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Acute Inferior-Lateral M.I. In A Patient With A Dominant Circumflex Artery

This ECG was obtained from a patient who suffered an obstruction of the circumflex coronary artery.  Unfortunately, he was in the approximately 15-18% of the population in whom the circumflex artery is dominant.  That means that it connects with the posterior descending artery, perfusing not only the lateral wall of the left ventricle, but also the posterior and inferior walls.  In this case, the obstruction is in the midportion of the artery, and the high lateral wall is spared.  The large number of leads with ST elevation indicate the large amount of myocardium affected.  Leads II, III, and aVF have ST elevation, as do Leads V3 through V6.  Lead aVL has reciprocal ST depression. The T waves in the affected leads are "hyperacute", or taller than normal.  This is usually an early change in acute M.I., and disappears after the onset of ST elevation.

It is not always easy to determine from the ECG that the circumflex artery is the culprit artery, rather than the right coronary artery, which perfuses the inferior wall in the majority of people.  Some clues are:  Lead III has ST elevation equal to that of Lead II, the low lateral wall (V5 and V6) are affected, and aVL has reciprocal depression but Lead I does not.

This is a very large M.I., due to the dominance of the circumflex artery.  The patient did not survive, in spite of aggressive treatment.

Dawn's picture

Inferior Wall M.I. Due To Circumflex Artery Occlusion

This ECG is from an 81 year old woman with an extensive history of coronary artery disease.  She was experiencing chest pain at the time of the ECG.  We can clearly see ST elevation in Leads II, III, and aVF, indicating an inferior wall ST-elevation M.I. (STEMI).  There are reciprocal ST depressions in Leads I and aVL.  There are subtle and less specific ST changes in V1 (flat ST and T), V2 (ST depression), V3 (ST elevation and inverted T wave), and V4 through V6 (slight ST elevation).  The flat, horizontal shape of most of the ST segments is another clue to her CAD.  What coronary artery do you think is the culprit for the ST elevation?

This patient received coronary angiography, so we do not have to guess at where her lesions are.  She was found to have an occluded left internal mammary artery (LIMA) graft.

The left anterior descending coronary artery (top of view) is very diseased, with some extremely narrow areas.  The circumflex artery is large and covers a lot of area, but it, too, is very diseased, with a critical occlusion (marked with arrow).  On this day, the circumflex artery received angioplasty and stents.  The patient's right coronary artery was patent.

In approximately 85% of the population, the RCA supplies the inferior wall of the heart.  In most of the rest, a branch of the circumflex supplies the posterior/inferior wall.

This patient also has a very interesting arrhythmia.  We see P waves (numbered) that appear regular for three beats, then we see no P waves for a pause.  Then, three more P waves appear.  There is no readily-seen "hidden" P wave in the ST segments or T waves.  Even though there appear to be "progressively prolonging PR intervals", the PR intervals of each group of three do not match the other group of three.  The first "PRI" - P wave number 1- and the last one - P wave number 7 - appear too short to be normal PR intervals.  The ventricular rate is regular, and the QRS complexes are slightly wide at  .10 sec.  The rate is 54 bpm.  This suggests junctional rhythm.

We are eager to hear your comments regarding this rhythm.

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