WK7 - ECG Flashcards
Which side of heart receives what blood?
R side receives de-oxygenated blood
L side received oxygenated blood
What are the layers of the heart? Start from the heart chamber
- Heart chamber
Heart wall: - endocardium
- myocardium
- visceral layer of serous pericardium (epicardium)
- pericardial cavity
- parietal layer of serous pericardium
- fibrous pericardium
2 main layers:
Inside = myocardium
Outside = pericardium
What are the coronary arteries?
- R & L coronary arteries emerge from aortic root sinus to supply blood to heart muscle
- L main coronary artery divides…
- L ANT descending (LAD)
- circumflex (LCx)
What is the coronary blood flow of LCA?
- main LCA
- cirucmflex branch
- ANT interventricular (descending) branch
- atrioventricular branch of circumflex
- lateral branch
- posterolat branches
- perforating branches to interventricular septum
What is the coronary blood flow of RCA?
- RCA - R ANT oblique position
- SA Node
- R main CA
- marginal branches
- AV node
- LV
- POS interventricular (descending) branch
What are the 4 primary characteristics of cardiac cells?
- excitability - EXT stimulus response (chemical, mechanical, electrical etc)
- contractility -shorten/return to original length
- automaticity - spontaneously initiate electrical impulse w/o being stimulated for another source (e.g. nerve)
- conductivity - receive electrical impulse/conduct to adjacent cardiac cell
Explain the conduction of cardiac impulses through the heart.
- electrical events preceed mechanical events
- SA node depolarisation
- RA (1st) and LA (2nd)
- atrial contraction
- AV node (delays conduction for ventricular filling from atrial contraction)
- Bundle of HIS –> R & L bundle branches –> purkinje ribres
- ventricular contraction
What are cardiac cells?
- form/conduct electrical impulses = depolarisation/contraction of heart
- contract in all-or-none manner
- possess short absolute/relative refractory periods to aid in hearts pumping action
What is on the axis of an ECG graph? Explain reference pause and how to read the boxes.
x = time
y = amplitude
1mV (10mm high) = reference pulse
One large 5mm*5mm box = 0.2s (200ms) time and 0.5mV amplitude
One small 1mm*1mm block = 40ms time and 0.1mV amplitude
Why is it important to obtain a 12 lead ECG?
To gain electrical activitiy of the heart muslce via..
1. 2 electrodes (+ve and -ve) - bipolar
2. 1 +ve electrode and 1 zero reference point - unipolar
What is Einthoven’s triangle?
It is made up of the limb leads I, II and III to make up the bipolar leads.
Einthoven’s Law states: Lead I + Lead II = Lead III
Einthoven reversed polarity of Lead II to view complexes upright
What are the different leads in an ECG?
- 3 standard limb leads = bipolar (I, II, III)
- 3 augmented leads = unipolar (aVR, VL, aVF)
- 6 precordial leads = unipolar (V1, 2, 3, 4, 5, 6)
Ground provides path least resistance for interference.
What is artefact (noise/intereference)?
Caused from suboptimal acquisition of data
- Patient movement - gross movements as well as tremor/shivering
- AC interference (alternating current)
- loose electrodes
- biotelemetry
- cardiac compressions
What is the P Wave?
atrial depolarisation = atria contracts
* sinus node depolarised
LOCATION: precedes QRS complex
CONFIGURATION: upright, rounded and smooth
BE AWARE: absent or inverted P waves = electrical current generated elsewhere than SA node
What is the PR interval?
Represents atrio-ventricular conduction time
LOCATION: beginning of P wave to beginning of Q wave (if no Q wave then to R wave)
CONFIGURATION: usally isoelectric
DURATION: 0.12-0.2s
Look at leads with clear P wave
What is the QRS complex?
ventricular depolarisation
LOCATION: follows PR interval
CONFIGURATION:
Q wave = 1st -ve deflection
R wave = 1st +ve deflection
S wave = 1st =ve deflection following R wave
DURATION: 0.02-0.12s (3 small squares)
What is the ST segment?
Represents end of ventricular depolarisation and beginning of ventricular repolarisation
- End of S wave deflection and beginning of ST segment = J-Point
LOCATION: after QRS complex, EXT from end of S-wave to beginning of T wave
DEFLECTION: usually isoelectric, but may vary -1.5-+1mm
What is the T wave?
ventricular repolarisation
LOCATION: follows QRS complex
CONFIGURATION: usually upright, rounded smooth and asymmetrical
What is the QT interval?
Time from beginning of QRS complex, representing ventricular depolarization
How to calculate heart rate based on ECG graph?
ECG’s printed on grid paper consisting of 5mm squares = 0.2s
Each large square is divided into 5 smaller 1mm squares = 0.04secs
1 Large Square = 300BPM
2 = 150bpm
3 = 100bpm
4=75bpm
5=60bpm
6=50bpm
Rhythm strip = 10s (count number of complexes in rhythm strip and multiply by 6
Ascertain 6s of rhythm from strip and count number of complexes and mulitply by 10
How to identify regularity?
- regular rhythm beats equal distance apart
- look for rhythm in rhythm strip (bottom)
Rhythms can be…
* regular
* irregular
* regularly irregular (bigeminal or trigeminal)
What are some abnormalities of the ST segment?
Depression
* up-sloping (non-significant)
* horizontal (significant)
* downsloping (significant)
Elevation
* any elevation >1mm requires urgent attention
What is sinus rhythm?
- 60-100bpm
- Rhythm = regular
- P waves = present and upright
What is sinus tachycardia?
- 100-180bpm
- regular rhythm
- P waves present/upright
