Lecture 6: Intro to the ECG Flashcards
what is a syncytium
one large cell having many nuclei that are not separated by cell membrane
what is a functional syncytium
- many cells functioning as one
- large groups of cells make electrical changes simultaneously
in which order are parts of the ventricular wall depolarised
1) septum
2) apex
3) atrioventricular groove
what is the ECG good for measuring
- heart rate, with Holter moniter
- especially when atrial rate is not equal to ventricular rate
where are the electrodes in lead II
pos: left leg
neg: right arm
ground: right leg (but could be almost anywhere)
how many leads are in a standard ECG
- 3 bipolar leads: leads I,II and III let us see in frontal plane
- 3 augmented leads in frontalplane
- 6 precordial in transverse plane
what does a wide or misshapen QRS wave suggest
- ectopic pacemaker
- bundle branch block
what does a large Q wave suggest
dead tissue, eg from an old myocardial infarction
what is sinus rhythm
when the heart rhythm is generated from the SAN
what are indicators that the heart is in sinus rhythm
- each P wave matched with QRS complex
- PR interval always normal, 4-5 little boxes
what is sinus tachycardia
tachycardia driven by SAN beating too quickly
what are the sizes of the boxes in an ECG
small box 40 ms
big box is 200 ms
5 big boxes is 1 sec
what is the height of each little box in an ECG
0.1 mV
where is the PR interval
start of P wave to start of QRS complex
where is the PR segment
end of P wave to start of QRS complex
where is the ST segment
end of QRS complex to start of T wave
where is the QT interval
start of QRS complex to end of T wave
PR interval duration
3 - 5 boxes
120 - 200 ms
QRS complex duration
2 - 3 boxes
80 - 120 ms
QT interval duration
9 - 11.5 boxes
360 - 460 ms
how do you calculate ventricular rate from an ECG
count between R waves
how do you calculate atrial rate from an ECG
count between P waves
how to calculate heart rate from ECG
300 divided by number of big boxes
what is the parasympathetic pathway of the heart
vagus nerve stimulates muscarinic receptors
what does atropine do
- muscarinic antagonist
- causes parasympathetic withdrawal
what is the sympathetic pathway to the heart
- stellate nerves
- beta agonists increase rate
- beta blockers decrease rate
what is a heart block
- type of dysrhythmia
- any blocking of impulse conduction of the heart
what are causes of AV heart blocks
- ischaemia of AV node or bundle
- compression of AV bundle by scar or calcified tissue
- inflammation of AV node or bundle
symptoms of AV heart blocks
- can be asymptomatic
- palpitations
- hypotension-like:
- dizziness
- malaise
- syncope
- if serious, risk of sudden cardiac death
what is 1st degree heart block
- PR interval > 5 little boxes
- caused by delayed AV node transmission
what is Mobitz Type I
- type of second degree heart block
- aka Wenckebach
- PR interval gets longer until QRS wave fails to follow P wave
- caused by AV node damage
what is Mobitz Type II
- type of second degree heart block
- aka Hay
- PR interval stays the same, some not followed by QRS wave
- caused by problem in bundle of his
what is third degree heart block
- atrial signals fail to reach ventricles
- PR intervals vary radically, sometimes >12 boxes
- very dangerous
what are premature beats
individual early beats triggered by irritable tissue
what are escape beats
individual late beats triggered by lack of stimulation from atria
what are premature ventricular contractions
- unusually wide ventricular activity
- no S wave and negative dip where T wave should be
what is atrial fibrillation
- very common in elderly
- disorganised electrical activity in atria
- no P wave, but flat or wiggly line
- ventricular rate is fast and irregular
- AVN only lets some signals from atria to ventricles
what is respiratory sinus arrhythmia
- sign of healthy heart, seen in children and athletes
- heart beat slightly faster during inspiration, slower during expiration
