Thursday, May 7, 2015

Paced rhythm, Modified Sgarbossa negative, but with a Wall Motion abnormality.

This case was posted by my colleagues at the Hennepin Ultrasound Blog, as Apical Wall Motion Abnormality or Electrical Asynchrony?

But there was no comment on the ECG, which is very interesting.

Case

A male in late middle age with a history atrial fibrillation, significant renal insufficiency, and implanted single chamber right ventricular pacemaker, but no known coronary disease, presented with 2 hours of sudden onset chest pain.  It felt like heavy pressure.  The pacer was placed 2 months prior, and the patient had no ECG recorded after placement to establish a baseline.

Here is his ED ECG:
There is a paced rhythm with proportionally discordant ST segments.   There are no concordant ST segments.  Thus, there is no evidence of STEMI.

Unlike Left Bundle Branch Block, there is comparatively little data on the accuracy of the Sgarbossa criteria in diagnosing acute MI (better, acute coronary occlusion) in the setting of a paced rhythm, and no data on the Modified Sgarbossa criteria.  There are two small studies showing good specificity of the traditional Sgarbossa criteria, but poor sensitivity.  There are 2 case reports (both by me and co-authors, references below) of STEMI diagnosed in paced rhythm by proportionally excessive discordant ST elevation (modified Sgarbossa criteria).   I have posted other cases in which STEMI was easily diagnosed in the setting of paced rhythm.  Here is one.  Here is another.  But we really don't know the sensitivity of concordant STE or proportionally excessively discordant STE in paced rhythm.  I suspect it is as good in paced rhythm as in LBBB.

So the ECG in this case does not meet any Sgarbossa criteria

However, this patient has very suspicious symptoms and you do not want to miss a coronary occlusion.

So a bedside echo was done; here is the parasternal long axis view:

It looks as if the apex is not moving well.



Here is the apical view:


There is clearly an apical wall motion abnormality.





And this apical view shows the WMA clearly as well.

A review of the patient's chart showed that the last formal echo had been normal, but had also been done prior to placement of the pacemaker.    Right ventricular pacing results in an abnormal sequence of activation and so there may appear to be a wall motion abnormality.

So the ECG shows no indication of occlusion, but the echo shows a new wall motion abnormality that can be completely due to the pacemaker.

The patient has a relative contraindication to coronary angiogram (renal insufficiency).

It was decided not to take the patient to the cath lab.  Troponins were negative and the pain resolved.

Formal ultrasound done later had the same findings.



This ECG was recorded 4 hours after the first:
The T-waves are slightly taller, but there are no abnormal ST segments.

Learning points:

1. Use the modified Sgarbossa criteria in paced rhythms.  The specificity is good. The sensitivity is unknown but probably similar to sensitivity in LBBB, which I believe to be as good as ST elevation in normal conduction, probably about 70-75% sensitive for coronary occlusion (though the sensitivity was much higher in our case control studies, which probably do not accurately reflect clinical practice).

2. The ECG in this instance was more reliable than formal echocardiography



Here is the ECG from the first case I link to:
This shows both concordant ST elevation in V2, and proportionally excessively discordant STE in V3.  There is also concordant ST depression in V6.


One difference between LBBB and Paced rhythm is that, in paced rhythm, the QRS in V5 and V6 is almost always negative (but positive in LBBB).  Therefore, any STEMI that manifests in V5 and V6 in LBBB will usually manifest by concordant ST elevation in these leads, whereas in paced rhythm, it must be excessively discordant ST elevation.



References

1. Sgarbossa EB, Pinski SL, Gates KB, et al. Early electrocardiographic diagnosis of acute myocardial infarction in the presence of ventricular-paced rhythm.(full text pdf) GUSTO-I investigators. Am J Cardiol. 1996;77:423–4.

2.  Maloy KR, Bhat R, Davis J, Reed K, Morrissey R.   Sgarbossa criteria are highly specific for acute myocardial infarction with pacemakers. (full text link)  West J Emerg Med. 2010;11(4):354-357.

modified Sgarbossa rule. (full text link) Ann Emerg Med. 2012;60(6):766-776.

4. Schaaf SG, Tabas JA, Smith SW. A patient with a paced rhythm presenting with chest pain and
hypotension. JAMA Intern Med. 2013;173(22):2082-2085.

5. Ukena C, Mahfoud F, Buob A, Böhm M, Neuberger H-R. ST-elevation during biventricular pacing. Europace 2012;14(4):609-611.

6. Karumbaiah K, Omar B. ST-elevation myocardial infarction in the presence of biventricular paced rhythm. J Emerg Med. 2013;45(2):e35-e40.

7. Walsh B.  Smith SW.  A Patient with a Biventricular Paced Rhythm Presenting With Chest Pain.  Challenges in Clinical Electrocardiography. JAMA Internal Medicine.  April 6, 2015.

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