LESSON 9 – Sinus Tachycardia and Sinus Bradycardia

Sinus tachycardia is a rhythm that meets all criteria of sinus rhythm, with a heart rate of 100 beats per minute or higher.

Some authors suggest that tachycardia should be defined starting from a heart rate of 90 bpm. It is reasonable to agree that a resting heart rate of 90 bpm is relatively elevated and should be described in the report as “accelerated sinus rhythm.”

Sinus bradycardia is a rhythm that meets all criteria of sinus rhythm, with a heart rate less than 60 beats per minute

Let us briefly review the criteria of sinus rhythm:

Criteria for Sinus Rhythm

• In lead II, and usually also in leads I and aVF, there are positive P waves of identical morphology, located at a constant distance from the QRS complex in all consecutive cardiac cycles.
• The number of P waves equals the number of QRS complexes.
• Heart rate is between 60 and 100 beats per minute. Values below this range indicate sinus bradycardia, and values above it indicate sinus tachycardia.
• RR intervals are regular:  variation between consecutive RR intervals does not exceed ±10%.

This is a typical example of sinus tachycardia.

The heart rate is 150 beats per minute

All criteria for sinus rhythm are fulfilled; however, the heart rate exceeds 100 beats per minute.

This is a typical example of sinus bradycardia.

The heart rate is 48 beats per minute

All criteria for sinus rhythm are fulfilled; however, the heart rate is less than 60 beats per minute.

I believe that for those who have already understood sinus rhythm, this topic was straightforward. However, in clinical practice, things are not always so clear-cut. Let us now complete the tasks “TACHYCARDIA” and “BRADYCARDIA.”