EKG

ECGINTERPRETATIONTim Dodd AEMCA, ACP Reviewed by: Corey Petrie, ACPRevised – February 2011 NEOPCPDan Langevin, PCP (IV)NEOPCP Paul Myre, ACP NEOPCP

Lecture OverviewAnatomy reviewElectrical impulse conductionECG paper constantsLimb placementsHeart rate determinationSteps to rhythm strip analyzesECG interpretations!

Learning ObjectivesTo gain a basic knowledge of cardiacelectrophysiologyTo understand the representations ofthe cardiac cycle on the ECGTo master techniques used for learningthe characteristics of the differentdysrhythmiasTo learn measurement and counttechniques essential for dysrhythmiainterpretation

Lead Placement and ECG “View” Our cardiac monitors have the ability to display ECG rhythms In manual mode it is possible to capture various leads or “views” of the electrical activity No matter which view is being displayed, the underlying rhythm does NOT change

Bipolar Leads or Limb Leads (I,II,III)

Limb LeadsEinthoven’s triangle is composed of the standard (bipolar) limb leads:Lead I: negative pole is right arm & positive is left armLead II: negative pole is right arm & positive left legLead III: negative pole is left arm & positive left leg

Lead Placement and ViewsNegative Positive Ground

Lead Placement and ViewsNegative Ground Positive

Lead Placement and Views NegativeGround Positive

BiPolar Leads I, II & III Lead I Lead III

- Limb Leads +Right Arm Lead I Left Arm - -Lead II Lead III ++ Left Leg

CardiacConduction

Cardiac ConductionEssentially 2 pumps Atria VentriclesMust operate in unison and in orderThree Primary Pacemakers Sinoatrial Node Atrio-Ventricular Junction Purkinje System

ElectromechanicsResting cells: negative interior positive exteriorChanges in this resting state causedepolarization and repolarization

Electrical FlowTowards negative electrode:downward deflection on paperTowards positive electrode:upward deflection on paperAs energy travels away from this axisamplitude on the ECG decreases

ECG “View” and Electrical FlowLead II offers the best “view”The normal electrical axis travelsthe 11-5 o’clock vector which is59 degreesLead II is at 60 degrees

SinoAtrial NodeContraction of the AtriaNormally depolarizes 60-80 times/min.Can depolarize up to 300 times/min.Follows special pathways –- IntraAtrial: Anterior, Middle, Posterior Internodal Tracts

AtrioVentricular NodePauses depolarization to allowventricular fillingCapable of depolarizing 40-60times/min. (in the absence of theSA Node input)

Ventricular PathwaysBundle of HisLeft and Right Bundle BranchesLeft bundle gives rise to anterior andposterior fasciclesEnds at the Purkinje fibersInherent depolarization rate < 40/min.



Conduction Pathways

Pathway – structure relationship Slide courtesy of York BH

ECG PaperHorizontal lines: distance inmillimeters and time in secondsVertical lines: voltage (amplitude) inmillimetersUses the Metric systemIs very good for accuracy

ECG PaperLight vertical lines are 0.04 second(1 mm) apartDark vertical lines are 0.20 second(5 mm) apart5 dark squares is 1 second

Cardiac Conduction

Cardiac Conduction: P Wave P Wave: Atrial Impulse .04 - .08 Seconds

Cardiac Conduction: PR Interval P Wave .04 - .08 Sec. PRI .12-.20 Sec.

Cardiac Conduction: QRS Complex P Wave .04 - .08 Sec. PRI .12 - .20 Sec. QRS .06 - .12 Sec.

Analyzing aRhythm Strip

Dysrhythmia Interpretation: 5 Step ApproachStep 1: What is the rate?Step 2: Is the rhythm regular orirregular?Step 3: Is the P wave normal?Step 4: P-R Interval/relationship?Step 5: Normal QRS complex?

Step 1- RateMethod 1Count the number of R waves for a six secondinterval and multiply by ten. 6 sec3 sec 3 sec(can be used for regular & irregular)

Step 1 - RateMethod 2: Count the number of 5mm squaresand divide into 300 (or memorize) 300 150 100 75 60 5043 3733 30 … slow

Step 1 - Rate RATE:Tachycardia exists if the rate is greaterthan 100 beats/min.Bradycardia exists if the rate is lessthan 60 beats/min.

Step 2 - Rhythm RHYTHM:Determine if the ventricular rhythm isregular or irregular (pattern to irreg.?)R-R intervals should measure the sameP-P intervals should also measure thesame

Step 2 - RhythmREGULARIRREGULAR

STEP 2 - Rhythm ExampleIrregularly Irregular

STEP 3 – Is the P Wave Normal Identify and examine P waves:Present?Appearance?Consistency?Relation to QRS?

STEP 3 - Is the P Wave Normal Normal Same ShapeNormal P wave with no QRS complex Associated with a QRS Complex?

STEP 4 – PR Interval/Relationship Consistent PRI of < 0.20 secs is normal,lengthened or variant PRI’s could indicate an AV block

STEP FIVE –QRS DURATION •A narrow QRS complex (< 0.12 sec), indicates the impulse has followed the normal conduction pathway •A widened QRS complex (> 0.12 sec), may indicate the impulse was generated somewhere in the ventricles

REMEMBER!!!Use a systematic approachGo through all the stepsTake your time!Compare with your characteristics listInterpret the dysrhythmia

QUESTIONS

Let’s Have Some Fun!

Sinus Mechanisms

Sinus NodeNormal Sinus Rhythm (NSR)Sinus BradycardiaSinus TachycardiaSinus ArrhythmiaSinus Arrest/PauseSinoatrial Exit Block

Normal Sinus Rhythm (NSR)Rate: 60-100 beats/minRhythm: regularP waves: uniform, + (upright) in lead II,one precedes each QRS complexPR interval: 0.12 - 0.20 seconds andconstantQRS duration: < 0.12 sec

Normal Sinus Rhythm (NSR)

Sinus BradycardiaRate: less than 60 beats/minRhythm: regularP waves: uniform in appearance, uprightand one precedes each QRS complexPR interval: 0.12 - 0.20 sec and constantQRS duration: < 0.12 sec

Sinus Bradycardia

Sinus TachycardiaRate: greater than 100-150 beats/minRhythm: regularP waves: uniform, upright, one precedeseach QRSPR interval: 0.12 - 0.20 sec and constantQRS duration: < 0.12 sec