Basics of ECG Interpretation Flashcards by Claire Hubert

Why is there a slow rate of rise in SAN action potential?

no sodium channels in center channels

calcium channels are slower

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The basis for pacemaker function is….

Slow, spontaneous diastolic depolarization

the unstable baseline

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Three conditions for re-entry are…

Closed loop

unidirectional block

transit time > refractory period

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The enzyme associated with overdrive suppression is…

Sodium potassium ATPase

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The spontaneous diastolic depolarization in SAN is due to …

Opening of funny channels

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What is the mechanism of overdrive suppression?

Hyperpolarization due to increased sodium efflux

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Refractory period plasticity is related to changes in…

Phosphorylation of potassium channels and increased potassium efflux

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The tendency for action potential amplitude and conduction velocity to decreased is known as…

Decrement also conduction

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Irregular blocking of impulses leads to impulse division and multi-directional impulse conduction resulting in…

Circus movements

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Delayed due to de-innervation and autonomic changes

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How much faster than a Purkinje fiber conducting an AP is Usain Bolt?

3 times as fast at 12 meters per second

Purkinje fibers are at 4 meters per second

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Where are each of these action potentials coming from?

SA and AV node don’t have the rapid depolarization due to calcium channels instead of sodium.
SA node occurs sooner because conduction system

Atrium repolarizes the fastest

Midmyocardium has the longest duration of action potential

Epicardium has the shortest

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Label this image.

Describe the path of the action potential.

What electrical event is measured by the PR interval?

What does the PR segment indicate?

What wave is never visible?

AP starts in SA node - AV node - HIS bundle - bundle branches - purkinje fibers

PR interval - measures the time it takes for AP to travel from SA node to purkinje fibers

PR segment - should be 0 volts, as this is the baseline

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What is represented by the QRS complex?

What electrical phases of ventricular myocytes AP are represented by the QRS complex?

QRS

Ventricular depolarization

Ventricular myocytes - phase 0 and 1

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Label this image

What part of the AP does the T wave represent, and what action?

When is the U wave visible?

What is the ST segment and what part of the action potential does that represent?

T wave - ventricular repolarization, phase 3

U wave - very slow heart rate can make visible

ST segment - baseline, J point is start, phase 2

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Label this image and what each interval/segment is indicative of.

What are the 3 segments/intervals that provide a baseline?

R-R and P-P are indicative of heart rate
*use beginnings of P waves*

QT interval represents the refractory period

T-P segment is another baseline

Baselines are
PR intervals
ST segments
TP segments

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Why are the QRS and T waves on an ECG concordant?

Because Depolarization and repolarization move in the opposite direction

Label this image.

Describe how these 12 leads lead to localization.

Which leads are the anterior/septal leads?

Which leads are the inferior leads?

Which leads are the lateral leads?

What lead shows us the cavity of the heart from the perspective of the right shoulder?

12 lead EKGs provide perspective from many different angles that allow localization of electrical events in the heart.

Anterior/Septal Leads
Septal - V1/V2
Anterior - V3/V4

Inferior Leads
II, III, aVF

Lateral Leads
High - I/aVL
Low - V5/V6

View from the right shoulder
aVR

Label this image, and describe the localization of each set of leads.

What arteries are associated with each region?

Lateral leads - Left anterior descending artery (LAD) diagonal or Left circumflex (LCx)

Inferior leads - Right coronary artery and/or LCx

Anterior/septal leads - LAD

Describe the R progression and S progression in precordial leads.

R waves should start small and get larger

S waves should start large and get smaller

This shows that in V1 you are not looking at the left ventricle more right atrium and septum, where as V6 is more left ventricle

What are the 5 steps of ECG Interpretation?

Rhythm and Rate
Timing/Intervals (PR, QRS, QT)
Mean Electrical Axis
Hypertrophy
Infarct

What does each small box represent horizontally? Big box?

What does each small box represent vertically? Big box?

Horizontal
small box - .04 seconds
big box - .20 seconds

Vertical
small box - 0.1 mV
big box - 1 mV

What is the heart rate given the following R-R intervals

1 big box

1 big box - 300 b/min

2 - 150 b/min

3 - 100 b/min

4 - 75 b/min

5 - 60 b/min

6 - 50 b/min

7 - 42 b/min

Around 50 b/min

About 150 b/min Actually 136 with math

About 100

About 75

What expectations do you have when looking at Lead II?

_Expections of Lead II_ P should be positive QRS should be positive may/may not Q wave, S wave T should be concordant with QRS

Describe the steps to assessing rate and rhythm | (step 1 of interpreting ECGs)

Steps to Examining rhythm Check rhythm strip (Lead II) 1. P waves - present and upright in Lead II 2. Are P waves related to QRS - does every QRS have a P and vice versa? 3. Regular rhythm - does P-P and R-R match 4. Rate

What are the steps to assessing timing/intervals | (the second step of interpreting ECGs)

1. is the PR interval normal and fixed 2. Determine width of QRS complex 3. is QT interval normal

What are the normal values for the following P wave QRS Complex Pathologic Q waves PR interval QT interval RR interval

P wave: 0.08-0.10 sec **QRS complex: 0.06-0.10 sec** Pathologic Q waves: over **25% of R wave (\>3mm)**, **\>30 msec** duration **PR interval: 0.16-0.20 sec** (children can be as low as 0.12) **QT interval: 0.36-0.44 sec** RR interval: 1.0-0.6 sec

Why do QTc values exist What heart rate are calculations for QTc based on? What is the quick way to estimate QTc? What is the most common formula used when calculating QTc formally?

Heart rate and refractory period change QT interval, making interpretation at high heart rates difficult Based on 60 b/min heart rate Quick: **when HR\>100 QT should be less than half the preceding RR interval** Bazett's formula is most commonly used QTc = QT / square root of RR

What is the most common lead in which QT interval is measured? What other leads would suffice? What leads should be avoided? What are the normal ranges of QT interval? What can alter QT interval?

_Most common lead: **Lead II**_ Also: Leads I and V5 Not: III, aVL, and V1 _Range: **0.36-0.46 msec**_ _Altered QT_ drugs electrolytes, micronutrients channel mutations exercise (shortens QT)

What are the concerns associated with prolonged QT?

_Prolonged QT_ Leads to longer refractory period and increased change of early depolarizations Increased risk of polymorphic ventricular tachycardia _Short QT interval_ Increased risk of paroxysmal A fib or V fib sudden cardiac death

What are the two methods to assessing axis while interpreting ECGs? (3rd step)

_1. Fast way - gets you in a 90 degree vicinity_ Check leads I and aVF If lead I is positive, the mean electrical axis has to be depolarizing in that direction (-90 to 90) If lead aVF is positive the mean electrical axis has to be depolarizing in that direction (0 to +/-180) _2. Isoelectric point_ Find the lead where the QRS complex has a positive and negative excursion that are equal, resulting in an amplitude of 0. This means the mean electrical axis must be perpendicular to this lead. That gives 2 options. To determine which is correct, you can check which other leads have positive amplitudes meaning the mean vector is depolarizing towards those leads. 3. Graphing technique with Leads I, II, and III Net amplitude of QRS complexes graphed

What can you learn through assessment of the mean electrical axis of an ECG?

_Insight about conduction through the heart_ Vector points away from an infarction Vector shifts toward bundle branch blocks Vector points toward hypertrophy If not in the normal range or mean electrical axis has moved from previous ECGs

Label me and what each quarter indicates? Where would the vectors point for the following conditions? - right heart hypertrophy - right bundle branch block - right sided infarction

Right heart hypertrophy - right axis deviation right bundle branch block - right axis deviation right sided infarction - left axis deviation

Which 2 leads can be used to quickly approximate the mean electrical axis? What combination of +/- would indicate a normal axis? What combination would indicate an extreme right axis deviation? Which combination would indicate a left axis deviation? Which combination would indicate a right axis deviation?

Leads I and aVF. Lead I points positively to the right side of the graph. So If lead I has a positive QRS complex then the mean electrical axis is definitely on the right side of the graph (-90 to +90) Lead aVF points positively to the bottom of the graph. So if this QRS remains positive that means the mean electrical axis is lying somewhere on the bottom half of the graph (0 to +/-180)

What are the 90 degree relationships between the leads?

I - aVF II - aVL III - aVR

What are the steps to assessing for hypertrophy? Which hypertrophy diagnosis is more reliable with ECG? | (the fourth step)

LVH is moderately accurate, RVH much less If ECG criteria is met, echo to confirm _Three criteria_ 1. Over 35 y/o * *2. Sokolov-Lyon criteria** 3. R wave in aVL\>11mm, in aVF\>20mm _Sokolov-Lyon Criteria_ - add the magnitude of the **S wave in V1** to the magnitude of the tallest **R wave in V5/6** - must be **over 35mm**