Electrophysiology Flashcards
Why do an ECG
- evaluate cuase of symptoms (e.g., chest pain)
- diagnosis of disease
- arryhtmia analysis
electrocardiogram benefits overview
Cheap
Quick
Non-invasive
Fundamental test for every admission
ecg Measures
surface manifestations of cardiac electrical activity
positive deflection upwards =
Depolarisation TOWARDS ECG lead
negative deflection downwards =
Depolarisation AWAY from an ECG lead
how many lead vectors make up an ECG
12
- 3 limb leads
- 3 “augmented” limb leads work on making a substiutute vector at a right anmgle between the two
- 6 unipolar precordial (chest) leads
6 limb leads cover which areas:
- 1
- 2
- 3
- AVR
- AVL
- AVF
6 chest leads
V1
V2
V3
V4
V5
V6
PQRST complex
what is the P wave
atrial depolarisation
first small bump
PR interval
start of P wave to the start of the G downwards deflection
this is the time taken for elecyrical deploarisation to spread from the atria to the ventricles- due to the AVN delay
QRS complex
depolarisation of the ventricles
start of Qdownwards deflection to start of T upwards deflection
ST segment
enf od S wave (from isoelectric line) to start of T wave upwards deflection
T wave
last upwards deflection
ventricular repolarisation
RR interval
peak of one R wave to the peak of the next R wave
this is the time between 2 QRS complexes??????
QT INTERVAL
beginning of QRS complex (downwards deflection of Q) to the end of the T wave
time for ventricles to depolarise and then repolarise
Normal heart conduction
Normal heart conduction starts in the right atria in the Sinoatrial node, depolarisation spreads across the atria causing contraction and ejection of blood out of the atria into the ventricle.
Once the depolarisation reaches the atrioventricular node on the interatrial septum there is a slight delay, allowing time for blood to fully empty the atria and enter the ventricles.
The AVN then sends the wave of depolarisation down the left and right bundle branches towards the purkinje fibres, electrically activating the ventricles and causing simultaneous systole of the ventricles.
how many seconds are 5 small squares on an ecg
200 ms/// 0.2s
how long are 5 big boxes
1 second
how many small boxes in one big box
5
Which leads give an anterior view of the heart
V1-V3
Which leads give an inferior view of the heart
limb leads 2,3 and AVF from the legs
Which leads give a lateral view of the heart
1, AVL, V5 and V6
Pacemamkers of the heart
SAN- the dominant pacemaker of the heart with an intrinsic eate of 60-100 bpm- directly affected by extrinsic stimuli
AVN- back up pacemaker intrinsic rate of 40-60 bpm
ventricular myocytes have a rate of 20-45 bpm
follow a system when reading an ECG
- check patient details e.g., on the right patient
- rate
- rhythm
- axis
- the alphabet ( P waves, PR interval, QRS complexes ,ST segment, T waves, QT interval)
What is a normal heartbeat?
tachycardia?
bradycardia?
normal= 60-100
tachycardia> 100 bpm
bradycardia < 60 bpm
how many seconds is 1 standard strip?
what do you times this number by to find HR?
10 seconds
Rate= total number of R waves x 6
how many large squares would there be in 1 minute?
1 sec = 25 mm = 5 large squares
1minute= 60 x 5 = 300 large squares
rate = 300 / number of large squares between R waves
What characteristics describe a normal sinus rhythm?
Normal looking P wave (indicates SAN)
P wave always followed by QRS complex
In a regular fashion
anything not meeting that criteria is not considered normal
how do you determine regularity
look at the R-R distances
are they regular? regularly irregular? Irregularly irregular?
What is the rhythm of this ECG?
regular rhythm approx 75 bpm
P waves present
1 P wave per QRS complex
Normal PR interval
Normal sinus rhtyhm
name 4 different kind of arrhythmias
- atrial fibrillation
- atrial flutter
- heart block (complete, atrioventricular, first degree, second degree, third)
- broad complex tachycardia
Explain atrial fibrillation
Very common arrhythmia, risk increasing with age
multiple wave fronts across the atria cause a sporadic wave form
manifests as an irregular baseline with no clear P waves
because these wave fronts hit the AVN in an irregular fashion, there is irregular electrical action in the ventricles, causing an irregular heartbeat—– irregulalry irregular QRS complex
`Explain atrial flutter
Affects atria.
Generally, affects 1 macro circuit (one repeating electrical circuit going through the atria). Presents as a sawtooth baseline on the ECG.
Can be regularly irregular or irregularly irregular depending on how long it takes for a wave front to complete a circuit.
Tends to go round the atria at 300bpm, AVN can’t conduct at this pace
so 1:1 hardly ever seen.
2:1 block means that every other flutter is acted on therefore 150 bpm.
3:1 block = 100 bpm
Explain complete heart block
Where there is absolute failure of the AVN, SAN still operational
Backup, intrinsic pacemaker function of his/ purkinje fibres takes over 30 -40 bpm
Slower and broader PQRS complex
P waves will still be happening at their original rhythm but will now be unrelated to the QRS, P and QRS out of rhythm together.
what is atrioventricular block
when conduction between the atria and ventricles of the heart is impaired
in normal conduction how long is norm al pR intervall
less than 0.2 seconds (5 small squares)
what is first degree heart block
The wife (P wave) is waiting at home. The husband (QRS) comes home late every night, but he always comes home, and it is the same time every night.
(impluse is delayed at AVN, and PR interval is greater than 0.2 secs > 5 small squares)
how many kinds of second degree heart block are there and what are they called
2
Mobitz1 (wenkebach) and Mobitz 2
describe second degree heart block; Mobitz 1/ wenkebach
The wife is waiting at home. The husband comes home later and later every night until one night he doesn’t come home at all? (what a wenker!)
Note: the husband must come home at least 2 nights in a row first to see this pattern
(PR interval will become greater and greater until there will be a dropped QRS complex and there are two consecutive P waves, after which the pattern will restart)
can be common in healthy people, like athletes. Just the AVN being under lots of vagal tone
Second degree heart block; mobitz 2
The wife is waiting at home. Sometimes the husband comes home and sometimes he doesn’t.
When he does come home, it’s always on time.
Note: this unpredictable behaviour is more serious than type 1 second degree heart block and usually requires counselling (pacing).
(P to R and R to R intervals will remain consistent, but there will be “missing” QRS complexes.
Explain complete third degree heart block
Wife (P wave) is no longer waiting at home. She and her husband (QRS) are on separate schedules and are no longer talking. Each spouse has a regular, individual schedule.
Note: This requires emergency counselling (pacing)
Atrial activity will continue with p waves at one rate. The ventricles (QRS) are depolarising in a slower escape rhythm- both will be regular, but will be uncoordinated)
Explain broad complex tachycardia
Due to a little bit of scar tissue in the myocardium that causes a mini circuit (usually greater than 180 bpm) in the ventricle.
Because this rate is greater than the SAN, this becomes the dominant pace.
Regular tachycardia, rate ~150 bpm
Broad QRS complexes
No obvious preceding atrial activity
Aka Ventricular tachycardia
explain axises on an ecg (Not a focus for year 2)
Axis refers to the overall electrical direction within the heart.
Electricity moving towards and electrode is POSITIVE
Electricity moving away from an electrode is NEGATIVE
If there is a change in the overall direction of the energy, the axis will be described as deviated- left, or right
Look at leads I and II
If both are positive, the axis is normal
ECG: left axis
Look at leads I, II and III
If lead 1 is positive, II is midlining/ negative, there is left axis deviation
The deflection are Leaving each other in the Left axis deviation
Right axis:
Look at leads I, II and III
Lead I is more negative, and III is positive, it is right axis deviation
Lead I and lead III are Reaching toward each other in Right axis
ST elevation signifies
infarction
pericarditis
ST depression suggests
ischaemia
how would low K+ affect a T wave
flat anmd prolonged
What arrhythmias presents with
regular unco-ordinated P wave and QRS complex
complete third degree heart block
which arrhythmia presents with
- an irregular base line with no clear P waves
- irregulalry regular QRS complex
a fib
Which arrhythmia presents with
- Slower and broader PQRS complex
- P waves will still be happening at their original rhythm
- 30-40 bp
Complete heart block
which arrhythmia presents with
- regular tachycardia at a rate of around 150 bpm
- broad QRS complexes
broad complex tachycardia
which arrhythmia presents with
sawtooth baseline
regulalry irregular or irregularly irregular
atrial flutter
