ECG Flashcards
What is the direction of depolarisation?
Endocardium to epicardium
Apex to base
What cells are capable of generating their own contraction and at what speed do they contract?
SAN (90-100), AVN, (40-60), Bundle of His (15-30), Purkinje fibres
What are the features distinctive to cardiac cells?
Intercalated disks - branching
Gap junctions - fast signalling
Many mitochondria
Large T tubules
What is the process of depolarisation and repolarisation?
Action potential arrives
VOCC open and Ca2+ enters
CICR
Ca2+ binds to troponin causing a contraction
Unwind and relax
Ca2+ leaves via: pump into SR, NCX, NaKATPase
What do the waves of an ECG represent
P - atrial depolarisation
QRS - ventricular depolarisation
T - ventricular repolarisation
Where do leads I, II, III, aVF, aVL and aVR look?
Yeah just know this one
What aspect of the heart do leads V1-6 look at?
1-2 septal
3-4 anterior
5-6 lateral
What leads look at the inferior, anterior and lateral heart and which artery is likely responsible for damage in these areas?
Inferior - RCA - II, III, aVF
Anterior - LAD - V2,3,4
Lateral - LCx - V5,6, I, aVL
What would you see on an ECG for left or right axis deviation?
Left leaving - I and III away. If II is negative it is pathological
Right returning - I and III toward each other
What are some causes of LAD and RAD?
LBBB, WPW
RBBB, WPW
Which way does an axis deviate towards when there is damaged myocardium and hypertrophy?
Away from damage, towards hypertrophy
How can you calculate heart rate?
300 / number of large squares
What is the normal range for a P wave?
Between 0.12 and 0.2 seconds
< 0.25mV
What is the normal range for QRS complexes?
<0.12s
<35mm
What is the normal range for T waves?
0.5-10mm
Positive
How long is a normal QT interval
Less than half RRP interval
Complications post MI (Darth Vader)
Death Arrhythmia Rupture Tamponade Heart failure Valve disease Aneurysm Dressler's syndrome Embolism Recurrence
What is the cut off for bradycardia and tachycardia?
<60bpm
>100pm
Recognise AF, atrial flutter, PVC, VT, heart blocks, VF, asystole, STEMI, NSTEMI
As a medical student you should really be able to do this
What is the mechanism behind ischaemia causing ST depression?
Ischaemia reduces Na+K+ATPase activity so K+ builds up in cell (questionable mechanism in my opinion) and Na/Ca as well cause depolarisation. Depolarisation generates nearby electrical currents raising the baseline of the ECG. When ventricles depolarise it goes to a seemingly lower level in relation to baseline
What is the cutoff for ST depression and elevation?
> 1mm above/below baseline in 2 leads
What is the mechanism behind ST elevation?
Injury delays depolarisation due to channels not letting sodium in
Why may T wave inversion be present?
Repolarisation occurs endocardium to epicardium
What are the criteria for pathological Q waves?
> 2mm deep
1mm wide
V1-3
What is the pathway of electrical conduction in the heart?
SAN-AVN-Bundle of His-RBB/LBB-Purkinje Fibres
