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ECG BASICS: Sinus Rhythm With Ventricular Bigeminy

Dawn's picture
Thu, 05/09/2013 - 13:20 -- Dawn

Nice, clear example of ventricular bigeminy with an underlying sinus rhythm.  We do not know from this strip if the sinus rhythm is a bradycardia at a rate of about 42 per minute, or if the underlying sinus rhythm is actually at a rate of 85 per minute, with every other sinus beat inhibited by the occurance of a PVC.  In the first possibility, the ventricular beats would be considered "escape" beats, positively contributing to the patient's heart rate.  In the second instance, the rather late-occurring PVCs would cause the heart to be refractory, preventing the sinus P wave from conducting it's impulse to the ventricles.   Sometimes, we can see signs of the sinus P wave "hiding" in the PVC, but in this case, if P waves exist, they fall almost exactly in the middle of the ventricular beats' QRS complex, making them invisible.  A good strategy would be to watch the strip continuously for some time, hoping to catch the conduction of two sinus beats in a row, solving the dilemma.

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Comments's picture

I would add several observations to this seemingly "ECG Basic Rhythm Example" of Ventricular BigeminyAs per Dawn - there is no way to be certain if this rhythm began as "sinus bradycardia" (at ~42/minute) interrupted by PVCs - or - IF instead the underlying sinus rhythm was at ~85/minute, with the rhythm again being interrupted by "PVCs". Whereas there often is indication of sinus P waves notching a portion of the QRST complex - there is no such indication in this example.

  • My guess is that the underlying rhythm is sinus at ~85/minute. IF in fact the underlying rhythm was sinus bradycardia at the slow rate of 42/minute (with the ventricular beats that occur every-other-beat being ventricular "escape" beats) - I would expect take-over by a ventricular escape rhythm at ~80/minute, since the coupling interval between each sinus beat (beats #1,3,5,7) and the ventricular beat (beats #2,4,6,8) should correspond to an escape rate of ~80/minute. If these were truly ventricular "escape beats" - Why should the "escape rhythm" stop after only 1 beat? Of course we can't be certain - and the above is conjecture ...
  • In any case (regardless of whether ventricular beats represent late = 'end-diastolic' PVCs or a ventricular escape rhythm) - the occurrence of late-cycle ventricular beats in this fashion is far less common than PVCs with much shorter coupling intervals. End-diastolic (late-cycle) PVCs, as well as AIVR (Accelerated IdioVentricular Rhythm) tend to occur in a limited number of clinical settings. Prominent among these is reperfusion following acute coronary occlusion, be this spontaneous reperfusion and/or reperfusion post-thrombolytic or interventional therapy. So Clinically - I wonder what the circumstances are.
  • Finally - the frequent occurrence of PVCs should bring to mind this clinical truism: "The significance of PVCs depends on the clinical setting in which they occur". PVCs - even if frequent and/or in relatively long runs - tend to be benign IF there is no underlying heart disease. In contrast, in the presence of significant underlying heart disease - frequent and repetitive ventricular ectopy is clearly cause for concern. As noted above - the late-cycle occurrence of ventricular beats in this situation makes us wonder if the setting relates to acute reperfusion, cardiopulmonary resuscitation, or some other circumstance in a patient with significant underlying heart disease. Additional rhythm strips and some history are needed to answer this.

Ken Grauer, MD   [email protected] 

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