An Easy Way to Interpret EKGs

“I’m not really comfortable with even basic EKG interpretation.” “I don’t really understand the whole block issue.” “I really need to take a review class on EKG interpretation.”

These are the comments I hear over and over again prior to teaching ACLS classes, both original and recertification. Many people are intimidated by EKGs and unclear on the proper way to interpret a dysrhythmia in lead II. To help answer these questions and help my students pass ACLS, many years ago I came up with an easy way to interpret EKG rhythms—and you don’t even need the EKG strip in hand. This basic review may benefit others as well.

A Four-Step Approach

There are certain EKG rhythms, lethal ones, that require quick interpretation—rhythms such as ventricular fibrillation, ventricular tachycardia, and asystole. I find the others can be easily interpreted using a four-step method. I always tell my students to imagine they were up all night at a side job monitoring patients, and in the morning, when the physicians arrived, they asked what rhythm these patients were in overnight. What would you tell them? Would you know the proper interpretation? What if there were a friend you could call to help you along? 

I tell the students to take a clean piece of paper and write the following four lines, one under the next. 

1. Is the rhythm’s rate slow, medium, fast, or very fast? Slow is below 60 bpm; medium is 60–100 bpm; fast is 101–149 bpm; and very fast is 150 bpm and above. 
2. Is the rhythm regular or irregular? Is the distance between every QRS the same or not?
3. Is there a P-wave in front of every QRS and a QRS after every P-wave?
4. Finally, use the process of elimination. 

By following this method, most interpretations of basic EKG rhythms become very simple. Let’s try a few examples.

If I told you I was thinking of a rhythm and you followed the process, your first question would be, “Is the rhythm slow, medium, fast, or very fast?” If I told you the rate is medium, you just eliminated anything slow, fast, or very fast. Your second question is, “Is it regular or irregular?” If I told you the rhythm is regular, you’ve eliminated anything irregular.

At this point you have a medium-rate rhythm that’s regular. With that information, what would be your rhythm interpretation? Most people would interpret this as a normal sinus rhythm. At this point you’d ask the third question just to confirm your interpretation: “Is there a P-wave in front of every QRS and a QRS after every P-wave?” If the answer is yes, you’ve confirmed a normal sinus rhythm. 

Let’s try another example: I’m thinking of a rhythm, and in response to the first question, I tell you the rhythm is medium. To question No. 2, it is also irregular. As these eliminate potential rhythms that are slow, fast, very fast, or regular, to what possibilities does this narrow your interpretation? If I then told you there is not always a P-wave in front of every QRS or a QRS after every P-wave, what would it be? Hopefully your answer is a-fib. 

Another easy one: The rhythm is 1) fast and 2) regular, and there’s a P-wave in front of every QRS and a QRS after every P-wave. What’s your interpretation? Correct: sinus tachycardia. If I told you the P-waves looked more like flutter waves or a shark fin or picket fence, the correct answer would be atrial flutter.

Last of the easy interpretations: The rhythm is 1) very fast (above 150 bpm) and 2) regular. At this point an educated guess might be supraventricular tachycardia. But to the final question, your response might be that the rate is going so fast it’s probably buried in the rhythm. 

At this point you should’ve gotten the hang of things and realized that if each EKG is approached the same way, interpretation becomes much easier.

AV Blocks

AV blocks always seem to be nerve-racking for my students. For the most part they are of four types: first-degree heart block; second-degree heart block type 1 (Weinkebach); second-degree heart block type 2 (which we used to call classical); and third-degree heart block (complete AV disassociation). The blocks are usually slow; two are regular, and two are irregular.

A first-degree heart block is a slow, regular rhythm with a PR interval greater than one big box, or 0.20. A third-degree heart block is a slow, regular rhythm whose P-waves and QRS map out with each other, but they have complete AV disassociation. Both second-degree heart blocks are slow and irregular, since they both drop a beat (QRS). The only difference is that second-degree type 1 has a widening PR interval with a dropped QRS, and second-degree type 2 has a constant PR interval with a dropped QRS.

Let’s try our formula here: If I told you I was thinking about a rhythm that is 1) slow and 2) regular, your choices are sinus bradycardia, first-degree heart block, and third-degree heart block. If I then tell you there’s a P-wave in front of every QRS and a QRS after every P-wave, your correct answer would be sinus bradycardia. If the PR interval is greater than 0.20, you would have a first-degree heart block.

What if you had a rhythm that is 1) slow and 2) irregular? That would leave you with one of the second-degree heart blocks. If I told you the PR interval widens until you lose a beat, what would your response be? Correct: second-degree type 1 (Weinkebach). If the PR interval remains constant until you lose a beat? Second-degree type 2.

Conclusion

At this point I ask my students if this review helped. Their response has always been 1) very fast, 2) regular, and 3) always positive. This methodology may not help with every rhythm, especially some of the more nuanced interpretations, but these four easy steps can contribute to a mastery of basic EKG rhythms and a successful interpretation of rhythms presented most frequently (and during ACLS).

Robert J. Lederman, NRP, CCP, FP-C, CIC, is an EMS educator and has been a practicing EMT and paramedic for more than 34 years. He currently works for Maimonides Medical Center in Brooklyn, N.Y.