart does not apply. STEP TWO Next, we need to look at the ‘P-R’ interval (PRI) which is the distance between the ‘P’ wave and the ‘R’ wave that is part of the QRS complex. Most of the time you can ‘eyeball’ the distance, but sometimes you may have to use something as a measuring device. By looking at this component, we are making our first decision on this chart. If the PRI does not VARY from complex to complex, the AV block is identified as a Type II AV block or Mobitz Type II (Figure 2). If the PRI does VARY, then we move to the next step. STEP THREE In this step, we will look at the ‘R-R’ interval (RRI). This is the distance from ‘R’ wave to ‘R’ wave from complex to complex. Again, you should be able to eyeball it, but if needed, you can use a measuring device. If the RRI is regular, then we have made another determination of a heart block. It would be a 3rd degree, or complete, heart block (Figure 3). In this case, we have determined that the PRI VARIES and the RRI does not VARY. This makes sense, since the atria and the ventricles are running at different rates, independent of each other. If the RRI VARIES, then we will have identified our remaining AV block, which as a AV Type I or Mobitz I. This also known as a “Wenckebach” (Figure 4). One way to remember this is that we determined that the PRI VARIED and the RRI VARIED. You can remember the sentence “Very Very Venckebach.” If this tool works for you, great. If not, keep searching and relying on your experienced co-workers and your educators to help you develop your own way of remembering heart blocks. If you have any unique methods that you use to remember these items, please send them to me if you want to share with others (tginapp @rcisreview.com). Contact Todd Ginapp with your questions at tginapp@rcisreview.com or on Facebook at www.facebook.com/RCISReview
References
NULL