You are working in the emergency department when you receive a report from an incoming EMS Unit. The medic reports that he is treating a 57-year-old male patient with no prior history who developed substernal chest pain while shoveling snow. The patient is reporting the pain as 8/10. The medic reports that the patient is pale and diaphoretic. In addition to his chest pain, the patient complains of feeling “lightheaded.” His BP is 86/40 with a pulse in the 50’s. His respirations are unlabored with a pulse ox of 96%. He has received Aspirin 325 mg and an IV of NSS that is running KVO at the time of the report. The following EKG is transmitted.
Your diagnosis is:
You would prepare for the patient by
You would consider the following to treat his chest pain
This ECG is indicative of acute inferolateral infarction. Notice the ST elevation in Leads II, III, and aVF as well as V4, V5, and V6. Remember that the diagnosis of ST-elevation Myocardial Infarction (STEMI) is made when the ECG shows 2 or more leads that view the same wall of the heart with ST-elevation greater than 1 mm. That criteria is definitely met with this ECG.
Now that we have made the diagnosis, let’s turn to the big question. What do we do about it. Everything we do for this patient should be aimed at reperfusion (opening of the occluded blood vessel). How this patient will do into the future will depend upon how much of his heart muscle is lost during the infarction. That is a function of how long the blood vessel is permitted to remain occluded. When at all possible, the vessel should be opened using Percutaneous Coronary Intervention (PCI) which can only be done in a cardiac catheterization laboratory that is equipped for intervention. For that reason, the cath lab staff should be notified immediately after the ED is notified that a patient with STEMI is en route to the facility. This saves time getting the patient immediately to the lab. The desired “door to balloon time” is less than 90 minutes. That means that in 90 minutes or less from the time the patient arrives in the emergency department, the cardiac catheterization laboratory should be able to have the vessel opened and blood flowing to the affected myocardium. Ideally, this happens within 120 minutes of the onset of symptoms. (This is assumed to be the time the blood vessels were occluded).
Treatment of hypotension and pain differs depending upon the type of infarction that the patient is experiencing. In this case, an inferolateral wall infarction. As many as 1/3 of these infarctions will have involvement of the right ventricle. In those patients, hypotension occurs because of a reduction in preload. (the right ventricle is unable to pump the blood forward to “load” the left atrium) If this patient is given Nitroglycerin for pain control, the BP will drop because Nitroglycerin causes dilation of the blood vessels and will further reduce preload. The result would be similar to giving NTG to a patient experiencing hypotension from bleeding. Narcotic pain relievers are used (with caution) for pain control. Blood pressure is treated in these patients with the administration of fluid. This increases preload (the amount of blood available to be pumped to the body) and therefore increases blood pressure. There is less possibility of pulmonary edema in this setting as blood backs up to where it came from (in this case the body). In right ventricular failure, it is safe to administer fluid. In the anterior wall MI we have to be cautious with fluid because the opposite is the problem. The left ventricle cannot pump forward and therefore backs up into the lungs. Therefore Pressors (like dopamine) are used for pressure and NTG is useful because it reduces the amount of blood the left heart has to pump.
Acute concerns for this patient include the development of bradycardia caused by various degrees of heart block. The side branches of the right coronary artery provide blood flow to the AV node and interruption of this flow can result in dysfunction of the node and various heart blocks. Below is the result of this patient’s cardiac catheterization.
You can see (where the arrow is) that the blood vessel appears to end. This is a proximal occlusion of the right coronary artery. It feeds the inferior wall of the left ventricular and in many patients the right ventricle as well.
Once a wire is placed, a balloon is inflated to open the vessel and a stent is placed to keep it open. This blood vessel supplies blood to a large amount of myocardium. If it remained closed, the amount of myocardium that this patient would have lost to infarction would have been significant. His mortality and morbidity would be high. By opening the vessel early in the infarction, myocardium is saved and his future is bright.