Week 10 - ECG Flashcards
what is the P wave
Atrial contraction. (this is only a holding area for blood it is then sent to the ventricles requiring a small contraction. electrical activity is proportional to muscle activity)
What is the QRS complex
Ventricular contraction
WHat is the T wave
Ventricular repolarisation. Return of the ventricular mass to its resting electrical state
Where is atrial repolarisation
this does occur but it is completel swamped in the QRS. AKa the QRS wave is so big it hides the atrial repolarisation
How does the elctrical current travel through the heart?
- starts at the right atrium in the SA node
- depolarisation spreads across atrium
- electrical discharge spreads to the ventricles via the AV node
- from ventricles electrical discharge goes through the bundle of his in he interventricular spetum to the left bundle branch
- then spreads to the purkinge fibres
Why is there a delay between the atrial and the ventricles?
allows time for blood to move from atria to ventricles ready to be pumped
What sets the rhythm of the heart
SA node sets the intrinisc rhythm
Where are the pacemakers in the heart?
SA node in the atrium. Highest frequency discharge Av node at AV junction (40-60bpm) Purkinje fibres (20-40bpm)
On an ECG what determines the shape of the QRS (up or down)
If wave of depolarisation is towards a lead then the deflection on the ECG will be upward
How do you calculate time the ECG trace
each large square is 0.2 seconds
each small squares is 0.04 seconds
What is the normal duraction of the QRS complex
less than 0.12 seconds (3 small squares). THis is the time taken for excitation to spread through the ventricles
What is the normal duration of the PR interval
0.12-0.2 seconds (3-5 small squares)
What is the PR interval
TIme take for the excitation to spread from the SAM node through the atrial muscles and the AV node down to the bundle of his and into the ventricular muscle
What are the characteristics of normal sinus rhythm
HR: 60-100bpm Rhythm: regular P wave: before each QRS PR interval: 0.12-0.2 seconds QRS < 0.12 seconds
What is ventricular ectopic beats
ventricular extrasystoles an example of abnormal timing
Extra beats but not arising from the SA node
depolarisation mixing with reploarisation
WHat is Prolongation of PR interval indicitive of
First degree heart block
WHat is first degree heart block
Prolongation of the PR interval. Longer than the 0.12-0.2 that is normal.
Is still coming supraventricularly as QRS is still normal
If you are experiencing a heart issue on the ECG, the QRS is abnormal but the P was is fine, where is it coming from
Ventricularly as apposed to suprventricularly
What is second degree heart block
And how does this look on an ECG
excitation fails to pass through the AV node or the bundle of his
On an ECG: P wave but no QRS complex
There are three variations of second degree heart block. What is the first (Mobitz type 2)
Most beats are conducted with regular PR interval but occasionally there is an atrial contraction without a subsequent COntraction
Second type of second degree heart block ( Wenkebatch phenomena
Progressive lengthing of the PR interval and then a failure to conduct of an atrial beat followed by a shorter / normal PR interval and a repitition of the cycle
Variation three of 2nd degree heart block
There may be alternate conducted and non conduction atrial beat. THe ration of P wave to ventricular complexes can vary E.g 2:1 or 3:2
What is third degree Heat Block
COmplete block
atrial contraction by no beats conducted in the ventricles
Atria and ventrical contracting independently
WHat is bundle branch block
Widening of the ventricular complex as depolarisation hasn’t spread via bundle branches
What type of rhythm has wide QRS complexes
Ventricular rhythms
What does narrow QRS complexes mean
Its a supraventricular rhythm
WHat are the 4 classifications of abnormal cardiac rythms
Cardiac Slowing ( escape beats and Bradycardia)
Early single beats
Sustained and fast rhythm (Tachycardia)
Total disorganisation (atrial or ventricular firing or fibrilation)
What are early single beats
Ventricular ectopic beats (r occurs on the T
Or Premature ventricular contraction (PVCs)
Atrial fibrilation
QRS is still there but there are many P waves in the middle
List some clinical symptoms and signs showing abnormal ECGS
LOC _ dizziness, near syncope and syncope Hypotentions Palpitation Abnormilites of the pulse chest pain SOB
Should the ST segment be lvel
Yes it should be. And should be at sam level as between T and P
What are the types of tachycardia
- supraventricular - Atrial flutter
2. ventricular - ventricular tachcardia
What does a horizontal ST segment indicitive of
Sign of ongoing ischemia
Can be normal for exercise with an increase in HR
What happens to the ST segment when having an acute myocardial injury
Elevation of the ST segment
