As a paramedic, 12 lead EKGs are pretty well standard for diagnosis of possible MIs. In class, we are taught how to read 12 leads on a basic level and to pretty well look for ST depression or elevation and recognise bundle branch blocks. But there is a lot more that a 12 lead can tell you. Anything from LQT syndrome, to RVI. When I went through class, we talked about right sided 12 leads, but not so much on how to read them and even less on when to do one. I think some people are intimidated by the idea of a right sided 12 lead, even experienced medics, because of the lack of familiarity and lack of usage. However, in some cases, it can be very critical.
One of the things you can almost surely diagnose with right sided 12 lead is a right ventricular infarction (heart attack of the right ventricle). This is actually much easier than is sounds. I think any paramedic can "diagnose" an MI by obtaining a good medical history and history of the illness, along with signs and symptoms (chest pain, shortness of breath, left arm or jaw pain, back pain between scapula, diaphoresis, paleness, nausea, vomiting, hypotension). When these signs show up, we suspect an MI and also obtain a 12 lead to look for signs of ischemia or infarct. I think most paramedics know how to do that. But some things aren't what they seem.
On a 12 lead, ST depression can indicate ischemia, but can be relative to infarct (mirroring a different lead). For example, ST depression in anterior leads can just be mirroring a posterior infarct, leading to a posterior 12 lead. The same can be used to diagnose a right ventricular infarction, which isn't seen on a standard left sided 12 lead. An RVI will present with the same symptoms as any other MI, but may also be accompanied by severe hypotension. These are also commonly associated with a right bundle branch block. If a RBBB is present along with these EKG changes, suspect a right sided MI.
An RVI is usually the result of the RCA being occluded. The RCA also supplies blood to the inferior walls of the heart. An inferior infarct, or ischemia, can be seen in the inferior leads (II, II, aVf). When a 12 lead shows possible inferior MI, you should suspect a right ventricular MI as well. You should also suspect RVI if there is depression in V2 and V3.
An RVI can be seen by performing a right sided 12 lead. To do a right sided 12 lead, just move V3-V6 to the right side, mirroring the pattern for a left sided 12 lead. All of these leads can show a right sided MI, but if the patient is experiencing an RVI, it will be definite in lead V4R. When I do right sided 12 leads, I will oftentimes just move the V4 electrode. Keep in mind that if you perform a right sided 12 lead, label the right sided leads with an "R" on the strip to remember which ones were done on the right side.
Treatment of RVI actually differs slightly from any other MI and that's why it's important to perform a right sided 12 lead. The preload of the right ventricle is significantly less than that of the left simply because it has less work to do. The left ventricle has to supply blood to the whole body whereas the right only circulates blood to the lungs. If the left ventricle preload is decreased, the afterload and cardiac output will decrease, but since there is a higher preolad, it takes more altering to drop it significantly. That is why nitrates can generally be used. With the right ventricle, if preload is decreased, there is less afteroad to the heart compared to the left, resulting in less oxygenated hemoglobin. In short, a poor right sided preload will affect left sided preload because of the lack of oxygen and blood returning to the left side.
Since the right side has less preload, the blood pressure can drop faster if the patient is having an RVI. And since an RVI is sensitive to nitrates, nitroglycerin can drop the blood pressure more significantly than any other type of MI. Because of that, nitrates should be used with caution, if they are used. In this case, it is important to give fluids. Generally, fluid overload is advised against in patients with an MI, but with these patients, their preload is diminished and need fluid resuscitation. Just be sure to monitor blood pressure and lung sounds as to not overload them. If nitroglycerin is to be given, be sure to have an IV established with fluids running beforehand and preferably have 2 IVs. Follow your own local protocol if NTG is required. Most protocols are a guideline and can be altered to treat the patient how they need to be treated.
Another treatment change will be in pain control. We have learned the treatment mnemonic "MONA" (morphine, oxygen, nitro, ASA), but in the case of RVI, morphine should be avoided or used with extreme caution, as with nitro. Morhpine initiates a histamine release (hence the itchiness as a side effect) and a part of the histamine release is vasodilation. This is something we are trying to avoid with these patients and that's also why we want to use caution with NTG. For these patients, something like Fentanyl may be considered instead.
Remember that these patients can go downhill rapidly and develop cardiogenic shock if we don't treat them properly. We can treat them with Aspirin and oxygen, though we should be avoiding high flow O2 as is can cause higher PaO2 levels and should be primarily used in hypoxia. Treat with pain control and use caution with nitrates and morphine. Up to half of inferior MIs are accompanied by RVI, though RVI is almost never alone. It is accompanied almost always by inferior changes as well. Remember, though, that early onset of an MI may not result in 12 lead changes. Perform a thorough exam and get a good history.
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