EKG Flashcards
(45 cards)
What is an EKG
-An ECG (also called an EKG) is an indirect measurement of electrical activity within the heart. A recording of the electrical currents within the heart is obtained by placing electrodes containing a conductive media to each extremity and numerous locations on the chest wall to create a 12 lead ECG. Each specific). The purpose of using 12 leads is to obtain 12 different views of the electrical activity in the heart and therefore a more complete picture.
3 lead or 5 lead system
-Current standard of practice in most hospitals call for Pt risk for cardiac events of dysrhythmias to be placed on continuous ECG monitoring using the 3 lead or 5 lead system. These systems use only 3 or 5 leads, placed on the PTs chest, which is less cumbersome and allows for more PT mobility than the 10 leads placed on the chest and extremities for 12 lead ECG
-Holter monitor uses a 3 or a 5 lead setup
-Although these modified systems do not provide the overview that a 12 lead ECG does, they do allow for the recognition of gross abnormalities in the electrical conduction of the heart. Identifications of a rhythm abnormalities on a 3 lead or 5 lead tracing often indicates the need to obtain a more detailed 12 lead view if the heart
Value of EEG/EKG
-The ECG provides valuable info about the cardiac status of a PT presenting with signs and symptoms suggestive of heart disease. For example if the PT presents with dyspnea and chest discomfort, an ECG can aid in the diagnosis of an ischemic cardiac event
When should an ECG/EKG be Obtained
-Because an ECG is noninvasive and does not present a risk to the PT, it is reasonable to obtain an ECG when the PT has signs and symptoms suggestive of an acute or chronic cardiac disorder such as myocardial infarction or congestive heart failure
-Of course the process of obtaining the ECG should never delay the initiation of critically needed care such as oxygen therapy, airway placement, or cardiopulmonary resuscitation (CPR) -An ECG is often used as a screening tool to determine the PTs health status before major surgery. An ECG is especially helpful in this situation if the PT is older or has a history of heart disease. If an abnormality is identified, it may need to be treated before the operation is performed
Anatomy and physiology of the Heart and Electrical Activity
-Before discussing the interpretation of the ECGs, it is important to revir=ew the cardiac anatomy and physiology related to electrical activity within the heart. The heart is made up of four chambers: two upper chambers called atria and two lower chambers called ventricles. The heart typically is described as having two sides, the right and left. The right atrium receives deoxygenated blood from the vena cavae and directs the blood into the right ventricle.
-Right ventricular contraction ejects blood into the pulmonary artery, which carries blood to the lungs for oxygenation. The oxygenated blood returns to the left atrium of the heart via the pulmonary vein, where it is directed into the left ventricle. Left ventricle contraction ejects blood into the aorta, which branches off into the systemic circulation. Since the left side of the heart pumps blood throughout the entire body, it normally has a significantly larger muscle mass than the right side
Types of Heart Cells
-Pacemaker cells: specialized cells that have a high degree of automaticity and provide the electrical power for the heart
-Conducting cells: Cells that conduct the electrical impulse throughout the heart -Myocardial cells: Cells that contract in response to electrical stimuli and pump the blood
Electrical Activity of Heart
-Myocardial contractions occur because of electrical stimulation. For blood to move effectively it must be coordinated, and the electrical conduction system which is made up of pacemaker and conducting cells are responsible for that coordination
Causes and Manifestations of Dysrhythmias
-Disturbances in cardiac conditions are called dysrhythmias. Dysrhythmias can occur even in healthy hearts. Often, minor dysrhythmias produce no symptoms and resolve without any treatment. More serious dysrhtymias indicate significant acute or chronic heart disease
-When serious dysrhythmias occur, medication or electrical therapy often is required to increase or decrease the ventricular rate or to suppress an irritable area within the myocardium. Occasionally surgical intervention or thrombolytic therapy is needed to prevent the progression of injury or infarct, thereby salvaging viable tissue
-the drug adenosine is given to reset the heart reset the heart rate
-The application and improve delivery of oxygen often is a key factor in reducing or eliminating cardiac irritability. Causes of dysrhythmias include the following
-Hypoxia: Hypoxia results from inadequate delivery of oxygen to mycorardum and may be referred to as ischemia. Inadequate delivery may be caused by reducing martial oxygen levels, reduced hemoglobin levels, reduced arterial oxygen levels, reduced hemoglobin levels, reduced perfusion levels, or a combo of such factors
-Ischemia can lead to myocardial injury and infarction. Myocardial cells deprived of oxygen do not conduct nor contract well
-Sympathetic stimulation: Physical or emotional stress from fear or anxiety and conditions, such as hyperthyroidism and CHF, can elicit dysrthmias.Sypathietic stimulation can also result in cardiac ischemia caused by an increased workload on the myocardium without concurrent increase blood flow such as on the case of diseased coronary arteries
Causes and Manifestations of Dysrhythmias
-Drugs:
-Drugs: many prescribed medications taken in non therapeutic range or in the presence of inadequate biotransformation or clearance may produce dysrhythmias. Illegal use of sympathomimetic agents, such as cocaine or meth (Ritalin), may cause myocardial irritability and even infarction.
Causes and Manifestations of Dysrhythmias
-Electrolyte imbalances:
-Electrolyte imbalances: Electrical activity in the heart results from the exchange of electrolytes within the cardiac tissue. As a result, abnormal serum concentrations of electrolytes, such as potassium, magnesium, and calcium, can cause dysrhythmias.
Causes and Manifestations of Dysrhythmias
-Rate:
Rhymes that are too slow or too fast result in inadequate cardiac output. Cardiac output is a product of strike volume and cardiac rate. Stroke volume is the volume of blood pumped by one ventricle during one beat. Therefore, if the heart rate is too slow and the stroke volume is not increased proportionally, the cardiac output will be reduced. On the other hand, if the heart rate is too fast, the ventricles do not have enough time to fill with blood and stroke volume may be significantly reduced, resulting in poor cardiac output.
Causes and Manifestations of Dysrhythmias
-Stretch:
-Stretch: Atrial or ventricular hypertrophy can produce dysrhythmias. Hypertrophy may be a result of a genetic disorder or a consequence of increased workload on the myocardium (e.g. Chronic, uncontrolled high blood pressure)
depolarization
-The spread of electrical stimuli throughout the heart causes depolarization of the myocardial cells. Depolarization occurs when a polarized cell is stimulated.Polarized cells carry an electrical charge on their surface, the inside of the cell is more negatively charged than the outside of the cell. The sudden loss of negative charge within the cell is called depolarization, which is a result of potassium moving out of the cell and sodium moving into the cell
repolarization
-The return of the negative electrical charge is called repolarization (fig 11-4) and is a result of potassium moving back into the cell and sodium moving out of the cell. This produces waves of electrical activity that travel back and forth across the heart
waves of electrical activity
-These waves of electrical activity are represented by waves detected by the ECG electrodes. The magnitude or amplitude of each wave is determined by voltage generated by depolarization of a particular portion of the heart.
Basic ECG Waves
P wave
-Depolarization of the atria creates the initial wave of electrical activity detected on the ECG tracing, known as the P wave. Because the atrai usually are small, the atria generate less voltage than the ventricles and resulting P wave is small
-Repolarization of the atria is not seen on the ECG because it usually is obscured by the simultaneous depolarization of the ventricles -These waves of electrical activity are represented by waves detected by the ECG electrodes. The magnitude or amplitude of each wave is determined by voltage generated by depolarization of a particular portion of the heart.
Basic ECG Waves
QRS complex
-Depolarization of the ventricles is represented by the QRS complex. Because the ventricular muscle mass is larger than the atria and produces more voltage during depolarization, the QRS complex is normally taller than the P wave in most cases (see fig 11-5) Ventricular repolarization is seen as the T wave. The T wave is normally upright and rounded.
Basic ECG Waves
U wave
-Just after the T wave but before the next P wave, a small deflection known as the U wave is sometimes seen . the U wave is thought to represent the final [phase of ventricular repolarization. In most cases the U wave is not seen. The clinical significance of its presence or absence is not know
Basic ECG Waves
-QRS complexes usually consist of several distinct waves,
-QRS complexes usually consist of several distinct waves, each of which has a letter assigned to it as a label. This labeling system is needed because the precise configuration of the QRS complex can vary from one lead to the next and from one patient to the next. Top establish a standardized labeling system, several guidelines have been developed. If the first deflection of the QRS complex is downward (neg) it is labeled a Q wave. The initial upward (positive) deflection is called an R wave.
S wave of QRS
-The first negative deflection following an R wave is called an S wave (Figure 11-6) If the QRS complex has a second positive deflection, it is labeled R (R prime), and if a second S wave is also present it is called S (S prime). A negative deflection can be called a Q wave only if it is the first wave of the complex. In clinical practice, each ventricular depolarization complex is called a QRS complex whether it has all three waves or not.
EKG Paper
• The electrical activity of the heart is recorded on paper that has gridlike boxes with light and dark lines running horizontally and vertically (Figure 11-7). The light lines circumscribe small boxes (1 x 1 mm) and the dark lines circumscribe larger boxes (5 × 5 mm).
EKG Paper mV
-On The vertical axis, voltage, or amplitude, of the ECG waves is measured. The exact voltage of any ECG wave can be measured because the electrocardiogram is standardized so that 1 mV produces a deflection 10 mm in amplitude. Therefore, the standard for most ECG recordings is 1 mV= 10mm. Each small square represents 1 mm.
measure amplitude
-To measure the amplitude of a specific wave, the isoelectric baseline must be identified. This is the flat line seen just before the P wave or right after the T or U wave. Any movement of the ECG stylus above the line is considered positive, any downward movement is considered negative.To measure the degree of positive or negative amplitude of a specific wave, the isoelectric line is used as a reference point marking zero voltage.
-R waves are measured from isoelectric lines to the top of the R wave. Q and S waves are measured from the isoelectric line to the bottom of the wave. P waves can be either positive or negative and are also measured from the isoelectric line to the top (if positive) or bottom ( if negative) of the wave.
