Week 2- ECG Interperation Flashcards
What does each little box represents?
- 0.04 seconds
What does 1 large box represents?
- Each large 0.2 secs
What is the P wave?
- Formed as the impulse is generated in the atria and represents atrial depolarization
- Smooth, round, upright shape
- Immediately precedes the QRS
- Duration is less than 110 ms (less than 3 boxes)
What should you look for in P wave?
- Look for no P waves
- If a P wave is present but not followed by a QRS complex (not followed by a QRS this indicates there is a block)
- Can give clues to the pacemaker site
- P waves that vary in size and configuration
- Morphology: upright or inverse
- If P waves look different then their coming from somewhere else not the SA node
What is the PR interval?
- Amount of time it takes for the atria to depolarize and for the impulse to travel through the AV node
- Slightly delay that normally occurs
- Measured from the start of the P wave to the point at which the QRS complex begins
What is the QRS complex?
- Narrow, with sharply pointed waves, and has a duration of less than 0.12s (3 or less boxes)
- If QRS is wide this indicates a block somewhere
- Represents depolarization of simultaneously contracting ventricles
- Beginning of the Q wave to the end of the S wave
- Should follow each P wave
What is the T wave?
- Represents ventricular repolarization
- Asymmetric less than half the overall height of the QRS complex, and be oriented in the same direction as the overall QRS
- Typically have a slower upstroke and faster down stroke
What are the steps to reading an ECG Rhythm?
- What is the heart rate?
- Are the P waves present? Are they regular? Do they all look alike? Are they inverted, absent, or retrograde? Are their fibrillation of flutter waves?
- Is the PR interval less or greater than 0.20 seconds?
- Is the QRS complexes narrow or wide
- Ratio is there a P wave for every QRS
- Is the rhythm regular, regularly irregular, or irregularly irregular?
How can we determine heart rate?
The 6 second method
- simplest & most accurate when rhythm is irregular or between approx 50-100
- Count the number of QRS complexes in a 6 sec strip, multiply by 10
The sequence method
- Regular rhythms and strips less than 6s long
- 300, 150, 100, 75, 60, 50, 43, 38, 33
- Find R wave on a heavy line and count off until you reach the next R wave
How do we determine the rhythm regularity?
- Measure the distance between R waves is one method used to evaluate rhythm regularity
(Regular, regularly irregular, or irregularly irregular)
What are the categories of Dysrhythmias?
- Disorder of impulse formation
- Disorder of impulse conduction
- Artifact
Disorder of impulse formation
- SA node failure
- Other pacemakers
- Ectopic focuses
Disorders of impulse conduction
- Delayed or blocked in the heart
Artifact
- 60 cycle interference
- Poor contact
- Damaged cable
Characteristics:
- Rate- 60-100 bpm
- P waves present & upright
- PR normal
- QRS narrow
- Ratio 1:1
- Rhythm is regular
NORMAL SINUS RHYTHM
Characteristics:
- Rate normal range (increases with inspiration and slow with expiration)
- P waves present & upright
- PR interval normal
- QRS is narrow
- Ratio 1:1
- Rhythm is regularly irregular
- Bainbridge reflex: sudden changes in pressure
(normal finding in children and young adults)
SINUS ARRHYTHMIA
Characteristics:
- Rate less than 60 bpm
- P waves present & upright
- PR interval normal
- QRS is narrow
- Ratio 1:1
- Rhythm is regular
SINUS BRADYCARDIA
Characteristics:
- Rate 100-160 bpm
- P waves present & upright
- PR interval normal
- QRS is narrow
- Ratio is 1:1
- Rhythm is regular
(Paediatrics & children)
SINUS TACHYCARDIA
Characteristics:
- Rate 140-250 bpm
- S/S: heart pounding, out of breath, sweating, hypotensive, chest pain
- P waves buried under the preceding T wave
- PRI: N/A
- QRS narrow (<0.012 secs)
- Ratio: N/A
- Regular rhythm
(Fast, narrow complexes can’t make out P waves)
SUPRAVENTRICULAR TACHYCARDIA (SVT)
- Rate change is sudden and unexpected
- P waves may be seen during the slow phase
- Each section has a regular rhythm
- RE-entry or bypass tracts (WPW)
- Fast, narrow complex begins and ends abruptly
- Caused by re-entry syndromes
PAROXYSMAL SUPRAVENTRICULAR TACHYCARDIA (PSVT)
When does RE-entry Syndrome occur?
- Re-entrant arrhythmias occur when an electrical impulse recurrently travels in a tight circle within the heart
- When conduction is abnormally slow in some area (for example in heart damage) the myocardial cells are unable to activate the fast sodium channel
- Part of the impulse will arrive late and potentially be treated as a new impulse
(series of beats - sudden onset)
What is RE-entry Syndrome?
- In the AV node, a wave of depolarization encounters a region that is non-conductive and deviates around it.
Down the left limb, the waves continues
Down the right limb, the wave encounters a group of cells that are still refractory and the wave is blocked - The wave (impulse) of depolarization spreads to the rest of the heart causing it to contract and repolarize.
Meanwhile, the previously blocked conduction limb is now able to conduct slowly in retrograde direction. - Now the impulse re-enters a polarized or repolarizing region and gives rise to an ectopic focus that may generate a single beat or give rise to a series of consecutive beats
What is pre-excitation syndrome?
- Impulse from somewhere in the atria reach the ventricles sooner than one transmitted down the normal conduction pathway
- In some individuals, pre-excitation occurs because there exists a muscle fiber that penetrates the AV ring that normally isolates the 2
- This acts as an accessory pathway
What are the types of pre-excitation syndromes?
- WPW (kent bundle)
- Manheim Fibers
- LGL
What is WPW (Kent Bundle)?
- Pathway through the AV ring that bypasses the AV node. Conduction is up from the ventricles to the atria or vise- versa
What is Manheim Fibres?
- From the AV node, bundle of His or branches (AV node - accessory pathways and bundle branches simultaneously)