Human EKG
Heart: Review
Electrical Pathway of the Heart
SA Node
AV Node
Right bundle
branch
Inferior vena cava
Bundle of His
Left bundle
branch
Purkinje
fibers
• Electrocardiogram
EKG or ECG
• Willem Einthoven-1903
• A record of the overall spread of electrical activity of the heart.
• What EKG actually records:
1)
NOT a direct recording of electrical activity. Recording a portion of electrical
activity induced in body fluids by cardiac impulse that reaches the surface of the
body.
2)
NOT a recording of a single AP in a single cell at a single point in time. Represents
the SUM of electrical activity in all of cardiac muscle cells.
3)
Represents comparisons in voltage detected by electrodes at two different points
on the body’s surface. Not actual potential.
Einthoven’s Triangle
• Determines the electrical axis of the heart.
• Equilateral triangle. The vertices are at the left and right shoulders and the
pubic region.
• The center corresponds to the vector sum of all electric activity occurring in
the heart at any given moment.
• Based on 3 lead system. Now have 12 lead systems that are much more
accurate.
• Einthoven’s law: At any instant the potential of any wave in lead II is equal
to the sum of potentials in leads I and III.
Ventricular
Depolarization
Atrial
Depolarization
Diastole
80 mmHg
Ventricular
Repolarization
Systole
120 mmHg
Why is atrial repolarization not represented on the figure?
Why Use EKG?
• Detect Arrhythmias
– Irregular heart beat
• May indicate medical disorder or be due to
physiological state.
– Bradycardia = decrease heart rate (sinus node problem OR
athlete)
– Tachycardia = increase heart rate (imbalance of electrolytes
OR exercise)
Group
Mean HB (BPM)
Resting Adult
60-100
Adult male
70
Adult female
75
Teenager
80-100
Child
90-110
Toddler
100-130
Infant
130-150
Athlete
50-60 (lowest ever 25)
Sleep
40
Exercise
220
Lance Armstrong
32-34 (resting) 201 (exercising)
Elephant
28
Shrew
> 800
Today’s Lab
• EKG and Heart sounds.
• Only do lab on 2 group members.
• Only have to do resting EKG once for each
member (ignore Experiment 1 in heart sounds
lab).
Homework!!!!
• Answer all labscribe questions.
• Write a results and methods section for this
lab. Please attach a data sheet with all of
your RAW data.
• RAW data should not be a part of your results
section!
Results Section
• Should concisely present your data. This section
should have figures and/or tables AS WELL AS a
paragraph explaining those data.
• Don’t interpret the data, however, you should
point out any trends (i.e. heart rate increases
with increased activity or average heart rate was
lower in males than females).