H.CARDIOLOGY

__OVERVIEW __ Cardiology includes the study of the structures of the heart, the cardiac cycle and heart sounds, electrical activity of the heart, blood vessels, atherosclerosis, cardiac arrhythmia's, the lymphatic system, cardiac output, blood flow, and blood pressure.
 * Cardiology **

The structure of the heart is a 4 chamber pump system. The heart is divided into pulmonary circulation which is circulation from the heart through the lungs and back to the heart and systemic circulation which is circulation from the heart through the body and back to the heart. The 4 chambers of the heart are divided by valves. There are 2 atrioventricular valves that separate the ventricles from the atrium to prevent the blood from flowing back into the ventricles and 2 semi-lunar valves that separate the heart from arteries leaving the heart and prevent back-flow of blood back into the heart. This is a link to a video that shows the heart structure.

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The heart is a two step pump. The first part of the pumping cycle is the contraction of the right and left atria followed by the contraction of the right and left ventricles. The contraction phase is called systole and the relaxation phase is called diastole. So when atrial contraction is occurring toward the end of diastole the ventricles and relaxed and when the ventricles contract during systole the atria are relaxed.

The pumping of the heart constantly changes pressure throughout the cardiac cycle. As the ventricles contract the intraventricular pressure rises. When the pressure in the left ventricle is higher than the aortic pressure the semi-lunar valves open and eject blood and the pressure in the left ventricle and aorta are about 120 mm Hg. As the ventricle empties the pressure falls below the pressure of the aorta and the semi-lunar valves shut resulting in a pressure fall in the aorta to about 80 mm Hg and the pressure in the left ventricle falls to around 0 mm Hg. When pressure in the ventricles is below the pressure in the atria the AV valves open and the blood fills the ventricles. The pressure is lower in the pulmonary circulation that in systemic circulation. The opening and closing of the AV and semi-lunar valves produce the heart sounds we recognize as "lub-dub".

If the blood flow pattern in the heart is abnormal it would produce and abnormal heart sound or a heart murmur. They can be caused by defective heart valves. If there is only a minor defect it is possible to have a heart murmur that does not compromise the pumping ability of the heart. But some people have more serious defects that can have serious consequences if not surgically corrected. For example the valves can be thickened and calcified, or not close properly which can be deadly if not recognized and treated. Heart murmurs can also be caused from septal defects which are holes in the septum between the right and left sides of the heart which can cause pulmonary hypertension and edema in the lungs. This is a good illustration of some causes of heart murmurs.

The heart is an intricate organ that demonstrates spontaneous electrical activity that acts as its own pacemaker. The pacemaker of the heart is the sinoatrial node or SA node which is located in the right atrium near the superior vena cava. During diastole the SA node experiences spontaneous depolarization known as the pacemaker potential. The membrane potential is between -60 mV and depolarizes to -40 mV. This depolarization is produced by the opening of a channel that opens in response to hyper-polarization. Automatic depolarization of the SA node occurs during diastole known as diastolic depolarization. There are other regions of the heart around the SA node and the atrioventricular bundle that may also produce pacemaker potentials. Spontaneous depolarization of these areas is slower than the SA node and are stimulated by the action potential of the SA node before they stimulate themselves. Action potential of the SA node spread to adjacent myocardial cells through gap junctions between the cells. Specialized conducting tissue in the heart is required to transfer the impulse from the atria to the ventricles. The specialized cells form the AV node, bundle of His, and Purkinje fibers. The order of the impulse is as follows: Atria, AV node, bundle of His, and Purkinje fibers. The electrocardiogram ECG or EKG is used to record the electrical impulses of the heart and graph the results in and electrocardiograph as shown below. The P wave is the spread of atrial depolarization. The QRS wave is the spread of depolarization into the ventricles. The T wave is the repolarization of the ventricles.

Blood vessels are the structures that transport blood throughout our bodies. The flow of blood is as follows arteries, arterioles, capillaries, venules, and veins. The structure of the veins and arteries consist of the outer layer tunica externa, the middle layer tunica media and the inner layer the tunica interna. The tunica externa is connective tissue, the tunica media is primarily smooth muscle, and the tunica interna has 3 parts, the endothelium, the basement membrane, and elastic fibers known as elastin. Arteries are elastic to accommodate the ventricles contractions and recoil like a rubber band. The smaller the arteries are the less elastic they are. The elasticity of the arteries helps push the blood through them.Capillaries are the narrowest blood vessels. They are the end of the circulatory system where gases and nutrients are exchanged between the blood and tissues before returning to the heart. There are 3 types of capillaries. Continuous capillaries have adjacent endothelial cells that are closely joined and found in the muscles, lungs, adipose tissue, and in the CNS. Fenestrated capillaries have wide intercellular pores that are covered by mucoprotein that serves as a basement membrane over the endothelium and occur in the endocrine glands and intestines. Discontinued capillaries have a great distance between endothelial cells that look like sinusoids in the organ and are found in the bone marrow, liver, and spleen. Veins contain most of the total blood volume in the body. There is a lower venous pressure in veins that in arteries and is therefore unable to return blood to the heart on their own. Veins pass through skeletal muscle groups that contract to help push blood through the veins. Veins also have valves in them to prevent backflow of blood.

Atherosclerosis is a common heart disease characterized by hardening of the arteries. Plaque in the arteries protrudes into the the lumen of the artery and reduces blood flow and can potentially form a blood clot. The risk of getting atherosclerosis is greatly increased by smoking, hypertension, high cholesterol, and diabetes. High cholesterol can occur from eating a diet high in cholesterol and saturated fats or may also be inherited. Cholesterol is carried to arteris by low-density lipoproteins (LDLs) which are produced by the liver. When people eat a large amount of cholesterol and saturated fat and people with a family history of high cholesterol have a high level of LDLs. High-density lipoproteins (HDLs) protect against atherosclerosis by carrying cholesterol away from the artery walls. The HDL levels are higher in women than in men, in people who exercise regularly, and also genetics play a large role in the HDL levels.

Ischemic heart disease is another concern for people. Ischemia results from a deficient oxygen supply because of inadequate blood flow. This can be increased by atherosclerosis. Myocardial ischemia shows increased concentration of lactic acid in the blood which is produced by anaerobic metabolism in the ischemic tissues. This can cause angina pectoris. Myocardial cells require aerobic respiration and can't metabolize anaerobically for more than a few minutes. If ischemia and anaerobic metabolism is prolonged it can result in cellular death and if this is sudden and irreversible it is known as myocardial infarction.

The lymphatic system is also important in the circulatory system. The lymphatic system is responsible for transporting interstitial fluid back into the blood, transporting absorbed fat for the small intestine to the blood, and lymphocytes provide immune defenses against pathogens. The lymphatic capillaries form vast networks in intercellular spaces in most organs where interstitial fluid, proteins, extravasated WBC's, microorganisms, and absorbed fat can enter. The lymph is then carried into larger lymph vessels called lymph ducts which empty into either the thoracic duct or right lymphatic duct. These ducts drain the lymph into the left and right subclavian veins returning plasma to the blood. The lymph vessels filter the lymph through lymph nodes before returning it to the blood.

Cardiac output is the volume of blood pumper per minute by each ventricle. It can be figure by taking the stroke volume times the cardiac rate. The total blood volume in the human body averages 5.5L. The cardiac rate is controlled by an automatic rhythm as a result of diastolic depolarization of the SA node. Sympathetic and parasympathetic nerve fivers to the heart are continuously active and can affect the cardiac rate. The pace set by the SA node therefore depends on the net effect of antagonistic influences that have a chronotropic effect on the heart rate. The stroke volume is regulated by end-diastolic volume (EDV), total peripheral resistance, and contractility. Venous return is the return of the blood to the heart through the veins. The venous return depends on the total blood volume and venous pressure.

Blood volume is influenced by the kidneys which are ADH and aldosterone act on the kidneys to regulate the blood volume. Two-thirds of the water in the body is intracellular fluid. The remaining fluid is 80% interstitial fluid and 20% blood plasma. The hydrostatic pressure of the blood can force fluid out of end of capillaries and into the interstitial spaces in tissues. Water returns into the venular end of the capillaries by osmosis because the colloid osmotic pressure of plasma is greater that that of tissue fluid. Lymph vessels return the excess interstitial fluid to the circulatory system. If interstitial fluids become excessive edema can occur. Our kidney play a very important part in regulating our blood volume. ADH released by the posterior pituitary gland stimulates the kidneys to reabsorb water from the kidney filtrate when the blood volume is low. Since ADH only promotes absorption of water it dilutes the blood volume. If dietary salt intake is too low the adrenal cortex secretes aldosterone to stimulate the kidneys to reabsorb salt which also promotes water retention. Due to the reabsorption of salt and water in proportion aldosterone does not dilute the blood.

Vascular resistance to blood flow is directly related to the pressure difference in a vessel and inversely related to the resistance to the blood flow through a vessel. The sympathetic nervous system stimulates vasoconstriction of arterioles in the viscera and skin regulating the vascular resistance affecting blood flow. Individual organs have the ability to maintain intrinsic regulation of blood flow through them. Myogenic control of blood flow can be described as constriction of dilation of vessels in a response to a rise or fall in blood pressure in that organ. Metabolic regulation of blood flow results when there is a chemical released by the organ causing dilation of the vessels in that organ.

Blood flow to the heart and skeletal muscles is very important and is controlled by both extrinsic and intrinsic factors. These mechanisms can increase blood flow during exercise when the metabolic requirements are increased. The heart contains numerous coronary arteries that supply blood to the heart. Due to this the heart is normally aerobically respired. During exercise as the metabolism of the myocardium is increased CO2, K+, and adenosine accumulate and deplete oxygen in the heart causing the vascular smooth muscle in the heart to relax and vasodilation to occur increasing blood flow. This is the intrinsic mechanism of the heart. The sympathetic cholinergic fivers in skeletal muscles together with epinephrine stimulate vasodilation in response to exercise. As exercise progresses intrinsic metabolic control takes over and vasodilation and increased blood flow to the skeletal muscles take over. During exercise due to the increase demands of the body cardiac output can increse up to five times or more. The skeletal and cardiac muscles receive a majority of the additional blood flow.

Blood flow to the brain and skin are also very important. Cerebral circulation in maintained mainly by intrinsic control. The autoregulation of cerebral circulation ensure a constant blood flow despite changes in arterial pressure. Myogenic regulation occurs during systemic arterial pressure changes to maintain a constant flow rate during rest, exercise, and emotional stress. Metabolic regulation occurs when certain areas of the brain are requiring additional blood flow. This causes local vessels to dilate and supply these active areas with more blood. Cutaneous blood flow to the skin is greatly regulated by thermoregulation. Blood flow to the skin is adjusted to maintain deep body temperature. Arteriovenous anastomoses found in the fingertips, palms, toes, soles of feet, ears, nose and lips shunt blood directly from arterioles to deep venules bypassing superficial capillary loops when the temperature is low. When temperatures is high the blood is diverted to the superficial capillary loops to decrease body temperature.

Blood pressure is regulated by blood volume, total peripheral resistance, and cardiac rate. Baroreceptors are stretch receptors in the aortic arch and carotid sinuses that are sensitive to blood pressure. A fall in blood pressure increases sympathetic nerve activity while the activity of the parasympathetic division decreases. This increases cardiac output and total peripheral resistance. The opposite is true with a rise in blood pressure.

__ESSENTIAL QUESTIONS__ What are the three most important variables that affect blood pressure? Describe each variable and how it affect blood pressure. Describe two reflexes that help maintain blood pressure within limits.

The complete cycle of contraction and relaxation of the heart is called the cardiac cycle. The contraction phase is called systole, and the relaxation phase is called diastole.



Heart rate is the rate of contraction per minute, and the stroke volume is the amount of blood pumped by the left ventricle during each contracion.

There are four heart valves and two atrioventricular (AV) valves between each atrium and ventricle, which prevent the back flow of blood into the atria; there are also two semiulnar valves -one located at the entrance to pulmonary artery and the second at the entrance to the aorta.



Regulation of the Heartbeat The sinoatrial (SA) node is the pacemaker of the heart. It is located in the upper wall of the right atrium. It stes the rate at which cardiac muscle cells contract.



The AV or atrioventrical node, located in the lower wall of the right atrium, delays the impulses from the SA node to allow the atria to completely empty before the ventricles contract.

The heart is the main organ involved in the cardiovascular system. The heart is divided into four chambers: two atria, the right and the left atrium(s), which revive venous blood; and two ventricles, the right and the left ventricle(s), which send the blood into arteries. The right ventricle pumps the blood to the lungs, where the blood becomes oxygenated; the left ventricle pumps the now oxygenated blood out to the body.



There are two types of circulation that occur in the cardiovascular system: pulmonary and systemic. Pulmonary circulation is the pathway the blood takes from the right ventricle of the heart through the lungs and back into the left ventricle of the heart. Systemic circulation is when oxygen rich blood is transported throughout the body.



The heart contains valves to keep the blood flowing in the right direction. The valves are the pulmonary semilunar valve, the aortic semilunar valve, the tricuspid valve and the bicuspid valve. These valves open and close allowing the blood to flow though the arteries and not back flow in the wrong direction.



The cardiac cycle is the repeating pattern of contracting and relaxing of the heart. The cycle is what we measure to figure blood pressure. Blood pressure is the measurement of the force applied to the walls of the arteries as the heart pumps blood though the body. The pressure is determined by the force and amount of blood pumped and the size and flexibility of the arteries. Blood pressure is constantly changing depending on activity and exercise, temperature, diet, emotions, posture, physical well being and medications. Blood pressure is regulated by blood volume (stroke volume), total peripheral resistance and the cardiac rate. Baroreceptor reflex consists of (1) aortic arch and carotid sinus Baroreceptor as sensors; (2) the vasomotor and cardiac control center of the medulla oblongata as the integrating center; and (3) parasympathetic and sympathetic axons to the heart and blood vessels as the effectors. Blood pressure falls and the baroreceptors compensate to increase the cardiac output and total peripheral resistance. If the blood pressure raises the sympathetic nerve activity declines while the parasympathetic nerve activity increases. The baroreceptor reflex act to keep blood pressure constant on a beat to beat basis. “Arterial stretch reflexes are located in the atria of the heart. These receptors are activated by increased venous return to the heart and in response stimulate reflex tachycardia, as a result of increased sympathetic nerve activity, inhibit ADH release, resulting in the excretion of larger volumes of urine and a lowering of blood volume; and promote increased secretion of artial natriuretic peptide (ANP). ANP lowers blood volume by increasing urinary salts and water excretion.

__SUMMARY __

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__**Electrical activity of the heart**__



The SA node, considered the pacemaker of the heart, exhibits a depolarization that causes action potentials that result in the automatic beating of the heart. Myocardial cells in the atria conduct the action potentials to the ventricles by conducting tissues, and an electrocardiogram is used to record the waves that correspond to these events. The sino-atrial node is the only region of the heart to demonstrate spontaneous electrical activity. As a result of spontaneous depolarization, called the pacemaker potential, action potentials originate in the SA node. Opening of the voltage-regulated Na+ and fast Ca2+ channels produces the action potentials when the spontaneous depolarization reaches a threshold value. Outward diffusion of K+ is the result of repolarization, and because a stable resting membrane potential is not reached, spontaneous depolarization occurs again. Electrical conduction from one myocardial cell to another sends the electrical impulse from the SA node through both atria. The impulse is then sent to the atrioventricular (AV) node, through the bundle of His and on to the Purkinje fibers which cause the ventricular muscles to contract. An electrocardiogram (ECG) records the changing pattern caused by the heart. Each cardiac cycle produces three ECG waves, P, QRS, and T. Atrial depolarization creates the P wave, where depolarization into the ventricles creates the QRS wave. Finally, repolarization of the ventricles creates the T wave.

__**Blood Volume**__
Fluid in the extracellular environment moves between the blood and interstitial fluid compartments by the forces acting across the capillary walls. The kidneys, ADH, aldosterone, and ANP also play roles in regulating blood volume. Dynamic equilibrium is a term used to describe the distribution of fluid between the plasma and interstitial compartments. Hydrostatic pressure of the blood pushes fluid from the arteriolar capillaries to the interstitial spaces of the tissues and the colloid osmotic pressure of the plasma being greater than that of tissue fluid causes water to return to the venular capillaries by osmosis. Starling forces are the opposing forces that affect the distribution of fluid across the capillaries.



The glomeruli of the kidney's produce a filtrate that enters the tubules for transfer and modification. The kidneys produce about 180L of blood filtrate per day, but only about 1.5L is excreted in the urine. The rest of the filtrate is reabsorbed back into the vascular system. The urine and blood volume are adjusted according to the needs of the body through the actions of hormones on the kidneys. Antidiuretic hormone (ADH) is released from the posterior pituitary when osmoreceptors in the hypothalamus detect an increase in plasma osmolality. This means that the ADH stimulates the kidneys to allow more water to reabsorb from the filtrate causing water retention and thus decreasing urine output. This fluid reabsorption decreases the osmolality of the blood. Aldosterone is a "salt-retaining hormone". Dietary salt is required to maintain blood volume and Na+ is easily filtered by the kidneys. The adrenal cortex secretes aldosterone to stimulate the kidneys to reabsorb Na+. Salt retention indirectly promotes the retention of water increasing the blood volume, but not the osmolality of the blood. This is because salt and water are reabsorbed in proportionate amounts. Another hormone which is antagonistic to adosterone is atrial natriuretic peptide (ANP). It is produced by the heart and is secreted in response to an increase in blood volume. Since it is antagonistic to aldosterone, it promotes the excretion of Na+ and water in the urine. When ANP is secreted ADH is inhibited. An increase of ANP along with a decrease in ADH work together as a negative feedback correction to lower the blood volume and maintaining homeostasis.



__**Circulatory Changes During Exercise**__


The vascular resistance in skeletal muscles decreases while the resistance to flow through the visceral organs and skin increases. Three simultaneous changes increase the flow of blood to the skeletal muscles: 1- increased cardiac output, 2- metabolic vasodilation of the exercising muscles, and 3- the diversion of blood away from the viscera and skin. The cardiac output can increase up to fivefold due to the increase in cardiac rate so the heart and skeletal muscles receive more blood flow. Due to the higher activity of the skeletal muscle pumps and increased breathing rate with exercise, the venous return is increased. A higher stroke volume can result from the combined decrease in total peripheral resistance and the increased contractility of the heart. Lowering of the resting cardiac rate and increase in resting stroke volume can result from endurance training. The cardiac rate can be lowered from a larger degree of inhibition of the SA node by the vagus nerve where the increased resting stroke volume can be due to an increase in blood volume. Adaptation such as these enable the athlete to achieve a higher absolute cardiac output during exercise. Large cardiac output is a major factor to improved oxygen delivery to the skeletal muscles that occurs with endurance training.

Sources:
Fox, Stuart Ira. (2009). //Human Physiology//. New York, NY: McGraw-Hill. __APPLICATION__ As a nurse I need to know how the cardiac cycle works because I may be called upon to help with a cardiac emergency. It is also good for a nurse to know and understand this information as it is vital to life. This is something a nurse measure on a regular basis and the doctor uses the information to aid in diagnosis.



As a nurse, especially on the Medical/Surgical floor where anything and everything comes through, it is important to have knowledge of all aspects of the human body. The nurse needs to know how the heart works, what adverse effects it has on the body when it isn't functioning properly, how the body can effect the heart, and how to take care of the patient who has heart or health issues related to the heart. For example, my cousin at the young age of 21 had a pacemaker inserted and 3 years later, also had a defibrillator implanted due to a virus that attacked his heart. As a nurse it is important to understand what these devices are and how they work. A pacemaker (my cousins was implanted) is a device implanted through the left Subclavian vein and provides action potential to the SA Node when the heart rate falls below the pacemakers low limit (usually 55-60 beats per minute). When heart rate is low, an electrical impulse will be sent to the heart and a contraction (beat) will occur. A defibrillator will sense when the heart is beating too fast and it will deliver an electrical shock to the heart and "reset" its rhythm to a more normal rhythm. My cousin stated that when his defibrillator would go off, it was the weirdest feeling ever and it felt like he was being punched from the inside out. Due to his condition and the implanted cardiac devices, he was not able to have MRI's, he was also told by his cardiologist to avoid high voltage machinery (ex: tv/radio transmitters, radar installations, and even some microwaves). It is important as a nurse to know if your patient has such devices and how they work, because if you are noticing your patient with a pacemaker has a heart rate of 40 beats per minute, you better get the doctor and ensure that the patient's pacemaker is working.

__CASE STUDY __ **[|Wake-Up Call]**
 * 1) How likely is this to be a heart problem? Asthma? Panic attack? Or...? **More likely to be a heart problem.**
 * 2) Why do you say this? What are the symptoms that are consistent with your preliminary diagnosis? Is there anything unusual?
 * 1) Why do you say this? What are the symptoms that are consistent with your preliminary diagnosis? Is there anything unusual?
 * I would say it is more likely to be a heart problem due to the symptoms she is having and also inhaling second hand smoke. Some of the symptoms she describes are cold sweats, difficulty breathing, having the feeling something terrible is about to happen, denies chest pain, lightheadednerss and feeling like her heart is beating a thousand times per minute. Here are the symptoms of Coronary Heart Disease that can be mild or vague; weakness, cough, fatigue, dizziness, backache and/ or feeling of indegstion, palpitations, SOB , sweating , vomiting, nausea, anxiety, paleness, cyanosis, fainting , pain or numbness in the shoulders or arms, edema in the legs. I have highlighted the symptoms that this person is having. Also note that although chest pain is the classical symptom to CAD, not all people expierience chest pain and chest pain usually suggest the person has had the underlying cause of CAD for a long period of time which is called Atherosclerosis.**

[] [|weakness], [|cough], [|fatigue], [|dizziness], [|backache] and/or a feeling of [|indigestion]. Other symptoms may include [|palpitations], sweating, [|shortness of breath], [|nausea], [|vomiting], [|anxiety], __paleness__, and [|cyanosis], (a bluish discoloration of the lips, feet and hands). Additional symptoms can include pain or numbness in the shoulders or arms, [|fainting], [|edema] or swelling of the ankles or legs. Read more at http://www.wrongdiagnosis.com/c/coronary_heart_disease/symptoms.htm?ktrack=kcplink [|weakness], [|cough], [|fatigue], [|dizziness], [|backache] and/or a feeling of [|indigestion]. Other symptoms may include [|palpitations], sweating, [|shortness of breath], [|nausea], [|vomiting], [|anxiety], __paleness__, and [|cyanosis], (a bluish discoloration of the lips, feet and hands). Additional symptoms can include pain or numbness in the shoulders or arms, [|fainting], [|edema] or swelling of the ankles or legs. Read more at http://www.wrongdiagnosis.com/c/coronary_heart_disease/symptoms.htm?ktrack=kcplink