ECG Flashcards
Outline the 9 steps of how an AP travels in the heart
- SA Node depolarises
- Atrial depolarization
- Delayed by 120-200ms at AV node
- Spreads to ventricle via Bundle of His
- Spreads through ventricle via LBB, RBB and Purkyne system
- Inter-ventricular septum is first depolarised
- Apex and free ventricular walls depolarised
- Base of ventricles depolarised
- Repolarisation in opposite direction to depolarisation
What are 2 meanings of ‘leads’
- Cable used to connect electrode to ECG recorder
2. Electrical view of heart obtained from a combo of electrodes
How many electrodes are placed and where
How many views/ leads are produced
What is the right leg electrode used for
4 on limbs
6 on chest
12 leads
Used as a grounding electrode, not for any leads
How do limb leads differ to Augmented Limb leads
Which electrodes are involved in, and identify the +ve electrode in;
- Limb lead I
- Limb lead II
- Limb lead III
Limb leads are Bipolar- 1+ve, 1-ve electrode
Augmented Limb Leads are Unipolar- 1 +ve electrode
- RA and LA- LA is +ve
- RA and LL- LL is +ve
- LA and LL- LL is +ve
Where are the positive electrodes on the leads;
- aVR
- aVF
- aVL
When using Augmented limb leads, what represents the negative electrode
- aVR: Right Arm
- aVF: Left Leg
3 aVL: Left Arm
The mid-point of the other 2 remaining electrodes
In regards to positive electrode and direction of depolarisation/ repolarisation, state 4 rules that determine the sign of deflection on an ECG
- Depolarisation towards +ve electrode= Upwards deflection
- Depolarisation away from +ve electrode= Downwards deflection
- Repolarisation towards +ve electrode= Downwards deflection
- Repolarisation away from +ve electrode= Upwards deflection
Of the limb and augmented limb leads ,
- Which leads look at left surface of heart
- Which leads look at inferior surface
- Which leads look at right atrium
- I, aVL
- II, III and aVF
- aVR
What represents the negative electrode in the Chest/ Precordial Leads
In what directions do the chest electrodes view the heart? In what plane?
Mid-point of electrodes on RA, LA and LL
Front to back + right to left, in horizontal plane
What 2 things do the amplitude of deflection depend on
- How directly the depolarisation wave is coming towards +ve electrode
- Amount of muscle mass conducting activity
How does the QRS complex appear if;
- Depolarisation directly towards +ve electrode
- Wave obliquely towards electrode
- Wave at right angle to electrode
- Wave directly away from electrode
- Tall upright complex
- Small upright complex
- No complex OR biphasic
- Tall downwards complex
When viewing from the apex, explain the ECG appearance of;
- SA node depolarisation
- Atrial depolarisation
- AV node delay + Spread through Bundle of His
- Depolarisation of IV Septum
- Depolarisation of apex and free ventricular walls
- Depolarisation spreading to base of ventricles
- Ventricular Repolarisation
- No deflection, as insufficient signal to be detected
- Small upright deflect, as low muscle mass and towards +ve electrode
- Flat line (Isoelectric segment)
- Small downward, as moving obliquely away
- Large upright, as directly towards and large muscle mass
- Small downward, as moving obliquely away
- Medium upwards, as moving away from heart
On an ECG scan,
- How much time is shown by 1 small square
- How much time is shown by 1 large square
- How much time is shown by 30 large squares
- 40ms
- 0.2s (200ms)
- 6s
How to calculate heart rate from ECG if irregular
Can this be used for regular Heart rates too?
Count number of QRS complexes in 6 seconds, then multiply by 10
Yes
On an ECG, a PR interval is measured from where to where?
How long is the normal range?
What do longer PR intervals indicate
From start of P wave to start of Q wave
0.12-0.2 seconds (3-5 small squares)
Delayed conduction through AV Node and Bundle of His
On an ECG, a QRS interval is measured from where to where?
How long is the normal range?
What do longer QRS intervals indicate
Start of Q wave to end of S wave
<0.12s (3 small squares)
Indicates that depolarisation arises in the ventricle, not from the Bundle of His. (Hence it is slower)
On an ECG, a QT interval is measured from where to where?
How long is the normal range?
What do longer QT intervals indicate
What can this lead to
Start of Q wave to end of T wave
If corrected, <0.44-0.45s (11 small squares)
Indicates prolonged ventricular repolarisation
Can lead to arrhythmia
What 4 questions do you ask to determine if Heart Rhythm is normal Sinus Rhythm
- Is the Rythm regular
- Is the heart rate normal (60-100)
- Are there P waves, and are they followed by QRS waves
- Are the intervals normal
What is Atrioventricular conduction block/ Heart block
What are the types
Delay/ failure of conduction of impulses from atria to ventricles via AV node and Bundle of His
- First degree
- Second degree (Mobitz type 1 and 2)
- Third degree
Identify 4 causes of an AV conduction block
- Degeneration of conduction system with age (Sclerosis and fibrosis)
- Acute myocardial ischaemia
- Drugs
- Valvular disease
What happens in First Degree AV Block
Which interval is affected and how
When conduction is slowed without skipped beats
PR Interval is longer than normal (>0.2s)
What happens in Second Degree AV Block- Mobitz Type 1 (AKA Wenkebach 2nd degree heart block)
PR intervals get longer until one QRS is skipped, then cycle starts again
What happens in Second Degree AV Block- Mobitz Type 2
PR intervals do not get longer, but QRS is suddenly skipped
What happens in Third Degree AV Block
What sets the new rhythm and at what BPM
Why is the Heart block the most dangerous
Atria and ventricles depolarise independently
(Complete failure of AV conduction)
Ventricular pacemaker sets rhythm at 20-40bpm
Too slow to maintain BP
How does a Bundle Branch Block appear and why
Normal P wave, PR Interval, Longer QRS complex
Because only bundle branches have delayed conduction
Where can an arrhythmia arise from
Atria; (Supraventricular)
- SA node
- AV Node
- Atrium
Ventricles
In an Atrial Fibrillation ECG describe the P waves, RR intervals and QRS complexes
No P waves-> Wavy baseline
Irregular impulses-> Irregular RR intervals
Normal QRS complexes (as ventricles depolarise normally)
Is Afib slow or fast? (<60 or >100?)
Compare coarse and fine fibrillation
Can be Slow OR fast
Coarse- Amplitude> 0.5mm
Fine- Amplitude< 0.5mm
- What is an Ventricular Ectopic Beat/ Contraction
- How do the QRS complexes appear
- An extra ventricular beat/ depolarisation that doesn’t spread via His-Purkyne system.
- Wider QRS complexes (Slower ventricular depolarisation)
What can a series of Ventricular Ectopic Beats (Contractions) cause?
Why’s this dangerous
Can cause Ventricular Tachycardia
VTACH can reduce Cardiac Output and cause Vfib
In Vfib, there is no co-ordinated contraction so no cardiac output leading to death.
Compare the 2 types of Myocardial Infarction, in reference to the ST segment
STEMI/ ST Segment Elevation: Full thickness of ventricular wall is affected
Non-STEMI/ ST Segment Depression: Not affected full thickness of ventricular wall
Describe the changes in an ECG after a STEMI at the following stages;
Acute Hours Day 1-2 Few days later Weeks later
Acute: ST elevation
Hours: ST Elevation, Smaller R wave, Q wave begins
Day 1-2: T wave inversion, Deeper Q wave
Few days later: Normal ST, T wave inverted to normal
Weeks later: Normal T and ST, Q wave persists
How does a pathological Q wave appear
1 small square wide
2 small squares deep
What are 2 ECG changes in Ischaemia AND a Non-STEMI
ST depression
T wave inversion
Identify 3 ECG features during Hypokalemia
Peaked p waves
T wave flattens and inverts
U waves formed (Between S and T)
Identify 4 ECG features during Hyperkalemia in order of increasing Serum [K]
<6.5: Tall tented T waves
6.5-7.5: P wave lost
7.5-8.5: QRS Widens
>8.5: QRS Widens further
