The heart’s job is simple: to pump blood to supply oxygen-enriched red blood cells to the tissues of the body. It is divided down the middle into two sides (left and right) by a wall called the septum. Each side has an atrium, or upper chamber, to receive incoming blood and a ventricle, lower chamber, to pump outgoing blood. The aorta is the body’s main artery and receives blood ejected from the left ventricle and delivers it to all the other arteries. The right side receives oxygen-poor (deoxygenated) blood from the veins of the body. The superior and inferior venae cavae enter the right atrium, which fills the right ventricle. After contraction, blood flows from the right ventricle into the pulmonary artery and travels through the pulmonary circulation in the lungs where it is reoxygenated. As the blood reaches the lungs, it receives fresh oxygen from the alveoli and carbon dioxide waste is removed from the blood and moved into the alveoli. The blood then returns to the heart through the pulmonary veins. Blood enters the left atrium and passes into the left ventricle where it must pump the blood into the aorta to supply all the other arteries of the body.
The heart contains an electrical conduction system which controls the heart rate and enables the atria and ventricles to work together. Normal electrical impulses begin in the sinus node, which is in the upper contract. The electrical impulses begin in the sinus node, which is in the upper part of the right atrium and is also known as the sinoatrial (SA) node. Electrical impulses cross a special electrical tissue called the atrioventricular (AV) node. Purkinje fibers ultimately cause the muscle cells of the ventricles to contract. Cardiac muscle cells have a special characteristic called automaticity that is not found in any other type of muscle cells. Normal impulses in the heart start at the SA node. The sinoatrial (SA) node is controlled by the autonomic nervous system. The autonomic nervous system has two parts: the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system is fight-or-flight, which makes adjustments to the body to compensate for increased physical activities. It speeds up the heart rate, increases respiratory rate and depth, dilates blood vessels in the muscles, and constricts blood vessels in the digestive system. The parasympathetic nervous system directly opposes the sympathetic nervous system. The parasympathetic nervous system slows the heart and respiratory rates, constricts blood vessels in the muscles, and dilates blood vessels in the digestive system.
The myocardium must have a continuous supply of oxygen. In times of physical exertion or stress, the myocardium requires more oxygen. This is achieved by increasing the heart rate or stroke volume, which is accomplished by increasing the amount of blood flowing by dilation of the coronary arteries. Dilation increases blood flow, heart rate, and stroke volume. Coronary arteries are the blood vessels that supply blood to the heart muscle and begin at the first part of the aorta. The right coronary artery supplies blood to the right atrium and right ventricle and, in most people, the bottom part of the inferior wall of the left ventricle. The left coronary artery supplies blood to the left atrium and left ventricle. These are veins on the outside of the heart almost and should not be confused with the coronary artery. Two major arteries branching from the upper aorta supply blood to the head and arms. The left and right carotid arteries supply the head and brain with blood. The left and right subclavian arteries supply blood to the upper extremities. Just as the subclavian artery enters each arm, it becomes the brachial artery, and just below the elbow it becomes the radial and ulnar arteries, supplying blood to the lower arms and hands. Then there is the descending aorta, which divides into the left and right iliac arteries, which supply blood to the groin, pelvis, and legs. As the iliac arteries enter the legs, they become the right and left femoral arteries. At the level of the knee, it divides into the anterior and posterior tibial arteries and the peroneal artery, supplying blood to the lower legs and feet. As blood travels through the arteries, it enters smaller and smaller vessels called the arterioles and eventually enters the capillaries. Venules are the smallest branches of veins where oxygen-poor blood starts to make its way back to the heart. The veins get larger and larger until they eventually form the large venae cavae (the superior and inferior vena cava). The superior (upper) vena cava carries blood from the head and arms back to the right atrium. The inferior (lower) vena cava carries blood from the abdomen, pelvis, and legs back to the right atrium. Mean arterial pressure (MAP) measures the average blood pressure and is displayed when a noninvasive blood pressure is measured. MAP is a good measure of perfusion. Cardiac output is calculated by multiplying the heart rate by the volume of blood ejected with each contraction, or stroke volume (over 1 minute). The constant flow of oxygenated blood to the tissues is known as perfusion. Good perfusion requires three primary components — the perfusion triangle (pump, container, volume). The pump (heart) must be pumping at the correct rate, the volume must be enough blood, and the container (vessels) need to be at the proper contraction or dilation.
Chest pain that stems from the heart comes from a condition called ischemia, which is decreased blood flow. Atherosclerosis, low blood flow to the heart tissue, is caused by coronary artery atherosclerosis, which is a disorder in which calcium and a fatty material called cholesterol build up and form plaque inside the walls of blood vessels, obstructing flow and interfering with their ability to dilate or contract. It eventually causes complete blockage known as occlusion and also involves other arteries as well. As a person ages, more fatty material is deposited and the lumen, or the inside diameter of the artery, narrows, which leads to rough and brittle atherosclerotic plaques which sometimes break off, causing bleeding that leads to a blood clot called a thromboembolism. A thromboembolism is a blood clot that is floating through blood vessels until it reaches an area too narrow for it to pass, causing it to stop and block, leading to hypoxia. If the blockage occurs in a coronary artery, the condition is an acute myocardial infarction (AMI), a heart attack. Infarction means the death of tissue.
Many patients who call for EMS assistance because of chest pain have acute coronary syndrome (ACS), which is a term used to describe a group of symptoms caused by myocardial ischemia (decrease in blood flow to the heart), which leads to chest pain through reduced supply of oxygen and nutrients. This can be a temporary situation known as angina pectoris, or a more serious condition, an AMI. Because the signs and symptoms are similar, they are just called ACS.
Angina pectoris, or angina, can result from a spasm of an artery and is normally a symptom of atherosclerotic coronary artery disease. Angina occurs when the heart’s need for oxygen exceeds its supply. Normal times of physical or emotional stress when the heart is working hard, a large meal, or sudden fear may also trigger an attack. When increased oxygen demand goes away, the pain typically goes away. It feels like someone is standing on the chest and is a crushing, squeezing pain. It is normally felt at the middle or sternum in the chest. It can radiate to the jaw, the arm (frequently the left arm), the midportion of the chest, and the epigastrium (the upper-middle region of the abdomen). It lasts for 3 to 8 minutes, rarely longer than 15 minutes. It is associated with shortness of breath, nausea, or sweating. It disappears promptly with rest, supplemental oxygen, or nitroglycerin (NTG), all of which decrease the need for or increase the supply of oxygen to the heart. Although scary, it doesn’t mean heart cells are dying and does not lead to death or permanent heart damage; however, it should be taken seriously because it says there could be a problem with the electrical system and a risk for problems with cardiac rhythm. If untreated, it is at very high risk of spontaneous AMI when unstable. When stable angina pectoris occurs, it happens after exercise or some activity that increases demand on the heart muscle beyond the heart’s capacity to increase its own blood flow. EMS often gets involved when stable angina goes to unstable angina and nitroglycerin no longer works. It can be difficult to tell the difference between angina pectoris and acute myocardial infarction, so you should always treat the patient as if they are having a heart attack.
Acute myocardial infarction signals actual death of cells in the area of the heart muscle where blood flow is obstructed. Cells cannot be revived and will turn to scar tissue and become a burden to the beating heart. You must take fast action in treating a heart attack. About 30 minutes after blood flow is cut off, heart muscle cells begin to die. After 2 hours, as many as half the cells in the area can be dead. In 4 to 6 hours, more than 90% of the cells will be dead. Opening the coronary artery with clot-busting (thrombolytic) medications or angioplasty (mechanical clearing of the artery) can prevent permanent damage to the heart muscle if done in the first few hours of onset. AMI is more likely to occur in the larger, thick-walled left ventricle, which needs more blood and oxygen than the right ventricle.
Hypertensive emergency is a systolic blood pressure greater than 180 mm Hg in the presence of impending or progressive organ damage. Symptoms are a severe headache, which could be a sign of cerebral hemorrhage. Other signs are a strong bounding pulse, ringing in the ears, nausea and vomiting, dizziness, warm skin, nosebleed, altered mental status, and even the sudden development of pulmonary edema. It can lead to a stroke or a dissecting aortic aneurysm. Position the patient with the head elevated and transport to the ED — paramedics may be able to administer medications that lower the blood pressure.
Treatment begins with proper positioning and, if indicated, giving the patient oxygen and reassessing oxygen saturation. For patients with mild dyspnea, a nasal cannula may be all that is needed; otherwise, use a non-rebreather mask. Titrate the oxygen to obtain an oxygen saturation between 95 and 99 unless ongoing difficulty suggests that respiratory distress is present despite a high pulse oximetry reading. If you suspect pulmonary edema, CPAP may be indicated. Depending on protocol, prepare to administer low-dose chewable aspirin and nitroglycerin. Make sure the patient doesn’t have a history of internal bleeding such as stomach ulcers. Nitroglycerin relaxes the muscle of blood vessel walls, dilates coronary arteries, increases blood flow and the supply of oxygen to the heart muscle, and decreases the workload on the heart. It is used to help relieve the pain of angina. Nitroglycerin lowers the blood pressure and can cause a severe headache. There can also be changes in the patient’s pulse rate to tachycardia or bradycardia. You should obtain the blood pressure right after dosage. Do not give it if systolic blood pressure is under 100 or if there is a head injury or recent use of erectile dysfunction drugs in the previous 24 to 48 hours. It is usually 3 doses. If the patient is hypotensive and has a nitroglycerin patch on, be sure to remove it. Also remove it if you need to use an AED and they are in cardiac arrest. It works within 5 minutes; if it doesn’t, they may take a second and third. Be sure it is placed under the tongue. If it has lost potency, they may not feel the fizzing under the tongue. It loses potency when exposed to heat and light, so a patient who has it in their pocket may experience a loss of potency.
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