what are the squares representative of in an ECG?
small square = 40ms
big square = 0.2s secs
how many bipolar leads are there and what do they do?
record electrical activity in 2 directions
(wrist, wrist, ankle)
how many unipolar arm leads are there and what do they do?
looks at electricity going too?
(shoulder, shoulder, abdomen)
how many unipolar chest leads are there and what do they do?
looks at incoming electrical activity, starts on the right and moves down and to the left
which leads assess electricity within the lateral myocardial territory?
leads 1, aVL, V5 and V6
which lead is usually inverted compared to anterior and inferior leads?
what are the 3 main peaks of the ECG waveform?
P = atrial depolarisation QRS = ventricular depolarisation (+ve if travelling toward, -ve if moving away) T = ventricular repolarisation
which waves are always positive except on the aVR?
P waves and T waves except on the aVR.
QRS waves face upwards on which side?
the left (positive)
QRS waves face downwards on which side?
the right (negative)
what is the P wave?
atrial depolarisation, SA node sends an impulse into the atria causing a contraction.
AV node sends a signal to the ventricles down His-Purkinje systems, slows conduction causing the PR interval.
what is the QRS complex?
takes up to 120ms (3 small squares) shows ventricular depolarisation.
what is the ST segement?
represents interval between depolarisation and repolarisation.
what is the T wave?
represents ventricular repolarisation
what is the QT interval?
represents time of depolarisation + repolarisation