introduction to the ECG Flashcards
1
Q
what is a syncytium?
A
one large cell having many nuclei that are not separated by cell membrane
2
Q
what is a functional syncytium?
A
many cells functioning at once
3
Q
what are the 3 types of cardiac myocytes?
A
- pacemaker cells= for setting the heart’s rhythm
- conducting cells= for transmitting rhythm throughout the heart
- contractile cells= for contracting to that rhythm (most numerous)
4
Q
explain how the speed of propagation varies? 4
A
- contractile= atrial and ventricular monocytes- 0.3-0.5m/s
- conducting system (modified cardiomyocytes) purkinjie fibres up to 5m/s
- throughout the AV node 0.05m/s
5
Q
how are cardiomyocytes linked? 2
A
- by low resistance pathways associated with gap junctions at the intercalated discs
- when one action potential depolarizes one cell–> initiating an action potential in adjacent cells
6
Q
describe the spread of impulse through the atria? 7
A
- internodal bundles conduct the impulse from the SA node to the AV node
- bundles ensure synchronous contraction of the aorta
- conducting via atrial muscle would be slow (0.3-0.5m/s)
- conducting via bundles in the atria
- there are 4 specialised bundles in the atria
- these contain purkinhie-like cells which are cardiomyocytes modified to conduct
- bundles are in direct contact with the atrial muscle
7
Q
explain the impulse at the AV node? 7
A
- AV node is the only point where the wave of depolarisation passes from the atria to the ventricles
- AV node delays the wave of excitation from atria to ventricles by 0.1-0.2 seconds
- the electrical delay means ventricles contract after the atria to permit longer and more effective ventricular filling
- to permit longer and more effective ventricular filling
- action potential conducted very slowly in the AV node (0.05m/s)
- AV node is composed of small, modified myocytes
- electrical connection between adjoining cells is weaker
8
Q
explain ventricular propagation? 3
A
- AV node connects to the bundle of His followed by the purkinjie fibre system
- purkinjie fibres transmit the impulse rapidly to the main mass of the ventricles
- from there, slower conduction between contractile monocytes can occur
9
Q
what are purkinjie fibres?
A
- very large monocytes- transmit the impulse faster- bigger diameter cells conduct faster
10
Q
what order does the heart depolarise in? 3
A
- septum
- spex
- atrioventricular groove
11
Q
what is an ECG? 5
A
- gross electrical measurement of the heart
- the electrical activity of the heart is measured on the skin
- the individual currents of the cardia monocytes are tiny
- these currents can be detected from the wrist and the ankle
- this is possible because the heart is a functional syncytium in which large groups of cells all make electrical charges simultaneously
12
Q
what can the ECG diagnose? 4
A
- excellent for rate- Holter monitor (ECG) allows 24/7 rate determination- especially useful when the articular rate is different from the ventricular rate
- many subtleties- not a one stop diagnosis and patient history is essential
- diagnosis requires other techniques
- very fast and affordable
13
Q
what is a lead?
A
2 or 3 different electrodes placed on the body in different positions
14
Q
what is the set up of lead II?
A
- positive electrode on left leg
- negative electrode on the right arm
- ground electrode on the right leg (although it could be almost anywhere)
15
Q
describe the 12 standard leads? 3
A
- 3 bipolar leads- I,II,III detect what happens in the frontal plane
- 3- ‘augmented’ leads
- 6 precordial leads
16
Q
how is switching between leads shown on an ECG?
A
vertical lines
17
Q
what does the P wave show?
A
depolarisation of the atria in response to SA node triggering
18
Q
what does the PR segment show?
A
delay of AV node to allow filling of the ventricles
19
Q
what does the QRS complex show?
A
depolarisation of ventricles, triggers main pumping contractions
20
Q
what does the ST segment show?
A
beginning of ventricular repolarization, should be flat
21
Q
what does the T wave show?
A
ventricular repolarisation
22
Q
describe the problems with the QRS complex? 2
A
- if the ORS is wide or misshapen, then ventricular conduction is abnormal
- large (deep) Q waves are a sign of dead tissue (only MI)
23
Q
what is the sinus rhythm? 4
A
- when the heart rhythm is generated from the sinoatrial node
- each P wave is followed by a QRS complex
- every ORS complex is preceded with a P wave
- when PR interval is always normal
24
Q
what is sinus tachycardia?
A
- tachycardia driven by the SA node beating too quickly- it has normal PR intervals
25
what is the normal PR interval and its duration?
start of the P wave to the start of the QRS complex
| 3-5 little boxes (120-200ms)
26
what is the normal QT interval and its duration?
from the start of the QRS complex to the end of the T wave
| 9-11.5 boxes (360-460ms)
27
what is the ST segment on the graph?
from the end of the QRS complex to the start of the T wave
28
what is the normal QRS complex duration?
2-3 boxes (80-120ms)
29
how long do these boxes count for on an ECG:
- little box
- big box
- 5 big boxes
- 40ms
- 200ms
- 1 second
30
how do you calculate ventricular rate on an ECG?
count between the R waves
31
how to calculate heart rate on an ECG?
count between P waves
32
how do you work out rate on an ECG?
300/big boxes
33
what does the parasympathetic input of the heart lead to? 5
- vagus nerve leads to
- muscarinic stimulation
- decreased heart rate
- decreased contractility
- decreased conduction velocity
34
what does the sympathetic input of the heart lead to? 3
- increase in heart rate
- increase in contractility
- increase in conduction velocity
35
what happens during parasympathetic withdrawal? 3
| what can cause it?
- increased heart rate
- increased contractility
- increased conduction velocity
- atropine--> muscarinic antagonist
36
what is a heart block? 2
- a type of dysrhythmia (bad rhythm)
| - any kind of impulse conduction that blocks the heart
37
what is an AV heart block?
- a delay or failure of atrial signal stimulating ventricle
38
what can be the cause of a AV heart block? 3
- ischaemia of AV node or AV bundle
- compression of AV bundle by scar of calcified tissue
- inflammation of the AV node or bundle
39
what are the symptoms of a heart block? 4
- can be asymptomatic
- palpitations
- hypotension like symptoms: dizziness, syncope
- risk of sudden death
40
what is a first degree heart block? 6
- when the PR interval is bigger than 5 little boxes
- all P waves are followed by QRS
- almost always asymptomatic
- often young people
- delayed AV node transmission
- rarely treated
41
what is mobitz type 1? 6
-second degree heart block
-some P waves are blocked are blocked and are not followed by QRS (some ORS are missing)
-wenckebach
-PR interval gets longer until QRS wave fails to follow the P wave
-likely cause is AV node damage
usually no treatment given
42
what is mobitz type 2? 8
- second degree heart block
- hay
- some P waves are blocked and are not followed by QRS
- PR interval remains the same
- likely a problem in the bundle of His
- high risk
- can progress to a 3rd degree heart block
- implant pacemaker
43
what is a third degree heart block? 6
- atrial signals consistantly fall to arrive at ventricles
- ventricular rate is consistent(30-40 bpm)
- time between atrial beats and ventricular beats is variable
- PR interval varies radically- sometimes more then 12 boxes
- intrinsic ventricular rate is low
- atrial beats are consistent
44
what are premature beats?
early and triggered by irritable tissue
45
what are escape beats? 2
- are late and triggered by natural rhythmicity of non-atrial tissue
- occur when the atrial signal is very delayed or prevented (in third degree heart block)
46
what is premature ventricular control? 4
- unusually wide and weird looking ventricular activity
- no S wave, instead a wide negative dip where the T wave should be
- often beat triggered in middle of myocardium- the two ventricles are electrically unsynchronised
- width is determined by slowed conduction velocity
47
what is atrial fibrillation? 6
- disorganised electrical activity in atria
- no P wave, instead a flat and wiggly line
- ventricular rate is fat and irregular: many signals reach the AV node
- AF is very common in the elderly
- can lead to thrombus formation in atrium due to slow flow of blood, this leads to a stroke risk
- anticoagulants can try and prevent thrombus
48
what is respiratory sinus arrhythmia? 5
- heartbeat is slightly faster during inspiration, slightly slower during expiration
- normal
- usually only present in children and athletes
- caused by respiratory centres in the brains medulla
- observe ventricular rate: inverse of RR interval
49
what does ST segment elevation show? 2
- acute sign of MI
| - isoelectric baseline: from end of T to the next P
