Wednesday, February 26, 2014

Prolonged chest pain and Intraventricular Conduction Delay similar to Left Bundle Branch Block

A 67 year old male with no previous cardiac history or risk factors woke up at midnight with right-sided chest pain. It was the "worst pain of his life," and it radiated around his ribs, through to his back, and up into his neck, all on the right side. He was profusely diaphoretic, nauseated, and he vomited twice. He took some aspirin which gave him some minor improvement in symptoms. He "toughed out" the night, and when his pain was still not getting better about 8 hours later, he asked his wife to take him to the ED.   

He arrived at about 8.5 hours after onset of symptoms, still with severe chest pain, and had this ECG recorded:
What do you think?

There was a baseline ECG available from 3 years ago:

What is your interpretation? What would you do at this point? See below for interpretations.

Interpretation of presenting ECG:
Sinus tachycardia at about 105 bpm. The computerized QRS duration is 120ms, qualifying this for an Intraventricular Conduction Delay.  It has morphology very similar to LBBB: there is a wide complex with dominant S waves in the anterior leads, so we presumably can apply the same rules as full-blown LBBB.

The treating physicians documented that this ECG is "Sgarbossa negative."  There is no concordant ST depression in V1-V3, and no ST elevation equal or greater than 5mm.  Is there concordant ST elevation?  This depends on whether the QRS is mostly positive or mostly negative in lead V5; if positive, then the ST elevation is indeed concordant..

Lead V4 alone would make this ECG "modified Sgarbossa positive"(reference 1, reference 2): it has a 3mm S wave with 2.5mm of ST elevation, making a STE/S ratio of 0.83.

How about lead V5?  The S-wave and R-wave are of nearly equal voltage; on the other hand, the S-wave is slightly wider than the R-wave. What matters most?  Is it the voltage?  Or is it the integral (area under the curve) that matters most?   In any case, the difference in voltage and in area is not great, and therefore there should be almost no ST deviation in that lead. 

Stated in other words: The "area under the curve" or "integral" is all the area contained between the waveform and the isoelectric line.  In LBBB, ST-T is normally discordant to the majority of the QRS, but is that "majority" measure by voltage (in mm of amplitude), or is it best measured by area under the curve?  In this case, in V5 the R-wave amplitude is greater, but the S-wave area is greater.  In either case, the difference is small.

Thus, leads V4 and V5 are diagnostic of STEMI.

Furthermore, one expects a small R-wave in V1 and V2 in LBBB.  Instead, there are Q-waves.  There is also a notch on the ascending limb of the S-wave in V2 and also slightly in V3.  These are reminiscennt of  "Cabrera's sign" (a notch greater than 50 ms on the ascending limb of the S-wave in one of V3-V5).  These are signs of previous MI, or of well developed "subacute" acute MI.  

All of these ECG findings, along with the clinical scenario, are all but diagnostic of a subacute STEMI in the setting of LBBB.

Initial troponin I was 50 ng/ml. Cardiology was summoned. They took him immediately to the cath lab, where they found an acute thrombotic 99% stenosis of the proximal LAD with TIMI 1 flow. There were also thrombotic lesions of the mid LAD and D1. They aspirated the thrombi and placed 3 stents at these lesions. No further troponin data was available.

Here is his ECG later that day:
T wave inversions in the anterolateral leads, consistent with reperfusion. Some ST elevation persists, but no longer meets any criteria. The QRS appears a little bit shorter than previous.

And here is his ECG the next day:

Still shows T wave inversions with persistent ST elevation.  This persistence may portend the development of an LV aneurysm.

He recovered well and was discharged several days later.

Should thrombolytics be given?

Thrombolytics are still recommended up to 12 hours after the onset of pain. (Sorry, no full text here: this is an analysis of thrombolytic trials from 1983-1993, and found that if pain has been present for 6-12 hours, then a mean of 18 lives were saved per 1000 patients treated with lytics vs. placebo).

The ECG is, in fact, an even better measure of acuteness of a STEMI. 

When there is subacute STEMI, the thrombolytic decision must be made carefully with attention to both risk and benefit.  This is a large anterior STEMI with persistent pain and ST elevation.  There are Q-waves, and the highly elevated troponin I confirms prolonged infarct.  ST elevation is still present, however, and T-waves have not yet inverted, so there is still significant salvageable myocardium at risk.  Depending on the patient's risk factors for bleeding, and on the door to balloon time for transfer to a PCI institution, thrombolytics may be indicated.  

Take Home Points:
 - the modified Sgarbossa rule is more sensitive than the original
 - even when the ECG doesn't have a perfect LBBB, if there is significantly abnormal depolarization with a wide QRS it must still follow the same rules of appropriate discordance and proportionality
-Signs of old or subacute MI may also be seen in the setting of LBBB

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