Electrocardiogram Flashcards
What is an ECG?
The ECG is a composite record of action potentials produced by all the heart muscle fibers during each heartbeat.
How does an ECG work?
Electrodes are positioned on the arms and legs (limb leads) and at 6 positions on the chest (chest leads).
The electrocardiograph amplifies the heart’s electrical signals and produces 12 different tracings from different combinations of limb and chest leads.
By comparing these records with one another and with normal records,it is possible to determine if:
- the conducting pathway is abnormal
- the heart is enlarged
- certain regions of the heart aredamaged
- the cause of chest pain.
What does the P wave represent?
Atrial depolarisation
What does the QRS complex?
Rapid ventricular depolarisation
What does the T wave represent?
Ventricular repolarisation
What does P-Q represent?
Atrial systole
What does Q-T represent?
Ventricular systole/atrial diastole
What does T-P reperesent?
Ventricular diastole
What does a large P wave indicate?
atrial enlargement
What does a large Q wave indicate?
MI
What does a large R wave indicate?
Enlarged ventricles
What does a flat T wave indicate?
Heart isn’t receiving enough oxygen
What does an elevated indicate?
Hyperkalemia
What is a first degree block?
P-R interval greater than 0.2s
What is a second degree heart block and explain the types?
This is where there is an intermittent absence of QRS complexes – and thus an indication that there is a blockage somewhere between the AV nodes and the ventricles.
Type 1:
- Progressive lengthening of the PR interval followed by an absence of the QRS, then a shortened PR interval and normal QRS, and the cycle begins again. The cycle is variable in length, and the R-R interval shortens with the lengthening of the PR interval
Type 2:
- This is where there is a regular rhythm, and a fairly constant PR interval, but every now and again there is an absent QRS (pictured above). basically for every QRS, there are 2 or 3 p waves.
2: 1 and 3:1 conduction - there is one normal cycle, then one cycle with an absent QRS (2:1) or there is one normal cycle, then two cycles without a QRS (3:1
What is a third degree heart block?
This occurs when atrial contraction is normal, but no beats are conducted to the ventricles.
The ventricles are still excited by their own internal ‘ectopic pacemaker’ system! Thus the definition of complete heart block is:
P wave ~90/min (more p waves than QRS complexes)
QRS ~36/min
Variable PR intervals
No relationship between P wave and QRS complexes, but both are present.
Abnormally shaped QRS due to abnormal spread of conduction throughout ventricles
QRS will generally be broad (~160ms – as opposed to a maximum of 120ms in a normal heart – 4 little squares as opposed to 3 little squares)
Right axis deviation
Escape rhythms present (more on these later)
What does sinus rhythm mean?
rhythm of the heart is being controlled by the SA node – i.e. this is the ‘normal’ way the rhythm of the heart
What is sinus tachycardia?
Fast heart rate
What is sinus bradycardia?
Slow heart rate
