The Conduction System PDF

The Conduction System p. 26-28  p.26 Where does an EKG come from? ⚫ The heart doesn’t just have a mechanical system…it has its own electrical conduction system, too! ⚫ Conduction System : source of electricity in the hea...

The Conduction System p. 26-28  p.26 Where does an EKG come from? ⚫ The heart doesn’t just have a mechanical system…it has its own electrical conduction system, too! ⚫ Conduction System : source of electricity in the heart  p.26 Electrical System ⚫ Electrical impulse travels through the heart in a wave-like motion ⚫ This impulse signals the muscles to contract (mechanical response!) ⚫ Electrical-Mechanical Delay: The electrical impulse sends the signal … the heart then reacts with a mechanical action ⚫ The electrical impulse & the mechanical response DO NOT happen at the same time!  p.26 3 Ways Myocardial Cells Differ from Skeletal Muscle 1. Contain specialized, high-speed conductive pathways ⚫ ensures a smooth, effective pump 1. Possess a long refractory period ⚫ ensure the signal will stop once it has traversed the heart, not continue to circle 1. DO NOT require an external stimulus ⚫ spontaneously fires at periodic intervals ⚫ known as the Property of Automaticity  p.26 CONDUCTION PATHWAY 1. SA Node 2. AV Node 3. Bundle of HIS 4. Right & Left Bundle Branches 5. Purkinje Fibers  p.26 SA NODE  p.26 Sinoatrial Node (SA Node) -Location & Role located at border of SVC & RA initiates a self-generated impulse into the atrial muscle fibers ○ initiates atrial contraction  p.26 SA Node: Primary Pacemaker Primary pacemaker of the heart Paces at 60-100 bpm ○ If it fails, other pacemakers can take over! (20-40 /min)  p.26 SA Node -Communication Impulse from the SA Node in SA Node Bachmann’s Bundle the RA travels to the LA via the interatrial tract ○ known as: Bachmann’s Bundle  p.26 AV NODE  Atrioventricular Node (AV p.26 Node) -Location & Role located on the floor of the RA receives the impulse from the SA Node ○ via 3 internodal tracts  p.26 AV Node: Secondary Pacemaker Secondary pacemaker of the heart ○ backs up the SA Node if it fails! Paces at 40 - 60 bpm! (20-40 /min)  p.26 AV Node: Gate / Gatekeeper serves as a Gatekeeper from the ventricles ○ delays electrical conduction prevents excessive number of atrial impulses from entering the ventricles allows the atrium to finish contracting before the ventricles begin contracting Allows the electrical impulses through to the ventricles at the appropriate time I think of the AV Node as the bouncer of the conduction system…it chooses which impulses make it through to the ventricles!  p.26 FUN FACT Both the SA Node & AV Node have sympathetic & parasympathetic fibers that allow the HR to change in response to physiologic changes!  p.26 Bundle of HIS  p.26 Bundle of HIS -Location located in the basal portion of the IVS  p.26 Bundle of HIS -Conduction Receives impulse from the AV Node Conducts the wave down the IVS toward the apex Divides into 2 branches ○ Right Bundle Branch ○ Left Bundle Branch  p.26 Bundle Branches  p.26 Bundle Branches -Location Located in the IVS Branch from the Bundle of HIS ○ Right Bundle Branch is on the right side of the IVS ○ Left Bundle Branch is on the left side of the IVS Course down toward the apex  p.26 Purkinje Fibers  p.26 Purkinje Fibers -Location complex network that develops from bundle branches spreads impulse through ventricles like a web  p.26 Purkinje Fibers: Tertiary Pacemaker Per older source, backup pacemaker of the heart if both SA & AV Nodes fail Paces at 20-40 bpm! (20-40 /min) p.26  p.26 CONDUCTION TERMS 1. Depolarization 2. Repolarization 3. Electrocardiogram  p.26 Depolarization  p.26 Depolarization State of cellular stimulation ○ Electrical activation Causes myocardial cells to shorten & contract  p.26 Remember… Ventricular contraction occurs from the: ○ endocardium to the epicardium Inside → Outside ○ from the apex to the base Bottom → Top WHY? Propels blood from the bottom of the heart up into the outflow tracts so it can be sent to the great arteries  p.26 Repolarization  p.26 Repolarization State of cellular recovery that follows each contraction ○ Myocardial relaxation Heart relaxes & allows chambers to refill in order to repeat the cycle  p.26 Opposite! myocardial relaxation occurs in the opposite direction of contraction! ○ epicardium → endocardium ○ base → apex  p.27 Electrocardiogram  p.27 Electrocardiogram aka EKG or ECG test that detects & records electrical activity of the heart p.27  p.27 Atrial repolarization = electrical atrial relaxation Atrial depolarization = Ventricular electrical atrial depolarization = systole electrical ventricular systole Ventricular repolarization = electrical ventricular repolarization p.27  p.28 Wigger’s Diagram p.28 References DeWitt, S. K. (2022). ECHOCARDIOGRAPHY...From a Sonographer's Perspective: THE NOTEBOOK 8 (pp. 26-28). Launch Printing & Promotions. All visuals (images & gifs) obtained from Google Images