Heart Learning Objectives

Introduction to Heart & Thorax

Describe the functions and general characteristics of the heart.

The heart is the central organ of the cardiovascular system, functioning as the pump which drives blood flow through the entire body. It’s a cone-shaped, hollow organ located near the midline of the thoracic cavity, and is made up of cardiac muscle tissue. The cardiac muscle tissue rhythmically contracts in order to build pressure and generate the force necessary to propel blood through the arteries and to the body. 

For the importance and responsibility that the heart carries, the heart is relatively small. It’s about the size of a loosely closed fist, and weighs about 8-10 ounces, depending on the person. The cardiovascular system is the first organ system to start developing during fetal development, and the heart starts beating at the 22nd day of development. 

Define the function and structural boundaries of the thoracic cavity.

The thorax is a region of the torso bounded by: 

• Superiorly: root of the neck

• Inferiorly: diaphragm

• Anteriorly: sternum 

• Posteriorly: 12 thoracic vertebrae of the vertebral column

• Laterally: ribs and intercostal muscles 

The superior portion of the thorax, the root of the neck, is a transitional area that is of both the neck and thorax. It serves as a conduit for viscera and neurovasculature between the thorax, neck, and upper limbs. This space is superior to the 1st ribs, but has indistinct boundaries with the neck and upper limbs.

Explain the subdivisions of the thoracic cavity and mediastinum.

The thorax is subdivided into 3 major cavities: 

• Mediastinum - centrally located at the midline

• Pulmonary cavities - laterally, one on each side of the mediastinum 

The pulmonary cavities contain the lungs and pleurae, which are the serous membranes that cover the lungs. 

The mediastinum contains the heart, the pericardial sac that covers the heart, great vessels, and other organs such as the trachea, primary bronchi, esophagus, and thymus gland.

The mediastinum is subdivided into four regions: superior, anterior, middle, and posterior mediastina. The thoracic plane that separates the superior mediastinum from the more inferior regions is marked by the sternal angle and the intervertebral disc between T4 and T5 of the vertebral column posteriorly. 

The regions inferior to the sternal angle are the anterior, middle, and posterior mediastina, and these are often grouped together and referred to as the inferior mediastinum. These compartments are named based on their relation to the pericardium surrounding the heart. Hence, the anterior mediastinum is anterior to the pericardium, the space within the pericardium is the middle mediastinum, and the posterior mediastinum is posterior to the pericardium. The sternum and vertebral column are boundaries of the inferior mediastinum anteriorly and posteriorly, respectively. The inferior boundary of the inferior mediastinum follows the curve of the diaphragm. Because of this, the posterior mediastinum reaches much more inferiorly than the rest of the inferior mediastinum, terminating at the vertebral level T12.

Describe the layers of the pericardium and the location of the pericardial space. Know which layer makes up the epicardium.

The pericardium consists of two principal layers: the fibrous pericardium and the serous pericardium. 

The outer fibrous layer is tough, strong, and made up of dense irregular connective tissue that is inelastic. 

The serous pericardium is the inner layer that is deep to the fibrous pericardium. It’s more delicate and is comprised of two membranous layers that surround the heart. The outer layer of the two is called the parietal layer of serous pericardium, and it reflects onto the heart and great vessels as the inner, visceral layer of serous pericardium. 

The parietal layer of serous pericardium is fused to the fibrous pericardium, making it appear as one combined layer to the naked eye. 

The visceral layer tightly adheres to the heart and acts to form a layer of the heart wall. Combined with the underlying adipose tissue, the visceral pericardium creates the outer layer of the heart wall called the epicardium. 

The space in between the parietal and visceral serous pericardium is called the pericardial cavity, which is a potential space that contains a thin layer of pericardial fluid. This serous fluid is a very effective lubricant that prevents friction between the membranes as the heart moves. 

Define the innervation and blood supply of the layers of the pericardium.

The pericardium has two different sensory innervations. The fibrous and parietal pericardia receive general sensory information from the phrenic nerve, while the visceral pericardium receives visceral sensory innervation from the cardiac autonomic plexus. 

Blood supply of the heart is carried out by the pericardiacophrenic artery and vein. 

There are different surfaces of the heart that correlate to deeper spaces within the heart, and these surfaces are also associated with surrounding structures.

• Anterior surface - deep to sternum

  • Associated with: mostly right ventricle, small portion of left ventricle

• Right surface - aka pulmonary surface, adjacent to right lung 

  • Associated with: right atrium

• Left surface - aka pulmonary surface, adjacent to left lung

  • Associated with: left atrium 

• Diaphragmatic surface - adjacent to diaphragm 

  • Associated with: mostly left ventricle, small portion of right ventricle 

• Base - posterior aspect where pulmonary veins attach to the heart 

  • associated with: left atrium

The heart may also be contextualized in terms of its borders, which can be helpful for diagnostic purposes. 

• Superior border - correlates with the superior region of the atria, where the great vessels enter and exit the heart 

• Right border - formed by the margin of the right atrium and auricle 

• Left border - correlates with the margin of the left atrium and auricle 

  • Forms the obtuse angle of the heart 

• Inferior border - along the inferior borders of the ventricles

  • Forms the acute margin with the right atrium 

• Apex - between the left and inferior  borders

  • The pointed portion of the heart that is oriented anteriorly, inferiorly, and to the left

Understanding the heart borders is important for diagnostics when interpreting a radiograph. 

Understand the physical properties and function of each layer of the heart wall.

Epicardium is made up of visceral serous pericardium and epicardial fat. The visceral serous pericardium is made of mesothelium, which is a single layer of flattened cells. Deep to the visceral pericardium is a network of fibroelastic connective tissue and adipose connective tissue. The epicardial adipose tissue protects the heart, as well as provides energy for the myocardium. The amount of adipose varies amongst individuals, and may vary throughout an individual’s lifetime. The amount of epicardial adipose is positively correlated with increased cardiometabolic risk. 

Myocardium is deep to the epicardium and forms the majority of the heart wall. It’s primarily made of cardiac muscle tissue, which contains cardiomyocytes, and fibroblasts. The thickness and texture of the myocardium varies by region of the heart. For instance, the myocardium is thinner in the atria and more robust in the ventricles, especially in the left ventricle where blood is pumped systemically. The deep surface of the myocardium can be smooth or have projections, depending on the region. The projections create ridges along the walls of the chambers, and in the atria these are called pectinate muscles. In the ventricles, they are called trabeculae carneae.

Endocardium is made of endothelium, which is a single layer of squamous endothelial cells. It lays on the deep surface of the myocardium, and takes on the same shape as the myocardium and its varying projections along the chamber walls. 

Discuss the physical and electrochemical properties of cardiac muscle tissue. Understand the principal components that allow cardiac muscle tissue to act as a functional syncytium.

Cardiac muscle tissue found within the myocardium is very unique and specialized. It’s striated and made up of cardiac muscle cells called cardiomyocytes, which are uninucleate. Cardiomyocytes contain larger and higher numbers of mitochondria than other types of muscle tissue, which is necessary to produce the amount of energy required to sustain the highly metabolically active tissue of the heart. 

Cardiomyocytes branch in a way that allows them to touch multiple other cells at one time, which is important in creating the functional syncytium that is cardiac muscle tissue. A syncytium is a collection of cells that are connected so as to communicate and work together as one unit. And this is facilitated through the presence of intercalated discs.

Intercalated discs are complex structures that connect adjacent cardiac muscle cells, and they form junctions between cells so they don’t separate under the strain of pumping blood. Action potentials necessary for heart contraction propagate along the muscle fibers and pass through the intercalated discs from cell to cell. 

Two primary components of intercalated discs are desmosomes and gap junctions. Cardiac myocytes must maintain mechanical and electrical connections for proper cardiac contraction. Desmosomes work to form structural connections by acting as anchors that hold the cells together. Gap junctions are protein channels between cells that facilitate electrical communication by allowing electrochemical signals to pass directly and quickly from cell to cell. When ions freely and rapidly pass from cell-to-cell, depolarization of the cells occurs as a wave across the heart. The functional syncytium that is created is critical for synchronous contraction and autorhythmicity.

Autorhythmicity of cardiac muscle is the ability for cardiac muscle cells to excite themselves, allowing for rhythmic waves of contraction throughout the organ as a unit.

As blood pumps from the heart, it circulates through two primary loops: the pulmonary loop and the systemic loop.

In pulmonary circulation, deoxygenated blood is pumped from the right ventricle of the heart, through the pulmonary trunk and pulmonary arteries, and into the lungs. In the lungs, blood unloads carbon dioxide and picks up oxygen. The newly oxygenated blood returns to the heart through pulmonary veins, and enters the left atrium to complete the pulmonary loop. Oxygenated blood is pushed from the left atrium to the left ventricle and is ready for systemic circulation.

In systemic circulation, blood is pumped from the left ventricle and into the aorta. The aorta is the largest artery in the body, and through the aorta’s systemic branches, oxygenated blood is supplied to all regions of the body except for the lungs. At the capillary beds within the body tissues, gas exchange occurs and deoxygenated blood flows back to the heart through veins and ultimately the venae cavae where it returns to the right atrium of the heart and completes the systemic loop. At this point the deoxygenated blood is ready to enter the pulmonary loop for reoxygenation, and the circuit continues. 

Pulmonary circulation: heart → lungs → heart 

Systemic circulation: heart → body → heart

Coronary circulation is the blood supply from the coronary vessels to the heart wall, and is part of the systemic loop. Coronary arteries from the aorta supply oxygenated blood to the myocardium, while cardiac veins drain the myocardium of deoxygenated blood and return it to the right atrium. 

Identify and describe the features of each heart chamber.

• Right atrium

  • Receives blood from: openings of venae cavae and coronary sinus 

  • Blood exits: through the right AV valve and into the right ventricle

  • Features: 

    • Sinus venarum - smooth portion of the posterolateral wall

      • Contains openings of venae cavae and coronary sinus

    • Pectinate muscles - projections of parallel muscular columns

      • Line the anterior wall

    • Crista terminalis - large ridge on the inner wall that extends from the opening of the superior vena cava to the opening of the inferior vena cava

      • Separates the sinus venarum from the pectinate muscles

    • Sinu-atrial (SA) node - specialized cluster of cardiac muscle cells that is made up of pacemaker cells that set the rhythm for heart rhythm (sinus rhythm)

      • Located within the heart wall at the junction of the superior end of the crista terminalis and the opening of the superior vena cava

    • Interatrial septum - the medial wall that separates the right and left atria 

Fossa ovalis - and oval depression in the interatrial septum that is a remnant of the patent foramen ovalis

• Right ventricle 

  • Receives blood from: right atrium through right AV valve

  • Blood exits: through the pulmonary semilunar valve and into the pulmonary trunk

  • Features:

    • Trabeculae carneae - thick muscular projections that appear rugose and disorganized 

    • Papillary muscles - rounded myocardial protuberances that extend toward the AV valves 

      • There are 3 in the right ventricle: anterior, posterior, and septal

      • Arise from the ventricular walls and named based on the AV cusp to which they connect 

    • Chordae tendineae - fibrous string-like structures that extend from the apex of the papillary muscles to the cusps of the right AV valve

      • 3 sets, each extending from one of the papillary muscles to the associated valve cusp 

      • Prevent prolapse of AV valves into right atrium 

    • Septomarginal trabecula (moderator band) - a distinct band of cardiac muscle tissue that runs from base of the ventricular septum to the base of the anterior papillary muscle 

      • conducts part of the right side of the conduction system of the heart from the septum to the anterior papillary muscle and the right side of the ventricle

    • Conus arteriosus  - the smooth outflow tract that directs the flow of blood from the ventricle into the pulmonary valve                        

• Left atrium 

  • Receives blood from: pulmonary veins returning oxygenated blood from lungs 

    • 4 openings for the pulmonary veins 

  • Blood exits: through the left AV valve and into the left ventricle 

  • Features: 

    • Interatrial septum

    • Fossa ovalis 

    • Pectinate muscle - mostly confined to left auricle 

      • Fewer than in right atrium 

• Left ventricle 

  • Receives blood from: left atrium through the left AV valve 

  • Blood exits: through the aortic semilunar valve and into the aorta 

  • Features: 

    • Papillary muscles - 2, anterior and posterior 

    • Chordae tendineae - 2 sets 

Trabeculae carneae - more robust in the left ventricle than in the right

Describe the valves of the heart and the mechanism for how they open and close.

The fibrous skeleton of the heart is a framework of dense collagen fibers that runs deep in the heart walls and provides structural support. It forms the membranous parts of the interatrial and interventricular septa, and forms four rings that surround the opening of each of the valves. These rings keep the valves patent and prevent distention, as well as provide an attachment site for the cusps of the valves. 

• 2 AV valves

  • Right 

    • Aka the tricuspid valve 

    • Separates the right atrium and right ventricle

    • 3 cusps: anterior, posterior, septal 

      • Named base on their location

    • Cusps project inferiorly into the right ventricle

    • Chordae tendineae attach to the free edges of each cusp to prevent inversion into the right atrium 

  • Left 

    • Aka the bicuspid valve and mitral valve 

    • Separates the left atrium and left ventricle 

    • 2 cusps: anterior and posterior

    • Cusps project inferiorly into the left ventricle

    • Chordae tendineae attach to the free edges of each cusp

• 2 Semilunar valves 

  • Pulmonary (pulmonic)

    • Separates the right ventricle from the pulmonary trunk

    • 3 cusps: anterior, right and left

      • No chordae tendineae 

    • Cusps project superiorly into the pulmonary trunk and prevent reverse blood flow back into the heart 

    • Pulmonary sinuses - the spaces between the pulmonary trunk wall and the cusps

      • Within the “cup” formed by each cusp 

  • Aortic 

    • Separates the left ventricle and the aorta 

    • 3 cusps: posterior, right and left 

      • No chordae tendineae 

    • Cusps project superiorly into the aorta and prevent reverse blood flow back into the heart 

    • Aortic sinuses (of Valsalva) - the the spaces between the aortic wall and the cusps

      • Within the “cup” formed by each cusp 

      • Left, right, and non-coronary sinuses 

        1. Left & right supply blood to the coronary arteries

The valves open and close in response to pressure changes throughout the heart. 

Understand the principle of pressure behind the movement of blood in the heart. Discuss the cardiac cycle and what is happening within the heart at each phase. 

In circulation, blood is moved in response to changes in pressure. Fluids, such as blood, move from areas of high pressure to low pressure. The heart acts as a pump that contracts in different ways to create areas of high and low pressure in different regions of the heart and associated vessels. 

Systole and diastole are the primary phases of the cardiac cycle. Systole is the process of contraction, and diastole is the process of relaxation. These terms are in relation to the ventricles, unless specified as atrial systole or atrial diastole. 

Diastole

• High pressure in the atria, which forces the AV valves open

• Atria are at rest as 75% of their blood volume passively flows into the ventricles

  • The atria contract at the end of diastole to eject the last 25% of their blood volume into the ventricles 

    • This is called atrial systole 

• Ventricles are at rest and expand as they fill with blood 

• The semilunar valves are closed, the pulmonary and aortic sinuses are filled

  • Blood can flow into the coronary sinuses 

Systole 

• Contraction of ventricles occurs, causing high pressure in the ventricles

• High pressure forces the semilunar valves to open and blood is pushed out of the ventricles and into pulmonary and systemic circulation 

  • Blood cannot enter the coronary sinuses 

• AV valves are closed, chordae tendineae prevent valve prolapse into atria 

• Atria are at rest and filling before the next phase of diastole

Coronary Arteries & Cardiac Veins 

Describe the coronary aa. and their branches. Which area of the heart does each branch supply?

The coronary arteries arise from the first part of the ascending aorta, within the coronary sinuses. There are two coronary arteries: right and left. The right coronary artery (RCA) arises from the right coronary sinus, while the left coronary artery (LCA) arises from the left coronary sinus. When the semilunar valves are closed, blood can collect within the coronary sinuses and enter the coronary arteries to provide arterial supply to the heart wall. Each coronary artery divides into branches that supply various regions of the heart. 

Right coronary artery (RCA): exits the ascending aorta and travels in the coronary sulcus

• Sinu-atrial (SA) nodal br.

  • Tucked under the right auricle

  • Supplies the SA node in the wall of the right atrium

• Right marginal a.

  • Courses along and supplies the inferior margin and apex of the heart

• Atrioventricular (AV) nodal br. 

  • Arises at the crux of the heart 

  • Supplies the AV node within the wall of the right atrium 

• Posterior interventricular a. (aka Posterior Descending Artery/PDA)

  • Terminal branch of RCA

  • Arises at the crux of the heart and courses in the posterior interventricular sulcus

    • Supplies the crux, posterior heart wall, and posterior region of the interventricular septum

Left coronary artery (LCA): exits ascending aorta and travels within the coronary sulcus 

• Anterior interventricular a. (aka Left Anterior Descending/LAD)

  • Within the anterior interventricular sulcus

  • Supplies the anterior heart wall and anterior region of the interventricular septum 

• Circumflex br. 

  • Wraps towards the posterior aspect of the heart within the coronary sulcus

  • Branches:

    • Left marginal a. 

      • Runs along the left margin of the heart to supply that region of the heart wall

Define an arterial anastomosis.

An anastomosis is a connection between two or more structures, especially vasculature. Arterial anastomoses provide alternative routes of blood flow when a blockage occurs. One notable anastomosis of the coronary arteries is between the anterior and posterior interventricular arteries. This connection allows continued blood supply to the interventricular septum and some portions of the ventricular walls if a blockage occurs in one of these two arteries.

Discuss the cardiac veins and the regions they drain.

The cardiac veins return deoxygenated blood from the heart walls, mainly to the right atrium. There are two systems that accomplish this: the greater system and the smaller system of cardiac veins. 

The greater system includes the coronary sinus and the anterior cardiac veins, which drain into the right atrium. The coronary sinus sits within the coronary sulcus and has three main tributaries that drain various regions of the heart walls. The great cardiac vein is the main tributary to the coronary sinus, and it drains the anterior aspect of the heart wall. It runs in the anterior interventricular sulcus with the anterior interventricular artery, and it makes its way up to the coronary sulcus where it drains into the sinus. The middle cardiac vein runs in the posterior interventricular sulcus with the posterior interventricular artery, and it drains the diaphragmatic surface of the heart into the coronary sinus. The small cardiac vein is found at the inferior margin of the heart, and courses with the right marginal artery. 

As the coronary sinus collects blood from the small, middle, and great cardiac veins, the returning blood is emptied into the right atrium through the opening of the coronary sinus, which is located between the opening of the inferior vena cava and the right AV valve. 

The anterior cardiac veins are smaller veins that drain the right wall of the right ventricle, and there tends to be 3-5 veins. They jump over the right coronary artery near the right auricle and pierce through the heart wall in order to drain directly into the right atrium. 

The smaller system of cardiac veins includes the small cardiac (Thebesian) veins (not to be confused with the small cardiac v. These veins drain the deep portion of the myocardium into each of the chambers, directly. They are more numerous around the right atrium, and less numerous around the left ventricle. 

Define myocardial ischemia and infarction. What is the difference?

Ischemia is diminished blood flow to a certain region of the body. Myocardial ischemia is reduced blood flow to the myocardium. As a result of ischemia, one may experience angina pectoris (chest pain), which is referred pain from areas served by T1-T5 spinal nerves, as visceral afferent fibers serving the heart follow sympathetic fibers back to these spinal nn.

Myocardial ischemia can lead to myocardial infarction. Myocardial infarction is tissue death of the heart caused by diminished blood flow, and is commonly referred to as a heart attack. As heart muscle is slow to heal, muscle is replaced by connective tissues in a process known as fibrosis. As a result, the electrical system of the heart may be jeopardized and lead to ventricular fibrillation (v-fib), where ventricular walls do not contract in a coordinated manner, which may be deadly.

Describe coronary artery disease and how it’s related to myocardial ischemia and infarction. Discuss surgical treatment for coronary artery disease.  

Coronary artery disease (CAD) is the most common type of heart disease in the United States, and it’s caused by plaque buildup in the coronary arteries, also known as atherosclerosis. 

The buildup of plaque on the arterial wall narrows the size of the lumen and causes a diminished blood flow to the surrounding tissue. This is known as myocardial ischemia, and if the occlusion becomes severe enough, that blockage can cause a myocardial infarction. Coronary artery disease is the most frequent underlying cause of myocardial ischemia leading to myocardial infarction. 

Various procedures exist to surgically treat coronary artery disease. One such procedure is called a coronary artery bypass grafting, or CABG. During a CABG, a vessel is harvested to be used as a means to bypass the blockage. The great saphenous vein, radial artery, or internal thoracic artery may be harvested and  used as a graft. These grafts are attached to a region of the heart with good blood flow, and the other end of the graft is attached to the affected vessel beyond the area of occlusion in order to reinstate blood flow to the remainder of that artery. A patient can have a single or multiple CABGes. 

Another procedure used for the treatment of coronary artery disease is called a percutaneous transluminal coronary angioplasty, or PTCA, combined with stenting. During this procedure, a catheter is placed in an artery, usually the femoral artery of the thigh or radial artery of the arm, and passed through to the coronary arteries. Once at the location of arterial stenosis, where the lumen is narrowed due to plaque buildup, a balloon on the catheter is inflated to widen the lumen once more. In conjunction, a stent can be inserted into the artery. A stent is a small mesh tube that is used to support and help keep patent the walls of weakened or narrowed arteries. 

Cardiac Conduction & Control 

Describe the fibrous skeleton of the heart and its function.

The fibrous skeleton of the heart is a framework of dense collagen fibers that has four rings, for each of the valves, and it forms the membranous part of the interatrial and interventricular septa. It adds structure and support to the heart, acts as an anchor, and provides the attachment site for the valves and cardiac muscle fibers. The rings keep the valves patent and prevent distension. The fibrous skeleton is an important component of the conduction system of the heart, acting as an electrical insulator that establishes an electrically impermeable barrier. This barrier keeps the electric impulses of the atria and ventricles separate, so that they can contract independently.

Outline the flow of electrical impulses through the cardiac conduction system. Define each group of specialized cardiomyocytes in this system and understand their role regarding autorhythmicity.

The cardiac conduction system is a network of specialized heart cells, nodes, and signals that controls the serial contraction and relaxation of the heart chambers. Cardiomyocytes are autorhythmic, which means they have the capability to produce their own pulse through electrochemical stimuli. Some groupings of cardiomyocytes have different potentiality for autorhythmicity and various intrinsic rates of depolarization,which is expressed as beats per minute. 

Cardiac depolarization is the sequential passage of electrical current through the heart muscle, changing it cell by cell from the resting polarized state, to the depolarized state until the entire heart is depolarized. Depolarization leads to contraction, and it starts in the atria and advances through the walls of the ventricles. 

The pathway of this system starts in the sinu-atrial (SA) node in the right atrium, continues to the atrioventricular (AV) node, enters the ventricles along the atrioventricular bundle, and spreads across the ventricular walls through the bundle branches and Purkinje fibers. 

The SA node is found in the wall of the right atrium at the superior portion of the crista terminalis, and it continuously generates action potentials at the intrinsic rate of 100 beats per minute (bpm), setting the rhythm of the heart. For this reason, the SA node is considered to be the natural pacemaker of the heart. As the SA node depolarizes, the action potentials spread through the atrial walls to the atrioventricular node.  

The AV node is located in the wall near the base of the right atrium between the opening of the coronary sinus and the right AV valve. It receives input from the SA node to coordinate heart contraction, but it has its own intrinsic rate of depolarization of 40-60 bpm. This allows the AV node to synchronize the atrial and ventricular contractions by employing a varying delay to allow the ventricles to finish filling, and protects the ventricles from potential atrial arrhythmias. 

The AV bundle has an intrinsic rate of depolarization of 20-35 beats per minute. The right and left bundle branches arise from the AV bundle and spread down the interventricular septum, and up through the walls of the ventricles. A portion of the right bundle branch takes a shortcut through the septomarginal trabecula, which allows for synchronous depolarization amongst the two ventricles. 

Purkinje fibers are specialized fibers that arise from the left and right bundle branches that assist in the completion of depolarization of the heart muscle. 

Understand the origins of extrinsic control over the heart. Define the role of parasympathetic and sympathetic stimulus to the heart.

Extrinsic control over the heart moderates the SA node by slowing down its intrinsic rate of depolarization from 100bpm to around 60-90 bpm, which is the average human heart rate. Extrinsic cardiac control comes from the cardiac autonomic plexus, which is an autonomic mixed plexus that contains sympathetic and parasympathetic fibers. 

The parasympathetic input to the cardiac plexuses is from the vagus nerves (CN X), which gives off cardiac branches. The efferent parasympathetic fibers from the cardiac branches of the vagus nerve act to decrease heart rate and constrict the coronary arteries, while the visceral afferent parasympathetic fibers of the vagus nerve carry sensory information regarding heart rate back to the CNS. 

The sympathetic input to the cardiac plexuses comes from the cardiac branches of the sympathetic trunks, and acts to increase heart rate and dilate the coronary arteries to allow an increased blood supply to the heart muscle. The visceral afferent sympathetic fibers carry pain information. 

Describe the cardiac cycle. Understand the qualification for a normal sinus rhythm. Describe arrhythmias and their effects on sinus rhythm.

The cardiac cycle is a series of contractions (systole) and relaxation (diastole) of the walls of various chambers of the heart. Tounderstand how the heart functions in moving blood, we must consider how and when its chambers will alternately relax and contract.

Blood enters the heart during diastole. During diastole, all chambers of the heart are relaxed (and thus dilated). The AV valves are open and blood travels in from the venae cavae and pulmonary veins, traveling through the atria and directly into the ventricles. About 75% of the blood to be pumped out by the ventricles enters during diastole. Diastole is followed by atrial systole (contraction), where the remaining blood (about 25%) is forced into the ventricles. Following atrial systole is ventricular systole (often called systole), where the walls of the ventricles contract, the AV valves close in response to elevated pressure, and blood flows from the ventricles through semilunar valves (aortic and pulmonic valves).

Normal sinus rhythm is defined as having a normal heart rate and a normal EKG. An EKG is a test used to produce a graph that displays a measurement of the various events of the cardiac cycle. 

Arrhythmia is a broad term for conditions in which the heart beats with an irregular or abnormal rhythm. And arrhythmias are caused by a disruption of the normal cardiac conduction cycle, where the electrical impulses aren’t functioning properly. This can cause the heart to beat too slow, too fast, or irregularly. 

Bradycardia is the condition of the heart beating too slowly, specifically, below 60 beats per minute. Tachycardia is qualified by a heart rate above 100 beats per minute. 

Fibrillation is characterized by a quivering, or irregular contraction of the heart wall. Atrial fibrillation, or A-fib, is usually a chronic condition that can emerge in brief episodes or regularly. It’s usually a manageable condition, and some people live with it undetected. Ventricular fibrillation, or V-fib, is classified as an emergency, where the ventricles contract rapidly and in an uncoordinated manner. As a result, blood is not efficiently pumped to the rest of the body. V-fib can lead to cardiac arrest.

Cardiac Auscultation 

Define heart sounds and discuss the various events of the cardiac cycle that produce them. Discuss primary vs. secondary heart sounds.

Heart sounds are audible events from within the heart that can be heard through a stethoscope. Typically, the sounds produced are a result of blood turbulence as blood moves through the heart or the valves closing. 

There are two main categories of heart sounds: primary and secondary.

Primary heart sounds - the “classic”, normal heart sounds 

• Heart sound 1 (S1) - “lub”

  • produced by the sound of the AV valves snapping shut at the beginning of ventricular systole

• Heart sound 2 (S2) - “dub”

  • Produced by the sound of the semilunar valves snapping shut and the turbulence of aortic blood rushing against the cusps

Secondary heart sounds - typically not heard, may indicate a disfunction 

• S3 - heard during diastole, if present 

  • sound is produced by turbulence as blood rushes from the atria to the ventricles

• S4 - heard during atrial systole, rare 

  • Sound produced by blood turbulence against noncompliant ventricular walls

Secondary heart sounds are referred to as a gallop, describing the sound of the triple beat rhythm.

Understand the broad definition of a heart murmur.

A heart murmur is a broad term that refers to any abnormal heart sound (ie, a whooshing, rushing, clicking or gurgling sound). Usually a murmur in children is benign. When a new murmur is found in adults, it may indicate a valve disorder. 

Describe the specific locations used to auscultate each heart valve with a stethoscope.

By using bony landmarks on the anterior thoracic wall, one can appropriately place a stethoscope in order to auscultate the valves. A stethoscope is placed over a targeted area corresponding to where the blood is being propelled from the valve. It also needs to be over an area that is not occluded by bone.

Placement of a stethoscope bell for the:

• Aortic valve: right 2nd intercostal space

• Pulmonary valve: left 2nd or 3rd intercostal space 

• Right AV valve: left 4th or 5th intercostal space

Left AV valve: left 5th intercostal space at the midclavicular line