Electrophysiology of the Heart: Simple Animation Guide

The heart consists of four main chambers: two atria on top and two ventricles below.The heart's electrical system begins with the sinoatrial node, or SA node, often called the heart's natural pacemaker.The electrical signal travels through the atria to the atrioventricular node, or AV node, which acts as an electrical relay station.From the AV node, the signal travels through the Purkinje fibers, a specialized network that rapidly conducts electricity to the ventricles.Let's examine the specialized conducting system in more detail.The electrical signal starts at the SA node, which fires about 60 to 100 times per minute.The signal spreads through the atria, causing them to contract.At the AV node, the signal is briefly delayed, allowing the atria to finish contracting before ventricular contraction begins.Finally, the Purkinje fibers rapidly distribute the electrical signal throughout the ventricles, causing coordinated contraction.This electrical system serves several critical functions in maintaining proper heart function.In cardiac cells, the movement of ions through specific channels creates electrical signals called action potentials.At rest, sodium and calcium are concentrated outside the cell, while potassium is concentrated inside.The cardiac action potential has distinct phases, each characterized by different ion movements.Phase zero involves rapid depolarization as sodium channels open, allowing sodium to rush into the cell.In phase one, early repolarization occurs as potassium channels briefly open.Phase two, the plateau phase, is unique to cardiac cells. Calcium enters while potassium exits, maintaining a prolonged depolarized state.During phase three, repolarization occurs as potassium channels open fully while calcium channels close.Finally, phase four is the resting phase, where the membrane potential returns to negative eighty millivolts.This carefully orchestrated movement of ions creates the cardiac action potential, which will trigger the next phase of heart conduction.The electrical signal begins at the sinoatrial node, also known as the heart's natural pacemaker.The signal spreads through the atria at a speed of one to one point two meters per second, taking about fifty to eighty-five milliseconds to reach the AV node.At the AV node, conduction slows dramatically to about five centimeters per second. This delay is crucial for proper heart function, allowing the atria to fully contract before ventricular activation.From the AV node, the signal travels rapidly through the bundle of His and its branches.Finally, the Purkinje fibers distribute the signal throughout the ventricles at speeds of two to four meters per second, ensuring coordinated contraction.This precisely timed electrical sequence ensures proper mechanical contraction, starting with the atria.Followed by powerful ventricular contraction that pumps blood to the body and lungs.The entire conduction sequence takes about one hundred and seventy-five to two hundred milliseconds, precisely coordinating each phase of the heartbeat.The ECG trace directly reflects the heart's electrical activity. Each wave corresponds to specific events in the cardiac cycle.The P wave represents atrial depolarization, as the electrical signal spreads from the SA node through both atria.The QRS complex shows ventricular depolarization, a rapid process that creates the characteristic sharp deflection on the ECG.The T wave represents ventricular repolarization, as the ventricles reset for the next heartbeat.The PR interval measures the time from atrial activation to ventricular activation, normally between 120 and 200 milliseconds.The QRS duration shows how long it takes for the ventricles to depolarize, typically 60 to 100 milliseconds.The QT interval represents the total time for ventricular depolarization and repolarization, usually 350 to 440 milliseconds.In a normal heart rhythm, this pattern repeats about 60 to 100 times per minute, creating a regular sequence of waves.Now let's examine common cardiac rhythm abnormalities and their ECG patterns.In a normal rhythm, the heart beats regularly at 60 to 100 beats per minute, with consistent spacing between complexes.In tachycardia, the heart beats too quickly, over 100 beats per minute. Notice how the complexes are closer together.Bradycardia occurs when the heart beats too slowly, less than 60 beats per minute. The complexes are spaced further apart.In heart block, some electrical signals fail to conduct properly. Notice how some QRS complexes are missing after P waves.These rhythm abnormalities affect blood flow throughout the body. In tachycardia, reduced filling time decreases cardiac output. In bradycardia, the slow rate may not meet the body's needs. Heart blocks can cause sudden drops in blood flow.