CV Flashcards
What are ECGs a measure of and what are they not a measure of?
Measures current of extracellular fluid by changes in many cardiac cells at once. Not direct changes in membrane potential of individual cardiac cells.
Describe the phases of myocyte action potential.
0: rapid depolarisation (Na+ in)
1: partial depolarisation (Na+ current stops, K+ out)
2: plateau (slow Ca2+ in)
3: repolarisation (Ca2+ current stops, K+ out)
4: pacemaker potential (slow Na+ in, slow K+ out)
Define P wave, PR interval, QRS complex, ST segment & T wave.
P: atrial depolarisation
PR: time for AD & electrical activation through AV node
QRS: ventricular depolarisation
ST: interval between depolarisation & repolarisation
T: ventricular repolarisation
Define tachycardia, bradycardia & dextrocardia.
Tachycardia: increased heart rate.
Bradycardia: reduced heart rate.
Dextrocardia: heart on right side not left.
What is the difference between acute anterolateral and acute inferior myocardial infarction?
AAMI: ST segments are raised in anterior (V3&4) & lateral (V5&6) leads
AIMI: ST segments are raised in inferior (II, III, aVF) leads
Why is atrial repolarisation normally not seen on an ECG?
it happens at the same time as the QRS complex so is hidden
What is the usual time for atrial and ventricular depolarisation and AV node delay?
AD: 0.08-0.1s
VD: 0.06-0.1s
AVND: 0.12-0.2s
In a normal ECG are P and T positive or negative?
P= positive in every lead except aVR T= positive in every lead except aVR, sometimes V1&V2
Electrical impulses in the heart are 3D but the ECG measures in 1D. What are 2 effects of this?
If impulse travels towards electrode it is big & if impulse travels away from electrode it is small/negative.
Atria are smaller & have fewer myocytes than ventricles so current looks smaller.
What do the ECG graph axes show and what does each square represent?
Voltage over time. Small square across=40ms, big square across=0.2s.
