ECG (2) - manifestations of disease Flashcards
what information about cardiac function does the ECG provide?
- the electrical rhythm of the heart
- the** size of the muscle mass** of the individual chambers of the heart
- the site of any abnormal pacemaker activity
- disorders in cardiac conduction
what is the sinus rhythm?
- any cardic rhythm in which depolarisation of the cardiac muscle begins in the SA node
- p wave is followed by the QRS complex
what is an arrhythmia?
- any deviation from the normal sinus rhythm
- some types of arrhythmias can be serious and life threatening
What is an example of an arrhythmia that is not of clinical concern?
- respiratory sinus arrhythmia
- characterised by faster heart rate during inhalation and slower heart rate during exhalation
what is sinus bradycardia vs sinus tachycardia?
- brady - slow- ie slower heart rate
- tachy - fast - rapid heart rate - associated with exercise, stress etc
how is the heart rate calculated in terms of the ECG?
- calculated from the time between peaks of successive R waves
what is the normal range for heart rate?
- 60-100 beats per minute
what are the different intervals of the ECG?
-
P-R interval - varies with heart rate, but it is the time it takes for the AP to travel through the atria and the AV node
* QRS interval- time taken for complete depolarisation of the ventricles - QT interval - time taken for the complete depolarisation and repolarisation of the ventricles
what is the electrical axis of the heart?
- the normal electrical axis is -30 degrees to 90 degrees
- it is the average direction of the ventricular depolarisation during ventricular contraction
what disease is involved with a reduced PR interval?
- wolff-parkinson white syndrome
- the excitation of ventricles is not delayed by the AV node
- causes a faster heart rate
What is ‘heart block’?
- refers to a defect in the conduction of the electrical activity of any point in the pathway betwen the SA node and the venrtcular muscle
what are problems with conduction from the atria to the ventricles called?
- atrioventricular block
what are problems with conduction through the bundle of His called?
Bundle block
How are heart blocks classified?
based on their severity
* first degree
* second degree
* third degree
What occurs in first degree heart block ?
- each wave of depolarisation starting in the SA node is conducted to the ventricles but there is an** abnormally long PR interval** - **long delay at the AV node **
- not normally a problem but may indicate other diseases eg coronary heart disease
what occurs in second degree heart block?
- there is a failure of excitation passing to the ventricles
- PR interval becomes longer until one **P wave fails to initate the QRS complex **
What occurs during third degree heart block?
- also called complete heart block
- the wave of excitation fails to excite the ventricles (there is an atrioventricular block)
- contains an abnormally shaped QRS complex, not associated with P waves- due to the ventricles showing a slow rhythm of their own
how does cardiac ischaemia and cardiac infarction influence the ECG?
- the damaged myocardio cells undergo depolarisation
- injury currents form
- they affect the ST segments
- during cardiac ischaemia, the ST segment is below the isoelectric axis - which indicates that the cells that repolarising earlier
What is atrial fibrillation?
- abnormal heart rhythm that is caused by rapid contraction of the atria
- the ECG trace shows no P waves and the base line is very irregular
What is ventricular fibrillation?
- ventricular fibers fail to contract in a normal way
* very irregular - no waves are able to be detected - the ventricles are** unable to pump blood around the body**
- can proceed to cardiac arrest ( stopping of the hearts function/ stops beating)
