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RCP 350: Applied Anatomy and Physiology

Case Study: Cardiovascular Physiology

Instructions:

Answer the following questions, ensuring that you:

• Type each question before each of your answers.

• Use complete sentences and paragraphs, when appropriate

• Cite the textbook name, textbook edition, textbook author, and page numbers for any resources that you use.

• Cite the URL for any web-based used as a reference

At 9:06 a.m., the blood clot that had silently formed in Walter’s left coronary artery made its sinister presence known. The 53-year-old advertising executive had arrived at the Dallas Convention Center feeling fine, but suddenly a dull ache started in the center of his chest and he because nauseated. At first, he brushed it off as aftereffects of the convention banquet the previous night. However, when it persisted, he made his way to the first aid station. “I’m not feeling very well,” he told the medical staff. “I think it may be indigestion.” The medical staff, on hearing Walter’s symptoms and seeing his pale, sweaty face, immediately thought of it may be heart attack. “Let’s get you over to the hospital and get this checked out.”

1. Describe how the heart as a muscle does its job of pumping blood. What happens if the cardiac muscle itself does not get enough blood?

1. What is actually meant by the term, “heart attack” in the medical perspective? What has occurred to the heart?

1. Why are the coronary arteries so easily blocked by clots?

Walter may have experienced heart damage from a clot in the left coronary artery. The medical staff knew it was critical for immediate medical intervention. While waiting for the ambulance, Walter was administered supplemental oxygen, placed on a heart monitor, and had an IV started for infusion of isotonic saline. With an IV in place, other drugs could be given rapidly if Walter’s condition should suddenly get worse.

1. Why might oxygen therapy have been started?

1. What effect would the infusion of isotonic saline have on Walter’s extracellular fluid volume, his intracellular fluid volume, and on his total body osmolarity?

When Walter arrived at the University of Texas Southwestern Medical Center emergency room, one of the first tasks was to determine whether he had actually had a heart attack. In the mean time his wife, Leah was called to alert her to her husband’s situation. Walter’s vital signs were assessed. He was given aspirin and heparin to decrease blood clotting and nitroglycerin to dilate coronary blood vessels. A sample of his blood was drawn for enzyme assays to determine the level of cardiac enzymes in Walter’s blood. When heart muscle cells die, they release various enzymes that serve as markers of a heart attack. A second tube of blood was sent for an assay of its troponin 1 level. Troponin 1 is a good indicator of heart damage following a heart attack.

1. What is troponin, and why would elevated blood levels of troponin indicate heart damage?

The results of cardiac enzyme and troponin 1 assays would not be available for several hours. If a coronary artery was blocked, damage to the heart muscle could be severe by that time. In Walter’s case, an electrocardiogram showed an abnormal pattern of electrical activity. “He’s definitely had an MI,” said the ER physician, referring to a myocardial infarction, or heart attack. “Let’s start him on a beta-blocker and t-PA.” t-PA is short for tissue plasminogen activator. T-PA activates plasminogen, a substance produced in the body that dissolves blood clots. When t-PA is given within 1 – 3 hours of a heart attack, it can help dissolve blood clots that are blocking blood flow to the heart muscle. This will help limit the extent of ischemic damage.

1. How do electrical signals move from cell to cell in the myocardium?

1. What happens to contraction in a myocardial contractile cell if a wave of depolarization passing through the heart bypasses it?

1. A beta-blocker is an antagonist to β1 adrenergic receptors. What will this drug do to Walter’s heart rate? Why is that response helpful following a heart attack?

The electrocardiogram indicated that Walter suffered a myocardial infarction, or blockage of blood vessels nourishing the left ventricle. The exact location of the damage depends on which artery and which branch or branches have become occluded.

1. If the ventricle of the heart is damaged, in which wave or waves of the electrocardiogram would you expect to see abnormal changes?

By 1300, Walter had been admitted to the cardiac care unit, where the cardiologist visited him. “We need to keep an eye on you here for the next week. There is a good chance the damage from your heart attack could cause an irregular heart beat.” Once Walter was stable, he would have a coronary angiogram, a procedure in which an opaque dye visible on X-rays shows regions where the lumen of the vessel narrows. Depending on the results of that test, the physician has several options he can recommend as possible treatments. – balloon angioplasty or coronary bypass surgery. Walter’s wife has heard of these and also knows of family and friends that have had other heart procedures done, such as open-heart valve surgery or implantation of an artificial pacemaker. She knows she needs to call her children to update them on their dad’s status, but uncertain about which procedure will be done.

1. If Walter’s myocardial infarction has damaged the muscle of his left ventricle, what do you predict will happen to his left cardiac output?

1. Explain the differences between the conditions that these procedures correct and how you know which would be applicable to Walter’s condition.

Leah knows Walter’s cardiologist because she was diagnosed with a heart murmur years ago. Her primary care physician caught it during a routine checkup. Instead of the normal lubb-dubb heart sound, she heard a sloshy wobble in place of the lubb. The heart sounds are made by snapping shut of heart valves.

1. Which of Leah’s valves might be leaking? Is that sloshy sound heard during atrial or ventricular systole? Is the dub sound heard during atrial or ventricular diastole?

The cardiologist jokingly blamed Walter for Leah’s heart murmur because he tugs at her heart strings.

1. Which heart valve/s is/are controlled by these “heart strings”? How do her “heart strings” actually help Leah’s heart valve/s?

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