ECG Flashcards
Describe the phases of myocyte action potential
Phase 0 rapid depolarisation - inflow of Na+
Phase 1 partial repolarisation - inward Na+ current deactivated, outflow of K+
Phase 2 plateau - slow inward Ca current
Phase 3 repolarisation - K+ outflow, Ca current inactivates
Phase 4 pace maker potential - slow Na+ inflow, slowing of K+ outflow
How can an impulse appear large on an ECG
If an impulse is towards the electrode than it will appear big (large voltage), if the impulse if away from the electrode it looks small or even negative
What are the lead positions (Einthoven’s triangle)?
Lead 1 - R arm to L arm +
Lead 2 - R arm to L leg +
Lead 3 - left arm to L leg +
What does the P wave of the ECG represent?
The P wave represents atrial depolarisation (small +ve wave)
Atria impulse is smaller since the atria are smaller so there are fewer myocytes - SAN node
What does the QRS wave of the ECG represent?
The QRS waves represents ventricular depolarisation (it is a larger peak than P wave)
What does the T wave of the ECG represent?
T wave represents ventricular repolarisation (final peak)
What is the PR interval?
This occurs due to the slow conduction between AV node and the His-punkinje system
What is right bundle branch block?
A right bundle branch block (RBBB) is a heart block in the electrical conduction system. During a right bundle branch block, the right ventricle is not directly activated by impulses travelling through the right bundle branch. The left ventricle however, is still normally activated by the left bundle branch.
BBB - shows a wide QRS
What is a sinus tachycardia?
Sinus tachycardia is an example of a supraventricular rhythm. In sinus tachycardia the sinus node fires between 100 and 180 beats per minute, faster than normal.
The ECG shows more frequent p waves, each followed by QRS
What is a sinus bradycardia?
Sinus bradycardia is a sinus rhythm with a rate that is lower than normal. In humans, bradycardia is generally defined to be a rate of under 60 beats per minute.
The ECG shows less frequent p waves, each followed by QRS
What is junctional rhythm?
A junctional rhythm occurs when the electrical activation of the heart originates near or within the AV node instead of from the SA node.
- There is a loss p waves
- Since the normal ventricular conduction system (His-Purkinje) is used, the QRS complex is frequently narrow.
What does an elevated ST segment suggest?
What does a depressed ST segment suggest?
STEMI - ST elevation = myocardial infarction
depressed = ischemia, angina
