Download Electrical Activity of the Heart

By: Andrea, Tory, Jackie, Madison, and Aaron
Conducting System
 Conducting system: a network of specialized cardiac
muscle cells that initiates and distributes electrical
impulses
http://www.nlm.nih.gov/medlineplus/ency/imagepages/18052.htm
Conducting System
 Made up of two types of cardiac muscle cells that do
not contract:
 Nodal cells: responsible for establishing the rate of
cardiac contraction and are located at the sinoatrial (SA)
and atrioventricular (AV)
 Conducting cells: distribute the contractive stimulus to
the general myocardium
 Major sites of the conducting cells are AV bundle,
Bundle Branches, and Purkinje fibers
Conducting System
 Sinoatrial node (SA node): a tissue mass embedded in
the posterior wall of the right atrium near the entrance
of the superior vena cava
 Pacemaker cells: cells of the SA node that set the pace
of cardiac contraction
 Atrioventricular node (AV node): transmits signal
from SA node to the ventricles
Conducting System
 AV Bundle: bundle of conducting cells extends along
the interventricular septum before dividing into left
and right bundle branches
 Left and Right bundle branches: radiate across the
inner surfaces of the left and right ventricles
 Purkinje fibers: convey the impulses to the contractile
cells of the ventricular myocardium
Conducting System
The conducting system of the heart
 The stimulus for contraction moves through the heart in a
predictable sequence of events
Step 1: SA node activity and atrial activation begin
Step 2: Stimulus spreads across the atrial surfaces and reaches the
AV nodes
Step 3: there is a 100 msec delay at the AV node. Arial contraction
begins. Elapsed time = 150 msec
Step 4: The impulse travels along the interventricular septum
within the AV bundle and the bundle branches to the Purkinje
fibers
Step 5: The impulse is distributed by Purkinje fibers and relayed
throughout the ventricular myocardium. Atrial contraction is
completed, and ventricular contraction begins
Conducting System
 A number of clinical problems result from deviations
from normal pacemaker functions
 Bradycardia: a condition in which the heart rate is slower
then normal (less than 60 bpm)
 Tachycardia: A faster then normal heart rate (100 bpm or
more)
 Ectopic pacemaker: abnormal conducting cell or
ventricle muscle cell may begin generating action
potentials so rapidly they override those of the SA or AV
node
The Electrocardiogram
 Electrocardiogram (ECG, EKG): a recording of the
electrical events occurring in the heart
http://www.wpclipart.com/medical/doctor_equipment/electrocardiogram.png.html
QRS Complex:
Impulse spreads to
ventricles triggering
ventricle contraction
T Wave:
Ventricles return
to resting state
P Wave:
Electrical impulse spreads
across atria and triggers
atrial contractions and the
atria begins contracting
100 msec after the start of
the P wave
Electrocardiogram (ECG/EKG)
 Analyzing an Electrocardiogram(ECG/EKG) involves
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measuring the size of voltage changes and determining
the temporal relationships of the various components
Ex. Smaller than normal electrical signal could mean
the mass of heart muscle has decreased
Cardiac arrthymias: abnormal patterns of cardiac
activity
5% of the normal population experiences a few
abnormal heartbeats each day
Clinical problems appear when arrhythmias reduces
hearts pumping efficiency