Introduction to Cardiology PDF

Introduction to Cardiology  Introduction  Cardiology is an exciting and highly competitive branch of medicine which is concerned with the identification, assessment and management of diseases affecting the heart and blood vessels.  Therefore, an in‐depth knowledge of the...

Introduction to Cardiology  Introduction  Cardiology is an exciting and highly competitive branch of medicine which is concerned with the identification, assessment and management of diseases affecting the heart and blood vessels.  Therefore, an in‐depth knowledge of the pathological processes and cardiovascular physiology and pharmacology are required for those wishing to proceed in this rapidly evolving speciality.  Risk Factors and Prevention Strategies for Cardiovascular Disease The decline in death rates from sudden death related to coronary heart disease may be related to increased preventive measures such as statins, aspirin, beta blockers, and lifestyle changes. – Other factors may include heightened public awareness, the increased availability of automated external defibrillators, improved cardiovascular diagnosis and therapy, cardiovascular drugs, improved revascularization techniques, and risk factor modification.  Risk Factors and Risk Factor Modifications – Although death rates from myocardial infarction (MI) have declined over the past several decades, coronary artery disease with resultant sudden death is still a major cause of morbidity and mortality in the United States today. – Factors that pose a high risk for cardiovascular disease include advanced age, male sex, and hereditary factors.  Risk Factors and Risk Factor Modifications (cont.) – Having a parent with heart disease increases the risk, as do some racial factors. o African Americans, Mexican Americans, American Indians, native Hawaiians, and some Asian Americans have a higher tendency to have heart disease than do Caucasians.  Risk Factors and Risk Factor Modifications (cont.) – Lifestyle modifications that reduce cardiac risk: o Cessation of smoking or smoke exposure o Medical management and control of blood pressure, diabetes mellitus, cholesterol, and lipid disorders o Exercise o Weight loss o Diet - Modifying cardiovascular risk factors can slow the rate of development of arterial disease. It also can reduce the incidence of acute myocardial infarction (AMI), sudden death, renal failure, and stroke. Prevention and Community Education Strategies – Paramedics can support activities that help detect or prevent cardiovascular disease. – These strategies include community educational programs about nutrition, cessation of smoking (smoking prevention for children), and screening for diabetes and hypertension. – Teaching CPR and early use of an AED is an important role of the paramedic.  Anatomy Review of the Heart Blood Supply to the Heart – The human heart is a muscular organ with four chambers. It is cone shaped and about the size of a closed fist. It lies just to the left of the midline in the thorax. – These three layers of heart tissue are the outer layer, the middle layer, and the inner layer. – The four chambers of the heart are the right atrium, right ventricle, left atrium, and left ventricle.  Anatomy Review of the Heart Blood Supply to the Heart (cont.) – The left main coronary artery supplies the left ventricle, the interventricular septum, and part of the right ventricle. – Coronary capillaries allow for the exchange of nutrients and metabolic wastes. The capillaries merge to form coronary veins. These veins deliver most of the blood to the coronary sinus. – The coronary sinus empties directly into the right atrium. The coronary sinus is the major vein draining the myocardium.  The blood supply provided by many connections (anastomoses) exist between arterioles to provide backup (collateral) circulation. These anastomoses play a key role in providing alternative routes of blood flow in the event one or more of the coronary vessels become blocked.  Physiology of the Heart The heart can be thought of as two pumps in one. One is a low-pressure pump (right atrium and right ventricle). This pump supplies blood to the lungs. The other is a high-pressure pump (left atrium and left ventricle). This pump supplies blood to the body. The other is a high-pressure pump (left atrium and left ventricle). This pump supplies blood to the body.  Physiology of the Heart The right atrium receives venous blood from the systemic circulation and from the coronary veins. Most of this deoxygenated blood in the right atrium then passes to the right ventricle as the ventricle relaxes from the previous contraction. Once the right ventricle has received about 70% of its volume, the right atrium contracts. The blood remaining in the atrium is pushed into the ventricle (known as the atrial kick). Contraction of the right ventricle pushes blood against the tricuspid valve (forcing it closed) and through the pulmonic valve (forcing it open).  The Cardiac Cycle The cardiac cycle is the period of time from the beginning of one heartbeat to the beginning of the next. It focuses on the mechanical activity of the heart that is coordinated by the electrical activity of the conduction system of the heart. A close examination of the 5 phases (or stages) of the cardiac cycle will give an indication of how precise its function is.  The Cardiac Cycle There are two main stages or conditions of the heart and they are Diastole and Systole.  Diastole (like the term ‘dilate’) means dilated or relaxed. Therefore diastole is the time during which cardiac muscle is relaxing. If the chambers are relaxing, then the pressure is low. If a chamber is relaxed with low pressure, then they are filling. Systole (to bring together or draw in) means contraction. Therefore, systole is the time during which cardiac muscle is contracting. If the chambers are contracting, then the pressure is high. If a chamber is contracting with high pressure, they are ejecting blood.  The Cardiac Cycle 1. The venous return of blood fills the atria 2. The returned blood will cause to buildup pressure in the atria and the AV valves to open and blood to flow from atria to ventricles. by the action of this pressure, ventricles are about 80% filled with blood. 3. Then contraction of the atria occurs: adds the final 20% to the end-diastolic volume (the total volume of blood in the ventricles at the end of diastole). 4. When ventricles are filled, contraction of the ventricles in systole occurs and ejects about two thirds of the blood they contain (an amount called the stroke volume) One-third of the initial amount left in the ventricles as the end- systolic volume. The ventricles then fill with blood during the next cycle.  Physiology of the Heart Cardiac Output – Cardiac output is the amount of blood pumped by the ventricles in 1 minute. It can be increased by increasing the heart rate, the stroke volume, or both. – Cardiac output is calculated as follows: Cardiac output = Stroke volume × Heart rate  Physiology of the Heart Stroke Volume – The stroke volume is the amount of blood ejected from the heart with each ventricular contraction. SV depends on: o The primary determinants of stroke volume are: o Preload - stretching of cardiomyocytes at the end of diastole. o Myocardial contractility - changes to stroke volume can be brought about through changes to contractility. o Afterload - pressure or load against which the ventricles must contract.  Physiology of the Heart Stroke Volume (cont.) ‒ Preload (the volume of blood returning to the heart) ‒ According to the Starling law, myocardial fibers contract more forcefully when they are stretched. ‒ The Starling law and its effect on stroke volume can be applied only to a certain limit of muscle fiber stretching. ‒ Beyond that limit, muscle fiber stretch actually diminishes the strength of the contraction. At that point, the heart begins to fail.  Physiology of the Heart Stroke Volume (cont.) – Afterload (the resistance against which the heart muscle must pump) o Afterload is the pressure within the aorta before ventricular contraction. It is a result of systemic vascular resistance (the total resistance against which blood must be pumped). o The greater the afterload, the more difficult it is for the left ventricle to pump blood to the body. In addition, the amount of blood ejected with ventricular contraction (stroke volume) is reduced.  Physiology of the Heart Stroke Volume (cont.) – Myocardial contractility (the performance of cardiac muscle) o The unique function of the myocardial muscle fibers and the influence of the autonomic nervous system play a major role in the function of the heart. o Ischemia or various drugs can decrease myocardial contractility. o Ischemia can reduce the total number of working myocardial cells (as occurs in MI). o Hypoxia or beta blockers can decrease the ability of the myocardial cells to contract.  Physiology of the Heart Nervous System Control of the Heart – In addition to the heart itself, the autonomic nervous system controls the behavior of the heart. – The autonomic nervous system innervates the atria and ventricles. – The parasympathetic nervous system is concerned mainly with vegetative functions.  Physiology of the Heart Nervous System Control of the Heart (cont.) – Parasympathetic control o Parasympathetic control of the heart is accomplished through the vagus nerve. o Control by these nerve fibers has a continuous restraining influence on the heart, primarily by reducing the heart rate and, to a lesser extent, contractility.  Physiology of the Heart Nervous System Control of the Heart (cont.) – Sympathetic control o Sympathetic nerve fibers originate in the thoracic region of the spinal cord. They form groups of nerve fibers called ganglia. o Strong sympathetic stimulation of the heart may notably increase the heart rate. o When rates are significantly high (> 150 beats/min), the time available for the heart to fill is decreased, producing a decrease in stroke volume.  Physiology of the Heart Hormonal Regulation of the Heart – Impulses from the sympathetic nerves are sent to the adrenal medulla at the same time they are sent to all blood vessels. – In response, the adrenal medulla secretes the hormones epinephrine and norepinephrine into the circulating blood in response to increased physical activity, emotional excitement, or stress. – Epinephrine has basically the same effect on cardiac muscles as norepinephrine.  Physiology of the Heart Role of Electrolytes – Myocardial cells are bathed in an electrolyte solution, as are all other cells of the human body. – The major electrolytes that affect cardiac function are calcium, potassium, and sodium. – Magnesium is a major intracellular cation that also plays an important role. – Changes in electrolytes can affect depolarization, repolarization, and myocardial contractility.