Monday, June 18, 2018

A Wide Complex Rhythm in an Intoxicated Patient

This patient presented with altered mental status and was thought to be intoxicated.  He did not have any other apparent medical issues.

I'm not certain why an ECG was recorded, but it was:
The computer and the overreading physician diagnosed "Sinus rhythm with LVH."
What is it?

This is an accelerated idioventricular rhythm (AIVR).  There is also isorhythmic dissociation (P-waves and QRS co-incidentally going the same rate, but without the P-waves consistently conducting through the AV node because frequently the ventricular rhythm usurps it (comes too early for the P-wave to conduct).

I point out the salient features on the annotated image below:
There is a wide QRS that is at regular intervals at a rate of about 65.
They are either not preceded by a P-wave, or by a P-wave that is too close to be conducting.
Black arrows points to normal P-wave that conducts to a normal QRS.
Green Arrows point to upright sinus beats that are close to the QRS and create a "fusion" beat, in which the ventricular beat and the normal beat meet up (fuse) and create a hybrid QRS that is longer than a normal one, but shorter than the idioventricular ones.
Red Arrows point to retrograde P-waves.  The idioventricular rhythm conducts up the AV node to the atrium, creating an upside down P-wave after the QRS.
Blue arrows point to upright P-waves that are within or after the QRS; they occurred too late to affect the QRS (they did not fuse).

See below how this resembles WPW and why it is not WPW.

AIVR is an automatic ventricular rhythm that is:
1.  Faster than a normal ventricular escape rhythm (which is also automatic at rates as high as 50).  AIVR is caused by enhanced automaticity (faster than normal automaticity).
2.  Slower than ventricular tachycardia (less than 100-120).  VT is a re-entrant rhythm.

It is a benign rhythm but may be seen in dangerous pathologies, particularly in the reperfusion phase of acute STEMI, digoxin toxicity, and sympathetic overload.

Clinical course

Although the overreading physician did not see the AIVR, the resident did diagnose "Idiopathic Ventricular Rhythm without Tachycardia," which does pretty well (but not exactly) describe the ECG, but does not conform to the standard terminology.  "AIVR" is much more accurate and precise.

The patient had negative troponins in the ED.   He was not on digoxin.  He did not have other evidence of sympathetic overload.

He metabolized his toxin, whatever it was, and was discharged.

It is important to know that AIVR can occur any time and does not necessarily imply significant pathology.

Since there is a great and succinct article on AIVR at Life in the Fast Lane, I do not feel the need to explain in greater detail:

The QRSs do resemble those of WPW; is this intermittent WPW? 
However, here we do not see the typical slurred upstroke (delta wave) of WPW; the QRS is uniformly wide, whereas a delta wave has a slower initial upstroke that later. 

Moreover, an interpretation of WPW would require there to be P-waves prior to these abnormal QRSs.

So it is not WPW.

Here is an example of intermittent WPW:
In this case, the computer also interpreted "Normal"
But complexes 3, 4, 5 have delta waves and a short PR interval.

Here is a case of WPW in which the QRSs do resemble those of AIVR:
Looks similar, right?  But here there are P-waves before every QRS and the first part of the QRS is more slurred.
You can read here why the PR interval is not short in this case of WPW:

A large R-wave in lead V1. And why is the PR interval not short?

Comment by KEN GRAUER, MD (6/18/2018):
Interesting case in which an ECG was probably not essential to management — but for which we are thankful, since it provides such an instructive teaching case! As per Dr. Smith — AIVR is generally a benign rhythm that will often be seen in dangerous pathologies (most commonly as a “reperfusion rhythm” in occlusion-related infarction). As Dr. Smith also emphasized — AIVR may on occasion be seen in otherwise healthy individuals who do not have underlying heart disease. So, as is the case with most cardiac rhythms — the clinical setting is KEY to determining the significance (or lack thereof) of the arrhythmia! I’ll offer a different viewpoint to one aspect of Dr. Smith’s interpretation:
  • I suspect there are no retrograde P waves here (which if present, might then be expected to reset the sinus rate). Instead, I favor the hypothesis that all colored arrows in Figure-1 represent sinus-generated P waves — with the underlying rhythm being sinus arrhythmia.
  • We see evidence of this variation in sinus rate at the beginning of the tracing. Thus the P-P interval between the 1st black and 1st green arrows measures 960 msec (corresponding to a rate of ~62/minute) — which is clearly longer than the P-P intervals once normal sinus conduction resumes for the last 2 beats on the tracing. Thus, the P-P intervals for these last few sinus beats = 740 and 720 msec (corresponding to a faster sinus rate of 81 and 83/minute, respectively).
  • It is because of this sinus arrhythmia with bradycardia that AIVR is seen! With periods of sinus rate slowing (as occurs at the beginning of Figure-1) — once the sinus rate drops below the 65/minute threshold of the slightly accelerated ventricular escape focus — AIVR takes over — until, the sinus rate speeds back up toward the end of the tracing.
Figure-1: Perhaps all P waves are sinus-initiated — with an underlying sinus arrhythmia + bradycardia leading to intermittent AIVR? (Details in my Comment above).
P.S.— AIVR is not always completely benign. As a result of “takeover” by this ventricular rhythm — the “atrial kick” is lost. In some settings — this loss of atrial contribution to cardiac output may result in hypotension. In those rare instances in which excessive slowing of sinus P waves results AIVR with hemodynamic compromise — Atropine may be the drug of choice. That said, in the vast majority of cases — AIVR will not produce symptoms, and no specific treatment is needed.

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