Smiths Modification and Pacemakers – is that a STEMI?

Ghu-roos. Prehospital diagnosticians. Call yourselves what you will.

We are here today to look through the pacemaker.
Like Alice through the looking glass; through to find any ischemia that potentially lurks within that paced rhythm. Don’t let that grey hair tell you about the futility of interpreting paced rhythms….just like they said with LBBB…..mmmm
So what can we do…

Example. 85 yr old caucasian male pt who initiates 911 after being unable to mitigate his chest pain with rest &/or nitrates as per usual. Today pt. pre administers nitrates prior to his daily walk as he knows he “will get chest pain to walk the small rise out of his home to gain the flats“. Pt. has an extensive cardiac history with quintuple bypass surgery a decade previous and just last year further stenting although he is not sure which artery. He presents to you with 6 on 10 central chest pain that will not resolve and feels like both pressure and burning. No radiation. No mitigation and very familiar in its presentation to his regular and frequent cardiac chest pain. No other associated symptomology. HR60 RR14 BP129/71 SPO297RA ETCO238mmHg BGL5.8 The pt. is taking all their medications as scheduled and no recent changes to Rx other than the addition of Plavix post angiography/stenting.

Your partner hands you the initial 12 lead that reveals the following…Applying Smith Modified Sgarbossa criteria provides you with the following;

  • V2 = T4.36/ST10 = 0.43
  • V3 = T6.54/ST12 =  0.54
  • V4 = T3.58/ST9 = 0.39










According to Smith Modified Criteria any T/ST variance >0.25 = both sensitive and specific for acute MI/STEMI.



Conundrum…you are closest to a non PCI capable Level 1 receiving facility and have access to a PCI facility although via diversion criteria is for STEMI only. Your organization does not support Paramedic’s interpreting their own 12 lead ECG and ECG must say STEMI  as interpreted by the LP15 algorithm for inclusion, transmission and thus diversion….what to do….

As you have a relationship with the ERP at your closest facility you reach out to them by phone and you are lucky enough to be able to have a clinical conversation with the receiving ERP. They agree with your treatment plan and ask you to divert to the PCI capable facility. You also consult with your online medical physician (EPOS) available to you who also agrees. You now transport your pt. to a cath/PCI capable facility and is accepted by cardiology upon arrival.

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. 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.

AVL ….predictor of the future

Can you look ahead. Can you see the future. Can you harness the Force appropriately. No. Neither can I; even despite being an Aquarius.

So what can I do to help me. Crystal ball you say?


AVL…..the crystal ball of EKG.

Mattu would refer to it as the Dangerfield lead…cant get no respect. Dr Henry J. Marriott identified this correlation 40 years ago but has seemingly escaped being included in our collectively perpetuating repertoire as pre hospital magicians.

More importantly than seeing into the future, is what you can see in the future. Prediction of evolving MI you say…whoa. Tell me more

Just say you went in an tied off the right coronary artery, for fun (type III fun), what would change first…thats right…AVL;
T wave inversion would occur.

Deviance from an almost-to flat T wave into a easily discernible flipped/inverted belly like T wave in AVL. You might even see some ST depression.
But what about LBBB… means nothing. Strain pattern? =both changes in AVL and Lead I. Horizontal heart…dont matter

OK, enough from us. Whet your appetite? Hope so.   Ill let Master Mattu take it from here.

In summary, experiencing chest pain….atypical findings, no baseline ECG to compare…no significant ischemic changes on 12 lead investigation….look to AVL…look to the future…advocate for those people you serve, repeat the ECG, consider the appropriate cath capable facility and at the very least have the discussion with your ERP.

Thanks for reading. Go well. AVL.