Paced Rhythm with Dynamic ST segments and Concordant T-waves - High Risk ACS

A 77 yo woman with h/o pacer for unknown reasons (no medical records available) and no h/o coronary disease presented with 24 hours of constant chest pain.  She decided to call 911 because she just couldn't walk any more.  Paramedics found her with normal vital signs, chest pain 8/10, and the following ECG:

There are p-waves followed by a paced QRS.  It is slightly unusual that there is an RBBB pattern.  Most pacers are in the apex of the RV and thus have all negative QRS in V1-V6.  Here the RBBB pattern suggests that the pacing wire is on the left (see below).  More importanly, although the ST segments are discordant in V4-V6, the T-waves are concordant.  This suggests ischemia, usually Non-STEMI in this context.  That the ST segments are discordantly elevated at the same time the T-waves are inverted suggests injury in these leads, but is not diagnostic.

When there is RBBB pattern in pacing, there are two distinct possibilities: 1) the lead has perforated into the LV or 2) there is a lead going through the coronary sinus to the LV.  In this case, fortunately, x-ray confirmed the latter.

I was worried that she had suffered a very large MI because her pain had lasted so long.  It did decrease to 3/10 after sublingual NTG.  She arrived in the ED and had the following ECG at 1030:

There are again p-waves with a paced QRS (one p-wave comes early, PAC), and the ST elevation in V4-V6 is largely resolved, and the T-wave inversion deeper. Along with the resolution of chest pain, this is nearly diagnostic of ACS.  Later, the pacer was interrogated and found to be 100% atrial synchronous biventricular pacing.

The troponin I returned at 12 ng/ml.  I was relieved that it was not much higher.  I gave her ASA, clopidogrel, and heparin and she went immediately to the cath lab and had an active ostial LAD lesion with a long hazy calcified segment that could not be stented.  She went for 2-vessel CABG.

Here is an ECG from 1530:

There is some continued dynamism of the T-waves

Echo showed an inferoposterior and a probable anteroapical wall motion abnormality.

She did well.

Addendum:

Here is an addition to this post in response to a question/comment:  "I am sorry to say that I do not find any literature about that topic. Therefore I kindly ask, why you comment on the dynamic ST-segment changes in this patient as a typical sign of acute MI. Could you comment on this or give additional literature."

 

There is some previous literature on this, but not a lot.  I have summarized the most recent article below.  There is also one from the 90’s, referenced  here.¹

There is little reason to suspect that paced rhythms act any differently than left bundle branch block or, if the activation is from the left, like RBBB.  In my experience of multiple cases (see here for a couple), and of cases of PVC’s (see here and here), concordant ST segments and excessively discordant ST segments (> 25% of the preceding S-wave or R-wave, as measured at the J-point) are very good for injury.  Even better are dynamic ST segments, as in this case.  There is no way for pacing alone to result in dynamic ST segments; one must assume dynamic ischemia until proven otherwise.

This is the more recent article: Maloy et al.(Maloy 2011)² assessed the Sgarbossa criteria¹ in 57 cases of paced ECG in biomarker-diagnosed AMI (not angiographic occlusions), and compared them to 99 troponin-negative paced controls who were otherwise of comparable age and sex.  There were no cases of concordant ST elevation.  Concordant ST depression in one of leads V1-V3 had sensitivity of 19% (95% CI 11–31%) and specificity 81% (95% CI 72–87%).  For ST-segment elevation >5mm and discordant with QRS complex, the sensitivity was 10% (95% CI 5–21%) and specificity 99% (95% CI 93–99%).  The authors do not publish the numbers of patients who met each criterion.  Only one patient (a control) met both criteria, so it appears that the sensitivity of the overall rule was 29%.  Given that only about 30% of troponin-diagnosed AMI are STEMI-equivalents (occlusion or near occlusion, as opposed to Non STEMI), this is surprisingly high sensitivity for a group that had no concordant ST elevation.

1.            Sgarbossa EB, Pinski SL, Gates KB, Wagner GS. Early electrocardiographic diagnosis of acute myocardial infarction in the presence of ventricular paced rhythm.  GUSTO-I investigators. Am J Cardiol 1996;77(5):423-4.

2.            Maloy KR, Bhat R, Davis J, Reed K, Morrissey R. Sgarbossa Criteria are Highly Specific for Acute Myocardial Infarction with Pacemakers. The western journal of emergency medicine 2011;11(4):354-7.