Session 8 Flashcards
How many extra cellular recordings do you get with systole?
2
What causes an upward going signal on an ECG?
Depolarisation moving towards the electrode.
What causes a downward signal on an ECG?
Depolarisation moving away from an electrode.
What does repolarisation towards an electrode look like on an ECG?
A downward going signal.
What does repolarisation away from an electrode look like on an ECG?
An upward going signal.
What does the amplitude of a signal depend on?
How much muscle is depolarising
How directly towards the electrode the excitation is moving
On an ECG what causes the P wave?
Atrial depolarisation.
On an ECG what causes the Q wave?
Septal depolarisation.
On an ECG what causes the R wave?
Main ventricular depolarisation.
On an ECG what causes the S wave?
The end of ventricular depolarisation.
On an ECG what causes the T wave?
Ventricular repolarisation.
Why is the P wave on an ECG small?
Because the muscle is small.
How does the action potential spread through the septum?
Down and out.
Why is the spread through the ventricles a large upward deflection?
Because it spreads quickly.
Why is there a flat line between the S and T wave?
Because the ventricles are staying contacted.
What does an ECG measure?
A change in electrical field only.
Why is the T wave slower and flatter than the other waves on an ECG?
Because each cell repolarises individually so it is slower.
Why do you move the ECG electrodes?
It allows detection and isolationist abnormal patterns of electrical activity.
What are amplifiers?
They have a positive and negative electrode.
How do amplifiers work?
They take the signal on the negative input and invert it.
They then add this signal to the positive signal.
They then amplify the total.
Takes direction into account - Think vectors!
How many leads are in a full ECG?
12
What are augmented leads?
2 negatives connected and one positive
How do augmented leads work?
The 2 negative signals are combined and converted to positive.
Combine with actual positive.
Get one view.
What are the limb leads?
I, II, III
AVR, AVL, AVF
How do limb leads view the heart?
In a superior to inferior way.
What are the chest leads?
V1, V2, V3, V4, V5, V6.
How do the chest leads view the heart?
Anteriorly to posteriorly.
What is the standard rate for an ECG?
300 squares /min so 0.2 seconds per square.
What does it mean if there is no P wave on an ECG?
The sick atrial node is not functioning.
What happens if the sino atrial node is not functioning?
The atrial ventricular node takes over.
What is the ability of the atrial ventricular node as a pacemaker?
It is relatively irregular so the heart best is also irregular.
What does it mean if the P-R interval is prolonged?
There is first degree heart block.
What does it mean if the P-R interval is irratic?
There is second degree heart block.
Why is the P-R interval erratic in second degree heart block?
Because only some of the action potentials can get through the atrial ventricular node.
What is third degree heart block?
Where second degree heart block has developed so no action potentials can get through the atrial ventricular node.
What can cause extra P waves?
There are randomly arranged extra pacemaker cells within the heart that can fire action potentials. This means there are extra P waves which are unrelated to the QRS complex.
What can cause a prolonged QRS complex?
Damage to the bundle of Hiss causing bundle branch block.
Due to an ectopic site and slow pathway (as action potentials are going back on themselves)
What can a NET deflection of 0 mean?
That the axis is perpendicular to the lead so cannot be seen.
What would the leads pick up in left axis deviation?
Lead 1 would be amplified.
Lead 3 will be its opposite.
When can left axis deviation occur?
In left ventricular hypertrophy - eg aortic stenosis.
What would the leads pick up in right axis deviation?
Lead 3 would be large.
Lead 1 wold be the negative of itself.
What could cause right axis deviation?
Right ventricle hypertrophy - eg obstructive lung diseases.
What does an S-T depression on an ECG show?
It is due to partial occlusion of the coronary arteries so the patient is likely to have angina.
What physiological process causes the S-T depression?
Thre is a lacks of O2 to the heart so the cells don’t stay depolarised.
What does an S-T elevation show?
A myocardial infarction.
What abnormality will permanently show on an ECG after a myocardial infarction?
Pathological Q waves due to the scar tissue not being an,e to conduct the electricity and the signal having to go around.
