Cardiac Interpretation Flashcards
Order of the electrical conduction system of heart
SA node → inter-nodal pathways → AV node → Bundle of His → L + R bundle branches → Purkinje fibers
12 Lead EKG and views
- 10 electrodes used → 12 different perspectives
- Limb leads - Vertical view
- RA, LA, RL (neutral or grounding lead), LL
- Precordial Leads - Horizontal view
- V1 to V6
- Chest
5 different views of heart (sections)
- Anterior wall
- Inferior wall
- Lateral wall
- Posterior wall
- Septal wall
Limb leads + where each lead is placed? How is each lead read (L → R)
which one is the neutral lead?
- Einthoven’s triangle
- Limb leads - VERTICAL VIEW
- RA, LA, RL (grounding lead), LL
- Lead 1: R arm → L arm
- Lead 2: R arm → L leg
- Lead 3: L arm → L Leg
Reads negative → positive
Which limb lead corresponds to which part of the heart?
- STANDARD LIMB LEADS
- I: R arm → L arm - lateral wall
- II R arm → L leg - inferior wall
- III L arm → L leg - inferior wall
Augmented Limb Leads view
- AVR - junk lead, non-specific view
- AVL - lateral wall
- AVF - inferior wall
Limb leads cheat sheet chart
aVR - square root of SQUAT
Precordial lead placement
Which view in general vs Limb lead view?
- Limb leads → vertical view
- Precordial leads → horizontal view
Views of heart on EKG - Precordial Leads (chart)
Again, LOOKING AT HORIZONTAL PLANE
Views of heart on EKG
*Contiguous leads*
Limb leads and chest leads together
Contiguous leads (slide 12)
EKG waveforms: P wave
What does it indicate when this wave is abnormal?
- Atrial DEpolarization (contraction)
- Starts in SA node
- P wave absent or abnormal - atria malfunction
EKG wave forms: QRS complex
What does it indicate when this wave is abnormal?
- Ventricular DEpolarization
- Atrial REpolarization
- Abnormal → ventricular issue
EKG wave forms: T wave
What does it indicate when this wave is abnormal?
- Ventricular repolarization
- Same - heart has trouble relaxing and filling with blood - diastole issue
Isoelectric line
Considered baseline
EKG waveforms should ALWAYS return to straight and flat level in between complexes
What makes a wave positive or negative?
- A wave of electrical depolarization moves parallel to the direction of a lead.
- If it moves towards the (+) pole of the lead, a (+) deflection occurs on the EKG.
- If it moves away from the (+) lead, towards the (-) pole of the lead, a (-) deflection occurs onEKG.
- Positive wave form → goes up from isoelectric line
- (-) lead → (+) lead
- Negative wave form → goes down from isoelectric line
- (+) lead → (-) lead
What does Lead II mimic?
- REMEMBER: LEAD II = R ARM → L LEG li>
- Trajectory mimics the natural conduction system of the heart (impulse/conduction of heart)
What is the Axis of the heart?
Overall direction of the electrical activity of the heart
What is the correct positioning of the axis?
Should be downward and to the left
Between -30 and +90 degrees
What does it indicate if the axis is deviated?
Think about the Axis chart of positives and negatives!
If axis is deviated, it can indicate various problems such as hypertrophy, BB, tissue damage, conduction abnormalities
Positive = above isoelectric line
Negative = below isoelectric line
RAD = R axis deviation
LAD = left axis deviation
Easiest way to determine axis? Which leads would you look at?
Look at Leads I (R arm → L arm) and aVF (interior portion of LV)
EKG graph paper, what two things does it measure?
Time (rate) - horizontal line
Amplitude (voltage) - vertical line
EKG squares = what numbers?
- Horizontal:
- 1 small square = 0.04s (40msec)
- 1 Large square = 0.2s (200msec)
- 5 Large squares = 1s (1000msec)
- Vertical:
- 1 small square = 1mm (0.01mV)
- 1 Large square = 5mm (0.5mV)
- 2 Large squares = 1mV
Steps to reading EKG
- Rate
- Rhythm: regular or irregular
- Does it look uniform? P wave present?
- Intervals? PR, QRS
- Basic rhythm/origin
-
Hypertrophy
- For now concentrate on ventricular
- ST segment abnormalities
How many seconds is the bottom lead on the EKG paper? Complete Lead II
10 seconds
Counting the Rate
- Sinus rhythm: count QRS complexes
- In general
- count R waves in 6s EKG strip (30 big boxes) X 10
Quick Read method order (numbers)
How to utilize method
- Look at BIG BOX LINES
- Look for R wave that is the closest to a BIG BOX LINE
- Count L → R
- 300 → 150 → 100 → 75 → 60 → 50
- Count until next R wave
How to determine rhythm on EKG paper?
Which method is the most accurate? Most convenient?
-
March it out - pen and paper method
- Draw two lines on index paper on two R waves
- March the index card along EKG reading to see if it’s equidistant from each other
- Calipers - MOST ACCURATE
- Counting small squares - time consuming
What does a lack of uniform or normal appearing P wave mean?
Atrial arrhythmia or AV block
PACs - premature atrial contractions
Premature atrial contraction (PAC)
Dips below isoelectric line
Beat is early and biphasic
If PR interval not same length throughout?
Think AV block!
PR = atria
Normal EKG interval ranges
KNOW THESE NUMBERS
- PR: 0.12 - 0.20s
- QRS: 0.07 - 0.11s
- QTc: = < 0.40
PR Interval
How it’s measured? What influences it to change?
- Measured from beginning of P wave to beginning of QRS complex
- Will change w/HR (fast HR = shorter PR)
What does the PR interval include in the conduction system
- Includes atrial depolarization, conduction from atria → ventricles through AV node + conduction through His-Purkinje system
- AKA communication between atria dn ventricles
Shortened PR interval VS. Lengthened PR
- Shortened PR = < .12s
- Conduction bypasses AV node → WPW
- Lengthened PR
- Heart block → delayed or lack of conduction through AV node
QT interval
Which waveforms does it include? How is it measured? What measurement is it dependent on?
- QRS complex, ST segment, T wave
- Measure of ventricular repolarization (technically JT segment but usually QT is used)
- HEART RATE - shorter at faster HR
Lengthened QT means?
Which meds will elongate?
- Widened QRS → BBB
- Sudden cardiac death
- Elongation can be caused by these meds:
- Antipsychotics
- Celexa
- Quinolones, Zithromax, Cipros
QRS complex
What does it indicate? Wide?
- Ventricular depolarization
- Wide > 110ms = slower conduction time through ventricles - conduction not occurring in Bundle of His
- Occurs w/BBB, other conduction delays
PVCs
- Widened QRS complex appearing earlier than normal
- QRS often goes in opposite direction (coming from ventricles up)
- Occasional PVCs not concerning
- > 3+ = VTach
- May increase w/hypokalemia
T wave
Inverted? Flattened? Peaked? Biphasic?
- Inverted = Ischemia
- Flattened = Hypokalemia
- Peaked = Hyperkalemia
- Biphasic - ischemia
Usually a positive deflection above isoelectric line
LVH Equation?
- REMEMBER → each small box = 1mm
- S wave in V1 (or V2) + R wave in V5 (or V6)
- If sum > 35mm
OR
- R wave in aVL > 11mm
count up!!
Cause of LVH repolarization changes
What can these result in?
- Can be dx on EKG w/good specificity
- Thick myocardium → need more electricity to conduct → higher amplitude in ventricular depol.
- QRS widening too! due to longer travel through whole heart
- Can result in abnormal ST segments or T waves = LVH w/strain or LVH w/repolarization abnormality
ST segment
What is measures? What if it’s abnormal?
J-point?
- After ventricular depolarization and before repolarization
- Should be flat
- Elevation → infarction
- Depression → ischemia
- Sometimes have a normal rapid upsloping, esp in tachy
- J-point: intersection of end of QRS and start of ST segment
Infarct location corresponding to Coronary artery
Which leads correspond to which heart?
Slide 62
