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Electrical Conduction of the
Heart
Electrocardiography
• A recording
of the electrical activity of the heart
•Gold standard for dx of cardiac arrhythmias
• Helps detect electrolyte disturbances
•detection of conduction abnormalities
• Screening tool for heart dz during stress tests
• Helpful with non-cardiac dz
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Electrocardiogram (ECG/EKG)
• Is a recording of electrical activity of heart conducted thru ions in
body to surface
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Conduction System of the Heart
SA node: sinoatrial node. The pacemaker.
Specialized cardiac muscle cells.
AV node: atrioventricular node.
conducted more slowly here
AV bundle
Right and left bundle branches: Braches to right and
left ventricles
Purkinje fibers
Normal conduction pathway:
SA node -> atrial muscle -> AV node -> bundle of His -> Left and
Right Bundle Branches -> Perkinje fibers ->Ventricular muscle
EKG
EKG
EKG Machine
Ischemic Heart Disease
• Is most commonly due to atherosclerosis in coronary
arteries
• Ischemia occurs when blood supply to tissue is low
• Often accompanied by angina pectoris (chest pain)
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Ischemic Heart Disease
• Detectable by changes in S-T segment of ECG
• Myocardial infarction (MI) is a heart attack
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Arrhythmias Detected on ECG
• Arrhythmias are abnormal heart rhythms
• Heart rate <60/min is bradycardia; >100/min is
tachycardia
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Arrhythmias Detected on ECG continued
• In fibrillation contraction of myocardial cells is
uncoordinated & pumping ineffective
– Ventricular fibrillation is life-threatening
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FYI
• In TV medical dramas, an isoelectric ECG (aka, flatline), is used
as a symbol of death or extreme medical peril.
• Technically, this is known as asystole, a form of cardiac arrest,
with a particularly bad prognosis.