Sinus tachycardia on an EKG

A 6-second lead II strip of sinus tachycardia on ECG (EKG) paper at 120 beats per minute, drawn by the ECG rhythm simulator’s model, with the criteria that define it and every interval measured from it.

Lead II, 6 seconds at 25 mm/s and 10 mm/mV: each small square is 0.04 s and 0.1 mV, each large square 0.2 s and 0.5 mV, and the step at the left is the 1 mV calibration pulse. Filled triangles mark P waves that reached the ventricles.

Try it: Open sinus tachycardia in the ECG simulator →

A study tool, not a clinical one

This page exists for learning what defines each rhythm and how it is measured on paper. It is not clinical decision support and must not be used to diagnose or treat anybody.

The strip is a model, not a recording. Every interval holds for the whole minute and every beat has the same shape, where a real rhythm varies with breathing, autonomic tone and drugs, and real complexes vary between people and between leads.
One lead is not a 12-lead ECG. The axis, bundle branch block patterns, ST changes and pre-excitation need all twelve leads, read by somebody trained to read them.
Definitions differ between sources. Guidelines, textbooks and institutions do not all draw the same rate and interval limits, so check which ones your course or institution uses.
Every criterion names its source. If one does not match what you were taught, check it against the source listed below, and tell us if we have it wrong. How the pages are checked is set out in the editorial policy.

What does sinus tachycardia look like on an EKG?

Sinus rhythm faster than 100 beats per minute: an upright P wave before every QRS, a constant PR, a narrow QRS and equal RR intervals. It is usually the sinus node responding normally to exercise, fever, pain, anxiety, blood loss or a drug, rather than a disorder of the rhythm itself.

Defining criteria

A sinus rate above 100 beats per minute. (Page et al. 2015)
The same P wave, PR and QRS as normal sinus rhythm. The simulator allows a rate of 101 to 180. (simulator model)

Rates and intervals on this strip

Rates and intervals of the sinus tachycardia strip above, from the simulator’s model
Ventricular rate	120 bpm
Atrial rate	120 per minute
P waves conducted	Every one
PR interval	160 ms
QRS duration	80 ms
QT interval	283 ms
QTc (Bazett)	400 ms
RR interval	500 ms
Regularity	Regular
Six-second count	12 QRS × 10 = 120 bpm

Measuring the strip

Each RR interval is 0.5 s, 12.5 small squares or 2.5 large ones, so the paper gives 1500 / 12.5 = 120 beats per minute. The PR is 160 ms, 4 small squares, and the QRS 80 ms, 2 small squares.

The TP segment is what a fast rate uses up. Each P wave starts 57 ms after the T wave before it ends, against 282 ms at 75 beats per minute, and with a PR of 160 ms the two meet at about 143 beats per minute. Above that each P wave rides on the T wave ahead of it, which is where P waves go missing in fast rhythms.

Settings the simulator allows for this rhythm

Each rhythm limits its settings to the values its definition allows, so the simulator can never draw it as something else.

Settings the ECG simulator allows for sinus tachycardia, and the value the strip above uses
Setting	Allowed	This strip
Sinus rate	101 to 180 bpm	120 bpm
PR interval	120 to 200 ms	160 ms
QRS duration	60 to 160 ms	80 ms

Telling it apart

A regular narrow-complex rhythm near 150 per minute is often atrial flutter with 2:1 conduction, its flutter waves hidden in the QRS complexes and T waves.
An irregularly irregular fast rhythm with no P waves is atrial fibrillation.
From 60 to 100 the same rhythm is normal sinus rhythm.

Sources

Page RL, Joglar JA, Caldwell MA, et al. 2015 ACC/AHA/HRS Guideline for the Management of Adult Patients With Supraventricular Tachycardia. Circulation. 2016;133(14):e506-e574. doi:10.1161/CIR.0000000000000311
Kligfield P, Gettes LS, Bailey JJ, et al. Recommendations for the Standardization and Interpretation of the Electrocardiogram, part I. Circulation. 2007;115:1306-1324. doi:10.1161/CIRCULATIONAHA.106.180200
McSharry PE, Clifford GD, Tarassenko L, Smith LA. A dynamical model for generating synthetic electrocardiogram signals. IEEE Transactions on Biomedical Engineering. 2003;50(3):289-294. doi:10.1109/TBME.2003.808805
Bazett HC. An analysis of the time-relations of electrocardiograms. Heart. 1920;7:353-370.