Heart Conduction System

Bell work Define: Depolarization and Repolarization What is an EKG/ECG?

The Heart: Conduction System The heart pumps blood through the body This is accomplished by contraction and relaxation of the cardiac muscle tissue in the myocardium layer.

Conduction System Continued…. Cardiac conduction system: The electrical conduction system controls the heart rate This system creates the electrical impulses and sends them throughout the heart. These impulses make the heart contract and pump blood.

CARDIAC CYCLE Creates Heart sounds Heard through stethoscope “LUB-DUB” sound 1st sound, AKA S1 – longest and loudest (closure of atrioventricular (AV) valves) Atrioventricular is Tricuspid and Mitral What would Right AV valve be? What would Left AV valve be?

2nd sound – closure of aortic and pulmonary valves (AKA Semilunar Valves) If valves do not close properly – you will hear an extra sound called a heart murmur

THE CARDIAC CYCLE SYSTOLE – CARDIAC CONTRACTION THE BLOOD IS FORCED OUT OF THE HEART TO THE LUNGS FOR OXYGENATION AND TO THE BODY FOR CIRCULATION (CONTRACTION) DIASTOLE – CARDIAC RELAXATION THE BLOOD IS RETURNED TO THE HEART FROM THE LUNGS AND THE BODY (RELAXATION) What is this measuring?

Septum

Components of the Conduction System Sinoatrial Node (Part I): located in back wall of the right atrium near the entrance of vena cava initiates impulses 70-80 times per minute without any nerve stimulation from brain establishes basic rhythm of the heartbeat called the pacemaker of the heart impulses move through atria causing the two atria to contract. at the same time, impulses reach the second part of the conduction system

Components of the Conduction System Continued …. Atrioventricular Node (Part II): located in the bottom of the right atrium near the septum cells in the AV node conduct impulses more slowly, so there is a delay as impulses travel through the node this allows time for atria to finish contraction before ventricles begin contracting

Atrioventricular Bundle A.K.A. “Bundle of His” From the AV node, impulses travel through to the right and left bundle branches These branches extend to the right and left sides of the septum and bottom of the heart.

Atrioventricular Bundle Continued…. These branch a lot to form the Purkinje fibers that transmit the impulses to the myocardium (muscle tissue) The bundle of His, bundle branches and Purkinje fibers transmit quickly and cause both ventricles to contract at the same time Like a “phone tree”

Atrioventricular Bundle Continued…. As the ventricles contract, blood is forced out through the semilunar valves into the pulmonary trunk and the aorta. After the ventricles complete their contraction phase, they relax and the SA node initiates another impulse to start another cardiac cycle.

1 - Sinoatrial node (SA node) 2 - Atrioventricular node (AV node) 3 – Bundle of His 4 - Right & Left Bundle Branches which lead to Purkinje Fibers

https://www.youtube.com/watch?v=RYZ4daFwMa8

Polarization Depolarization and Repolarization 1. Cardiac cells at rest are considered polarized, meaning no electrical activity takes place 2. The cell membrane of the cardiac muscle cell separates different concentrations of ions, such as sodium, potassium, and calcium. This is called the resting potential.

Polarization 3.  Electrical impulses are generated by automaticity of specialized cardiac cells 4.  Once an electrical cell generates an electrical impulse, this electrical impulse causes the ions to cross the cell membrane and causes the action potential, also called depolarization 5.  The movement of ions across the cell membrane through sodium, potassium and calcium channels, is the drive that causes contraction of the cardiac cells/muscle

Polarization 6.  Depolarization with corresponding contraction of myocardial muscle moves as a wave through the heart 7.  Repolarization is the return of the ions to their previous resting state, which corresponds with relaxation of the myocardial muscle

Polarization 8.  Depolarization and repolarization are electrical activities which cause muscular activity 9.  The action potential curve shows the electrical changes in the myocardial cell during the depolarization – repolarization cycle 10.  This electrical activity is what is detected on ECG, not the muscular activity.

EKG COMPONENTS P WAVE – INDICATES ATRIAL DEPOLARIZATION CAUSING ATRIAL CONTRACTION QRS COMPLEX – INDICATES VENTRICULAR DEPOLARIZATION CAUSING VENTRICULAR CONTRACTION ST SEGMENT – INDICATES MYOCARDIAL DAMAGE T WAVE – INDICATES VENTRICULAR REPOLARIZATION CAUSING VENTRICULAR RELAXATION

EKG

How To Read EKG EKG paper is a grid where time is measured along the horizontal axis. Each small square is 1 mm in length and represents 0.04 seconds. Each larger square is 5 mm in length and represents 0.2 seconds In order to correctly identify heart rhythms, you will need to print off 6 second strips

How to Read EKG Can determine HR from EKG strip Each strip is 6 seconds To determine HR: Count R waves and multiply by 10

HEART RHYTHMS NORMAL SINUS RHYTHM (NSR) SINUS TACHYCARDIA between 60 – 100 BPM, regular rhythm SINUS TACHYCARDIA > 100 BPM, regular rhythm SINUS BRADYCARDIA < 60 BPM, regular rhythm

Normal Sinus Rhythm 60 – 100 Beats per minute

Sinus Tachycardia  A fast heart rhythm with a rate of more than 100 beats per minute.

Sinus Bradycardia A slow heart rhythm with a rate below 60 beats per minute.

Arrhythmias Abnormal heart rhythms that can be mild to life threatening.

Irregular Rhythm

HEART RHYTHMS PREMATURE ATRIAL CONTRACTION (PAC) ATRIAL FLUTTER ATRIAL FIBRILLATION (A-FIB) PREMATURE VENTRICULAR CONTRACTION (PVC) DANGEROUS PVCs VENTRICULAR TACHYCARDIA (V-TACH) VENTRICULAR FIBRILLATION (V-FIB) ASYSTOLE

PAC Premature atrial contraction (PAC) Can occur in anyone but usually goes unnoticed. Most common forms of arrhythmias.  the premature discharge of an electrical impulse in the atrium, causing a premature contraction.  A PAC is premature, because the it occurs earlier than the next regular beat should have occurred.

Atrial Flutter the electrical signal travels along a pathway within the right atrium. It moves in an organized circular motion, or "circuit," causing the atria to beat faster than the ventricles of your heart.

Atrial Fibrillation Many impulses begin and spread through the atria, competing for a chance to travel through the AV node. The resulting rhythm is disorganized, rapid and irregular. Because the impulses are traveling through the atria in a disorderly fashion, there is a loss of coordinated atrial contraction.

Premature Ventricular Contraction (PVC) Early, extra heartbeats that originate in the ventricles. Most of the time, PVCs don’t cause any symptoms or require treatment. This type of arrhythmia is common and can be related to stress, too much caffeine or nicotine, or exercise. They can be also be caused by heart disease or electrolyte imbalance.

Ventricular Tachycardia A rapid heartbeat that originates in the ventricles. The rapid rhythm keeps the heart from adequately filling with blood, and less blood is able to pump through the body. V-tach can be serious, especially in people with heart disease.

Ventricular Fibrillation An erratic, disorganized firing of impulses from the ventricles. The ventricles quiver and cannot generate an effective contraction, which results in a lack of blood being delivered to the body. This is a medical emergency that must be treated with cardiopulmonary resuscitation (CPR) and defibrillation (delivery of an energy shock to the heart muscle to restore a normal rhythm) as soon as possible.

Superventricular Tachycardia SVT Supraventricular tachycardia (SVT) is a cardiac arrhythmia characterized by very rapid or erratic beating.  heart racing/palpitations, dizziness or light-headedness, chest pain, breathlessness

Asystole Asystole is defined as a cardiac arrest rhythm in which there is no discernible electrical activity on the ECG monitor. 

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