Myocardial infarction: pathophysiology, clinical presentation, and management

MI Case Study: Myocardial Infarction

At 10:05 A.M., the blockage that had been silently growing in Paul

Parker's left coronary artery made its sinister presence known. The 54-year-old accounting executive had arrived with his family at the Denver zoo feeling fine, but suddenly a dull ache started in the center of his chest and he became nauseated. At first he brushed it off as the aftereffects of a company dinner the night before. However, when it

persisted, he told his wife who suggested that he go to the Aid Station.

"I'm not felling very well," he told the EMT at the station. "I think it may be indigestion." The EMT, on hearing Paul's symptoms and seeing his pale, sweaty face, immediately thought of a heart attack. "Let's get you over to the hospital and get this checked out."

The blockage in Paul's coronary artery had restricted blood flow to his heart muscle and his cells were beginning to die from lack of oxygen

(hypoxia). When someone has a heart attack, medical intervention is

critical to prevent additional damage and possibly save the patient's life. While waiting for the ambulance, the EMT gave Paul oxygen, hooked him to a heart monitor, and started an intravenous (IV) injection of normal (isotonic) saline.

Question 1: Why did the EMT give Paul an IV, and oxygen?

Mainstream EMT protocol for Myocardial Infarction or possible myocardial infraction includes the establishment of an IV line (large bore) as well as the administration of oxygen (VNH, 2005). The reason for this is both for patient support (the oxygen) and for possible administration of medications during treatment (especially after arrival in the emergency room). Not only does establishing an IV line allow for the administration of medication enroute, but it also can help save valuable time in the emergency room should a MI be concluded.

Question 2: Explain to his (nonmedically oriented) family what is happening.

"Let me explain to you about what is going on with Paul right now. It seems that Paul is indeed having a heart attack, or what we call a "Myocardial Infarction." Although this is a serious condition, let me first say that we are doing everything possible to assure a successful outcome for him. In simple terms, there has for some reason been a lack of oxygen and other nutrients to some of the muscle cells in his heart. Typically, this is caused by the closing or narrowing of the artery that supplies the effected part with blood. Although in some cases the outcome is not good, in cases such as Paul's, where the problem was detected and is being actively treated, there is a very good chance that the irregular rhythm caused by the injured portion of the heart can be corrected. Although the heart will retain a scar, many people go on to lead quite normal lives after recuperation. Try to take it easy, and rest assured that Paul will be taken care of to the best of our ability."

Question 3: When you analyzed his ECG, you referred to several different leads, such as lead I. What are leads?

Leads are the Electrodes that are typically attached to the chest, neck, arms, and legs to record the pathway of electrical impulses through the heart muscle. The results of this can tell us how the heart is functioning, and can also pinpoint specific problems.

Question 4: Why is it possible to record an ECG on the body surface without direct access to the heart?

Within the body, there is a natural electrical system. This causes the heart to pump at regular intervals to the various parts of the body. Because this is an electrical process, we can get the electrical "map" or picture of what is going on by measuring the way that electrical impulses are conducted through various parts of the body including the chest, arms and legs. Much as one can see if a car battery is working properly by measuring the voltage through the wires, the body can conduct electricity in a predictable way. The ECG allows us to get this information from the body surface and then allow physicians to interpret this information for possible abnormalities (WebMD, 2005).