A first look at the ECG Flashcards
What plane does the limb lead look at?
The standard limb leads look at the electrical events across the vertical and frontal plane.
What are the three limb leads and what do they record ?
- Standard limb lead one: Records right arm to left arm. Goes towards POSITIVE electrode
- Standard limb lead 2: Records from the left leg to the right arm
- Standard limb lead 3: Records from the left arm to the left leg
What part of the action potential is not transmitted at all?
Slow events such as the plateu of the action potential are not transmitted at all.
Where does the PR interval start and end ?
The PR interval starts at the start of the P wave and ends at the start of the QRS .
What is the time of the PR interval and which transmission is it due too?
The time taken here is due to the transmission through the atrioventricular node. This is normally between 0.12-0.2 seconds.
What does the QRS interval represent?
The QRS interval is the time for the whole of the ventricle to depolarise. This is normally 0.08s.
What does the QT interval represent?
This is the time taken from the ventricles depolarising to repolarise again
Why is atrial repolarisation not seen on the ECG?
Atrial repolarisation concides with ventricular depolarization. Ventricles depolarisation involves much more tissue depolarising much faster so it swamps any signals from atrial repolarisation.
Why is the QRS complex so complex?
This is because different parts of the ventricles depolarise at different times in different directions
The first thing that depolarises is the interventricular septum which depolarises from left to right (negative blip)
The bulk of the ventricle depolarises from the endocardial to the epicardial surface (positive blip)
The upper part of the interventricular septum depolarises (negative blip)
Why is the T wave posisitve going
Wave of repolarisation is moving away from the electrode in the left leg. Therefore the electrode in the left leg is going to become more positive relative to the electrode in the right arm, resulting in a positivie going T wave.
Is action potential longer in endocardial cells or in epicardial cells?
The action potential is longer in endocardial cells than epicardial cells. The wave of repolarisation runs in the opposite direction to wave of depolarisation
What information do the preocordial (chest) leads give you?
They are arranged in the front of the heart and therefore look at the same event but in horizontal or transvers plane.
What gives the R wave ?
The main wave of depolarisation in the ventricles gives us the R wave which moves from the endocardial surface to the epicardial surface.
What does STEMI stand for ?
STEMI stands for ST-segment elevation myocardial infarction (heart attack)
What does NSTEMI stand for?
NSTEMI stands for non ST-segment elevation myocardial infarction
What does elevation of sT segment suggest ?
Elevation of the ST segment suggests that htere is something seriously wrong with the heart and is an indication on how serious the MI the person has had
