Figure 40-4 What is the rhythm?
From Arrhythmia Recognition: The Art of Interpretation, courtesy of Tomas B. Garcia, MD.
Take a look at the strip in Figure 40-4. If you can figure out the diagnosis right away, you are doing great. Keep reading, though, because we are going to go through an exercise in the logic we have shown you in this chapter.
Figure 40-4 What is the rhythm?
From Arrhythmia Recognition: The Art of Interpretation, courtesy of Tomas B. Garcia, MD.
The first thing to look at in our “Patient’s IQ Points” program is the patient. For the purposes of this discussion, we will say that the patient is hemodynamically stable and he is here to see you because he was experiencing some palpitations. The peripheral pulse rate is about 150 BPM. Huh? That number sounds familiar.
Overall Impression of the Rhythm
We can see that the rhythm is fast. The QRS complexes are small and narrow and there is a lot of undulation in the baseline. Your first impression should be that this is a narrow-complex tachycardia at about a rate of 150 BPM. The rate of 150 BPM should make you think of atrial flutter. Are we right? Let’s go on.
Question 1: Is the Rhythm Fast or Slow?
Answer: The obvious answer is fast. The ventricular rate is about 150 BPM. Take a look at Figure 40-5. From the answer to this one question, we have already dramatically narrowed down our list of differentials to the ones in the pink blocks. The number of possibilities has gone from 21 to 11.
Figure 40-5 The differential diagnosis of the rhythm shown in Figure 40-4 as it is narrowed down by answering some simple questions.
© Jones & Bartlett Learning.
DescriptionQuestion 2: Is the Rhythm Regular or Irregular?
Answer: The ventricular response is regular. We have just narrowed the pink list down again, this time to the rhythms represented by the seven blue rectangles.
Question 3: Do You See Any P Waves?
Answer: This is a tougher question to answer. What are those negative waves right before the QRS complexes? Are they inverted P waves, or are they the T waves from the previous complexes? Well, if they were the T waves from the prior complexes, the QT intervals would be terribly prolonged. This can happen, but it’s not too common to have that long of a QT interval with such a fast ventricular rate. Could the inverted waves be F waves? There’s atrial flutter again. Let’s move on.
Question 4: Are All of the P Waves the Same?
Answer: The inverted waves right before the QRS complexes are all the same. Are they inverted P or F waves? Still not sure. Let’s move on.
Question 5: Are the P Waves Upright in Lead II?
Answer: No, if those are P waves, they would have to be inverted. F waves would most likely be inverted in lead II. We cannot state it with certainty, but it could be either an inverted P wave or an F wave. That narrows down our differential diagnosis to four rhythms represented by the purple boxes.
Question 6: Are the PR Intervals Normal and Consistent?
Answer: The intervals are definitely consistent. We still don’t know if they are P waves, though.
Question 7: What Is the P:QRS Ratio?
Answer: This raises a very important point. We are now at the major branching point for this arrhythmia. If we say that those are inverted P waves, then the conduction ratio should be 1:1. If we say that these are F waves, then the conduction ratio would be 2:1. There is one more possibility to consider from looking at our list of possibilities: focal AT with block. If this were focal AT with block, what would the ratio be? 2:1, just like in atrial flutter.
Let’s take another close look at our strip (see Figure 40-6). Place one pin of your calipers at the bottom of the inverted wave before the QRS complex. Now, place the other pin at the bottom of the next inverted wave right before the next QRS complex. That would make 0.38 seconds the presumed P-P interval if the conduction ratio were 1:1. What would the P-P interval or F-F interval be if the conduction ratio were 2:1? It would be half of the distance that we have in our calipers or 0.19 seconds. Set your calipers to 0.19 seconds and go back to the inverted wave. Does the other caliper pin fall on any other inverted area? Yes! That means that the ratio of conduction is 2:1 and we have narrowed down our list of differentials to two possibilities: either focal AT with block or atrial flutter (see blue dots on Figure 40-6). This is a little bit of gold mining. Let’s move on.
Figure 40-6 The presumed P-P interval is 0.38 seconds. Half of that interval would be 0.19 seconds. Setting your caliper pins to this measurement and walking it through the strip shows a recurrent inverted wave represented by the blue dots. This could be seen in focal atrial tachycardia with block or atrial flutter.
From Arrhythmia Recognition: The Art of Interpretation, courtesy of Tomas B. Garcia, MD.
Question 8: Are the QRS Complexes Narrow or Wide?
Answer: The QRS complexes are narrow. This question really doesn’t help us much in this strip.
Question 9: Are the Complexes Grouped or Not Grouped?
Answer: Not grouped. There is no evidence of Mobitz I, Mobitz II second-degree AV block, or third-degree AV block on this strip.
Question 10: Are There Any Dropped Beats?
Yes, there are dropped beats. In question 7, we stated that the P:QRS ratio is 2:1, with either two P or two F waves to each QRS complex. We narrowed down our differential diagnosis to either a focal AT with block or atrial flutter. Even though answering this question did not provide us with any additional clues as to the underlying rhythm, it did strengthen our differential further by narrowing it to one of the two just mentioned.
Answer: This is another critical point in evaluating this strip. So far, we have figured out that the ventricular rate is 150 BPM, the conduction ratio is 2:1, and that the atrial rate is, therefore, 300 BPM. This sure sounds like atrial flutter. The problem is that focal AT with block could also rarely be that high. The key point in differentiating between the two possibilities is the baseline. If there are isoelectric or flat segments between the P waves, then it is focal AT with block. If there is a constant undulating pattern, then it is atrial flutter. So, how do we figure it out? Go mining. . . .
We want you to exercise your mind a bit at this point. Look closely at the top strip in Figure 40-7, and mentally remove the QRS complexes. This should be easy to do in this strip because the QRS complexes are so small. When you do that, you see a nice undulating pattern like the one at the bottom of Figure 40-7. The final diagnosis is atrial flutter.
Figure 40-7 Mining for gold on this strip involves mentally removing the QRS complexes from the rhythm strip to see the underlying supraventricular rhythm. As you can clearly see on the blue (bottom) strip, this is atrial flutter because of the constantly undulating baseline formed by the F waves.
© Jones & Bartlett Learning.
Going through these mental exercises may seem like an exaggeration, but it isn’t. An organized approach is the best way to interpret an arrhythmia. Eventually, with time and practice, you will be able to perform this process in seconds. However, you are still learning. Get yourself used to the system, or whatever system you decide to use, and build a strong foundation. We hope that you have enjoyed this chapter and that you will carry the information in it with you forever in your clinical life. Now, let’s go practice.
Have I Mined for Gold?