ECG Review Flashcards
Describe a standard protocol for ECG analysis Describe key measurements in initial ECG analysis Using the protocol recognise rate, rhythm, P wave, QRS wave and ST wave variations. Describe a method for determining the electrical axis of the heart.
What is the standard protocol for ECG analysis?
Rate, rhythm, P wave, PR wave, QRS wave
What are the normal measurements in ECG analysis?
Rate - 60-100bpm Rhythm - regular P wave - 0.08s PR wave - 0.12-0.2s, greater than 0.2s is sign of heart block QRS - less than 0.12s
What does the PR interval represent?
The impulse travelling from the AVN to the Bundle of His to the ventricles. Therefore the time between the start of the depolarization of the atria and start of depolarisation of the ventricles.
What does the QRS interval represent?
The synchronous contraction of the ventricles and the sequence of the different part of the ventricles contracting
Why does conduction slow down at the AVN?
So that the atria can fully contract and empty before the ventricles fill up.
Why is the PR interval important to look at?
This is where the AVN slows down and this is where a lot of things go wrong and you can get heart block.
What can a prolonged PR interval indicate?
Hypokalaemia, acute rheumatic fever or carditis.
What is rheumatic fever?
an inflammatory disease that can involve the heart, joints, skin, and brain. The disease typically develops two to four weeks after a streptococcal throat infection
What is the first part of the ventricle to contract?
The chorda tympani as it has to pull on the AV valves for them to shut so the ventricles to then contract and empty blood out.
What should the QRS wave look like?
It should be narrow and short.
What does a prolonged QRS wave indicate?
Some ventricular muscle is taking longer than normal to depolarise and so is damaged
Why is the ST wave flat?
It means all the muscle has been depolarised as you only get a large ECG signal when muscle membrane potential is changing and so ECG waves do not last as long as action potentials.
What are the 2 layers of the ventricular muscle and which contracts first?
Endocardial inner layer contracts slightly earlier
Epicardial outer layer contracts later
What does an ECG tell you?
The differences in depolarisation in the heart.
What happens in ischemic conditions?
The duration of the endocardial action potential is reduced as this layer is more susceptible to the effects of ischemia but the outer epicardial has normal duration so you end up with an inverted T wave.
