What is the electrocardiograph?
The actual device doing the recording
What is the electrocardiogram?
The measurement of potential differences between distant sites on the body surface
When is the measured potential difference greatest?
When the lead axis is parallel to the direction of the dipole
What does the dipole represent?
An electrical vector
What determines the magnitude of the electrical vector?
Magnitude is determined by the mass of cardiac muscle that is involved in the generation of the signal
What determines the direction of the electrical vector?
Direction is determined by the overall activity of the heart at any instant in time and varies during the cardiac cycle
When is an upward deflection seen on an ECG?
When the wave of depolarisation is moving towards the recording electrode
What is the duration of a normal P wave?
Which part of the atrial action potential does the P wave correspond with?
What is the duration of a normal QRS complex?
What does the QRS complex represent?
Ventricular depolarisation masking atrial repolarisation
At what parts of the ECG is it completely isoelectric and why?
PR segment: atria completely depolarised ST segment: ventricles completely depolarised TP interval: all regions repolarised
What does the T wave represent?
What does the PR interval represent?
Mostly AV node delay
What is the normal duration of the PR interval?
Where does the PR interval start and end?
At the beginning of the P wave At the beginning of the QRS complex
Which region of the ECG represents systole?
Why is the recording from the AvR lead inverted?
Wave of depolarisation is moving away from the lead
Why might poorly resolved P and T waves be seen in lead 3?
The lead axis is approximately perpendicular to the vector
Why is it likely that the P and T waves seen in lead 2 will be well resolved?
The lead axis is approximately parallel to the vector
What questions should be answered while determining the rhythm from the rhythm strip?
Is electrical activity present? Is the rhythm regular or irregular? What is the heart rate? P-waves present? What is the PR interval? Is each P-Wave followed by a QRS complex? Is the QRS duration normal?