Premature ventricular contractions (PVCs) on an EKG

A 6-second lead II strip of sinus rhythm with premature ventricular contractions on ECG (EKG) paper, one every fourth beat, drawn by the ECG rhythm simulator’s model, with the compensatory pause and the P wave each PVC hides measured.

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, open triangles those that did not.

Try it: Open premature ventricular contractions 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 a PVC look like on an EKG?

An early, wide QRS with no P wave before it and a T wave pointing the opposite way. The sinus node usually keeps its timing, so the beats either side of the PVC are two sinus cycles apart, a full compensatory pause. A PVC every second beat is ventricular bigeminy, every third trigeminy and every fourth quadrigeminy.

Defining criteria

An early QRS with no P wave before it, 140 ms wide in the model, past the 120 ms that makes a QRS wide. (Surawicz et al. 2009)
A T wave pointing opposite to the QRS, from a beat that spreads through the muscle rather than down the bundle branches. (simulator model)
A coupling interval of 45 to 80 percent of the sinus cycle in the simulator, so the PVC always starts before the next sinus P wave could reach the ventricles and never fuses with a sinus beat. (simulator model)

Rates and intervals on this strip

Rates and intervals of the premature ventricular contractions strip above, from the simulator’s model
Ventricular rate	75 bpm
Atrial rate	75 per minute
P waves conducted	3 of every 4
PR interval	160 ms
QRS duration	80 ms, PVCs 140 ms
QT interval	358 ms, PVCs 418 ms
QTc (Bazett)	400 ms
RR interval	520 to 1080 ms
Regularity	Regularly irregular
Six-second count	8 QRS × 10 = 80 bpm

Measuring the pause

The PVC comes 0.65 × 800 = 520 ms after the QRS before it, and the next sinus beat 1080 ms after the PVC: 520 + 1080 = 1600 ms, exactly 2 × 800.

The sinus P wave due in that pause arrives on time, 120 ms after the PVC starts and inside its 140 ms QRS, finds the AV node refractory and is not conducted. It is there on the strip, under the open triangle, but hidden in the PVC.

Because the pause makes up exactly for the early beat, the mean ventricular rate stays at the sinus rate, 75 beats per minute. A PVC early enough to land on the T wave of the beat before, R on T, is the timing linked with ventricular tachycardia and fibrillation in a vulnerable heart.

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 premature ventricular contractions, and the value the strip above uses
Setting	Allowed	This strip
Sinus rate	50 to 100 bpm	75 bpm
PR interval	120 to 200 ms	160 ms
Coupling interval	45 to 80 percent of the sinus cycle	65 percent of the sinus cycle
QRS duration	60 to 160 ms	80 ms
Premature beat	Every second, third, fourth or sixth beat	Every fourth beat

Telling it apart

A PAC has an early P wave, a narrow QRS and a pause shorter than two sinus cycles.
The ventricular escape beats of complete heart block are wide with no P wave before them too, but they come late, not early.

Sources

Surawicz B, Childers R, Deal BJ, Gettes LS. AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram, part III: intraventricular conduction disturbances. Circulation. 2009;119(10):e235-e240. doi:10.1161/CIRCULATIONAHA.108.191095
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.