© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 1 Fast & Easy ECGs, 2E Dysrhythmias Fast & Easy ECGs, 2nd E – A Self- Paced Learning Program 1010

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 2 Fast & Easy ECGs, 2E Origination and Conduction of Heartbeat Each heartbeat arises as an electrical impulse from the SA node It then spreads across the atria depolarizing the tissue and causing both atria to contract The impulse then activates the AV node but it is slightly delayed there allowing the atria to finish contracting and pushing any remaining blood from their chambers into the ventricles The impulse then spreads through both ventricles via the Bundle of His, right and left bundle branches, and the Purkinje fibers, causing a synchronized contraction of the ventricles and thus, the pulse

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 3 Fast & Easy ECGs, 2E SA Node Depolarization Through the property of automaticity, the heart’s pacemaker cells spontaneously depolarize They have what can be described as an unstable resting membrane potential

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 4 Fast & Easy ECGs, 2E SA Node Depolarization Because the SA node reaches it’s action potential more quickly than the other pacemaker cells, it is the heart’s primary pacemaker

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 5 Fast & Easy ECGs, 2E Nonpacemaker Myocyte Depolarization Phase 4 – In the polarized state, nonpacemaker myocytes have a resting membrane potential of -80 to -90 mV which remains stable until the cell is stimulated

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 6 Fast & Easy ECGs, 2E Nonpacemaker Myocyte Depolarization Phase 0 – Depolarization begins once the myocyte receives an impulse from a neighboring cell – Na+ quickly enters the cells through fast Na+ channels, some Ca++ enters the cells through slow Ca++ channels and the K+ channels close – With all this Na+ and Ca++ entering the cell, it becomes more positively charged – The charge overshoots neutral, rising to about 130 mV – When a certain level is reached, depolarization of the entire cell occurs

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 7 Fast & Easy ECGs, 2E Nonpacemaker Myocyte Depolarization Phase 1 – Voltage-gated Na+ channels close, and a small number of the K+ channels open stopping the fast inflow of Na+ and allowing some K+ to move out of the cell – Chloride (Cl-) ions enter the cell – These ion movements lower the positive charge inside the cell somewhat

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 8 Fast & Easy ECGs, 2E Nonpacemaker Myocyte Depolarization Phase 2 – Ca++ enters the cell through voltage-gated L-type Ca++ channels, prolonging the depolarization – This movement of Ca++ into the cell counteracts the potential change caused by the movement of K+ out of the cell – Ca++ then reacts with myosin and actin causing the cell to contract I I

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 9 Fast & Easy ECGs, 2E Nonpacemaker Myocyte Depolarization Phase 3 – Ca++ channels close and many K+ channels open allowing a rapid outflow of K+, causing the cell interior to become more negatively charged – Ca++ and Na+ are pulled out of the cell interior by Na+ and Ca++ pumps helping to achieve and maintain the very negative resting membrane potential of the myocyte I I

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10 Fast & Easy ECGs, 2E Absolute Refractory Period During this period, no stimulus, no matter how strong, will depolarize the cell – Helps assure the rhythmicity of the heartbeat – Assures that after contraction, relaxation is nearly complete before another action potential can be initiated – Prevents spasm-producing (tetanic) contractions in the cardiac muscle This period includes Phases 0, 1, 2, and part of phase 3

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 11 Fast & Easy ECGs, 2E Relative Refractory Period During the later phase of repolarization a sufficiently strong stimulus will depolarize the myocardium

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 12 Fast & Easy ECGs, 2E Dysrhythmias Refers to any ECG rhythm that differs from normal sinus rhythm Heartbeat may be slower or faster than normal, irregular, or conduction through the heart may be delayed or blocked

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 13 Fast & Easy ECGs, 2E Effects of Dysrhythmias Some are of little consequence and simply annoying while others are life-threatening medical emergencies that can lead to cardiac arrest and sudden death

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 14 Fast & Easy ECGs, 2E Effects of Dysrhythmias Most common symptom is palpitations, an abnormal sensation felt with the heartbeat

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 15 Fast & Easy ECGs, 2E Effects of Dysrhythmias Symptoms such as lightheadedness, dizziness, fainting, chest pain, shortness of breath, sweatiness, and/or pallor may be seen in dysrhythmias that cause decreased cardiac output We refer to this as being symptomatic

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 16 Fast & Easy ECGs, 2E Effects of Dysrhythmias Some dysrhythmias slow the heart rate decreasing cardiac output Others decrease the stroke volume by making the heart beat too fast (which decreases cardiac output by not allowing the heart to fill properly)

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 17 Fast & Easy ECGs, 2E Effects of Dysrhythmias Cardiac output can also be decreased when the atria don’t contract properly or contract at all (eliminating the atrial kick which normally pushes blood into the ventricles

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 18 Fast & Easy ECGs, 2E Dysrhythmias Sometimes the first clinical manifestation of a cardiac dysrhythmia is sudden death

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 19 Fast & Easy ECGs, 2E Types of Dysrhythmias Include: – bradycardia – tachycardia – early (premature) beats – dropped beats, or QRS complexes – irregular rhythms

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 20 Fast & Easy ECGs, 2E Bradycardia Heart rate less than 60 beats per minute Can occur for many reasons and may or may not have an adverse affect on cardiac output In the extreme, it can lead to severe reductions in cardiac output and eventually deteriorate into asystole

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 21 Fast & Easy ECGs, 2E Bradycardia Can arise from the SA node – Sometimes this is normal – Can also be caused by increased parasympathetic (vagal) tone or a variety of medical conditions Can be brought about by failure of the SA node – Escape pacemaker should arise from the AV node or ventricles but is likely to result in bradycardia Can also be caused by AV heart block

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 22 Fast & Easy ECGs, 2E Bradycardia Can also be seen when the atria repeatedly or chaotically depolarize and bombard the AV node so rapidly that not all the impulses are conducted through to the ventricles – If the number of atrial impulses reaching the ventricles falls to less than normal, it results in a slower than normal ventricular rate

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 23 Fast & Easy ECGs, 2E Tachycardia Heart rate greater than 100 beats per minute Has many causes Leads to increased myocardial oxygen consumption Extremely fast rates can have an adverse affect on cardiac output When it arises from the ventricles it may lead to a chaotic quivering of the ventricles called ventricular fibrillation

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 24 Fast & Easy ECGs, 2E Tachycardia Is referred to as one of five types: – narrow QRS complex regular rhythms, – wide QRS complex regular rhythms, – narrow QRS complex irregular rhythms, – wide QRS complex irregular rhythms, – wide QRS complexes of unknown origin. Being able to differentiate between the five types of tachycardia will help determine what type of treatment should be employed

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 25 Fast & Easy ECGs, 2E Early Beats Fire early, before the SA node has a chance to initiate the impulse Can arise from anywhere in the heart, including the atria, AV junction, or ventricles The R-R interval between the normal complex and premature complex is shorter than the interval between two normal complexes Frequent premature beats may progress to atrial, junctional, or ventricular tachycardia or deteriorate into ventricular fibrillation I I

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 26 Fast & Easy ECGs, 2E Dropped Beats Dropped beats occur when the SA node fails to initiate an impulse resulting in a pause in the ECG rhythm Usually, the SA node recovers and fires another impulse If the SA node fails to fire, then an escape pacemaker from the atria, AV junction, or ventricles initiates an impulse I I

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 27 Fast & Easy ECGs, 2E Dropped Beats Dropped QRS complexes can occur from a partial or intermittent block at the AV junction Some impulses originating from the SA node fail to conduct to the ventricles, resulting in one or more dropped ventricular beats This is seen as more P waves than QRS complexes and R-R intervals that are longer wherever there is a dropped ventricular beat Dropped QRS complexes can also occur when a premature beat arises from the atria but fails to conduct to the ventricles

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 28 Fast & Easy ECGs, 2E Irregularity Is caused by some type of dysrhythmia including: – early beats and dropped beats – dysrhythmias that speed up and slow down in a cyclical manner – those that originate from more than one site (sometimes from many sites) – some types of AV heart block

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 29 Fast & Easy ECGs, 2E Causes and Mechanisms of Dysrhythmias Include – increased parasympathetic tone – myocardial hypoxia, injury and infarction – increased automaticity – reentry – triggered beats – proarrhythmia

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 30 Fast & Easy ECGs, 2E Increased Parasympathetic Tone Stimulation of the parasympathetic nervous system causes the heart rate to slow and impulse conduction through the AV node to be prolonged Can lead to bradycardia, sinus arrest and/or AV heart block

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 31 Fast & Easy ECGs, 2E Myocardial Hypoxia, Injury, and Infarction An oxygen deprived myocardium is extremely susceptible to dysrhythmias Pulmonary disorders that interfere with adequate intake of oxygen are major causes of dysrhythmias Damage to portions of the heart’s conduction system can result in blockage of impulse formation and/or conduction Sometimes myocarditis can precipitate dysrhythmias

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 32 Fast & Easy ECGs, 2E Increased Automaticity Results from stimulation of the sympathetic nervous system Causes the cells to spontaneously depolarize more quickly The resulting heart rhythm depends on where the impulse originates I I

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 33 Fast & Easy ECGs, 2E Increased Automaticity If it is the SA node, the rhythm remains normal but faster than 100 beats per minute If it is an ectopic focus, any number of dysrhythmias may ensue – May cause a single, occasional early beat or it can produce a sustained abnormal rhythm Sustained rhythms produced by an ectopic focus in the atria or atrioventricular junction are less dangerous than those that arise from the ventricles

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 34 Fast & Easy ECGs, 2E Causes of Increased Automaticity Emotional stress or physical exercise, caffeine, amphetamines, ischemia, hypoxia, atrial stretching or dilation hyperthyroidism, or a myriad of other medical conditions, such as hypovolemia, congestive heart failure, etc

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 35 Fast & Easy ECGs, 2E Reentry Occurs when an electrical impulse reenters a conduction pathway rather than moving from one end of the heart to the other and then terminating

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 36 Fast & Easy ECGs, 2E Reentry Some hearts have an accessory pathway located between either the right atrium and the right ventricle or the left atrium and the left ventricle – These accessory pathways allow electrical impulses to bypass the AV node and depolarize the ventricles Some hearts have a dual conduction pathway through the AV node Under the right circumstances, reentry can occur in both accessory pathways and dual conduction pathways through the AV node

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 37 Fast & Easy ECGs, 2E Reentry Depending on the timing, reentry can generate a sustained abnormal circuit rhythm Reentry circuits are responsible for a number of dysrhythmias, including atrial flutter, most paroxysmal supraventricular tachycardia, and ventricular tachycardia

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 38 Fast & Easy ECGs, 2E Reentry A unique form of reentry is referred to as fibrillation – Results when there are multiple micro-reentry circuits in the heart chambers and they are quivering due to chaotic electrical impulses Atrial fibrillation occurs in the atria Ventricular fibrillation occurs in the ventricles

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 39 Fast & Easy ECGs, 2E Triggered Beats Occur when problems at the level of the ion channels in individual heart cells lead to partial repolarization – Partial repolarization causes repetitive ectopic firing called triggered activity Depolarization produced by triggered activity is known as afterdepolarization and can bring about atrial or ventricular tachycardia Are relatively rare but can result from the action of antidysrhythmic drugs, cell injury, and other conditions

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 40 Fast & Easy ECGs, 2E Proarrhythmia Refers to the development of new or a more frequent occurrence of pre-existing dysrhythmias that are caused by antidysrhythmic therapy or drugs used to treat other conditions

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 41 Fast & Easy ECGs, 2E Dysrhythmias Can originate from the SA node, atria, AV junction, or ventricles and can occur due to AV heart block

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 42 Fast & Easy ECGs, 2E Identifying Dysrhythmias Examination of the ECG rhythm on the ECG monitor must be done in a systematic, organized way

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 43 Fast & Easy ECGs, 2E Lead II Is the most commonly used lead for identifying dysrhythmias Has an excellent view of normal conduction of the impulse through the heart

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 44 Fast & Easy ECGs, 2E Modified Chest Lead 1 (MCL 1 ) Is another lead used for continuous cardiac monitoring Place positive electrode in the fourth intercostal space in the right sternal border (same position as precordial lead V 1 ) I I

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 45 Fast & Easy ECGs, 2E Modified Chest Lead 1 (MCL 1 ) Is effective for monitoring the QRS complexes of dysrhythmias, P wave changes, AV bundle- branch defects, and premature ventricular beats Is helpful in differentiating between the different types of tachycardia (supraventricular versus ventricular)

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 46 Fast & Easy ECGs, 2E Treatment of Dysrhythmias Many dysrhythmias require no treatment as they are either benign or resolve on their own The method used to manage dysrhythmias depends on whether or not the patient is stable or unstable Patients who are symptomatic are considered unstable because symptoms indicate decreased cardiac output

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 47 Fast & Easy ECGs, 2E Treatment of Dysrhythmias Several treatment options are available to treat dysrhythmias and are employed on the basis of the mechanism or etiology of the dysrhythmia Commonly used treatments include physical maneuvers, electricity therapy, and the administration of certain medications

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 48 Fast & Easy ECGs, 2E Electrical Therapy Synchronized cardioversion Defibrillation Pacing

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 49 Fast & Easy ECGs, 2E Physical Maneuvers Vagal maneuvers

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 50 Fast & Easy ECGs, 2E Medications For slow heart rates, a drug that blocks the effects of the parasympathetic nervous system, such as atropine, may be initially used The bradycardic patient may also be treated by directly stimulating the sympathetic nervous system through the use of drugs that have sympathomimetic properties, such as epinephrine or dopamine Medications referred to as antidysrhythmics can be used to suppress tachydysrhythmias and ventricular fibrillation There are many classes of antidysrhythmic medications with different mechanisms of action and many different individual drugs within these classes

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 51 Fast & Easy ECGs, 2E Medications Although drug therapy is used to prevent dysrhythmias, nearly every antidysrhythmic drug has the potential to act as a proarrhythmic Several groups of drugs slow conduction through the heart, without actually preventing the dysrhythmia – These drugs are used to control the rate of a tachycardia and make it tolerable for the patient Anticoagulant medications and antiplatelet drugs can reduce the risk of clotting that is associated with certain dysrhythmias

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 52 Fast & Easy ECGs, 2E Summary Each heartbeat arises as an electrical impulse from the SA node and spreads across the atria, depolarizing the tissue, causing both atria to contract The impulse then activates the AV node where it is delayed slightly The impulse then spreads through both ventricles via the Bundle of His, right and left bundle branches, and the Purkinje fibers, causing a synchronized contraction of the primary pumping chambers of the heart

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 53 Fast & Easy ECGs, 2E Summary Through the property of automaticity, the heart’s pacemaker cells spontaneously depolarize Because the SA node reaches it action potential more quickly than the other pacemaker cells, it is the heart’s primary pacemaker

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 54 Fast & Easy ECGs, 2E Summary In the polarized state, the myocytes have a resting membrane potential of -80 to -90 mV In nonpacemaker myocytes, this membrane potential remains stable until the cell is stimulated The temporary change in electrical potential that occurs between the inside and the outside of a nerve or muscle fiber when a nerve impulse is transmitted is called the action potential The action potential of the myocytes consists of five phases labeled 0 to 4

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 55 Fast & Easy ECGs, 2E Summary One of the things we look for during examination of the ECG is the presence of dysrhythmias A dysrhythmia is an ECG rhythm that differs from normal sinus rhythm Some dysrhythmias are of little consequence and simply annoying while others are life- threatening medical emergencies that can lead to cardiac arrest and sudden death

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 56 Fast & Easy ECGs, 2E Summary The most common symptom of dysrhythmias is palpitations Symptoms such as lightheadedness, dizziness, fainting, chest pain, shortness of breath, sweatiness, and/or pallor may be seen in dysrhythmias that cause decreased cardiac output – Referred to as being symptomatic Sometimes the first clinical manifestation of a cardiac dysrhythmia is sudden death

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 57 Fast & Easy ECGs, 2E Summary Types of dysrhythmias include bradycardia, tachycardia, early (premature) beats, dropped beats, or QRS complexes and irregular rhythms Causes and mechanisms of dysrhythmias include increased parasympathetic tone, myocardial hypoxia, injury and infarction, increased automaticity, reentry, triggered beats, and proarrhythmia Dysrhythmias can originate from the SA node, atria, AV junction, or ventricles and can occur due to AV heart block

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 58 Fast & Easy ECGs, 2E Summary Typically, dysrhythmias can be identified through the use of one lead, most commonly lead II Another lead commonly used to detect dysrhythmias is the MCL 1 Examination of the ECG rhythm on the ECG monitor must be done in a systematic, organized way

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 59 Fast & Easy ECGs, 2E Summary Many dysrhythmias require no treatment as they are either benign or resolve on their own Managing dysrhythmias depends on whether or not the patient is stable or unstable Patients who are symptomatic are considered unstable because symptoms indicate decreased cardiac output Many treatment options are available to treat dysrhythmias including physical maneuvers, electricity therapy, and the administration of certain medications