ECG Rhythm Identification
Identify Cardiac Rhythms in 5 Simple Steps
Your cardiac block might be the hardest block of didactic. Without proper rhythm identification, you will not be able to treat the patient appropriately. It seems there is a lot of difficulty with this and students tend to “look for zebras”. Trust your gut. Our monitors are great but do not always pick things up so it’s imperative that you manually interpret and ekg prior to looking at what the computer interpretation is. We have preceptors and FTO’s out here that do not let you see the computer interpretation until you have quickly manually identified the rhythm. If you are not on internship yet, I encourage you to practice attempting to interpret prior to reading the computer interpretation.
Here, we are going to go over the 5 simple steps to rhythm identification. This is meant as an introduction to reading rhythms, not an advanced rhythm interpretation method. You should study the “rules” of rhythms to accurately identify the rhythm.
5 Step Rhythm Identification Method:
Is the rhythm FAST or SLOW?
Is the rhythm REGULAR or IRREGULAR?
Are P-WAVES present?
Are all the p-waves the same?
Does each p-wave have a QRS complex?
Is the PR Interval (PRI) normal or and constant?
4. Are the QRS complexes NARROW or WIDE?
Are there any dropped QRS complexes?
Are there any grouped QRS complexes?
5. Are there any T-WAVE abnormalities?
Is there any ST elevation ?
Are there reciprocal changes?
Is there T-wave inversion?
Is there T-wave elevation?
Identify the rhythm.
With this method, we can utilize the rule of each rhythm and process of elimination. It was initially made with identifying the rhythm as step 5 and did not mention anything about T-waves but I thought it was more appropriate to consider t-wave abnormalities as a step. We know ST elevation is a HUGE consideration in ecg assessment and interpretation so how could not make this addition?
FAST or SLOW
First process of elimination begins with determining if the rhythm is fast or slow. If the rhythm is slow, fast or normal, we still need more information to continue but you can eliminate half the rhythms right off the bat.
Normal: 60-100 bpm
Bradycardia: >60 bpm
Tachycardia: >100 bpm
REGULAR or IRREGULAR
Next, in our identification process, we need to determine whether the rhythm is regular or irregular. We do this by checking the R-to-R interval. To do this, we must identify the R wave. The R wave is the first upward deflection after the P wave.
In context to the electrical conduction through the heart, the R wave represents the electrical stimulus as it passes through the main portion of the ventricular walls (ventricular depolarization).
We can also determine the heart rate with the R-to-R interval. It may be difficult in a 12-lead ekg but in a six second strip you can determine a heart rate.
Regular: Consistent R-to-R (ex. NSR)
Irregular: Inconsistent R-to-R (ex. AFib)
As we move onto p waves, we also go over regularity.
P-WAVES
After determining regularity, we should observe whether the p waves are present. P waves represent atrial depolarization. If there are no p waves present, we could be looking at a junctional or ventricular rhythm, meaning the impulse is being generated PASSED the SA node, which we know is the heart’s natural pacemaker.
SA node intrinsic rate 60-100
AV node intrinsic rate 40-60
Ventricular intrinsic rate 20-40
Now, if the p waves are present then we must determine if they have a QRS complex to match it. A dropped QRS complex could indicate a second degree AV block. Multiple p waves with a single conducted QRS complex to match could indicate Atrial Flutter with a conduction rate. P waves marching out means consistent atrial depolarization. If they don’t have consistent QRS complexes, it means the beats are not reaching the ventricles. This should help you understand blocks a little bit better but we will be posting an article all about blocks in the near future so look forward to that!
Regular: Consistent p wave present (ex. NSR)
Irregular: Inconsistent p wave present (ex. Second degree AV Block)
Regularly Regular: Consistent R-to-R and consistent p waves (NSR)
Regularly Irregular: Consistent R-to-R but inconsistent p waves (Mobitz II)
Irregular Irregular: Inconsistent R-to-R and inconsistent p waves (Afib)
The last confirmation during our p wave assessment is determining whether the PR Interval is normal and consistent. What does normal mean? A normal PRI is 0.12-0.20 seconds, or 3 small boxes to 5 small boxes. This represents the time it takes for depolarization to reach the ventricles from the atria, passing through the AV node. A PRI longer than 0.2 seconds (5 small boxes) indicates a first degree AV block. A PRI shorter than 0.12 seconds (3 small boxes) indicates pre-excitation syndrome (WPW, SVT).
QRS Complexes
So far, we have a good idea what rhythm the patient might be in. We have determined the rate (fast or slow), we have determined the regularity, and we have determined the presence of a normal or abnormal PRI. The last step in our 5 step process is to assess the QRS complexes.
Before we move onto whether they’re dropped or grouped, we must determine if the QRS complexes are narrow or wide. This represents how long it takes for the conduction to depolarize throughout the ventricles.
The Q wave is any negative deflection before the R wave. Normal depolarization is left to right in the interventricular septum. Under normal circumstances, Q waves are not seen in the right-sided leads (V1-3). As we have learned, the first upward deflection after the p wave represents the R wave. The S wave is any downward deflection after the R wave. A large S wave can indicate hypertrophy in the ventricles.
A narrow QRS is <0.12 ms (3 small boxes) and indicates the electrical conduction is originating supraventricularly. A wide QRS is >0.20 ms (5 small boxes) and indicates the electrical conduction is originating in the ventricles or due to aberrant conduction. The height of the QRS signifies the voltage of the complexes.
Dropped beats could indicate a failure to conduct electrical impulses. We should be looking throughout our assessment for any ectopy. Since this is a beginner guide, we won’t dive too deep into ectopic beats but we will focus on a couple. Premature Ventricular Complexes (PVCs) and premature atrial complexes (PACs) are ectopic beats that can be caused by things from dehydration to hypoxia. Most people describe the condition as if their heart skipped a beat. If they occur infrequently, they are usually benign as they are spontaneous electrical impulses. Placing the patient on oxygen or administering fluids could resolve the issue. However, they can become dangerous. Over 3 consecutive PVCs is deemed a “run of VTach (ventricular tachycardia)” which can succeed into sustained VTach.
Other examples of ectopic beats becoming consistent would be PACs, PJCs, or PVCs beating at a consistent ratio, leading bigeminy or trigeminy.
T-Wave Abnormalities
The part of an ecg every EMT seems to be able to identify! ST Elevation. There are intricate ways to rule in, or rule out, an MI like using sgarbossa’s criteria. Since this is not advanced, we will focus on a few simple ways to identify it. Before you continue further, please review your leads and correlating anatomy (Inferior Septal Anterior Lateral/ISAL). We will not go over leads and arteries in this post but a future one.
When it comes to ST elevation, we are looking for >1mm (one small box) on >2 contiguous leads. Again, you must be familiar with your locations (ISAL) to understand contiguous leads. 1mm elevation in lead II and 1 mm elevation in V3 ARE NOT contiguous. We are looking for reciprocal changes when identifying a STEMI because it dramatically increases the likelihood of an AMI.
T wave elevation is not the same thing as ST elevation. The ST segment represents the interval between ventricular depolarization and repolarization. The T wave is the positive deflection after each QRS complex.It represents ventricular repolarization. Left bundle branch block produces T-wave inversion in the lateral leads I, aVL and V5-6. Right bundle branch block produces T-wave inversion in the right precordial leads V1-3. Peaked T waves (>½ the hight of the QRS complex) could indicate hyperkalemia.
There are STEMI imposters which include LBBB, LVH, pericarditis, and electrolyte imbalances. Ensure to always revert back to the underlying rhythm to identify the rhythm.
Identify the Rhythm
At this point, we can put it all together to identify the rhythm. Remember, when making a treatment plan, consider the patient’s presentation and signs and symptoms. Consider the stability of the patient and the possibility of deterioration.
