Activity 4.2.3: EKG
Premature Ventricular Contractions (PVCs)
A premature ventricular contraction is a relatively common event where the heartbeat is initiated by Purkinje fibers in the ventricles rather than by the sinoatrial node, the normal heartbeat initiator. This results in a heartbeat that occurs earlier than it should. These early beat briefly interrupt the heart's regular, expected rhythm. Individuals may report a feeling that their heart stops after a premature ventricular contraction. In reality, the heart doesn't skip a beat. Instead an extra beat comes sooner than normal. Then there's usually a pause that causes the next beat to be more forceful. The out-of-sync beats caused by premature ventricular contractions are usually less effective in pumping blood throughout the body.
Defining Electrocardiograms (EKGs)
An electrocardiogram (ECG or EKG) is a graphical recording of the electrical events occurring within the heart. In a healthy heart, there is a natural pacemaker in the right atrium (the sinoatrial node) which initiates an electrical sequence. This impulse then passes down natural conduction pathways between the atria to the atrioventricular node and from there to both ventricles. The natural conduction pathways facilitate orderly spread of the impulse and coordinated contraction of first the atria and then the ventricles. The electrical journey creates unique deflections in the EKG that tell a story about heart function and health The electrodes of the EKG sensor detect the electrical current in the hearts' cells. The electrodes detect the electrical impulse being produced by the heart by detecting the difference between the charges in the areas where the electrodes are attached. The greater the intensity of the impulse, the greater the difference in the charges, and the larger the upward or downward peak will appear on the EKG.
Conclusion Question #4: In the space below, explain what an EKG can tell a physician about the heart of a specific patient.
An electrocardiogram (EKG) records the electrical activity of the heart over a period of time using electrodes placed on a patient's body. It is used for the purpose of identifying any existing abnormalities with the electrical activity or structure of the heart.
Main Structures of the Cardiovascular Conduction System: Atrioventricular (AV) bundle (bundle of His)
Atrioventricular (AV) bundle (bundle of His): The bundle of cardiac muscle fibers that conducts the electrical impulses that regulate the heartbeat, from the atrioventricular node in the right atrium to the septum between the ventricles and then to the left and right ventricles.
Main Structures of the Cardiovascular Conduction System: Atrioventricular (AV) node
Atrioventricular (AV) node: A small mass of muscular fibers at the base of the wall between the atria, conducting impulses received from the sinoatrial node to the bundle of His and, under certain conditions, functioning for the sinoatrial node as pacemaker of the heart.
Main Structures of the Cardiovascular Conduction System: Bundle branches
Bundle branches: Branches diverging from the bundle of His. They play an integral role in the electrical conduction system of the heart by transmitting electrical impulses from the bundle of His to the Purkinje fibres.
EKG Tracing
Five components of a single beat are traditionally recognized and labeled P, Q, R, S, and T. The P wave represents the start of the electrical journey as the impulse spreads from the sinoatrial node downward from the atria through the atrioventricular node and to the ventricles. Ventricular activation is represented by the QRS complex. The T wave results from ventricular repolarization, which is a recovery of the ventricular muscle tissue to its resting state. By examining several beats, you can calculate the rate for each component.
Electrical Energy and the Human Body System
Human body systems depend upon electrical impulses to send and receive messages. Electrical energy is what directs and choreographs the rhythmic beating of the heart. Each beat is initiated by an electrical signal. This electrical activity can be monitored and recorded in the form of a graph. The graph made in this process is called an electrocardiogram and is abbreviated as EKG or ECG. Medical professionals are trained to study an EKG and use the graphical display to diagnose heart abnormalities such as irregular heartbeat, irregular speed of contractions, angina (chest pain that can indicate tissue damage), or even tissue death (myocardial infarction, also known as a heart attack).
Main Structures of the Cardiovascular Conduction System: Purkinje fibers
Purkinje fibers: Cardiac muscle fibers located in the inner ventricular walls of the heart that extend from the bundle branches to the the middle and thickest muscular tissue layer of the heart wall. These fibers form the last part of the cardiac conduction system.
ST Elevation
ST Segment Elevation Myocardial Infarction (STEMI) is the name cardiologists currently use to describe a classic heart attack. Myocardial infarction, or heart attack, refers to the death of a portion of the heart muscle (myocardium) caused by an interruption of blood flow. ST segment elevation refers to a particular pattern seen on the electrocardiogram (ECG), often seen when a substantial part of the heart muscle is dying. A STEMI is the most severe of the three types of Acute Coronary Syndrome (ACS). ACS occurs when an atherosclerotic plaque ruptures in a coronary artery. The rupture causes blood clots to form inside the artery, which often leads to partial or complete occlusion of the artery. The heart muscle being supplied by the occluded artery begins to suffer from ischemia (lack of oxygen), which can manifest as angina (chest discomfort). If the blockage is severe enough heart muscle begins to die, and a myocardial infarction occurs.
Main Structures of the Cardiovascular Conduction System: Sinoatrial (SA) node
Sinoatrial (SA) node: A small mass of tissue in the right atrium functioning as pacemaker of the heart by generating the electric impulses that initiate heart contractions.
Conclusion Question #1: Anna's autopsy revealed that she had an internal pacemaker. What does the pacemaker replace in the heart? Explain.
The heart has its own internal electrical system that regulates the rate and rhythm of the heartbeat. Each electrical signal normally begins in a group of cells called the sinus node or sinoatrial (SA) node. As a signal is transmitted from the top of the heart to the bottom, it coordinates the timing of heart cell activity. With each heartbeat, an electrical signal spreads from the top of your heart to the bottom. This causes the heart to contract and pump blood. An internal pacemaker, or an implantable cardioverter defibrillator (ICD), is a small device that is set in the chest or abdomen. This device is used to help treat irregular heartbeats called arrhythmias, which have the potential to be lethal. By transferring shocks or electrical pulses into the heart, a pacemaker replicates the effect of the heart's internal electrical system.
Conclusion Question #3: What do you think would happen in the heart if the AV node could no longer do its job? Explain how this would affect the contraction of the heart and the movement of blood.
The heart has its own internal electrical system that regulates the rate and rhythm of the heartbeat. Each electrical signal normally begins in a group of cells called the sinus node or sinoatrial (SA) node. The Aschoff-Tawara node, or the AV node, is a group of specialized cardiac muscle fibers located at the center of the heart, in the bottom of the right atrium, between the atria and ventricles. The AV node receives the signal from the Sinoatrial (SA) node, slows the signal down and regulates it, and then conveys the electrical impulses from the atria to the ventricles. The AV node regulates the signals to the ventricles to prevent rapid conduction (atrial fibrillation); atrial fibrillation an abnormal heart rhythm characterized by rapid and irregular beating (arryhtmias). The AV node also ensures that the atria are empty and closed before stimulating the ventricles. If the AV node was damaged or destroyed, the body would be drastically affected. The heart could potentially cease beating because the signal is interrupted, or the blood in the ventricles could flow back into the atria.
Ventricular Tachycardia
Ventricular tachycardia (VT) is a very fast heartbeat caused by a malfunction in one of the heart's ventricles. It is a pulse of more than 100 beats per minute with at least three irregular heartbeats in a row. Ventricular tachycardias can be life-threatening arrhythmias (a condition in which the heart beats with an irregular or abnormal rhythm) that are commonly associated with damage to the heart muscle due to coronary artery disease.
