Thursday, April 6, 2017

Wide complex tachycardia and an ICD that is not firing

A 40-something woman with a history of MI and ischemic cardiomyopathy and previous VT, with an implanted cardioverter-debrbrillateror (ICD) and on no antidysrhythmics had the acute onset of fluttering in the chest along with dizziness while she was sitting.  She called 911 after 15 minutes without resolution.

She was found alert with a normal BP and good oxygen saturations, not in distress.  There was no CP or SOB.

Here is the prehospital rhythm strip:
Regular, Wide Complex Tachycardia

Very wide complex, regular, rate 150
Here is the 12-lead:

Here is a printed version of the prehospital ECG.  It shows more detail:

Wide-complex tachycardia at the rate of 150 bpm. 
The R-wave is upright in aVR and the initial part of the QRS is wide.
These ECG features, with ischemic cardiomyopathy and presence of an ICD, all highly suggest VT.

Patient was given a trial of adenosine 6 mg which did not convert to sinus rhythm, so the medics performed synchronized electrical cardioversion after giving 5 mg of midazolam.

Comment: Electrical cardioversion is not inappropriate, but also not necessary, as she was very stable.  The downside is that sedation with midazolam is not always so benign.  It can result in hypotension or hypoventilation.  Fortunately, she had neither and did not remember the cardioversion later.

Here is her post-conversion prehospital ECG:

Sinus Rhythm at a rate of 77
Rather bizarre very wide complex, neither RBBB nor LBBB.  

This wide complex should make you scrutinize the morphology of the tachycardia to ascertain whether this wide complex that we see in sinus rhythm is the same wide complex seen during the tachycardia.  If it is identical, then the rhythm would have been SVT.

On arrival, the patient stated that she had never felt her ICD fire.   This suggests that her rhythm was not her usual VT, but some other rhythm which her ICD is not programmed to detect.  She also stated she had had several episodes of self-terminating palpitations in the past week.

She denied any CP or SOB at any time.

An ECG was recorded:
Now there is sinus with obvious ventricular pacing and PVCs.

If you look closely at the QRS, it is identical to the prehospital ECG (the one that has sinus rhythm).
This proves that the post-cardioversion prehospital was also paced and explains that baseline bizarre wide complex.
Pacer spikes are often very difficult to see.

Electrolytes were normal.  We interrogated the ICD in the ED and found that the ventricular rate had indeed been 150 and the atrial rate 95 (this confirms AV dissociation, proving VT).  The tachycardia detection rate was 167.  The previous VT for which the ICD was implanted had a rate of 180 which thus would have been detected by the 167 threshold.

The tachycardia today at 150 was NOT detected; this turns out to be a second source of VT at a slower rate.

No underlying provoking factor was found (ACS, electrolytes) and the ICD was reprogrammed for a rate of 150.

It was decided not to start any antidysrhythmic, as that might not work, might have adverse effects, and could possibly change the rate of any future VT rendering the ICD ineffective again.


  1. Yet another great case. Could you discuss further your approach to visualizing pacer spikes when not seen? Particularly EKG dynamic range and filtering. Is it accurate that in addition to turning 'pacer' sensing on etc that lowering the filtering upper range can help too (e.g. down to 50 hz)? Is this something you ever do? It's hard to find a good clinical discussion on this. Thanks as always.

    1. I don't know the answer. The computer is usually quite good at detecting them.


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