CARDIAC CONDUCTION Flashcards
How does an electrocardiogram ( ECG) work?
Detects very small differences in electrical potential at two points in the body due to movement of cellular depolarisation along the axis of measurement points
How many electrodes are placed on the skin in an ECG?
- 10 electrodes (6 around the heart + 4 on the extremities)
- one electrode acts as +ve and the other acts as -ve = difference gives us the lead
How many leads are measured in an ECG and what is the relevance of a lead?
12 - each lead gives a different electrical picture of the heart
What does a P wave show?
Atrial depolarisation
What does the QRS complex show?
Ventricular contraction (or ventricular depolarization)
What does a T wave show?
Ventricular repolarisation
What does the QT interval show?
Duration of the action potential
What does the ST segment show?
The plateau phase of the action potential (after ventricles have depolarized)
What does the R-R interval show?
Time between heartbeats
What does amplitude (height) of an ECG wave represent?
Height of waves - is directly proportional to the mass of the cardiac tissue generating it
What does the shape of an ECG wave depend on?
Type of electrode and the direction
How to measure heart rate?
- 300 ÷ by the number of large boxes between two R waves (ONLY FOR regular rhythm) - For irregular rhythms – 10 x number of R waves in 6 seconds
What factors must one look at to analyse the ECG?
- Identify QRS complex (ventricular contraction)
- Heart rate
- Heart rhythm
- P waves
When decides whether there is conduction problems above ventricles (supraventricular e.g. SA/AV node or atria), what factors should you look at?
- P wave
- PR interval
If the P wave’s shape is altered, what does this represent?
AVN block
If the PR interval is too long, what does this represent?
AV Block
If the PR interval is too short, what does this represent?
Wolff-Parkinson-White syndrome
When decides whether there is conduction problems in ventricle (ventricular arrhythmia), what factors should you look at?
- QRS interval
- QT interval
If the QRS interval is deep & wide, what does it represent?
Myocardial infraction
If the QRS interval is notched, what does it represent?
Right or left bundle block
If the QT interval is prolonged, what does it represent?
Failure to repolarise quickly enough (long refractory period)
If the QT interval is shortened, what does it represent?
Repolarisation too fast (short refractory period)
What are different types of irregular rhythms?
- Regularly irregular - recurrent pattern of irregularity
- Irregularly irregular - (i.e. completely disorganised
What is sinus tachycardia and sinus bradycardia?
Rhythm is regularly irregular; however, it is too fast or slow
What does no P wave in an ECG possibly signify?
Atrial fibrillation as atrial myocytes are ectopic pacemakers (not the SA node)
What condition produces an irregularly irregular ECG pattern?
Ventricular fibrillation - ectopic signals from many foci cause sections of ventricles to contract independently (no pattern)
What condition causes a gradual change in amplitude and a twisting of the QRS complex?
Torsade de Pointes
What does a long P-Q interval possibly signify?
First degree heart block (AV block) - conduction through AV node slowed
What does missed QRS complexes (ventricular beats) signify?
Second-degree heart block - some impulses don’t go through AVN = no ventricles depolarisation
What condition causes the P wave to be absent or disconnected from QRS?
Third-degree heart block - AVN doesn’t produce any impulses
What is a STEMI?
A myocardial infarction that has ST elevation (but can occur without MI)
