Lecture 7: 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
What are the 3 types of cardiac myocyte cell?
Pacemaker cells
Conducting cells
Contractile cells
How quickly do contractile cells propagate the signal?
0.3-0.5m/s
How quickly do conducting cells (purkinje fibres) propagate the signal?
Up to 5m/s
How quickly does the AV node propagate the signal?
0.05m/s
How quickly do internal bundles propagate the signal?
1m/s
What are the 4 internal bundles?
Anterior (to AVN)
Middle (to AVN)
Posterior (to AVN)
Bachmanns (to LA)
How long is the delay of excitation from atria to ventricles by AV node?
0.1-0.2s
What is a lead on an ECG?
A configuration of electrodes
Describe lead 2.
Positive electrode on left leg, negative electrode on right arm and ground electrode on right leg
What are the 12 standard leads?
3 Bipolar
3 Augmented
6 Precordial
What is shown by the QRS complex?
Transmission of depolarisation through the ventricular myocardium
What is shown by P-wave?
Depolarisation of the atria
What is shown by PR segment?
Delay of AV node to allow filling of ventricles
What is shown by T wave?
Ventricular repolarisation
What is shown by ST segment?
Beginning of ventricle repolarisation - should be flat
What is sinus tachycardia?
Tachycardia driven by the SA node beating too quickly - normal PR intervals and each P is matched with a QRS
What is the normal duration of PR interval?
3-5 boxes
120-200ms
What is the normal duration of QRS complex?
2-3 boxes
80-120ms
What is the normal duration of QT interval?
9-11.5 boxes
360-460ms
How many ms is one little box?
40ms
How many ms is one big box?
200ms
How do you calculate beats per minute?
Rate = 300/big boxes
1 big box = 300bpm 2 = 150 3 = 100 4 = 75 5 = 60 6 = 50 10 = 30
What is atropine?
Muscarinic antagonist
reduces parasympathetic activity
What are the causes of heart block?
Ischaemia of AVN
Compression of AVN
Inflammation of AVN
What are the symptoms of heart block?
Can be asymptomatic Palpitation Dizziness Malaise Syncope Risk of sudden death
What is first degree heart block?
When PR interval is greater than 5 little boxes (200ms)
But all Ps followed by QRS
Young people, rarely treated
What is Mobitz type 1 second degree heart block?
Wenchebach
PR interval gets longer until QRS wave fails to follow P wave
Likely cause is AV node damage
No treatment given
What is Mobitz type 2 second degree heart block?
Hay
Some P waves are blocked and are not followed by QRS, PR interval remains the same
Likely problem is bundle of his
High risk
What is third degree heart block?
Atrial signals consistently fail to arrive at ventricles, ventricular rate is consistent (30-40 bpm)
Time between atrial beats is variable
PR interval varies radically
What is an escape beat?
When the atrial signal is very delayed or prevented - triggered by the natural rhythmicity of non-atrial tissue
What is a premature beat?
Triggered by irritable tissue
What do premature ventricular contractions look like on ECG?
Unusually wide ventricular activity
No S wave, instead a wide negative dip where the T wave should be
What does AF look like on ECG?
No P wave, instead flat line or wiggly line
What is respiratory sinus arrhythmia?
Heart beat slightly faster during inspiration and slightly slower during expiration
What is the iso-electric baseline?
From the end of T to the next P
