V. Images of the Heart

Physicians can use x-rays (a type of "radiograph") to examine the heart. Briefly, during a radiological exam x-rays are beamed "through" the patient. Tissues of the body will absorb the x-rays--the more dense (like bone) that the tissue is, the more x-rays will be absorbed. Structures absorbing x-rays appear white on an x-ray, whereas low density or air-filled tissues will not absorb x-rays well and will appear black.

A diagram of a typical thoracic (chest) x-ray is shown below. Note that the heart and vessels are white, whereas the lungs on either side are black, Do you know why this is?

Answer: the lungs are filled with air and therefore absorb few x-rays and appear black on an x-ray. Note the typical features of a "heart shadow" in the x-ray below.

AA: Aortic Arch A: Aorta PA: Pulmonary Artery LA: Left Atrium S: Superior Vena Cava RA: Right Atrium LA: Left Atrium LV: Left Ventricle

8. Study the x-rays with your lab leader. Compare the normal heart x-ray with the pathological (diseased) examples. What is the problem in each x-ray?


VI. Heart Problems

Heart Attack

Heart disease is the number one cause of death in this country, leading to over 750,000 deaths per year. 80% of these die of ischemic heart disease (low blood flow from the coronary vessels to the heart), Ischernic heart disease can lead to a heart attack. The medical term for a heart attack is myocardial infarction. That means that a part of the heart muscle has literally died because the blood flow to a part of it has been completely cut off. Look again at the coronary arteries on the surface of the heart. When they get clogged up with plaques (a process called atherosclerosis), the blood supply cannot meet the oxygen demands of the muscle and the person gets chest pain which is referred to as angina pectoris (another kind of ischemic heart disease). In addition to chest pain, it is common to get pain radiating down the left arm. This is because the nerves supplying the heart originate at the same place as the nerves innervating your arm, and the signals can be mixed up. If a blood clot forms on one of these plaques the blood flow is not just lower than what the heart needs--there is absolutely no blood flow. Without blood for thirty minutes the heart muscle dies. When too much muscle dies either the heart pump itself fails (congestive heart failure) or the conduction system does not work properly (ventricular arrhythmia) and the person dies. The heart attack will most likely occur when one or more of the main coronary arteries discussed earlier are blocked.

High blood pressure, smoking, and high LDL cholesterol (bad kind of cholesterol) significantly accelerate the formation of plaques. Some of the major factors in keeping atherosclerosis in check include not smoking, exercising, controlling one's weight, and controlling blood sugar levels if diabetic.

Valve Problems

The valves we discussed above can occasionally become hardened and cease to close completely during contraction, allowing blood to regurgitate back into the atria. If a valve no longer works, what can be done about this?

Answer: surgically replace the valve! Sure, this makes a hard operation sound easy, but synthetic valves and Gortex chordae tendinae are great replacements for the real thing.

Congenital Birth Defects

Sometimes, the fetal heart does not develop properly. Fetal circulation is different than adult circulation. The mother supplies the fetus with oxygen and nutrients because the fetal lungs are not exposed to air. Therefore, the fetal heart is also different from the adult heart. One difference is that the ductus arteriosus (a small vessel) in the fetus connects the pulmonary artery to the aorta. One problem is that the ductus arteriosus can remain open after birth, redirecting blood from the aorta (which should be going out to the rest of the body) to the pulmonary artery (and back to the lung). This is called a patent ductus arteriosus. Another problem is called a ventricular septal defect, or "hole in the wall of the heart". In this case, the wall between the right and left ventricles does not close completely and deoxygenated blood from the right ventricle is sent to the left ventricle and out to the body.

Drugs

Drugs such as cocaine, speed, and heroine all adversely affect the heart.

9. View atherosclerotic heart-notice how plaques are deposited on the vessel walls, and note how the coronary vessels are mildly blocked in another specimen. Also view heart with hardened valves and the synthetic valve and chordae tendinae which can replace it.