Basic EKG Theory and Interpretation
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What is EKG?
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*A record of the heart's electrical activity * records the electrical impulses that stimulates the heart to contract *important information from EKG: -Heart rate and rhythm -cardiac ischemia -cardiac hypertrophy -myocardial infarctions
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Why do I need to learn how to read EKG?
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*identify heart rate *determine the seriousness of an arrhythmia -Benign, warning, or life threatening *determine appropriate action -continue with intervention/activity -reduce intensity of intervention or activity -request help
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Basic principles
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*when the heart is stimulated it contracts *rest= heart cells are charged/polarized (- inside, + outside) *contraction= cells \"depolarize\" (+ inside, -outside) *depolarization= advancing wave of positive charges within the cells *depolarization causes progressive contraction of the myocardial cells as the wave of positive charges within the cells *depolarization causes progressive contraction of the myocardial cells as the wave of positive charges advances down the interior of the cells.
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Basic principles continued
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repolarization= myocardial cells regain the negative charge within each cell repolarization= electrical phenomenon and the heart remains physically quiet during this activity * EKG= records the electrical activity of depolarization and repolarization
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What are the rules of electrical flow?
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*If electricity flows toward the negative electrode, the patterns produced on the graph paper will be inverted * If electricity flows toward the positive electrode, the patterns produced on the graph paper will be upright.
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What does a P wave represent? What does the QRS complex represent? What does a T wave represent?
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P wave= atrial depolarization QRS= ventricular depolarization atrial repolarization T wave= Ventricular repolarization
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Standard EKG
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*12 separate leads -6 chest leads (V1-V6) -6 limb leads * 3 sets of leads -Limb Leads (eithoven's) *each limb lead records from a different angle-> different view of the same cardiac activity -augmented leads -precordial (chest) leads *chest leads-sensor placed on chest is positive
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The 3 sets of leads are formed by which 3 body parts?
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Right arm Light arm Left foot
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Where is the heart located in Eithoven's triangle?
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-Eithoven's triangle has the heart in the approximate center -bipolar leads- reflect the difference in potential between the 2 points
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Lead 1 goes from where to where? Lead 2 goes from where to where? Lead 3 goes from where to where?
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Lead 1: goes from left arm (LA) to right arm (RA) Lead 2: Left leg (LL) to R arm (RA) Lead 3: Left leg (LL) to left arm (LA)
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What does aVR mean?
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augmented voltage right (aVR): between the RA and the average LA/LL augmented voltage left (aVL): between the LA and the average RA/LL augmented voltage foot (aVF): Between the LL and the average LA/RA
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Limbs leads intersect at how many degrees and from how many lines in reference to the frontal plane?
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Limb leads intersect at 30 degrees 6 lines of reference in the frontal plane
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precordial (chest leads): how many and how are they placed?
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V1, V2, and V3 are placed from anterior to posterior V4, V5, and V6 are placed from right to left
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Precordial or Chest leads
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*record electrical potential under the electrode compared to central connection *ECG becomes progressively more positive, reflecting mass through which depolarization passes.
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What is the conduction pathway of the heart?
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SA node-> both atria-> AV node->Bundle of HIS-> R and L bundle branches-> Purkinje fibers->Myocardial cells
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Conduction pathway and EKG: Where is the SA node and what does it do?
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*SA node is located in the posterior wall of the R atrium *Initiates electrical impulse for cardiac stimulation *depolarization stimulates both atria
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What does a P wave represent? What is the time frame for a P wave?
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* P wave represents when both of the atria contract concurrently. It is recorded as less than or equal to .11 seconds
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What is the P-R interval? What does it represent? How long is that interval?
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* Beginning of P to the beginning of QRS complex *represents AV conduction time; Atrial De/Repolarizations * 0.12-0.20 * Pause at the AV node is recorded as the PR interval * Allows for ventricular filling
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Conduction pathway: How long of a pause is there to allow the blood to enter the ventricles? What does the pause represent? After the pause where does the impulse go?
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*electrical impulse then reaches the AV node= 1/10 second pause to allow blood to enter the ventricles. -(Pause= period of time it takes the blood to pass through AV valves into the ventricles) *After 1/10 second pause, the AV node= stimulated, intiating electrical impulse that starts down the AV bundle into the Bundle of HIS
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Conduction pathway continued What initiates ventricular depolarization?
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* The stimulus progressing away from AV node=initiates ventricular depolarization (contraction) * The AV Bundle (Bundle of His)=extends down from the AV node-> divides into the right and left bundle branches within the interventricular septum.
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What does the QRS complex represent? Over what time period does it take place over?
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* it represents the depolarization/contraction of the ventricles * it is less than or equal to .10 seconds *Purkinje fibers transmit the electrical activity of the stimulation of the ventricles
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The QRS Complex: What does the R wave represent?
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* R wave= 1st upward wave of the QRS complex * S wave= any downward wave preceded by an upward wave * Q wave= the 1st downward deflection (may be absent depending on lead)
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Conduction Pathway & EKG: What does the ST segment represent? What does the T wave represent?
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ST segment: -pause after the QRS complex T wave: -follows the pause -represents ventricular repolarization
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Recording EKGs: Orientation to the paper 1. The smallest boxes for EKG represent how many mm? 2. how many small boxes make a bigger box?
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1. 1mm 2. 5mm= 5 boxes, grouped in 5 by 5 squares with bolder lines demarcating the group
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Each small box (1mm), represents how many seconds? Each large box (5mm), represents how many seconds?
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* Each small box of 1mm represents .04 seconds * Each large box of 5mm represents .20 seconds
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When paper speed is a standard (25 mm/sec), how many boxes (large and small) on the horizontal axis is equivalent to 1 min?
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* 1 minute on the horizontal axis= 300 large or 1500 small boxes *6 seconds= 30 large or 150 small boxes
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Time is on which axis? Voltage is on which axis?
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Time is on the horizontal axis Voltage is on the vetrical axis
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1mV displaces how many small or large boxes? Each small box is equivalent to how many mV? What is amplitude related to?
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*1mv is equal to 10 mm= 10 small boxes or equal to 2 large boxes. *Each small box is equivalent to 0.1 mV *Amplitude is related to mass depolarizing -the larger the amplitude, the greater the mass
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What is the normal amount of time for a PR-interval? How many boxes is that equivalent to? How many seconds is a normal QRS wave? How many boxes is that equivalent to?
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*PR interval: -.12-.20 sec - 3-5 boxes *Normal QRS - .08-.10 - < 2.5 boxes
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What would be the interpretation of the intervals that are too great?
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...
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What would be the interpretation of intervals that are too short?
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...
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1 minute equals how many large and small boxes? 6 seconds is equiavlent to how many large and small boxes?
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* 300 large or 1500 small boxes * 30 large boxes or 1500 small boxes
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What if a beat occurred on every bold line, what would the rate be? What if a beat occurred on every other bold line? How about every 3rd line?
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* If a beat occurred on every bold line, the rate would be 300 bpm * If a beat occurred on every other bold line, the rate would be 150. * If a beat occurred on every third line, the rate would be 100.
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1st method : How do we calculate the number of beats per minute using a six second strip considering we have a regular rhythm?
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* We count the number of Rs per 6 second interval and mulitple the number by 10 to get beats per minute.
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2nd method to calculating HR?
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Count the # of squares between two beats (each small square being 0.04 secs), then divide 1500 by the number of small squares -Example: If there are 22 small squares between two beats, so 1500/22= 68 beats per minute.
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3rd method of calculating HR?
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Count the # of dark squares between two beats, then divide 300 by this number -Example: 4 large squares between 2 beats, so 300/4=75 beats per minute
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Quick Count Method (Regular Rhythm)
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*Find the R wave that occurs on dark line. (If no R wave on a dark line, use \"tic marks\" on paper) *300, 150, 100 75, 60, 50, 47
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What are the steps to EKG interpretation?
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1. P wave: present or absent 2. P wave regularity: regular or irregular 3. PR interval: time from beginning of P wave until the beginning of the QRS complex (atrial depolarization/repolarization) 4. QRS: present or absent? 5. QRS: regular or irregular rate? 6. QRS interval: normal or abnormal? 7. T wave: elevation or depression?
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What area of the heart normally sets the heart rate? What is the term used to describe potential pacemakers that take over when the normal pacemaker does not work?
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*SA node * Ectopic Foci
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When do Ectopic pacemakers function? Where are their possible locations?
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-Only function in disease or emergency conditions -Possible locations: *atria *AV node *ventricles
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When do AV node Ectopic pacemakers take place? What is the normal rate of the AV node and Ventricles if they become pacemakers?
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*Atria Ectopic Pacemakers -May be faster or slower than normal * AV node Ectopic Pacemakers -Begins if normal stimulus fails to come from atria -Normal rate of AV node is 60 beats/min *Ventricular Ectopic Pacemakers: -rate of 30-40 beats/min
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Rhythm interpretation
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*Normal Sinus rhythm *Sinus Bradycardia *Sinus Tachycardia *Atrial Flutter *Atrial Fibrillation *Ventricular tachycardia *Ventricular fibrillation *Asystole *AV blocks *Premature Atrial Contractions *Premature Ventricular Contractions
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Normal Sinus Rhythm HR: ? Rhythm: ? P wave: ? PR interval (in seconds):? QRS (in seconds): ?
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HR: 60-100 bpm Rhythm: regular P wave: Before each QRS, identical PR interval (in seconds): 0.12-0.20 QRS (in seconds): < 0.12
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Sinus Bradycardia HR Rhythm P wave PR interval (in seconds) QRS (in seconds)
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HR: less than 60 bpm Rhythm: Regular P wave: Before each QRS, identical PR interval: 0.12 to 0.20 QRS (in seconds): <0.12
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Sinus Tachycardia HR Rhythm P wave PR interval (in seconds) QRS (in seconds)
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HR: greater than 100 bpm Rhythm: regular P wave: Before each QRS, identical PR interval (in seconds): 0.12 to 0.20 QRS (in seconds): ,< 0.12
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What are the clinical implications of tachycardia?
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*Does not necessarily imply pathological change *Caused by an increase in demand for cardiac output *Occurs for many reasons
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What are the clinical implications of bradycardia?
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*Does imply pathological change *Caused by lack of sympathetic input, medication *may be caused by physical training
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Atrial Flutter HR Rhythm P wave PR interval (in seconds) QRS (in seconds)
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HR: -atrial: 220-430 bpm -ventricular: <300 bpm Rhythm: regular or variable P wave: Sawtoothed appearance PR interval: N/A QRS (in seconds): < 0.12
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Atrial Fibrillation HR Rhythm P wave PR interval (in seconds) QRS (in seconds)
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HR: -atrial: 350-650 bpm -ventricular: slow to rapid Rhythm:Irregular P wave: Fibrillatory (fine to course) PR interval: N/A QRS: <0.12 seconds
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Clinical Implications of Atrial Fibrillation??
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Etiology -Advanced age -Cardiac Conditions -Digoxin toxicity -Renal Failure A serious rhythm, although stable -decreased cardiac output due to lack of \"atrial kick\" -when response is >100 bpm, cardiac output may be compromised -potential for developing emboli -anticoagulant therapy
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Clinical Implications of Ventricular Tachycardia??? Etiology and Symptoms?
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* Etiology (but not limited to) -ischemia -acute myocardial infarction -CAD -hypertensive heart disease -medication toxicity (digitalis, quinidine) *Symptoms -lightheadness and syncope -weak and thready pulse *Emergency situation: -decreased CO & BP -may progress to ventricular fibrillation and death *Treatment: meds, cardioversion, defibrillation
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Ventricular Fibrillation HR Rhythm P wave PR interval (in seconds) QRS (in seconds)
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HR: 300-600 bpm Rhythm: Extremely irregular P wave: Absent PR interval (in seconds): N/A QRS ( in seconds): Fibrillatory baseline
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Ventricular Asystole HR Rhythm P wave PR interval (in seconds) QRS (in seconds)
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HR: Absent Rhythm: Absent P wave: Absent or Present PR interval: N/A QRS (in seconds): Absent
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AV Blocks: What is the difference between a First degree Block versus a Third degree Block in terms of: P wave PR interval (in seconds) QRS (in seconds) Characteristics
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1st degree Block P wave: Before each QRS, identical PR interval (in seconds): greater than 0.20 QRS (in seconds): greater than 0.12 Characteristics: Regular rhythm 3rd degree Block P wave: Normal but not related to QRS PR interval: None QRS (in seconds): N/A Characteristics: No relationship between P& RS
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What are the differences between a Right Bundle Branch Block and a Left Bundle Branch Block in terms of: *P wave *PR interval *QRS (in seconds) *Characteristics
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Right Bundle Branch Block -P wave: Before each QRS, identical -PR interval (in seconds): 0.12 to 0.20 sec -QRS (in seconds): >0.12 sec -Characteristics: RSR' in V1 Left Bundle Branch Block -P wave: Before QRS, identical -PR interval (in seconds): 0.12 to 0.20 sec -QRS (in seconds): greater or equal to 0.12 sec -Characteristics: RR' in V5
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Premature Contractions: what are the two types?
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*initiated by ectopic foci *types: -1. Premature Atrial Contractions (PAC's) -2. Premature Ventricular Contractions (PVC's) * can be benign or dangerous
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What is a Premature Atrial Contraction (PAC's)?
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*ectopic focus in atria initiates an impulse before the next impulse is initiated in the S-A node. *underlying rhythm is sinus *P wave of the early beat is present; looks different than the normal \"P\" wave; may be buried in the preceding T wave
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What is the etiology of a PAC?
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*etiology -emotional stresses and infection -caffeine, nicotine and alcohol -hypoxemia, myocardial ischemia -rheumatic heart disease -atrial damage * irregular pulse * if there are hemodynamic consequences, supraventricular tachycardia or atrial fibrillation may develop
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What is a Premature Ventricular Complex?
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*Ectopic focus originates an impulse in the myocardium of one of the ventricles * P waves are absent *QRS becomes \"wide and bizarre\" *The S-T and T wave are abnormal * A skipped beat can be palpated when checking pulse
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What is the etiology of a PVC?
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*caffeine/nicotine *stress/ overexertion *electrolyte imbalance/ acid-base imbalance *cardiac diseases *irritation of the myocardium *pharmacological toxicity *ischemia
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Premature Ventricular Complexes
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*Most common ventricular conduction abnormality *Benign or dangerous * We may be making a patient ischemic as we cause them to exercise * Thus it is very important you identify immediately and decide on an appropriate course of action
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What are the implications of a PVC?
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* Of concern if ventricular ectopy increases with activity * increased activity=increased \"irritability\" * 3 or more PVCs in a row=ventricular tachycardia * increased irritability leads to dangerous arrhythmia * ventricular tachycardia
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How does one recognize ischemia?
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Ischemia/MI -Q waves changes -ST segment changes
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Q wave interpretation
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*initial depolarization of the ventricles *represents Myocardial Necrosis *Duration less than or equal to 0.03 (less than 1 sm box) *Normally appears in lateral leads (Lead 1, AVL, V 5 & V6) *abnormal if: -depth > .04 seconds and/or 25% the height of the QRS complex
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S-T segment interpretation
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* reflects early ventricular repolarization * ST elevation *ST depression (greater than or equal to 1.5 mm) - Up-sloping (injury) - horizontal - down-sloping (ischemia)
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Indications of ischemia
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*ST segment depression= subendocardial ischemia *ST segment elevation=transmural ischemia
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Where is the J point?
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*The J point occurs at the end of the QRS complex and at the beginnign of the ST segment
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What does ST segment elevation indicate?
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*Indicates infarction in progress *ischemia
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What makes up the ischemic triad?
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1. Significant Q wave 2. Elevated ST segment 3. Inverted T wave * ST segment is elevated indicating myocardial injury * The inverted T wave indicates myocardial ischemia *The Q wave is 0.4 second wide and more than 25% the height of the R wave. It indicates myocardial necrosis
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What are indicators of acute MI?
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* Presence of Q wave in the leads that normally don't have Q waves. Q wave > 25% height of the QRS. *Depression/inversion of ST segment-reduced blood flow to heart *Injury- indicates acuteness of an infarct. ST segment elevation denotes injury *ST segment is that segment of baseline between the QRS complex and the T wave
