Basic ECG Rhythm Identification Part II Learning Objectives
ECG Interpretation - Part II Basic ECG Rhythm Identification Part II Learning Objectives • By the end of the class, you will be able to: • Identify the basic anatomy and conduction system of the heart • Describe electrode position for ECG and telemetry equipment • Identify basic ECG rhythms • Identify dysrhythmias and relevant implications and nursing interventions • State policies and procedures related to ECG monitoring 20090529 1 ECG Interpretation - Part II Atrioventricular Blocks 1° Heart Block 20090529 P <0.12 sec, upright, consistent morphology PRI > 0.20 sec QRS 0.04 – 0.12 sec, consistent morphology QRS complex is never dropped Regularity regular P-to-P interval, regular R-to-R interval Rate 60 – 100 bpm or slower 2 ECG Interpretation - Part II 1° Heart Block - Causes • Conduction delay within the right atrium, the AV node, the His-Purkinje system, or a combination of these • Higher prevalence reported in athletes • Prevalence increases with age • Coronary artery disease and angina • Idiopathic degenerative diseases of the conduction system • Drugs: Calcium channel blockers, betablockers, digoxin, and amiodarone 1° Heart Block - Symptoms • Generally asymptomatic at rest • Markedly prolonged PR interval may reduce exercise tolerance in some patients with left ventricular systolic dysfunction • Syncope may result from transient high-degree AV block 20090529 3 ECG Interpretation - Part II 1° Heart Block - Interventions • If possible, discontinue medications with potential for AV block • Permanent electronic pacemakers may be indicated in those with severe bradycardia or syncope • Atropine 2° Heart Block Type I 20090529 P <0.12 sec, upright, consistent morphology PRI PRI gets progressively longer until a P wave is blocked, cycle begins again following the blocked P wave QRS 0.04 – 0.12 sec, consistent morphology QRS complex is dropped if a P wave is blocked Regularity regularly irregular Rate variable 4 ECG Interpretation - Part II 2° Heart Block Type I - Causes • Disease of the AV node • Can occur in individuals with high vagal tone such as athletes or young children • Can occur in infants and young children with structural heart disease and in individuals following valvular surgery • Myocardial infarction • Drugs: beta-blockers, calcium channel blockers, amiodarone, digoxin 2° Heart Block Type I - Symptoms • Most patients are asymptomatic • May experience light-headedness, dizziness, or syncope • Patients often have a regularly irregular heartbeat. • Bradycardia may be present 20090529 5 ECG Interpretation - Part II 2° Heart Block Type I - Interventions • If asymptomatic, no intervention. • If symptomatic, ACLS guidelines for bradycardia, including the use of atropine and transcutaneous pacing • If MI suspected, treat with an appropriate anti-ischemic regimen • Re-evaluate medication regimen 2° Heart Block Type II 20090529 P <0.12 sec, upright, consistent morphology PRI may be normal or prolonged, but it is constant until one P wave is not conducted to the ventricles QRS 0.04 – 0.12 sec, consistent morphology QRS complex is dropped if a P wave is blocked Regularity irregular due to dropped QRS Rate variable 6 ECG Interpretation - Part II 2° Heart Block Type II - Causes • Almost always a disease of the distal conduction system (His-Purkinje System) 2° Heart Block Type II - Symptoms • More likely to experience light-headedness, dizziness, or syncope, although they may be asymptomatic • Patients may have chest pain if the heart block is related to ischemia • Bradycardia 20090529 7 ECG Interpretation - Part II 2° Heart Block Type II - Interventions • Same interventions as for Type I, plus evaluation of patient for • Transcutaneous pacing • Transvenous pacemaker • Type II can rapidly progress to complete heart block 3° Heart Block 20090529 P <0.12 sec, upright, consistent morphology PRI variable when QRS present QRS 0.04 – 0.12 sec, consistent morphology, but QRS may be wide, there is no correlation between atrial and ventricular rates Regularity irregularly irregular Rate Atrial rate usually 60-100. Ventricular rate usually 20-40. Atrial rate is always faster than ventricular rate. 8 ECG Interpretation - Part II 3° Heart Block - Causes • Co-administration of AV-nodal, betaadrenergic- and calcium channel- blocking agents. • MI • Cardiomyopathy (Lyme disease, rheumatic fever) • Profound hypervagotonicity • Metabolic disturbances such as hyperkalemia 3° Heart Block - Symptoms • • • • • • • • 20090529 Confusion, lethargy, syncope Tachypnea, dyspnea Severe chest pain Hypotension, tachycardia Pallor, diaphoresis Sudden death Signs/symptoms of (concurrent) MI Signs/symptoms of CHF 9 ECG Interpretation - Part II 3° Heart Block - Interventions • • • • • • ACLS guidelines Prepare for transcutaneous pacing Evaluation for permanent pacemaker Avoid valsalva AV nodal medications should be withheld Anti-ischemic therapy should be started Critical Points: AV Blocks Are there any lonely P’s? Yes No 1° AVB Gradually prolonged 2° Type I 20090529 How is the PR interval before the lonely P’s? Constant 2° Type II Not gradually prolonged Not constant 3° 10 ECG Interpretation - Part II 20090529 11 ECG Interpretation - Part II Ventricular Rhythms 20090529 12 ECG Interpretation - Part II Idioventricular Rhythm P not present PRI unmeasurable QRS > 0.12 sec Regularity usually regular Rate 20 - 40 (IVR) 40 - 100 (accelerated IVR) Idioventricular Rhythm - Causes • Subordinate or second-order pacemakers fire when the prevailing sinus rate becomes too low (or lower than the rate of the second-order pacemaker cells) • Sinus bradycardia combined with enhanced automaticity of the subordinate site is the common pathophysiology. • Myocardial ischemia • Digoxin toxicity • Electrolyte imbalance (hypokalemia) 20090529 13 ECG Interpretation - Part II Idioventricular Rhythm - Symptoms • • • • Similar to acute myocardial infarction. May present with bradycardia Hypotension An irregular heart rhythm may develop because of the alternating predominance of the sinus rate and idioventricular rate Idioventricular Rhythm - Interventions • Treat the primary disease process that allows the escape rhythm to take over pacemaker control of the heart • Pharmacological or electrical suppressive therapy is rarely needed because the ventricular rate is usually less than 100 bpm • If symptomatic or hemodynamically compromised, increasing the atrial rate with atropine, isoproterenol, or atrial pacing 20090529 14 ECG Interpretation - Part II Premature Ventricular Contraction Unifocal P <0.12 sec, upright, consistent morphology may be blocked by PVC PRI 0.12 – 0.20 sec except during PVC QRS > 0.12 sec for PVC, morphology of PVC will vary from other QRS complexes but all PVCs will have the same morphology Regularity regular P-to-P interval, regular R-to-R interval except during PVC Rate variable Premature Ventricular Contraction Multifocal 20090529 P <0.12 sec, upright, consistent morphology may be blocked by PVC PRI 0.12 – 0.20 sec except during PVC QRS > 0.12 sec for PVC morphology of PVCs vary because of multiple ectopic sites Regularity regular P-to-P interval, regular R-to-R interval except during PVC Rate variable 15 ECG Interpretation - Part II Premature Ventricular Contraction Bigeminy P <0.12 sec, upright, consistent morphology may be blocked by PVC PRI 0.12 – 0.20 sec except during PVC QRS > 0.12 sec for PVC, every other QRS complex is a PVC, morphology will vary if more than one ectopic site Regularity regular P-to-P interval, regular R-to-R interval except during PVC Rate variable Premature Ventricular Contraction Couplet 20090529 P <0.12 sec, upright, consistent morphology may be blocked by PVC PRI 0.12 – 0.20 sec except during PVC QRS > 0.12 sec for PVC, PVCs will appear in pairs morphology will vary if more than one ectopic site Regularity regular P-to-P interval, regular R-to-R interval except during PVC Rate variable 16 ECG Interpretation - Part II Premature Ventricular Contraction Burst or Run of VT P <0.12 sec, upright, consistent morphology may be blocked by PVC PRI 0.12 – 0.20 sec except during PVC QRS > 0.12 sec for PVC, burst or run: 3 or more consecutive PVCs morphology will vary if more than one ectopic site Regularity regular P-to-P interval, regular R-to-R interval except during PVC Rate variable PVCs - Causes • Reentry occurs when there is a blockage in the Purkinje fibers and a second area of slow conduction • Creation of areas with differing conduction and recovery times due to MI • During ventricular depolarization, the area of slow conduction activates the blocked part after the rest of the ventricle has recovered, resulting in an extra beat. • Enhanced automaticity with hyperkalemia 20090529 17 ECG Interpretation - Part II PVCs - Symptoms • • • • Patients are usually asymptomatic Palpitations Syncope with frequent PVCs Runs of PVCs can result in hypotension PVCs - Interventions • Correct underlying contributory causes when appropriate • PVCs are usually not problematic any may not need intervention other than closer monitoring 20090529 18 ECG Interpretation - Part II Torsades de Pointes P if present, may be obscured PRI unmeasurable QRS variable but usually wide and bizarre morphology; may progress to ventricular tachycardia or ventricular fibrillation Regularity irregular Rate 150-250 bpm Torsades de Pointes - Causes • Triggered by an early premature ventricular contraction (R-on-T phenomenon) • Unlike ventricular tachycardia, TdP is most often preceded by a prolonged QT interval • With prolonged repolarization, myocardial cells become less refractory to electrical stimuli and more likely to depolarize prematurely. • Hypokalemia and hypomagnesemia • Antiarrhythmic drugs 20090529 19 ECG Interpretation - Part II Torsades de Pointes - Symptoms • QT interval increased markedly (usually to 600 msec or greater) • Torsades usually occurs in bursts that are not sustained; the rhythm strip usually shows the baseline QT prolongation. • No physical findings are typical of Torsades Torsades de Pointes - Interventions • Administration of beta blockers to decrease risk of stress-induced arrhythmias. • Treat hypokalemia, hypomagnesemia • Isoproterenol infusion • Electrical cardioversion or defibrillation • Overdrive pacing to reduce pauses 20090529 20 ECG Interpretation - Part II Ventricular Tachycardia P unmeasurable, usually absent or my be hidden by QRS PRI unmeasurable QRS > 0.12 sec, wide and bizarre morphology, tombstone look Regularity regular or irregular Rate 100 – 250 bpm Ventricular Tachycardia - Causes • • • • • • • • • 20090529 Coronary artery disease MI with scarring Cardiomyopathy Cardiac hypertrophy Cardiac surgery with scarring Sleep apnea Hypokalemia Hypomagnesemia Aggressive adrenergic stimulation 21 ECG Interpretation - Part II Ventricular Tachycardia - Symptoms • • • • • • • Palpitation, tachycardia Decreased level of consciousness Lightheadedness and syncope Chest pain may be due to ischemia Anxiety Dyspnea, tachypnea Pallor and diaphoresis Ventricular Tachycardia - Interventions • Defibrillation per ACLS protocols • If the hemodynamic status is stable, rhythm conversion may be achieved with cardioversion or intravenous medication • AICD • Correct underlying causes 20090529 22 ECG Interpretation - Part II Ventricular Fibrillation (V Fib) P unmeasurable, usually absent or my be hidden by QRS PRI unmeasurable QRS unmeasurable, no QRS complex is discernable because multiple ventricular sites are firing at the same time Regularity irregular Rate unmeasurable Ventricular Fibrillation - Causes • Coronary artery disease is the most common cause • Signal reentry • Electrolyte abnormalities (low K and Mg) • Ischemia • Sleep apnea 20090529 23 ECG Interpretation - Part II Ventricular Fibrillation - Symptoms • Palpitation, lightheadedness, and syncope from diminished cerebral perfusion • Chest pain may be due to ischemia • Anxiety • Pallor and diaphoresis • Tachypnea • Hypotension • Decreased level of consciousness • Syncope Ventricular Fibrillation - Interventions • If the hemodynamic status is stable: rhythm conversion with cardioversion or intravenous medication • AICD • Endocardial catheter ablation • Meds: procainamide, lidocaine, amiodarone, and a handful of intravenous beta-adrenergic blocking agents (metoprolol, esmolol, propranolol) 20090529 24 ECG Interpretation - Part II Ventricular Standstill / Asystole P none PRI none QRS none Regularity none Rate none Asystole - Causes • Heart fails to generate ventricular depolarization • Ischemia or from degeneration of the SA node or AV conduction system • Severe tissue hypoxia with metabolic acidosis • suffocation, near drowning, stroke, pulmonary embolus, hyperkalemia, hypothermia 20090529 25 ECG Interpretation - Part II Asystole - Symptoms • Patient will be unconscious and unresponsive • Agonal breaths • No detectable heart sounds • No palpable peripheral pulses Asystole - Interventions • Only 3 drugs recommended by the AHA: epinephrine, vasopressin, and atropine • ACLS • Transcutaneous or transvenous pacing 20090529 26 ECG Interpretation - Part II 20090529 27 ECG Interpretation - Part II 20090529 28 ECG Interpretation - Part II 20090529 29 ECG Interpretation - Part II Bundle Branch Blocks Bundle Branch Blocks • When a bundle branch becomes injured, it may not conduct electrical impulses appropriately, resulting in altered pathways for ventricular depolarization. • Electrical impulses cannot use the preferred pathways, so it may move instead through muscle fibers • Electrical movement is slower and the direction of the impulses changes, leading to loss of ventricular synchrony 20090529 30 ECG Interpretation - Part II Bundle Branch Blocks • A mnemonic to remember the ECG changes is WiLLiaM MuRRoW: • With a LBBB there is a W in V1 and an M in V6 • With a RBBB there is a M in lead V1 and a W in lead V6 Left Bundle Branch Block 20090529 31 ECG Interpretation - Part II Left Bundle Branch Block P <0.12 sec, upright, consistent morphology PRI 0.12 – 0.20 sec QRS > 0.12 sec because of bundle branch block notch seen in QRS complex (going counter clockwise/left) Regularity regular or irregular Rate variable Right Bundle Branch Block 20090529 32 ECG Interpretation - Part II Right Bundle Branch Block P <0.12 sec, upright, consistent morphology PRI 0.12 – 0.20 sec QRS > 0.12 sec because of bundle branch block notch seen in QRS complex (going clockwise/right) Regularity regular or irregular Rate variable Paced Rhythms 20090529 33 ECG Interpretation - Part II Indications for Cardiac Pacing • Sinus bradycardia • Sick sinus syndrome • Atrial arrhythmias • to restore atrial kick • to overdrive pace • 3rd degree HB • Congenital • Iatrogenic • Acquired (“senile”) TYPES OF PACING • Transcutaneous • Transvenous • Epicardial 20090529 34 ECG Interpretation - Part II TRANSCUTANEOUS PACING • Non-invasive via skin and chest wall • Mostly used for emergent pacing • Electrodes: • placed on anterior and posterior chest walls • connected to pulse generator by pacing cables TRANSCUTANEOUS PACING • Preferred electrode placement • Round (-) electrode • left anterior chest • over the heart (closer to the apex) • Square (+) electrode • left posterior chest • over the back of the heart 20090529 35 ECG Interpretation - Part II TRANSCUTANEOUS PACING • Anterior - anterior placement (if anterior-posterior is not possible) • round electrode • left anterior chest • mid-axillary over 4th ICS • Square electrode • right anterior chest • below clavicle Transcutaneous Pacing • Apply to clean, dry skin • Clip, do not shave excessive hair • Assess for both electrical and mechanical capture • Skeletal muscle contraction does not indicate mechanical capture by heart • May cause pain with impulse delivery • Analgesia and/or sedation PRN 20090529 36 ECG Interpretation - Part II TRANSVENOUS PACING • • • • Electrode inserted into RV via introducer Tip comes in direct contact with RV wall Can be left in place for 72 hrs Complications: • • • • • • Infection/ phlebitis/thrombosis Pneumothorax RV wall perforation Dysrhythmias Dislodgement Diaphragmatic pacing EPICARDIAL PACING • Pacing wires: • attached to atrial or ventricular epicardium • exits chest wall to right or left side of sternal incision • must be clearly labeled atrial (right of sternum) or ventricular (left of sternum) • must be kept dry, insulated and intact • Gloves should be worn at all times when handling wires 20090529 37 ECG Interpretation - Part II mA versus mV • mA (milliamps) • electrical energy to pace heart • higher mA setting means a higher amount of electricity delivered to the heart • mV (millivolts) • measure of sensitivity • amplitude or height of intrinsic impulse that will be assessed by the pacemaker to prevent it from firing SENSITIVITY • Sensing - ability of the pacemaker to “see” intrinsic electrical activity • The higher the mV, the less sensitive the device is to intrinsic events • The higher the “fence”, the less is seen “behind the fence” • The lower the mV setting, the higher the sensitivity to native beats) • The lower the “fence”, the more is seen “behind the fence” 20090529 38 ECG Interpretation - Part II SENSITIVITY The lower the mV, the more intrinsic beats are seen Amplitude (mV) 5.0 2.5 1.25 Time 20090529 39 ECG Interpretation - Part II The higher the mV, the fewer intrinsic beats are seen Amplitude (mV) 5.0 2.5 1.25 Time Pacemakers 20090529 40 ECG Interpretation - Part II Pacemaker Components • Pulse generator or box • houses battery and circuitry that delivers electrical charge and directs pacing • Pacing lead or wire • insulated wire which carries impulse from pulse generator to heart muscle • Electrode tip • non-insulated part of wire which carries impulse from pulse generator to heart muscle 20090529 41 ECG Interpretation - Part II Pacemaker Codes • • • • Remember P - S - R First letter - chamber Paced Second letter - chamber Sensed Third letter - Response of the pacemaker when atrial or ventricular activity is sensed (inhibit or trigger) 1st Letter 2nd Letter 3rd Letter Chamber(s) paced A = atrium Chamber(s) sensed A = atrium Response to sensing I = inhibit (demand mode) V = ventricle V = ventricle T = triggered D = dual (both atrium & ventricle) D = dual (both atrium & ventricle) O = none D = dual (both atrium & ventricle) O = none (asynchronous) 20090529 42 ECG Interpretation - Part II COMMON PACEMAKER CODES • • • • • D A D V D D A V V O D I I I O DDD - Universal Pacemaker • Chamber paced - atrium and ventricle • Chamber sensed - atrium and ventricle • Response to sensing for atrial or ventricular activity: • • • • Intrinsic P (followed by QRS) No pacing Intrinsic P (with no QRS) pacing Intrinsic P below set rate pacing Intrinsic QRS below set rate pacing • Mimics physiologic cardiac cycle and maintains AV synchrony 20090529 43 ECG Interpretation - Part II AAI - Atrial Demand • Chamber paced – atrium • Chamber sensed – atrium • Response when intrinsic atrial activity is sensed no pacing • Must have functioning AV node & ventricular conduction system • Used in sinus bradycardia or sick sinus syndrome DVI - AV Sequential • Chamber paced – atrium and ventricle • Chamber sensed – ventricle • Response to sensing for ventricular activity: • No intrinsic QRS pacing (atrium & ventricle) • Intrinsic QRS no pacing • Used in heart blocks or sick sinus syndrome 20090529 44 ECG Interpretation - Part II V V I - Ventricular Demand • Chamber paced – ventricle • Chamber sensed – ventricle • Response when intrinsic ventricular activity is sensed no pacing • Response when there is no intrinsic ventricular activity pacing • Used in complete heart block Paced Beats • Pacing spike • represents electrical impulse that the pacemaker sends to the heart • in atrial pacing, occurs before P wave • in ventricular pacing, occurs before QRS • P wave • different in shape from intrinsic beat, wave may be inverted • QRS complex • wide and bizarre 20090529 45 ECG Interpretation - Part II Review Of Terminology • Demand pacing • pacing in which the pacemaker fires only when the intrinsic heart rate falls below a specified parameter • Asynchronous pacing • pacing in which the pacemaker fires at a fixed rate, independent of underlying cardiac activity Review Of Terminology • Firing • the generation of an electrical signal from the pacemaker in order to generate a physiological response • Capture • when a pacer spike is followed by a P wave (atrial) or a QRS complex (ventricular) • Sensing • the ability of the pacemaker to detect the intrinsic electrical activity of the heart 20090529 46 ECG Interpretation - Part II Failure To Fire Or Pace • The pacemaker does not work when it is supposed to work • Most common causes • oversensing • battery failure • generator malfunction Failure To Capture • The heart does not contract in response to pacing • Most common causes: • • • • 20090529 setting set too low battery failure generator malfunction change in patient’s condition 47 ECG Interpretation - Part II Oversensing • Extraneous electrical signals are inadvertently sensed, inhibiting pacemaker from firing when it was supposed to • Most common causes: • sensitivity too high • electromagnetic interference • loose connections Failure To Sense • Pacemaker does not detect the intrinsic beat and generates a spike during or after the beat • Most common causes: • sensitivity too low • pacing wire problems 20090529 48 ECG Interpretation - Part II Myocardial Ischemia/Infarction 20090529 49 ECG Interpretation - Part II ST Segment • Segment between the J point and the beginning of the T wave • Need to use a reference point • Compare ST segment to TP segment • Do not use PR segment as reference ST TP ST Segment • ST elevation (b) • > 1 mm above baseline • concave or coved 20090529 • ST depression (c) • > 1 mm below baseline • horizontal or downward sloping 50 ECG Interpretation - Part II ST Segment Analysis • For each complex, determine whether the ST segment is elevated one millimeter or more above the TP segment Policies & Procedures Please review: Cardiac Monitoring (General) Policy: Adult Telemetry Monitoring 20090529 51 ECG Interpretation - Part II Monitored Patients Policy: Adult Telemetry Monitoring Procedure: Cardiac Monitoring (Adult) • Outside critical care settings, cardiac and pulse oximetry monitoring is provided on the LSU, 8 South, 10 CVT, 13 L and 14 M • Telemetry is available to all services • The clinical indication for ECG monitoring must be specified on the order form • The provider order must also specify parameters for notification of the provider Monitored Patients • Triage of telemetry beds will be performed by the charge nurse in conjunction with the ordering provider and hospital supervisor • Whenever possible, patients will be admitted to the monitored unit that is most appropriate for the admitting service 20090529 52 ECG Interpretation - Part II How do you determine the most appropriate units for patients who require cardiac/CPO monitoring? 20090529 53 ECG Interpretation - Part II Monitored Patients • Routine rhythm analysis is performed and documented at least q 12 hours and within the first 2 hours of the shift • Bedside RNs must verify and co-sign the tele tech’s rhythm assessment, even when another RN is acting as the tele tech • Changes in rhythm will be documented and communicated to provider • The charge nurse will assess competency of float nurses caring for telemetry patients The Telemetry-Competent RN • If you provide care to a monitored patient, you must have documentation of your competency: • ECG rhythm interpretation test • Telemetry CBO (competency-based orientation) • Know your resources • Know how to escalate a situation using the chain of command 20090529 54 ECG Interpretation - Part II Questions? 20090529 55
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