Premature ventricular contraction electrocardiogram

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mugilan Poongkunran M.B.B.S [2]

Overview

When looking at an electrocardiograph, premature ventricular contractions are easily spotted and therefore a definitive diagnosis can be made. The QRS and T waves look very different to normal readings. The spacing between the PVC and the preceding QRS wave is a lot shorter than usual and the time between the PVC and the proceeding QRS is a lot longer. However, the time between the preceding and proceeding QRS waves stays the same as normal due to the compensatory pause.

Electrocardiogram

1. The beats are premature in relation to the expected beat of the basic rhythm.
2. Ectopic beats from the same focus tend to have a constant coupling interval (the interval between the ectopic beat and the preceding beat of the basic sinus rhythm).
   • They do not vary from each other by more than 0.08 seconds if the focus is the same.
   • PVCs with the same morphology but with a varying coupling interval should make one suspect a parasystolic mechanism.
   • A longer RR interval is followed by a relatively longer coupling interval.
3. The QRS complex is abnormal in duration and configuration. There are secondary ST segment and T wave changes. The morphology of the QRS may vary in the same patient.
   • If the PVC originates from the RV then the QRS has a LBBB morphology.
   • The duration of the QRS is >0.12 seconds, but a narrower QRS may occur if the focus is higher in the septum.
   • The T wave is inverted and the ST segment is depressed.
4. There is usually a full compensatory pause following the PVC.
   • The sum of the RR intervals that precede and follow the ectopic beat (or the RR interval that contains the PVC) equals two RR intervals of the sinus beats.
   • Because of sinus arrhythmia, the RR interval that contains the PVC may not be exactly twice the duration of the RR interval of the adjacent sinus beat, even though a full compensatory pause does exist).
5. Retrograde capture may or may not occur.
6. They may occur in various frequency and distribution patterns such as bigeminy, trigeminy (occurrence of a PVC every third beat), quadrigeminy (occurrence of a PVC every fourth beat), and couplets (two ventricular premature complexes in a row). These are called complex PVCs.
   • The Rule of Bigeminy:

     1. PVCs frequently occur after a long RR interval
     2. The compensatory pause of the precipitated PVC constitutes another long RR interval, which in turn favors the appearance of another PVC
     3. Therefore bigeminy tends to perpetuate itself

7. Occasionally PVCs may be interpolated:
   • Between 2 beats without disturbing NSR
   • Occurs mostly when the NSR is slow and the PVC is early
   • The PR following the PVC is nearly always prolonged because of concealed retrograde conduction of the ectopic ventricular impulse, which renders the AV junction partially refractory.