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Dawn's picture

Inferior Posterior Wall M.I. In Cabrera Format

Submitted by Dawn on Sat, 08/26/2023 - 16:53

Does something about this ECG look "different" to you?    This ECG shows a “classic” presentation of inferior-posterior M.I. when it is caused by a lesion in the right coronary artery (RCA). There are ST elevations in leads II, III, and aVF.  Reciprocal ST depression is seen in Leads I and aVL.  There is also reciprocal ST depression in Leads V1 – V3.  These more rightward anterior leads are reciprocal to the posterior (or posterior-lateral) wall, so the ST elevation is actually posterior.  Another sign that this is an RCA lesion is that the ST elevation in Lead III looks worse than the STE in Lead II.  It would be helpful to check the right precordial leads, or at least V4 Right, as elevation there would indicate right ventricular M.I. 

Depending on how experienced you are at evaluating ECGs, you might have immediately noticed something “different” about this tracing.  It is printed in Cabrera format, which groups the leads (viewpoints) more geographically than a traditional ECG does.  In addition to grouping the leads more geographically, instead of aVR, the machine records - aVR.  That reverses the negative and positive poles of aVR, putting the positive ("seeking") electrode at 30 degrees - halfway between Leads I and II.   Those of us who have been looking at ECGs for decades often feel a bit disconcerted by this format, because we have developed almost an intuitive way of seeing the ECG as a “map”, and this rearrangement thwarts our brains’ approach to the ECG.  I would imagine, however, that this might make interpretation a bit easier for someone who is not prejudiced by the standard way of printing.  This method is especially helpful when looking for inferior wall M.I., as we see here, because the lateral leads are together in a row, and the inferior leads are grouped together. 

Dawn's picture

Inferior Posterior M.I.

Submitted by Dawn on Mon, 07/24/2023 - 14:41

This is a "classic" ECG of very good quality for you to use in a classroom setting.

The Patient:  A 57-year-old man who complains of a sudden onset of "sharp" chest pain while on a long bike ride.  The pain does not radiate, and nothing makes it worse or better.  He is pale, cool, and diaphoretic.  His medical history is unknown.

The ECG:  This ECG could be considered "classic" for an inferior wall ST elevation M.I. caused by occlusion of the right coronary artery.  ECG findings include:

*   Normal sinus rhythm

*   Marked ST elevation in Leads II, III, and aVF.  The elevation is higher in Lead III than in Lead II, a reliable sign of RCA occlusion.

*   Reciprocal depression in Leads aVL and I.  ST depression in the setting of acute transmural ischemia (STEMI) is almost ALWAYS due to  reciprocal change. The fact that this STD is localized to leads that are reciprocal to the inferior wall is proof of the nature of the STD.

*   Reciprocal depression in V1 - V3.  More localized depression.  What wall is reciprocal to the anterior-septal wall?  The posterior (postero-lateral).  Since the inferior wall is really the lower part of the posterior wall, inferior wall M.I. is often accompanied by posterior wall M.I.

An additional lead, V4R, is helpful in this situation, since the right ventricle is often affected in RCA occlusions.  The EMS crew reports that V4R was negative for ST elevation, but we do not have a copy.

Small q waves have formed in Lead III, and we would watch for progression of this sign, as it can indicate necrosis.

Outcome:  The patient went to the cath lab, but we have no further followup.

 

Our thanks to Ashley Terrana for donating this tracing.

 

 

Dawn's picture

Inferior-lateral M.I. With QRS Fragmentation

Submitted by Dawn on Sat, 08/13/2016 - 23:33

SUBTLE ST CHANGES   This ECG was obtained from an 87-year-old man who was experiencing chest pain.  Due to the subtle ST elevation in Leads II, III, aVF, V5, and V6, (inferior- lateral walls) the ECG was transmitted to the hospital by the EMS crew, and the cath lab was activated.  The patient denied previous cardiac history. 

In addition to the subtle ST elevation, there is ST depression in V1 through V4, which represents a reciprocal view of the injury in the inferior-posterior-lateral wall.  Because the anterior wall is superior in its position in the chest, it is opposite the inferior/posterior wall, and can show ST depression when the inferior-posterior area has ST elevation. This ECG was the 6th one done during this EMS call.  Prior to this one, the ST segments were elevated less than 1 mm.  This is a good example of the value of repeat ECGs during an acute event.  

RIGHT VENTRICULAR M.I.?     This ECG was done with V4 placed on the right side, to check for right ventricular M.I., which is a protocol for this EMS agency. When the right coronary artery is the culprit artery (about 80% of IWMIs), RVMI is likely.  In RVMI, we would usually see reciprocal ST depression in Leads I and aVL, but the STE is very subtle here, so the depression would likely be also.  When the culprit artery is the left circumflex artery (<20%), lateral lead ST elevation is more likely, as we see here in V5 and V6. 

WHAT ABOUT RHYTHM?     The rhythm is sinus with PACs.  PACs are considered to be benign in most situations, but in a patient with acute M.I., any dysrhythmia can be concerning. The QT interval, measured as QTc (corrected to a heart rate of 60 bpm), is slightly prolonged at .458 seconds (458 ms).  Over .440 seconds is considered prolonged in men, and over .500 sec. places the patient at increased risk of developing torsades de pointes.  CAD and myocardial ischemia can lead to this modest increase in QTc.

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