Download ECG Event Represented Duration (Sec)

Objective 12
Electrocardiograms
Electrocardiogram:
a graphical recording of the potential changes
that occur in the heart during a cardiac cycle
Electrocardiograph:
a device used to measure these changes
Lead:
a combination of electrodes that are used to
detect electrical changes; there are 12
standard leads (3 bipolar, 9 unipolar)
William
Einthoven
Characteristic Waves and Intervals of a Typical ECG:
ECG
Event Represented
Duration (Sec)
P Wave
atrial
depolarization
0.08 – 0.10
P-R Interval
time impulse is being
transmitted through
the atria and delay at
AV node
0.12-0.2
Name
QRS Complex
Event Represented
Duration (Sec)
ventricular depolarization
0.06 – 0.10
ST Segment
time between the end of
0.08-0.12
ventricular depolarization
and ventricular repolarization
T Wave
ventricular repolarization
0.16-0.24
Objective 13
Common Arrhythmias
Analysis of ECG tracings include an evaluation of these
characteristics:
1. Overall rate and rate of individual wave formations
2. Rhythm
3. Shape, height, and duration of wave formations
4. Deviation from the baseline
Common deviations include:
Sinus bradycardia:
impulses arise at the SA node at a
slow rate < 60 bpm
Note: in well conditioned athletes this may not be an abnormality
Sinus Tachycardia
impulses arise at the SA node at an
accelerated rate > 100 bpm
Causes may include:
•Exercise
•Excessive sympathetic stimulation
•Ischemia
•Increased temperature
When ectopic foci suppress SA node inherent rate:
Atrial Flutter
a single ectopic pacemaker produces an
atrial rate of 200-300 per minute
Reentry causes
many arrhythmias
Usually an ectopic pacemaker or a reentry
Atrial Fibrillation
several ectopic foci cause an atrial rate of
350-600 per minute; some reach ventricle
notice the presence of QRS complexes
Ventricular Fibrillation
several ectopic foci generate potentials
independently; there is no effective
contraction of the ventricular
myocardium, and therefore, no pulse
Atrioventricular block
First degree AV block: all
impulses are conducted from the
atria into the ventricles, but with
a greater than normal delay; P-R
interval > 0.20 seconds
Second degree: some, but not all
impulses are conducted from the
atria into the ventricles; further
defined as 2:1, 3:1, 4:1, etc; there
is a consistent P-R interval
Third degree: called complete AV
block; no impulses are conducted
from the atria into the ventricles;
the P-R interval varies because
the atria and the ventricles are
contracting independently
Bundle Branch Block:
conduction by one of the bundle branches is
impaired; ECG shows a widening of the QRS
complex
RBBB
LBBB