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Inferior-posterior wall M.I.

Inferior-lateral M.I. With QRS Fragmentation

Sat, 08/13/2016 - 23:33 -- Dawn

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.

Inferior Wall M.I. With Subtle ST Elevation

Mon, 01/18/2016 - 00:24 -- Dawn

This ECG is a good example of an inferior wall M.I. that was confirmed and treated in the cath lab.

The ST segments are elevated in Leads II, III, and aVF, but the amount of elevation may look subtle to some.   When the amount of elevation seems small, what other signs can help us recognize acute ST-elevation M.I.? 

PATIENT HISTORY AND PRESENTATION   This patient had acute chest pain, and was over the age of 50. We do not know his past medical history. His chest pain was described as substernal and epigastric, radiating to his back.  He had nausea and diaphoresis.  His past medical history is unknown, but it would be significant if he had a history of coronary artery disease, past M.I., smoking, metabolic syndrome, strong family history of heart disease, etc.

ST SEGMENT ELEVATION DISTRIBUTION   In acute STEMI, the elevation will be seen in “related leads”. That is, the leads that are affected will reflect a region of the heart that is supplied by the same artery. Some M.I.s are larger than others, affecting more leads, because some obstructions are more proximal than others in the artery.  This ECG shows STE in the inferior wall leads:  II, III, and aVF.  The culprit artery for this patient was the right coronary artery, which supplies the inferior and posterior wall of the left ventricle, the right ventricle, and the right atrium in the majority of people.

RECIPROCAL ST DEPRESSION   Finding reciprocal ST depression in the leads that are OPPOSITE the affected leads is a very reliable sign to confirm that the STEs are due to an acute M.I.  In fact, often the reciprocal depression is “stronger” or easier to see than the elevation.  It is important to teach your students how the standard leads are oriented to the heart, so they will recognize the 12-Lead ECG as a “map” of the heart.  The reciprocal ST depression in this ECG is seen in Leads aVL and I (subtle), which are across the frontal plane from Lead III.   We also note reciprocal ST depression in the precordial leads, especially notable in Leads V1 through V3.  This can reflect the injured area extending up the back of the heart from the inferior wall (posterior wall).  The R waves in V2 and V3 are a bit higher than normally expected, which could indicate a reciprocal view of pathological Q waves on the posterior wall.  Print the ECG out on paper, turn it upside down, and look at V2 and V3 through the back.  V2 and V3 will look like a “classic” STEMI.  This should be approximately the view you would get from additional posterior leads.

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