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125 Cards in this Set
- Front
- Back
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What is atrial kick?
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contraction of the atria during the final phase of diastole to complete ventricular filling. Adds the last 30% to ventricular capacity.
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In what types of rhythms is atrial kick lost?
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It's lost in the type of arrhythmias that have asynchronous contraction between the atria and ventricles. Loss of atrial kick decreases CO and may lead to HF.
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What is heart sound S1 caused by?
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The closure of the AV valves causes this heart sound. At the end of diastole, the increased pressure in the ventricles, compared with the lessening pressure in the atria, helps close the AV Valves.
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What is heart sound S2 caused by?
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The closure of the semilunar valuves (aortic and pulmonic) causes this sound. They are opened during ventricular systole and they close as the pressure in the outflow arteries exceeds that of the ventricles.
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Where does the right ventricle receive venous blood from?
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This ventricle receives blood from the superior vena cava (from head, upper extremities and chest wall), inferior vena cava (from the trunk, abdominal organs, lower extremities), and the coronary sinus (from the myocardium).
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Whar areas does the right coronary artery supply blood to?
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It supplies blood to the right atrium, the right ventricle, the inferior wall of the left ventricle, the posterior one-third of the interventricular septum, and (in most people) the posterior wall of the left ventricle. In 55% of the population, it supplies the SA and AV nodes and the bundle of His and hte posterior fascicle of left bundle branch.
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What vessels does the left main coronary artery branch into?
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It branches into the left anterior descending and left circumflex arteries.
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What areas of the heart does the Left Anterior Descending Artery supply?
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It supplies blood to the anterior lateral wall of the left ventricle, the anterior two-thirds of the interventricular septum, the majority of the right bundle branch, the anterior fascicle of the left bundle branch, and a portion of the posterior fascicle of the left bundle branch.
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What areas of the heart does the Left Circunflex Artery supply?
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It supplies blood to the left atrium, the anterior lateral and posterior lateral walls of the left ventricle, and in 10% of the population, the posterior wall of the left ventricle. It supplies the SA node in 45% of the population, and the AV node and bundle of His in 10% of the population.
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What is considered the dominant coronary artery?
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The coronary artery that gives rise to the PDA or posterior descending artery. It's commonly the terminal branch of the right coronary artery. In these cases, the patient has a right-dominant system (85-90% of population)
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What coronary artery is of wider caliber and perfuses the largest portion of the myocardium?
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The left coronary artery. If a patient's posterior descending branch is a continuation of the left circumflex artery, the patient has a left-dominant system.
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Collateral vessels/collateral circulation
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The extensive network of small arteries that provide the potential for cross flow between coronary arteries. It exists at birth and grows in size along with the rest of the coronary circulation. If blockage occurs in major artery, the collateral vessels enlarge and provide additional bloodflow.
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How are nerve impulses carried from the sensory receptors to the brain?
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They are carried via the afferent or sensory pathways to the medulla.
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How does the sympathetic (accelerator) nervous system innervate the heart?
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It innervates the heart through nerve fibers arising from the thoracic segment of the spinal cord.
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What does stimulation of the sympathetic (accelerator) nervous system result in in terms of effect on the heart?
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it results in the release of norepinephrine, which increases HR, speecs conduction through the AV node, and increases the force of ventricular contraction.
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How does the parasympathetic (inhibitory) nervous system innervate the heart?
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It innervates the heart through vagal nerve fibers, which originate in the medulla oblongata.
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What does stimulation of the parasympathetic (inhibitory) nervous system result in in terms of effect on the heart?
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It results in the release of acetylcholine, which decreases HR, slows conduction through the AV node, and causes a small decrease in the force of ventricular contraction. There is minimal parasympathetic innervation of the ventricles.
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What areas, innervated by thoracic segments T1 through T4, are common areas for referred cardiac pain?
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The areas are the skin or skeletal muscles sharing nerve supplies from T1-T4, such as epigastric area, anterior chest wall, sternum, jaw, shoulders, scapula, arms, wrists, and hands.
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What are pacemaker cells?
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They are specialized cells of the electrical conduction system responsible for generating electrical impulses
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What are myocardial cells?
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They are the working or mechanical cells of heart. They consist of contractile protein filaments called actin and myosin. When stimulated, the filaments shorten and slide together, causing myocardial cell contraction.
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What are the four primary cell characteristics of cardiac cells?
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Automaticity, Excitability, Contractility, and Conductivity.
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What is automaticity?
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The ability of pacemaker cells to generate their own electrical impulses spontaneously. This ability is specific to the pacemaker cells.
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What is excitability?
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The ability of cardiac cells to respond to an impulse. This ability is shared by all cardiac cells.
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What is conductivity?
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the ability of cardiac cells to receive an electrical impulse and transmit it to other cardiac cells. This characteristic is shared by all cardiac cells.
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What is contractility?
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The ability of myocardial cells to shorten and cause muscle contraction. This characteristic is specific to myocardial cells.
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Factors that control distribution of ions: Membrane Channels
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pores or openings through which ions pass back and forth between extracellular and interacellular spaces. Some are always ope, some are open or closed, others are selective allowing only one kind of ion through and excluding all others. These pores open and close in response to stimulus (chemical, mechanical, or electrical)
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Factors that control distribution of ions: Concentration Gradient
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particles in solution move, or diffuse from areas of higher concentration to areas of lower concentration. If particles are uncharged, the movement proceeds until they're uniformly distributed in the solution.
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Factors that control distribution of ions: Electrical Gradient
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Like charges repel, opposites attract.
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Factors that control distribution of ions: Sodium - potassium pump
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The mechanism that actively transports ions across the cell membrane against its electrochemical gradient. Moves the sodium out of the cell, and the potassium back into the cell, causing the cell to again become more negative than positive (repolarize).
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Electrolyte
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a substance whose molecules dissociate into charged particles (ions) when placed in water, producing positively and negatively charged ions. Cation = positive ion. Anion - negative ion.
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Depolarization
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Generated by pacemaker cells, a period of stimulation of the cardiac cell. At this point, the inside of the cell becomes more positive than negative. This process proceeds from the innermost heart layer to the outermost heart layer. Depolarization of one cardiac cell acts as a stimulus on adjacent cells, causing them to depolarize. Muscle contraction follows depolarizaton.
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Is depolarization the same as muscle contraction?
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No, muscle contraction follows depolarization. Depolarization is an electrical event that results in the mechanical event of muscle contraction.
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Repolarization
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Period of rest, or cardiac cell recovery when it returns to its polarized state (rested). Repolarization proceeds from the outermost layer of the heart to the innermost layer.
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What does the ECG illustrate?
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Propagation of the electrical impulses from cell to cell produces an electric current that can be detected by skin electrodes and recorded as waves or deflections onto graph paper.
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SA Node
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Located in the wall of the upper right atrium near the inlet of the superior vena cava, this is the primary pacemaker of the heart and posesses the highest level of automaticity (higher inherent firing rate). It generates 60-100 BPM.
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Bachmann's bundle
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The interatrial tract, or tract between the right and left atria.
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Internodal Tracts
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The electric impulse travels from the SA nodethrough the right atria via these tracts. This causes atrial depolarization and contraction of the atria (atrial kick). The impulses then travels to the AV node.
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AV Node
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Secondary pacemaker, at 40-60 BPM. Takes over if SA node fails to generate electric impulses, or if their conduction is blocked. It is located in the lwoer gith atrium near the interatrial septum, and relays the electric impulses from the atria to the ventricles. It is the only normal conduction pathway between the atria and ventricles.
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What are the three main functions of the AV Node?
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1 - DELAY - to slow conduction of the electric impulse through the AV node, allowing time for the atria to contract and empty contents into ventricles (atrial kick) before ventricles contract. The delay in the AV node is represented on the ECG tracing as the flat line of the PR Interval. 2 - BACKUP - pacemaker for SA node, at 40-60 BPM. 3 - BLOCKs some impulses from being conducted to ventricles when atrial rate is rapid, protecting ventricles from dangerously fast rates.
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Bundle of His
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Accepts impulse from AV node. Divides into two important conducting pathways, the right bundle branch and the left bundle branch.
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Right and Left Bundle Branches
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The right bundle branch conducts electric impulse to right ventricle. The left divides into two parts, the anterior fascicle that carries electric impulse to anterior wall of left ventricle, and the posterior fascicle, which carries electric impulse to posterior wall of left ventricle. Both branches end in a network of conduction fibers, Purkinje fibers.
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Purkinje Fibers
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These conduction fibers terminate the bundle branches and become continuous with the ventricular muscle mass. They carry the electrical impulse directly to the contractile cells of the ventricle. Conduction of electric impulse through this system is the fastest of any tissue in the conduction system.
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At what rate do the ventricular pacemakers fire?
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20-40 BPM. The farther away from the SA node, the slower the rate.
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What are the three phases of refractoriness?
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Absolute refractory period, relative refractory period, supernormal period
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Absolute refractory period
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During this period, cells can't respond to stimulus. It extends from onset of QRS complex to peak of T wave. Depolarized cardiac cells are in the process of repolarizing, and aren't back to threshold potential yet
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Threshold potential
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the level at which a cell must be repolarized before it can be depolarized again.
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Relative Refractory Period or Vulnerable Period of Repolarization
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During this period, cardiac cells have repolarized sufficiently to respond to a strong stimulus. It begins at peak of T wave and ends with end of T wave.
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Why is the relative refractroy period also called the vulnerable period of repolarization?
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It's is so called because a strong stimulus occuring during this time may usurp the primary pacemaker of the heart (SA Node, usually) and take over pacemaker control. (i.e. PVC causing ventricular tachycardia)
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Supernormal period
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During this period (at the end of the T wave, just before comple repolarization) the cardiac cells will respond to a weaker than normal stimulus.
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What do the horizontal lines on the ECG graph paper measure?
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They maesure duration of waveforms in secnods of time. Each small square represents 0.04 seconds. Each large square (comprised of 5 small squares) represents 0.20 seconds. Five large squares = 1 second.
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What do the vertical lines on the ECG graph paper measure?
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They measure the voltage or amplitude of waveform in mm. Each small square measured vertically represents 1 mm in height.
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What are the 3 basic waveforms on the ECG?
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P wave, QRS complex, T wave
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What segments and intervals are on the ECG?
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Between the waveforms are the following segments and intervals: PR interval (which includes the PR segment), the ST segment, the QT interval.
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What does the P Wave depict or represent on the ECG?
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It represents atrial dePolarization. The sPread of the imPulse from SA node throughout the atria.
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What is the length of a normal P wave?
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A normal P wave is 0.1 second. less than 2.5 small squares high or wide
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What is the amplitude of the normal P wave?
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The amplitude shouldn't exceed 2.5 mm
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What lead would the P wave be in?
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Lead II.
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What does a normal P wave indicate?
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It indicates that the electric impuse responsible for P wave originated in the SA node and that normal depolarization of both atria have occurred.
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What does more than one P wave before a QRS complex indicate?
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It indicates a conduction disturbance such as occurs in second and third degree heart block.
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What is happening mechanically when the P wave occurs?
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The atrial depolarization coincides with the contraction of the atria.
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What are the characteristics of a normal P wave?
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smoth and round, positive in lead II, no more than 2.5 mm in height, no more than 0.10 seconds in width, with one P wave to each QRS complex.
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What might an abnormal P wave be caused by?
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It'd be caused by an abnormal sinus P wave or an ectopic P wave.
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When does an abnormal sinus P wave occur?
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When electrical impulse leaves the SA node and travels through abnormal atrial tissue, resulting in P waves of greater amplitude or width. Tall Peaked P wave can be enlarged right atrium, or RAE (also called p pulmonale because it's common in severe pulmonary disease such as COPD, status asthmaticus, acute pulm embolism, acute pulm edema. Also common with congenital heart disease). Enlarged LEFT atrium produces wide, notched P wave. P Mitrate for Left Atrial Enlargement LAE because rheumatic mitral disease. Also from mitral and aortic valve disease, HTN, CAD, Cardiomyopathies.
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When does an ectopic P wave occur?
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It's a P wave that arises from a site other than SA nodes. They're abnormal in size, shape, direction (small and pointed or inverted) or absent.
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What would a tall, peaked abnormal P wave be from?
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Abnormal sinus P wave from RAE
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What would a wide, notched abnormal P wave be from?
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Abnormal sinus P wave from LAE
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What would a small & pointed, inverted, or absent P wave be from?
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Ectopic P waves
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How is the PR interval measured?
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It's measured from the beginning of the P wave as it leaves baseline, to the beginning of the QRS complex.
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What does the PR Interval represent?
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It represents time from the onset of atrial dePolaRization to onset of ventricular dePolaRization it encompasses the P wave and the PR segment.
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What is the length of a normal PR Interval?
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Normal PR Interval is 0.12 – 0.20 seconds (three to five small boxes on ECG graph paper)
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What does a normal PR interval indicate?
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It indicates that the period of time from the onset of atrial depolarization 9P wave) to onset of ventricular depolarization (QRS Complex) is normal.
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Why would a PR interval be shorter than normal?
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If electric impulse is conducted from atria to ventricles through an accessory conduction pathway that bypasses AV node, depolarizing ventricles earlier than usual (WPW (Wolff-Parkison-White) syndrome is an example). Short PR interval also might occur if impulse originates in an ectopic pacemaker site in the AV node.
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Why would a PR interval be longer than normal?
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It'd be longer if electric impulse is abnormally delayed traveling throught he AV Node, such as in first-degree AV block and hypothyroidism, or from drugs like digitalis, beta-blockers, or calcium-channel blockers. It's also associated with aging and may be first sign of conduction system disease.
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What is the PR Segment and what is it used for?
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It is part of the PR interval, a short isoelectric line between the end of the P wave and the beginning of the QRS complex. It's used as a baseline to evaluate elevation or depression of the ST segment.
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What does the QRS Complex represent?
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It represents ventricular depolarizaton, or spread of the impulse through the ventricles (conduction of bundle of HIS). NOTE: it is a larger complex, representing the larger area of the heart, the ventricles.
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How is the QRS complex measured?
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it's measured from the beginning of the QRS complex (as the first wave of the complex leaves baseline) to the end of the QRS complex (when last wave of complex begins to level out into the ST segment…wherever that straight line begins, whether above or below baseline).
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What is the J point?
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The point where the QRS complex ends.
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How many wave deflections are in a normal QRS complex?
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Three - the Q wave (negative waveform before the R), the R wave (a positive waveform), and the S wave (a negative waveform after the R). Sometimes all 3 are not present.
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What is the length of a normal QRS Complex?
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Normal QRS is 0.10 or less (two and a half squares on the ECG graph paper)
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What is an abnormal QRS like?
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An abnormal one would be wide, with duration of 0.12 seconds or more
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What would an entirely negative complex with no R wave be called?
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A QS complex. R waves are always positive, so if it is not positive at all, it's a QS Complex.
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What is a second R wave called?
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It's called R prime and is written R'
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What is a seond S wave called?
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It's called S prime and is written S'
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What is the criteria for a wave to be labeled separately?
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It must cross the baseline.
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What is the name for a wave that changes direction but doesn't cross the baseline?
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it's called a notch.
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What is the amplitude of a normal R wave?
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2-15 mm or squares high.
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What do capital letters or lowercase letters used to designate?
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Capitals are for waves or large amplitude (5 mm or more) and lowercase leters for small amplitude (less than 5 mm).
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What does a normal QRS complex indicate?
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It indicates that the electric impulse has been conducted normally from the bundle of HIS to the purkinje network through the right and left bundle branches and that normal depolarization of the both ventricles have occurred.
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What is the largest complex on an ECG?
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The QRS complex is the largest complex.
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What would cause an abnormally wide QRS complex?
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1 - Bundle branch block. 2 - early arrival of impulse (i.e. premature beats) at bundle branches before repolarization complete, allowing early depolarization of ventricles resulting in aberrant ventricular conduction. 3 - abnormal accessory conduction pathway bypasses AV node and allows early depolarization of ventricles and aberrant ventricular conduction. 4 - elecric impulse from ectopic site in ventricles
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How is the ST segment measured?
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It starts with the end of the QRS complex (J point) and ends with the onset of the T wave.
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What does the ST Segment represent?
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It represents the end of ventricular depolarization and beginning of ventricular repolarization (think "Stop vent depol Start vent repol")
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What does a normal ST segment look like? What are deviations?
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Normal ST segment should be flat. It's elevated (may bei horizontal, convex, concave) if above baseline (a line established by PR segment), and depressed (may be horizongal, downsloping, sagging) if below. To determine the degree of displacement, measure at a point 0.04 second (1 small squaer) past the J point. Displacement is significant if more than 1 mm (1 small square) and is seen in two or more leads facing same area of heart.
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What does an elevated ST segment signify?
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It's a sign of myocardial injury like acute MI. Could also be from coronary vasospasm (Prinzmetal's angina) pericarditis, ventricular aneurysm, hyperkalemia, early repolarization (normal variant, seen in healthy people although it looks like MI or pericarditis)
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What does a depressed ST segment signify?
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It's an ECG sign of myocardial ischemia. Also, left and right ventricular hypertrophy, left and right bundle-branch block, hypokalemia, drug effects (i.e. digitalis - which causes sagging ST which looks scooped out).
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What does the T wave represent?
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It represents the latter phase of venTricular repolarizaTion.
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When does a normal T wave begin and end?
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It starts as the deflection gradually slopes upward from the ST segmentand ends when the waveform returns to baseline.
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What are the characteristics of a normal T wave?
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They're rounded, asymmetrical (peak is closer to the end than to the beginning), positive in lead II, and amplitude less than 5 mm. It always follows the QRS complex, because repolarization follows depolarization.
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What do abnormal T waves look like?
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They may be symmetrical, may be abnormally tall, low, flattened, biphasic, or inverted.
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What would cause an abnormal T wave?
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Causes are myocardial ischemia, myocardial infarction, pericarditis, hyperkalemia, ventricular enlargement, bundle-branch block, subarachnoid hemorrhage, and drugs like quinidine or procainamide.
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What does the U wave represent? Is it always present?
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It represents further repolarization of the ventricles. It is not always present.
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What does the QT Interval represent?
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It represents the time between onset of ventricular depolarization and the end of ventricular repolarization. So it's for both ventricular depolarization and repolarization (think both letters, both functions or "QT means re- and de-").
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What's the length of a normal QT interval?
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it varies with age, sex, and HR. As HR increases, it shortens. At HR decreases, it lengthens. It's measured more accurately if corrected for HR.
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How should the length of a QT interval compare to HR to be considered normal?
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Normal QT interval should be less than half distance between two consecutive R waves when rhythm is regular for at least two cardiac cycles. Should be made in a lead where T wave is most prominent and doesn't include U wave.
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What are the steps to determine of QT interval is normal or abnormal according to a person's HR?
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1 - count nmber of small boxes between two consecutive R waves and divide by two. 2 - Count number of small boxes in QT interval. 3 - compare difference. If QT interval measures less than half RR interval it's probably normal. If same as half, it's borderline. If over half, prolonged. 4 - multiply number of small squares in QT interval by 0.04 seconds to determine the duration of QT interval.
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What does a normal QT interval indicate?
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It indicates that ventricular depolarization and repolarization have occurred within a normal amount of time.
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What does a short QT interval indicate?
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It represents an increase in rate of repolarization of ventricles, and is insignificant.
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What does a prolonged QT interval indicate?
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It represents a delay in ventricular repolarization. The refractory (vulnerable) period is longer, so it allows more time for an ectopic focus to take control. It puts ventricles at risk for life threatening dysrhythmias like torsades de pointes.
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What would cause a prolonged QT interval?
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it could be caused by electrolyte deficiencies (hypokalemia, hypomagnesemia, hypocalcemia), hypothermia, bradyarrhythmias, liquid protein diets, myocardial ischemia, antiarrhythmics, psychotropic agents (phenothiazines, tricyclic antidepressants), and heredity. It can also occur without known cause (idiopathic)
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What is a U wave?
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small rounded wave deflection sometimes seen after T wave. Last phase of ventricular repolarization. Positive in lead II, less than 2 mm in amplitude (always smaller than preceeding T wave). Can best be seen when heart is slow
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What are causes of abnormally large U waves?
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Causes like hypokalemia, cardiomyopathy, Left ventricular enlargement, some drugs (digitalis, quinidine, procainamide). Also indicative of delayed ventricular repolarization and (liked prolonged QT interval) predisposes individual to developing ventricular tachycardia called torsades de pointes.
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What are the five steps of analyzing ECG Strips?
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1 - Determine regularity of R waves; 2 Calculate the Heart Rate; 3 - Identify and examine P-Waves; 4 measure P-R Interval; 5- Measure QRS Complex
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What does one cardiac cycle consist of?
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One heartbeat, or one PQRST sequence. It represents a sequence of atrial contraction and relaxation followed by ventricular contraction and relaxation, and repeates over and over again, 100,000 times per day.
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How can regularity of the cardiac rhythm be assessed?
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Measure from one R wave to the next R wave, called the R-R interval.
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What is an R-R interval?
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the amount of time from one heartbeat to the next.
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What is an isoelectric line?
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The flat line, or baseline in the ECG during which electrical activity is absent.
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Positive or upright deflection
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Any waveform above the isoelectric line. An electric current flowing towards a positive pole will produce this deflection.
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Negative or downward deflection
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Any waveform below the isoelectric line (i.e. the Q going downward). An electric current traveling toward the negative pole causes this deflection.
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Biphasic deflection
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A deflection having both a positive and and negative components (like the whole P wave, the whole QRS complex, and the whole T-wave deflection). Current flowing away from the poles causes these deflections. These deflections may be equally positive and negative, more negetave than positive, or more positive than negative....depending on the angle of current flow to the pole. This is why QRS complexes can have different shapes and sizes.
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What does the size of the wave deflection depend on?
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It depends on the magnitude of the electric current flowing toward the individual pole. The magnitude is determined by how much voltage is generated by depolariation of a particular portion of the heart. For example, the QRS complex is normally larger than the P wave because depolarization of the larger muscle mass of the ventricles generates more voltage than does depolarization of the smaller atrial muscle mass.
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Step 1 - Determining regularity (rhythm) of the R waves?
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Measure from R wave to R wave. If it varies by 0.12 seconds (3 square) or more, it's irregular. If it varies less or not at all, it's regular.
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Step 2 - Calculate HR.
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Calculates ventricular rate. Look at 6 second strip (30 boxes). Rapid rate calculation - count # of R waves in six second strip and multiply by 10, or the number of R waves in 3 second strep and multiply by 20. Can be used with regular and irregular rhythms. Precise rate calculation - Count number of small squares between two consecutive R waves and divide into 1,500 (the number of small squares in a one minute strip). Don't use precise method for irregular rhythms.
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Step 3 - Identify and examine P waves
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One P wave should precede each QRS complex. All P waves should be pretty much identical in size, shape, position.
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Step 4 - Measure the PR interval
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Measure from beginning of P wave as it leaves baseline to beginning of QRS complex. Count umber of squares in interval and multiply by 0.04 seconds.
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Step 5 - Measure QRS Complex
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Measure from beginning of QRS complex as it leaves basline until end of QRS complex when ST segment begins. Count squares, multiply by 0.04 seconds.
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