EKG Tutorial: Sinus rhythms

Electrocardiography

Sinus rhythms

From a clinical standpoint, it is important to focus the examination on the patient and not the ECG. Many dysrhythmias can be completely benign. How does the patient feel? How long has the patient felt this way? A full history can be as useful as a good ECG.

A methodical approach will be much more effective than simply memorizing the appearance of the many dysryhthmias. Always begin you analysis by asking the following questions:

Is the rate fast or slow? Are the atrial and ventricular rates the same?
Are the P-P interval and R-R interval regular or irregular? If the rhythm is irregular, is it consistent or irregular irregularity?
Is there a P-wave before each QRS? Is there a QRS before every P-wave?
Are the P-waves and QRS complexes identical and normal in configuration?
Are the P-R and QRS intervals within normal limits?

Sinus Rhythms are a class of rhythms which originate at the SA node. Sinus rhythms generally travel through the entire conduction system without inhibition.

They are characterized by:

a conducted P-wave
P-R interval between 0.12 and 0.20 seconds
The QRS width should be 0.04 to 0.12 seconds and be all QRS's are preceded by a P-wave.

In reality, nothing is normal. Every patient has his own unique ECG patterns. Nevertheless, scientists like to have a baseline for everything. In a perfect world, we'd all have a Normal Sinus Rhythm. If your's doesn't look exactly like this, you probably aren't going to die in the next five minutes. At least read the rest of the tutorial before you panic...

The criteria for a Normal Sinus Rhythm is:

P-wave before each QRS with an interval of 0.12 to 0.20 seconds in duration.
A QRS width of 0.04 to 0.12 seconds
Q-T interval of less the 0.40 seconds.
The rate for a normal sinus rhythm is 60 to 100 beats a minute.

*Normal Sinus Rhythm*
P-R interval	0.12 to 0.20 seconds
QRS duration	0.04 to 0.12 seconds
Rate	60 to 100 beats a minute

If the rate is below 60 beats a minute but the rest is the same it is a Sinus Bradycardia.

Brady- means slow.. Like your brain after you watch the Brady Bunch!

*Sinus Bradycardia*
P-R interval	0.12 to 0.20 seconds
QRS duration	0.04 to 0.12 seconds
Rate	less than 60 beats a minute

Yes... the QRS complexes look completely different... That's okay. I already said that we're all different. Relax.

If the rate is between 100 to 150 beats a minute with the same intervals it is a Sinus Tachycardia.

Tachy- means fast. (Think of what happens to your heart rate when you sit on a tack)

*Sinus Tachycardia*
P-R interval	0.12 to 0.20 seconds
QRS duration	0.04 to 0.12 seconds
Rate	100 to 150 beats a minute

When the pattern becomes irregular with normal intervals it is a Sinus Arrhythmia

*Sinus Arrhythmia*
P-R interval	0.12 to 0.20 seconds
QRS duration	0.04 to 0.12 seconds
Rate	60 to 100 beats a minute, regular rhythm with periodic irregularity

Clinically, these could all be perfectly fine. Any of them could also be deadly. It is possible to show a regular Sinus Rhythm on the ECG with no contraction of the heart! Check your pulse. Is it there? Good. Now quit worrying so much.

Electrocardiography

Sinus rhythms

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