Friday, May 3, 2013

Left Bundle Branch Block with Less Than 1 mm of Concordant ST Elevation (in the Setting of Hypertrophic Cardiomyopathy)

A male in his 60's with a known history of hypertrophic cardiomyopathy (HOCM) presented for chest pain.  He thought  it was "acid reflux," and it started a few hours prior to his presentation to a non-PCI capable hospital.  He denied any associated symptoms.  His pain was not relieved with NTG.  He had an minimally elevated troponin at the referral institution, (assay unknown).  He was diaphoretic and clutching his chest.  Here is the first ECG:

There is sinus rhythm with LBBB and high voltage, and all leads have appropriate and proportional discordance EXCEPT for lead V4, which has less than 1 mm of (inappropriate) concordant ST elevation.  Lead V5 also has significantly less discordance than expected.

Definitions in Left Bundle Branch Block:

Appropriate Discordance: The ST segment (and usually the T-wave) should be in the opposite direction of the majority (not the end) of the QRS in all leads.  It should be proportionate, with the ST/S ratio being < 0.25 or ST/R ratio < 0.30.

Concordance: When the ST segment and/or T-wave is in the same direction as the majority of the QRS. This is abnormal for LBBB and, if 1 mm, a specific sign of STEMI-equivalent.

Modified Sgarbossa Rule:
Any one of:
1.     1 mm of concordant ST elevation in at least one lead.  Usually leads I, aVL, V5 and V6.  May also involve inferior leads.
2.     1 mm of concordant ST depression in at least one of leads V1-V3.
3.     Excessively discordant ST elevation, as measured by ST elevation (at the J-point, relative to the PR segment) to S-wave ratio of > 0.25

What should the ECG look like if there is both HOCM and LBBB?  I don't think anyone knows.

The patient was transferred to a PCI capable hospital where this ECG was recorded:

Now the concordant ST elevation is in lead V5, but since V4 now has a predominantly negative QRS, the difference is a result of lead placement differences between the two ECGs.  V6 has an inappropriately isoelectric ST segment.


An ECG from 5 years previous was available:

This shows inappropriate concordance of less than 1 mm in V4, and inappropriate isoelectric ST segments in V5, so all this configuration is not new for this patient who has known HOCM.


Strictly speaking, none of these meet the first Sgarbossa criterion of 1mm of concordant ST elevation.  In our study of patients with ischemic symptoms and LBBB, of 33 occlusions and 129 without occlusion, we had initially hypothesized that ANY concordant ST elevation (not just 1 mm) would be specific for coronary occlusion.  We did not publish the data (yet), but less than 1 mm of concordant STE occurred too frequently among the control group to be used as a specific criterion for STEMI-equivalent.

Out of an abundance of caution, the cath lab was activated and the coronaries were clean.

The troponin at the referral institution was normal.

The echocardiogram showed:


Normal estimated left ventricular ejection fraction, about 60%.
Left ventricular hypertrophy concentric, marked.
Dynamic left ventricular outflow/subvalvular obstruction (due to HOCM)
Asynchronous interventricular septal motion due to left bundle branch block.

The outcome

The patient developed abdominal pain in addition to chest pain, had a tender abdomen, and was diagnosed with cholecystitis!!!

Summary

1. Perhaps HOCM in the setting of LBBB can have concordant ST elevation
2. Concordant ST elevation of less than 1 mm has a specificity less than if it is greater than 1 mm
3. Troponins at or near the 99% cutpoint may give discordant results, especially with different assays.

8 comments:

  1. What a great case! Thanks for this wonderful website and your willingness to share much of what you have learned and researched over the years. I consider myself an ECG nerd and love learning more about my favorite subject. Keep up the great work.

    ReplyDelete
  2. Dr Smith,

    The ST/R ratio > .3, which would be excessive discordant ST depression, would that indicate Sub-endocardial ischemia, reciprocal ST depression or a STEMI equivalent? Could you please elaborate if possible? Thanks!
    I also think that you mentioned somewhere that this ratio has a very high sensitivity.
    (Great lecture this past Sunday, Congrats!)
    Thanks as usual.

    ReplyDelete
    Replies
    1. Saif, I wish I knew. You've prompted me to look into our data and see what we can find for the infarct-related artery in these cases. But I'm not sure it will give the answer.
      Yes, in our study the sensitivity of 1 lead with excessive discordance, as measured by > 0.30, whether ST depression or elevation, was 100% sensitive and 88% specific for occlusion.
      Thanks,
      Steve Smith

      Delete
  3. The first tracing also highlights the risk of possible false-positive excessive discordance when using an electrocardiograph that clips QRS complexes. I don't think any of the complexes in that ECG are positive by the Smith-modified discordance criteria, but it's easy to imagine how QRS clipping could lead to falsely-elevated discordance ratios when the QRS is really 2-3 times larger than it appears on paper.

    Nice case, and it matches my limited experience with these cases of minor concordant elevation.

    ReplyDelete
    Replies
    1. Vince,
      Good point. Sometimes you have to estimate where the R- or S-wave would end -- not ideal!
      Steve

      Delete