Sinus tachycardia
A sinus rhythm faster than normal for the patient, still originating from the SA node.
Key ECG features
- ✓Rate high for the patient
- ✓Normal P before every QRS
- •Regular rhythm
- ±P merging into the preceding T at fast rates
✓ required · • typical · ± may be present
ECG characteristics
A normal P wave precedes every QRS at a rapid, regular rate. At very fast rates the P wave merges into the preceding T wave, which can make it hard to separate from a supraventricular tachycardia.
This illustration is schematic. Dashed line is a normal rhythm. The grid is not drawn to scale.
Common causes
Usually an appropriate response to a demand rather than a primary rhythm disturbance: pain, fear, excitement, fever, hypovolemia, anemia, hyperthyroidism (particularly in cats), or drug effect.
Why it matters
Interpretation hinges on identifying the driver. An explained sinus tachycardia is expected and treating the rhythm itself is the wrong move; an unexplained, sustained resting tachycardia warrants investigation.
Differentiate from
- Supraventricular tachycardiaBoth are fast and narrow. Sinus tachycardia has a normal P wave before every QRS, an identifiable driver, and a rate that rises and falls with it; SVT starts and stops abruptly.