Cardiac Conduction - Electrocardiograms - Part A - How to Interpret Electrocardiograms

Oct 26, 2026

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Cardiac conduction system explains how the SA node, AV node, and His-Purkinje system generate and transmit electrical impulses that drive atrial and ventricular contraction, including depolarization and repolarization. The document then introduces electrocardiograms as measurements of cardiac electrical activity, describing waveforms (P wave, QRS complex, T wave) and key intervals. It also outlines an online activity for recording answers while learning to interpret ECGs using EKG Basics and a table of contents with specific questions.

LanguageEnglish

CategoryHealthcare

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Pages10

Reading Time25 min

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Electrocardiograms

Part A. How to Interpret Electrocardiograms

Cardiac Conduction The cardiac conduction system is complex,but there are three crucial parts: ·The Sinoatrial (SA)Node Also known as the pacemaker;this is asmall bundle of cells capable of startingthe electrical impulse that will cause theheart to beat ·The Atrioventricular(AV)NodeA small bundle of cells that can receivethe electrical impulse from the SA node,and continue the electrical signal downinto the ventricles. ·His-Purkinje System These fibers actually carry the electrical impulse to the ventricles,causing a contraction.The impulse starts at the His bundle fibers.continues into the right bundle branch and leftbundle branch,and ends in Purkinje fibersspread throughout the ventricles. The Heartbeat The sinoatrial(SA)node begins the contraction by sending an impulse through both atria,causingthem to contract and reach the atrioventricular(AV)node.The AV node continues the impulse,sending it down the Bundle of His,right and left bundle branches,and into Purkinje fibers within theventricles causing both ventricles to contract. Name(s): Period: Date: Background The heart has its own system in place to create nerve impulses and does not actually require thebrain to make it beat.This electrical system is called the cardiac conduction system.It is made up ofspecialized tissues and cells embedded in the heart that send impulses directly to the atria andventricles,causing them to contract.In the normal cardiac cycle,the left and right atria contracttogether first followed by the contraction of the ventricles together. http://2.bp.blogspot.com/-rYtanZ5CjBE/T54xh0eE5OVAAAAAAAAADM/tRYbXfTnGzM/ As the impulse moves through the heart,cardiac muscle tissue contracts as the cells depolarize.Depolarization is caused by a flood of ions(sodium and potassium)across the cell membrane anddrives the cells,and therefore cardiac muscle tissues,to contract.Once the impulse has passed,thecardiac cells must reset to be able to send another impulse.This is called repolarization and occurswhen the ions move back through the cell membrane,causing the cardiac muscle tissue to relax. The SA node will create anywhere from 60-100 electrical impulses per minute.Each of theseimpulses causes your heart to beat and translates to your heart rate.The electrical impulse causesthe heart to depolarize and contract,followed by repolarization and relaxation,at a constant rate.Thenormal rhythm and rate is called the sinus rhythm.The cardiac conduction system is also capable ofincreasing or decreasing the number of electrical impulses depending on the amount of oxygenneeded by the body.For example,when you run a mile your need for energy increases,causing theneed for more oxygen,and resulting in an increase in the heartbeat and respiratory rate to bring moreoxygen into the body. # Electrocardiograms An electrocardiogram is a measurement of the electrical activity and impulses created by the heart.Itis most often referred to as an EKG or ECG.Electrodes are placed on the chest and each electricalimpulse is translated into a wave pattern on a grid.The grid allows for the calculation of the durationand amplitude of each impulse,as well as whether the impulses are abnormal or irregular.Flat lineson the grid represent no electrical activity,upward spikes represent electrical activity ordepolarization,and downward spikes represent repolarization. Specific waves on the ECG grid represent depolarization and repolarization in different parts of theheart.The diagram below shows how each of these waves should normally appear on an ECG grid. · P wave-depolarization and contraction of the right and left atria ·QRS complex-depolarization and contraction of the right and left ventricles ·T wave-repolarization and relaxation of the ventricles ·PR interval-time between the depolarization of the atria and the ventricles ·QT interval-time for the ventricles to depolariz

FAQs

What are the three crucial parts of the cardiac conduction system?

The three crucial parts are the Sinoatrial (SA) node, the Atrioventricular (AV) node, and the His-Purkinje system. Together they start and transmit the electrical impulse that makes the heart beat.

How do depolarization and repolarization relate to the heartbeat?

Depolarization happens when ions (such as sodium and potassium) flood across the cell membrane, causing cardiac muscle tissue to contract. Repolarization occurs when ions move back through the cell membrane, allowing the cardiac muscle to relax.

What do ECG wave and interval labels like P wave, QRS complex, and QT interval represent?

The P wave corresponds to depolarization and contraction of the atria, the QRS complex corresponds to depolarization and contraction of the ventricles, and the T wave corresponds to repolarization and relaxation of the ventricles. The QT interval represents the time for the ventricles to depolarize and repolarize.

Oct 26, 2026

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