Question:
Mr King is a 68-year-old gentleman with a history of hypertension and coronary heart disease who has been admitted onto the coronary care unit following a sudden onset ofchest tightness/ pain, nausea and perfuse sweating.His blood pressure is fluctuating between ranges of 100/50, 90/65 and 150/95.Pulse rate is irregular and ranges between 60, 95 and 115.Oxygen saturation level is 9.Qro. Respiratory Rate 22 and he is finding it difficult to breathe.He has been diagnosed with an AcuteMyocardial Infarction,his angiogram has revealed a compete occlusion of the left coronary artery.The aim of his treatment is to restore blood flow to the coronary arteries and the heart muscle.Therefore an angioplasty (stenting) was performed.Explain conduction pathways in the heart.Identify the different stages of the cardiac cycle.
Heart is an important part of human body regulating different functions including the central function of circulatory system. The circulatory system helps in circulation of blood in each and every part of the human body, making it most important part of human body systems(Torrent et al, 2005). The heart is a part of the circulatory system which is quite complex due to structural and functional attributes. The current case study described above deals with one cardio-vascular system disorder known acute myocardial infraction. The subject of this case study is a 68 year male who has been admitted to coronary unit post complaining of chest pain, profuse sweating and difficulty and breathing. Patient medical history reveals subject was a patient of coronary heart disease and hypertension. Initial diagnosis concluded as a case of acute myocardial infarction from fluctuating blood pressure, heart rate and oxygen saturation levels as mentioned in the case. . On further investigation through angiogram, he was found to have an occlusion in left artery demanding Stenting. Post stenting it is very important to monitor the patient heart status and circulatory system. Form, nursing point of view, the rationale behind the intervention must be understood in order to address complications if raised any. Thus, this piece of case study analysis deals with a basic understanding of acute myocardial infarction, left artery occlusion as a causal factor, consequences, importance of restoration of blood flow to the coronary arteries and heart.
Pathway of Analysis
The case study analysis will following pathway in order to provide the reader clear view of the medical disorder in context of cardiovascular system.Brief description of structure of heart- circulation of blood to and fro from heart, different functions of arteries, capillaries and veins, risk factors (abnormal heart rate) and it effect upon subject heart muscle, blood pressure maintenance mechanism and reason behind fluctuation of blood pressure in subject.
The heart is a four chambered organ about fist size located in a floral cavity (mediastinum) left on the Sternal bone. The upper two chambers and lower two chambers of the heart are called as atria and ventricles respectively. The wall separating the both sides having atrium and ventricles is known as septum. The pumping action of heart which pumps blood to different parts of the heart. The orientation of blood to right direction is maintained by the valves resent n both side of heart (Hinton and Yutzey, 2011). The heart contains the following parts with functions shown in brief below.
The bundle of his: these are the muscle fibers that begin from the atriovetricular node and reaches to the interventricular septum. Its function is to conduct electrical impulse and regulates the heart beat.
The AV node: The function of AV node is to pass electrical signals obtained from atria to the ventricles. It also controls the heart rate.
The SA node: It is one of the major elements in the conduction of the different cardiac systems. It also functions as controlling heart rate. It conduct electrical impulses through the heart muscles resulting into stimulation of heart to contract and pump blood.
Tricuspid valve situated in between right atrium and ventricle to prevent back flow of the blood.
Pulmonary valve situated between pulmonary artery and right ventricle.
Mitral valve which is located between left atrium and left ventricle.
Aortic valve present between left ventricle and aorta.
The tricuspid valve and mitral valve forms atrioventricular valves which allow blood to flow from atrium to ventricles. The role of these atrio-ventricular valves is to allow blood to pass through but inhibit regurgitation of blood.
The other two valves are categorized under semilunar valves due to their structural resemblance with a half moon. These two valves are present in between ventricles and arteries, which pumps the blood away from the heart. On the right side of the heart, pulmonary valve can be found which prevents back flow of blood pulmonary trunk to the right ventricle. On the contrary, aortic valve indicates towards valve present on the left side of the heart which prevents back flow of blood from the aorta to the left ventricle (McDonagh, 2011).The atrio-ventricular valves attach with strong string like structures known as code tendinae. Unlike these valves, the semilunar valve doesn’t have chordae tendinae to hold them and depends upon blood pressure to shut back for proving blood regurgitation.The above mentioned parts of heart constitutes major parts, the other parts include different nodes, lining of heart, artery veins and capillaries.To understand the cardiovascular disorder of the male subject, understanding of normal blood circulation is an essential part of case study analysis. Thus, these parts address the blood circulation pathway in heart and links to the current case to reveal what led such medical condition.
The main objective of heart, circulatory system is to supply oxygenated blood to different parts of the body. During the contraction, the blood gets pushed through two different systems or loops. The first loop is known as systemic loop where heart pumps oxygenated blood to different parts of the body, organs, tissues and cells and collects carbon-di-oxide waste. In the second loop system known as pulmonary loop, the carbon di –oxide collected is deposited in lungs and new oxygen molecules are picked by the blood. The systemic and pulmonary cycle of heart are controlled by left and right side of heart(John, 2011).
The systemic loop initiates as soon as oxygenated blood from lungs enter the upper left chamber of heart into right atrium. Post filling of left atrium, due to pressure the mitral valve opens and the blood flows from left atrium to left ventricles. During the contraction of heart, the blood from left ventricles goes to aorta. Aorta is regarded as largest artery in the body. The blood brought down by the aorta goes to different parts of the body through different arteries and capillaries. The used blood are carried by a network of veins to the heart. All the blood used by the body are returned to heart through major two veins- superior vena cava which collects blood from upper part of the body and inferior vena cava which collects blood from lower region of the body. Both these veins empty the collected blood to the right atrium of the body (Murray, Dalley and Agur, 2013).
After the blood reaches the right atrium the pulmonary cycle begins. Through tricuspid valve, the right atrium pumps the blood to right ventricle. With contraction of the ventricle, the blood from right ventricle enters into pulmonary artery where it gets bifurcated into two sub branches. One leading to right lungs and one leading to left lungs. Through pulmonary veins, the oxygenated fresh blood enters into the left atrium to be pumped out of the heart(Star, Evers, Star, 2012).
Although, both the cycles are different in mechanism they occur at same time point. The heart contractions initiates at atria where the blood enters from atria to ventricles. The ventricles contract to push the blood out of the heart to lungs and to different parts of the body. The heart muscle relaxes after this and allows the deoxygenated blood from different parts of the body to be collected and fill the atria again. Thus, this is the normal circulatory physiology which helps in supply of oxygen to different parts of the body (Phibbs, 2007).
The very first manifestation of acute myocardial infraction is life threatening arrhythmia which enhances the automacity of the myocardium. Further there occur electrolyte imbalance and hypoxic condition that also contributes towards development of severe cardiac arrhythmia. Arrhythmia is of many types such as ventricular tachycardia, total AV blocking and ventricular fibrillation. It has been reported that these arrhythmias has caused several sudden deaths in patients having acute coronary diseases. The peri-infarction arrhythmias may be developed due increased activity of sympathetic activity, increase in the concentrations of catecholamine’s circulating in the blood and their release in the heart muscles from nerve endings. This ultimately results into autonomic imbalance and promotion of the arrhythmias (Graham et al, 2011). The first few hours for the patients having acute myocardial infarction is very crucial as the chances of onset of atrial fibrillation are very high. There can be many causes for this such as LV failure, RV infarction and injury to atria. All these conditions lead to increased left atrial pressure that result into atrial fibrillation along with acute myocardial infarction. Prior to cardio version a mild anaesthesia or conscious sedation is advised, the later one is more preferred. Getting control on the ventricular response is the immediate objective for the patients with stable condition. A beta-blocker can be used for the patients having no risk of developing hypotension, such as metoprolol can be given intravenously in every five to ten minutes with the dose 5mg and the maximum dose can be of 15mg. Alternative to this is administration of diltiazem intravenously which decreases the rate of ventricular. However this particular medication should be used very carefully for the patients having moderate to severe heart problems (Graham et al, 2011).
In the above case study the subject was diagnosed myocardial infarction and found left artery occlusion. An angioplasty was performed to restore the blood flow. An angioplasty was performed to restore the blood flow. Stroke can occur due to blockage of arteries. When arteries get blocked the damaged heart cells fails to receive blood and eventually dies. This leads to further damage and death of patient. Once the patient is brought under control an angioplasty or stenting is performed to remove the blockage therefore in the present case study it is quite essential to restore the blood flow to damaged portion of heart.
Post stenting. The subject blood pressure fluctuates repeatedly. Therefore from nursing point of view, it is essential to know how blood pressure is monitored and regulated in human body. The human body has sensors which can sense blood pressure fluctuations in the body. These fluctuation are passed to heart, arteries, veins and kidneys whereby they make necessary changes to maintain the blood pressure.
The two types of receptors which sense changes in blood pressure are baroreceptors and chemoreceptors. Baroreceptors which are located at carotid sinus used to sense arterial blood pressure. Chemoreceptors sense changes in oxygen and carbon-di-oxide levels at different parts. Chemoreceptors are present in aortic bodies and carotid bodies.
Apart from these receptor systems, other systems such as cerebral cortex, limbic system, hypothalamus, passes information to the cardiovascular system if any condition rises which affects blood pressure. Such as aggression, fear, flight response, stress (Fox, 2008).
If the following variables can be adjusted or changed, the blood pressure can be maintained. When the heart rate or stroke volume changes, it affects the cardiac output. The blood flow inside veins can be regulated either by vasodilation or vasoconstriction mechanisms. Change in length of blood vessel or blood thickness can alter the blood pressure too.
The cardiovascular center regulates blood pressure either by regulating the diameter of the blood vessel or by regulating the cardiac output. This cardio vascular region is present in the medulla oblongata region. This cardiovascular region has three different regions which maintain blood pressure in three different ways. The cardiac center regulates cardiac output by changing the heart rate and contraction of blood vessels. The nerve impulses are conducted by sympathetic cardiac nerves. When heart rate needs to be decreased, it is regulated by parasympathetic nerves of cardiac center. The blood vessels diameter is regulated by vasomotor region of cardiac center. In general nerve impulses gets transmitted over sympathetic motor neurons which are known as vaso motor nerves, innervate the smooth muscles present in arteries in order to maintain the vasomotor tone i.e. a steady vasoconstriction status required in the region (Sherwood, 2008).
Kidney also helps in maintaining the blood pressure. The renin angiotensin and aldosterone system maintains the blood pressure. When the blood pressure rises, renin is secreted by juxtaglomerular cells of kidney into the blood. The renin helps in conversion of plasma protein angiotensinogen to angiotensin I. Angiotensin I is converted into angiotensin II with the help of enzymes secreted by lungs. Angiotensin II raises blood pressure by two ways either by constriction of blood vessels secondly by releasing aldosterone which reduces urine output and increase blood pressure.
Conclusion
The above analysis showed how complex the cardiac system is and how it regulates different function in the body. This implicates, the nurse who will be taking care of the subject in the present case must have through understanding of pathophysiology as well as physiological functions of heart.
References
Fox, S. I. (2008). Human physiology. McGraw-Hill Higher Education.
Hinton, R. B., & Yutzey, K. E. (2011). Heart valve structure and function in development and disease. Annual Review of Physiology, 73, 29-46.
John, E. H. (2011). Guyton and Hall textbook of medical physiology.
McDonagh, T. A., Gardner, R. S., Clark, A. L., & Dargie, H. (Eds.). (2011).Oxford textbook of heart failure. Oxford University Press.
Moore, K. L., Dalley, A. F., & Agur, A. M. (2013). Clinically oriented anatomy. Lippincott Williams & Wilkins.
Sherwood, L. (2008). Human physiology: from cells to systems. Cengage Learning.
Starr, C., Evers, C., & Starr, L. (2012). Biology Today and Tomorrow with Physiology. Cengage Learning.
Torrent-Guasp, F., Kocica, M. J., Corno, A. F., Komeda, M., Carreras-Costa, F., Flotats, A., … & Wen, H. (2005). Towards new understanding of the heart structure and function. European journal of cardio-thoracic surgery, 27(2), 191-201.
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