If you look closely at the 2006 ICD-9-CM codes, you’ll notice two new terms in the 410.xx series:
- ST-Elevation Myocardial Infarction (STEMI)
- Non-ST-Elevation Myocardial Infarction (NSTEMI)
The diseases are not old and the abbreviations have been around for a long time. However, people do not uniformly understand what these abbreviations mean (and I hope they are on your hospital’s accepted abbreviation list).
The term acute MI (myocardial infarction) appears in the 410.xx series. But without more details, it’s unclear which fourth digit coders should use. This is where an explanation of the new terms will come in handy.
The fourth digits between 0 and 6 demand that the physician explains which wall of the heart segment or segments are involved. The 410.xx codes include:
- 410.01-Anterolateral wall myocardial infarction
- 410.11-Other anterior wall myocardial infarction
- 410.21-Inferolateral wall myocardial infarction
- 410.31-Inferoposterior wall
- 410.41-Other inferior wall
- 410.51-Other lateral wall
- 410.61-True posterior wall
- 410.81-Myocardial infarction of other specified sites (papillary muscle, atrium alone, septum alone, etc.)
- 410.91-Myocardial infarction with no definition of where it happened or how much was involved.
Codes 410.0x-410.6x are all transmural myocardial infarctions, a condition that involves an acute ischemic event that knocks out the thickness of the heart muscle wall and results in considerable muscle death.
When physicians use the term subendocardial myocardial infarction (SEMI), or non Q-wave myocardial infarction (NQWMI), coders use 7 for the fourth digit. So a coder assigns 410.71 for a patient admitted with a new acute NQWMI.
Where do all of these terms come from?
The coronary arteries originate at the base of the aorta and are distributed over the surface of the heart. Periodically, over the surface of the right and left ventricles, small branches come off and penetrate into the heart muscle. The deeper the arteries penetrate, the smaller they become until, by the time the arteries reach the inner or endocardial lining of the heart, they are tiny vessels.
So if a blood clot or a ruptured atheromatous plaque in one of these tiny vessels causes blockage of one of these tiny arterial branches, there’s not much damage to the heart wall. The amount of heart muscle damaged by blockage of one of these tiny vessels is small-and not a lot of chemicals are released. The portion of the heart muscle that dies in this circumstance exists right under the endocardial lining of the heart. It’s sub-endocardial.
But if a clot or ruptured atheromatous plaque blocks one of the large vessels on the surface of the heart, it causes death of a whole bunch of heart muscle that the artery should feed. When this occurs, a lot of chemicals are released and there is full thickness (or almost full thickness) death of heart muscle in the part of the muscle wall involved. This is called a transmural (through the whole wall) infarct.
When a tiny piece of heart muscle is knocked off, there’s not much change in the electrical conductivity of the heart in the area near the damage because so much normal muscle is still there overlying where the damage took place. When there is negligible damage to the heart muscle thickness and not much change in the electrical conductivity fed to the EKG leads placed over the area of injury, there will be no visible ST wave changes and Q-waves.
This subendocardial infarct then is also known as a non-Q-wave MI or a non-ST segment elevation MI. In other words, whichever of the abbreviations the physician uses (SEMI, NQWMI, NSTEMI), they’re all the same animal. They’re all 410.71.
When a full thickness or almost full thickness insult takes place and a good size portion of the heart muscle wall is knocked off, there is an electrical hole in the EKG in the leads overlying the damaged myocardium. There are occasionally Q-waves (deflections of over 1 mm where there should be none or they should be less than 1 mm) and there may be ST-wave changes over the area of injury.
In other words, electrically, these are STEMI (ST segment elevation myocardial infarctions) or QWMI (Q-wave myocardial infarctions). Abbreviation folks rarely use this last term (QWMI), but it’s possible. And, since electrical deflection changes over the damaged heart muscle are visible, physicians can deduce which wall has sustained the injury-and the coders will assign the appropriate 410.0x to 410.6x code to the event.
Sure, physicians can go ahead an order a nuclear scan and see which wall was involved with the STEMI, but it’s much more fun to deduce it from the EKG tracing.
What do we have to do with these definitions of heart attacks for the medical staff? As the 1970’s rock said about “War - what is it good for?”¯ Absolutely nothing.