Normal Sinus Rhythm

When talking about treating a patient for something that we consider abnormal, it's always helpful to define and understand what normal looks like, in this case, for a normal sinus rhythm.

In this lesson, we'll look more closely at an example of a normal sinus rhythm on an ECG for a pediatric patient and see what findings and measurements are considered normal, and what to be on the lookout for that would be considered abnormal.

*Normal Sinus Rhythm ECG

1. The Heart Rhythm

The first thing you'll want to look at is the heart rhythm. Does the heart rhythm look regular? Or does it look irregular? In the above graphic, it's regular.

2. The Heart Rate

Next, you'll want to look at the heart rate of the patient. What is the patient's heart rate? Is it normal? Or is it too slow or too fast?

Remember, to determine the patient's heart rate you'll want to observe the following areas on the ECG paper printout and perform the following calculations.

The horizontal axis of ECG paper grids is where time is measured. Each small square is 1mm in length and represents .04 seconds. Each larger square is 5mm in length and represents .2 seconds. Therefore a 6 second interval would be 30 large squares.

To determine the heart rate, count the number of QRS complexes over this 6 second interval and multiply by 10.

It's also important to understand that when it comes to pediatric patients, normal heart rates vary based on the age of the patient. For example, a normal heart rate for a 12-year-old will probably be bradycardic for an infant or a newborn.

You may recall seeing some important stats or metrics in the PALS welcome lesson, and the normal ranges for heart rates by age might be worth repeating here.

Heart Rates by Age

3. P-Wave

After looking at the heart rate, check to see if the patient's P-waves look normal by asking yourself the following few questions.

• Are the patient's P-waves present?
• Do they occur regularly?
• Is there one P-wave for each QRS complex?
• Are the P-waves smooth, rounded, and upright?
• Do all the P-waves have a similar shape?

4. PR Interval

Next, look at the PR interval on the patient's ECG readout and ask yourself the following questions:

• Is the PR interval normal, meaning less than .20 seconds or is it contained within one large square on the readout?
• Is the PR interval constant?

5. QRS Complex

The last thing you should look at to determine if the sinus rhythm is normal or not is the QRS complex and ask yourself these questions while you do:

• Is the QRS interval less than .09 seconds?

• Is the QRS complex wide or narrow? If it's narrow, such as on the ECG printout above, then that's considered normal.
• Are the QRS complexes similar in appearance or are there noticeable differences?

So, what is your cardiac interpretation? Based on these questions and on the findings from the ECG readout above, it's safe to say that the patient has a regular sinus rhythm.

1. We have a regular rhythm.
2. We have a normal heart rate.
3. The P-waves look normal, with each being followed by a QRS complex.
4. The PR interval is less than .20 seconds.
5. The QRS is less than .09 seconds.

Unless the patient has no pulse or other serious signs or symptoms, it's safe to assume that there is nothing of significance, in a negative sense, from this patient's cardiac rhythm.

PALS Arrythmias: A Foundational Fact to Keep in Mind

When it comes to arrhythmias in pediatric patients, consider the following when evaluating the heart rate and rhythm in any seriously ill or injured child:

• Establish what the child's typical heart rate and baseline rhythm is
• Establish the child's level of activity and clinical condition, including baseline cardiac function

Children with congenital heart disease may have underlying conduction abnormalities. Interpret the child's heart rate and rhythm by comparing them to the child's baseline heart rate and rhythm. Children with poor baseline cardiac function are more likely to become symptomatic from arrhythmias than children with normal cardiac function.