ECG Basics · Lesson 7 · Reading the paper

Regular, or not?

Before naming a rhythm, decide whether the R–R spacing is constant, follows a repeating pattern, or has no pattern at all.

Measure RR, not impressions

Mark several R waves (on paper, a sheet edge or calipers) and compare the spacing. The strips below show each RR interval in milliseconds, taken from the engine trace.

Regular

Constant RR within normal beat-to-beat variation. Sinus rhythm, atrial flutter with fixed conduction and most monomorphic VT are regular.

Regularly irregular

The spacing changes, but in a repeating pattern, often in groups. Mobitz I (Wenckebach) shows groups that end with a dropped beat; ventricular bigeminy shows short–long pairs.

Irregularly irregular

No two RR intervals predictably alike, with no repeating pattern. Think of atrial fibrillation first; multifocal atrial tachycardia and frequent multifocal ectopy are alternatives. Look for P waves to tell them apart: none in AF, three or more different P shapes in MAT.

Sinus rhythm is not perfectly regular. Breathing changes the rate a little (respiratory sinus arrhythmia), and the live simulator's Natural variation setting reproduces this. Set it to 0% to see a metronome-regular model.
See it move in the live simulatorRespiratory sinus arrhythmiaMobitz IAtrial fibrillationMAT

References

  1. Mason JW, Hancock EW, Gettes LS, et al. Recommendations for the standardization and interpretation of the electrocardiogram, Part II: electrocardiography diagnostic statement list. Circulation 2007;115:1325–1332.