Conduction of impulses from bundle of his to bundle

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Conduction of Impulses From Bundle of HIS to Bundle branches to Purkinje fibres Ventricular depolarization – QRS complex Initiates ventricular contraction
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Conduction of Impulses Reversed repolarization wave T-wave Initiates ventricular relaxation
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Figure 18.17 Atrial depolarization, initiated by the SA node, causes the P wave. P R T Q S SA node AV node With atrial depolarization complete, the impulse is delayed at the AV node. Ventricular depolarization begins at apex, causing the QRS complex. Atrial repolarization occurs. P R T Q S P R T Q S Ventricular depolarization is complete. Ventricular repolarization begins at apex, causing the T wave. Ventricular repolarization is complete. P R T Q S P R T Q S P R T Q S Depolarization Repolarization 1 2 3 4 5 6
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Other Pacemaker regions AV node 40 beats / min Purkinje fibres ~20 beats / min Ectopic beats (extrasystoles) Both are depolarized by SA node before they depolarize themselves
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Electrical Conduction in the Heart Figure 14-18 1 2 3 4 5 5 4 3 2 1 THE CONDUCTING SYSTEM OF THE HEART SA node AV node Purkinje fibres Bundle branches AV bundle AV node Internodal pathways SA node SA node depolarizes. Electrical activity goes rapidly to AV node via internodal pathways. Depolarization spreads more slowly across atria. Conduction slows through AV node. Depolarization moves rapidly through ventricular conducting system to the apex of the heart. Depolarization wave spreads upward from the apex.
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The Electrocardiogram Three major waves: P wave, QRS complex, and T wave Figure 14-20
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Electrocardiogram (ECG) P-wave Atrial depolarization Initiates atrial contraction QRS complex Ventricular depolarization and atrial repolarization Initiates ventricular contraction T-wave Ventricular repolarization Initiates ventricular relaxation
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Einthoven’s Triangle Figure 14-19 Electrodes are attached to the skin surface. A lead consists of two electrodes, one positive and one negative. Right arm Left arm Left leg I II III
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Abnormalities in Rate Tachycardia Rapid heart rate of more than 100 beats per minute Sinus (normal) or ventricular Bradycardia Slow heart rate of fewer than 60 beats per minute
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Abnormalites in Rhythm Sinus rhythm normal 60 to 120 b/min Arrhythmias Examples Atrial flutter Atrial fibrillation Ventricular fibrillation Heart block Fibrillation uncoordinated
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Cardiac Myopathies Damage of the heart muscle Myocardial ischemia Inadequate delivery of oxygenated blood to heart tissue Necrosis Death of heart muscle cells Acute myocardial infarction (heart attack) Occurs when blood vessel supplying area of heart becomes blocked or ruptured
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Electrical Activity Normal and abnormal electrocardiograms Figure 14-23
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Representative Heart Conditions Detectable Through ECG
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Electrical Activity Correlation between an ECG and electrical events in the heart Figure 14-21 P Q R T S P T wave: ventricular repolarization PQ or PR segment: conduction through AV node and AV bundle P wave: atrial depolarization ELECTRICAL EVENTS OF THE CARDIAC CYCLE Repolarization START P Q P Q R P Q R T S R wave P Q R S S wave Q R P Q wave Ventricles contract ST segment The end P Atria contract S
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