PSIO 532 Study Guide - Midterm Guide: Pr Interval, T Wave, Sinoatrial Node
Graduate Physiology PSL
ECG Waves
➔ Name the parts of a typical bipolar (Lead II) ECG tracing and explain the relationship
between each waves, intervals and segments in relation to the electrical state of the
heart
P wave – represents atrial depolarization → there is
little muscle in the atrium so the deflection is small
(SA nodes fire → send signals to the right atrial
contractile cells causing the right atria to contract
Q wave – represents depolarization at the bundle of
His and septal depolarization, again, this is small as
there is little muscle there
R wave – represents the main spread of
depolarization, from the inside out, through the base
of the ventricles (going towards the apex); this involves large amounts of muscle so the
deflection is large; the R wave is the most widely used waveform; R-R interval; any
initial rise regarding ventricular contraction will be called the R-wave
S wave – shows the subsequent depolarization of the rest of the ventricles upwards
from the apex of the heart (going from apex to base) → squeezing the blood out of the
ventricles; this part of the STILL indicates depolarization
T wave – represents repolarization of the myocardium after systole is complete; this is a
relatively slow process – hence the smooth curved deflection; it’s a repolarization
because the ions are moving in the opposite direction
Intervals are very important in demonstrating how different parts of the heart are talking to
each other.
➔ PR interval
o Represents P wave plus the P-R segment
o Normal duration: 0.12-0.20 sec
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