Human EKG

Heart: Review

Electrical Pathway of the Heart

SA NodeAV Node

Bundle of His

Right bundle branch

Left bundle branch

Inferior vena cava

Purkinje fibers

EKG or ECG• Electrocardiogram

• 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.

Atrial Depolarizati

on

Ventricular Depolarization

Ventricular Repolarizati

on

Diastole80 mmHg

Systole120 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).