ECG Flashcards
What is the ECG?
Cardiac excitation generates electrical currents in the ECF that can be detected on the skin
How is an electrical potential generated?
One cell is at rest and the one next to it is depolarized
What are 2 features of the electrical signal?
Direction according to excitation sequence
Magnitude according to cardiac muscle mass
What can the ECG investigate?
Abnormal conduction and cardiac hypertrophy
What direction is a positive deflection?
Towards an electrode
What direction is a negative deflection?
Away from an elctrode
How is the detected signal determined?
Average direction of the electrical current and the positioning of the electrodes
What is the P wave on an ECG recording?
Atrial depolarization
spread of impulses from SA node
What does the delay period from P to R represent?
Time taken for the action potential to get to the AV node
What is the Q wave on an ECG recording?
Depolarization of septum passes from left to right
negative deflection
What is the R wave on an ECG recording?
Depolarization of ventricles spreading from apex
What is the S wave on an ECG recording?
Depolarization of ventricles spreading towards atria
What does the QRS complex allow?
Ventricular contraction
What is the T wave on an ECG recording?
Repolarization of ventricles from epicardium towards endocardium
Why is the T wave an upwards deflection?
The last muscle cells to depolarise are also the first to repolarise
What happens in the S to T delay period?
Ventricular contraction and emptying
What happens from Q to T?
Ventriculars are at rest and are filling
What do bipolar limb leads record?
Each wrist
Left ankle
Forms a triangle around the heart
What do unipolar leads measure?
Chest leads V1-V6
What is the electrical axis of the heart?
-30 degrees to 90 degrees
What is the measure of the aVf angle?
90 degrees
What is the measure of the aVL angle?
-30 degrees
What is the measure of the aVr angle?
-150 degrees
What plane do bipolar limb leads record?
Frontal plane
What plane do unipolar limb leads record?
Transverse plane