Chapter 1 for 12 Lead Training -RHYTHM BASICS- Ontario Base Hospital Group Education Subcommittee 2008 TIME IS MUSCLE

RHYTHM BASICS AUTHOR REVIEWERS/CONTRIBUTORS Tim Dodd, AEMCA, ACP Hamilton Base Hospital REVIEWERS/CONTRIBUTORS Al Santos A-EMCA, ACP Donna L. Smith AEMCA, ACP Hamilton Base Hospital 2008 Ontario Base Hospital Group

Chapter 1 Overview Anatomy review Electrical impulse conduction ECG paper constants Limb placements Heart rate determination Steps to rhythm strip analyzes ECG interpretations!

Chapter 1 Objectives To gain a basic knowledge of cardiac electrophysiology To understand the representations of the cardiac cycle on the ECG To master techniques used for learning the characteristics of the different dysrhythmias To learn measurement and count techniques essential for dysrhythmia interpretation

Cardiac Monitoring and Lead Placement

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

5 Lead Electrode Placement RA (White): Place near right mid-clavicular line, directly below the clavicle LA (Black): Place near left mid-clavicular line, directly below the clavicle V (Brown): Place to Right of sternum at the 4th intercostal Space LL (Red):Place between 6th & 7th intercostal Space on left mid-clavicular line RL (Green): Place between 6th and 7th intercostal Space on right mid-clavicular line

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

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

Lead Placement and Views Lead I Negative Positive Ground

Lead Placement and Views Negative Ground Lead II Lead II ECG cables are three colour coded cables, white, red, black (green) White – right anterior chest, below clavicle Red – mid axillary line below left nipple line – not on the hand… will be a continuation of left arm lead!!! Black – left anterior chest, below clavicle Factors affecting ECG quality: ECG electrode directly over bone dried out electrodes loose connections frayed cables improper lead selection Positive

Lead Placement and Views Negative Ground Lead III Positive

BiPolar Leads I, II & III Lead I Lead III Lead II

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

Cardiac Conduction

Cardiac Conduction Essentially 2 pumps Atria Ventricles Must operate in unison and in order Three Primary Pacemakers Sinoatrial Node Atrio-Ventricular Junction Purkinje System

Electromechanics Resting cells: negative interior, positive exterior Changes in this resting state cause depolarization and repolarization

Electrical Flow Towards negative electrode: downward deflection on paper Towards positive electrode: upward deflection on paper As energy travels away from this axis amplitude on the ECG decreases

ECG “View” and Electrical Flow Lead II offers the best “view” The normal electrical axis travels the 11-5 o’clock vector which is 59 degrees Lead II is at 60 degrees

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

AtrioVentricular Node Pauses depolarization to allow ventricular filling Capable of depolarizing 40-60 times/min. (in the absence of the SA Node input)

Ventricular Pathways Bundle of His Left and Right Bundle Branches Left bundle gives rise to anterior and posterior fascicles Ends at the Purkinje fibers Inherent depolarization rate < 40/min.

Any beat or rhythm not generated from the SA node is considered an escape beat and/or escape rhythm

Conduction Pathways

Pathway – structure relationship Slide courtesy of York Base Hospital

ECG Paper Horizontal lines: distance in millimeters and time in seconds Vertical lines: voltage (amplitude) in millimeters Uses the Metric system Is very good for accuracy

ECG Paper Light vertical lines are 0.04 second (1 mm) apart Dark vertical lines are 0.20 second (5 mm) apart 5 dark squares is 1 second

Cardiac Conduction P Wave - Depolarization of the atria - usually SA node - upright P-R Interval - impulse conduction through AV node - from beginning of P wave to beginning of QRS complex - delay results from tissue density increasing - 0.16 to 0.20 seconds QRS Complex - depolarization of the ventricle - 0.08 to 0.12 seconds - large amplitude due to increased mass of ventricle producing more activity Q Wave - septal wall depolarization - first negative deflection on ECG complex after P wave R Wave - ventricular wall depolarization - large mass of ventricle S Wave - lateral wall depolarization - downward deflection T Wave - ventricular repolarization U Wave - not well understood

Cardiac Conduction: 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 a Rhythm Strip

Dysrhythmia Interpretation: 5 Step Approach Step 1: What is the rate? Step 2: Is the rhythm regular or irregular? Step 3: Is the P wave normal? Step 4: P-R Interval/relationship? Step 5: Normal QRS complex? Listed are the 5 steps to ECG interpretation. When interpreting the ECG it is important to follow the 5 steps to avoid what is known as “Pattern Recognition” whereby the interpreter assumes a rhythm is of one type by just looking at it whereas the rhythm would be identified correctly if the steps were followed. Use this system repeatedly throughout this presentation and following practice to aid students comfort level in identifying ECG’s.

Step 1- Rate Method 1 Count the number of R waves for a six second interval and multiply by ten. 6 sec 3 sec 3 sec Points to consider: reliable only when rhythm is regular good for fast or slow rates (can be used for regular & irregular)

Step 1 - Rate Method 2: Count the number of 5mm squares and divide into 300 (or memorize) 300 150 100 75 60 50 43 37 33 30 … slow Points to consider: start count where QRS complex touches large line reliable for regular rhythms only -not recommended for bradycardic rhythms

Step 1 - Rate RATE: Tachycardia exists if the rate is greater than 100 beats/min. Bradycardia exists if the rate is less than 60 beats/min.

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

Step 2 - Rhythm REGULAR IRREGULAR Measure the R to R intervals to determine if the rhythm is regular in nature. It is acceptable to allow for a difference of + or – one small square when determining regularity of the rhythm Points to consider: regular rhythms are produced by natural pacemakers regularly irregular rhythms are significant of heart blocks -fast rhythms are difficult to determine if a regular pattern exists IRREGULAR

STEP 2 - Rhythm Example Irregularly Irregular

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

Associated with a QRS Complex? STEP 3 - Is the P Wave Normal Normal P wave with no QRS complex Same Shape P waves that appear to be the same shape indicate that the impulse which generated them most likely came from the same place. Associated with a QRS Complex?

PR Interval/Relationship STEP 4 – PR Interval/Relationship Consistent PRI of <.20 secs is normal, lengthened or variant PRI’s could indicate an AV block Look for a marraige of P waves to QRS-T complexes. Normal complexes will always have the components as in the diagram. Look for both P waves with no corresponding QRS-T complexes as well as QRS-T complexes with no associated P wave. The P-R Interval is the time required for the impulse to travel through the AV node. Impulses generated in the atria should take between 0.16 to 0.20 seconds to travel through the AV node. Any delay of > 0.20 seconds is significant of a conduction delay through the AV Node.

STEP FIVE –QRS DURATION A narrow QRS complex (< 0.12), indicates the impulse has followed the normal conduction pathway A widened QRS complex (> 0.12), may indicate the impulse was generated somewhere in the ventricles Measure from the first deflection (+ve or –ve) to where the QRS complex comes back to the isoelectric line. The normal range for the QRS width is 0.8 to 0.12 seconds or < 3 small squares You can say with certainty that if the QRS complex is narrow the inpulse had a supraventricular origin. If on the other hand the QRS comlex is wide, the impulse was either generated in the ventricles or was aberrently conducted. In either case, the normal specialiszed pathways where not used thus a widened wave.

REMEMBER!!! Use a systematic approach Go through all the steps Take your time! Compare with your characteristics list Interpret the dysrhythmia

QUESTIONS?

Education Subcommittee START QUIT Well Done! Education Subcommittee