How are atrial premature complexes differentiated from ventricular premature complexes (VPCs)?

Updated: Nov 26, 2016
  • Author: Jatin Dave, MD, MPH; Chief Editor: Jose M Dizon, MD  more...
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Answer

The presence of ectopic P waves, usually absence of full compensatory pause (R-R interval containing the premature contraction is < 2 times the R-R interval of basic rhythm), and a relatively narrow QRS complex morphology help differentiate atrial premature complexes from VPCs. The compensatory pause results when the sinus node is not reset by VPCs. This typically occurs when the ectopic impulse colides with the sinus impulse remote to the sinus node (either at the AV node or in the ventricles), or when it otherwise fails to propogate to the atrium and enter and reset the sinus node.

On occasion, the ectopic impulse conducts retrogradely to the sinus node; resets the sinus node; and a shorter, noncompensatory pause occurs. If the sinus impulse is able to conduct despite the VPC, then the VPC is termed interpolated and no compensatory pause occurs. However, the presence or absence of a compensatory pause is not a diagnostic finding for a VPC, as a beat of ventricular origin may retrograde traverse the AV node and enter and reset the sinus node; conversely, beats of non-ventricular origin may not always enter and reset the sinus node, and sinus node function is not always predictable. 


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