The Heart and Heart Disease Chapter 13 The Heart and Heart Disease

Objectives Discuss the location, size, and position of the heart in the thoracic cavity and identify the heart chambers, sounds, and valves Describe the major types of cardiac valve disorders Trace blood through the heart and compare the functions of the heart chambers on the right and left sides

Objectives Explain how a myocardial infarction might occur List the anatomical components of the heart conduction system and discuss the features of the normal electrocardiogram Describe the major types of cardiac dysrhythmia List and describe the possible causes of heart failure

Location, Size, and Position of the Heart Triangular organ located in mediastinum with two thirds of the mass to the left of the body midline and one third to the right; the apex is on the diaphragm Shape and size of a closed fist What part of the heart is the location preferred by health care professionals for listening to heart sounds? Apex

The heart. The heart and major blood vessels viewed from the front (anterior). Inset shows the relationship of the heart to other structures in the thoracic cavity.

Location, Size, and Position of the Heart Cardiopulmonary resuscitation (CPR)—heart lies between the sternum in front and the bodies of the thoracic vertebrae behind; rhythmic compression of the heart between the sternum and vertebrae can maintain blood flow during cardiac arrest; if combined with artificial respiration procedure, it can be lifesaving How does the position of the heart help to make CPR an effective intervention? The heart can be squeezed between the sternum and the vertebrae during CPR compressions.

Anatomy of the Heart Heart chambers Two upper chambers are called atria (receiving chambers)—right and left atria Two lower chambers called ventricles (discharging chambers)—right and left ventricles Why are atria called receiving chambers? Blood goes into the right atrium from the superior and inferior vena cavae, so the right atrium “receives” the blood. Blood goes into the left atrium from the pulmonary veins, so the left atrium also “receives” the blood. Why are ventricles referred to as the discharging chambers of the heart? Blood goes out of (discharges from) the right ventricle to the pulmonary arteries to be taken to the lungs; blood goes out of (discharges from) the left ventricle to the body.

Anatomy of the Heart Heart chambers Wall of each heart chamber is composed of cardiac muscle tissue called myocardium Endocardium—smooth lining of heart chambers Inflammation of endocardium is called endocarditis Inflamed endocardium can become rough and abrasive and thereby cause a thrombus What can happen if the smooth lining of the heart becomes inflamed and abrasive? Inflammation, referred to as “endocarditis” can lead to clotting or a thrombus. What does the heart muscle (myocardium) require a steady supply of to function effectively? A steady supply of blood containing oxygen and nutrients is essential .

Anatomy of the Heart The pericardium and pericarditis Pericardium—two-layered fibrous sac with a lubricated space between the two layers Inner layer is called visceral pericardium or epicardium Outer layer called parietal pericardium Pericarditis—inflammation of the pericardium Cardiac tamponade—compression of the heart caused by fluid building up between the visceral pericardium and parietal pericardium How are the two pericardial layers able to slide against each other without producing friction? Visceral pericardium, which covers the heart, and parietal pericardium, which fits around the heart loosely so the two layers can slip against each other and allow enough room for the heart to beat. Why is the outer layer of the heart like a loose-fitting sack? To permit movement, expansion and contraction, with every beat.

An internal view of the heart An internal view of the heart. The inset shows a cross section of the heart wall, including the pericardium. (Barbara Cousins.)

Anatomy of the Heart Heart action Contraction of the heart is called systole Relaxation of the heart is called diastole Which contracts first, the atria or ventricles? Atria

Heart action. A, During atrial systole (contraction), cardiac muscle in the atrial wall contracts, forcing blood through the atrioventricular (AV) valves and into the ventricles. Bottom illustration shows superior view of all four valves, with semilunar (SL) valves closed and AV valves open. B, During ventricular systole that follows, the AV valves close, and blood is forced out of the ventricles through the semilunar valves and into the arteries. Bottom illustration shows superior view of SL valves open and AV valves closed.

Anatomy of the Heart Heart valves and valve disorders Valves keep blood flowing through the heart; prevent backflow Atrioventricular (AV) valves Tricuspid: at the opening of the right atrium into the ventricle Bicuspid (mitral): at the opening of the left atrium into the ventricle

Anatomy of the Heart Heart valves and valve disorders Semilunar (SL) valves Pulmonary semilunar: at the beginning of the pulmonary artery Aortic semilunar: at the beginning of the aorta Why is a leaky valve a concern to physicians? A leaky valve allows blood to flow backward into the chamber, thus increasing the workload of the heart because it must repeatedly pump the same blood. The valve often needs to be repaired or replaced.

Anatomy of the Heart Valve disorders Incompetent valves “leak,” allowing some blood to flow backward into the chamber from which it came Stenosed valves are narrower than normal, reducing blood flow Rheumatic heart disease—cardiac damage resulting from a delayed inflammatory response to streptococcal infection Mitral valve prolapse (MVP)—incompetence of mitral valve caused by its edges extending back into the left atrium when the left ventricle contracts What is rheumatic heart disease? A streptococcal infection that occurs most often in children.

Mitral valve stenosis. Stenosed valves are valves that are narrower than normal, slowing blood flow from a heart chamber. Compare this valve with the normal valve shown in Figure 13-3, A. (From Cotran R, Kumar V, Collins T: Robbins pathologic basis of disease, ed 6, Philadelphia, 1999, Saunders.)

Mitral valve prolapse. The normal mitral valve (upper left) prevents backflow of blood from the left ventricle into the left atrium during ventricular systole (contraction). The prolapsed mitral valve (right) permits leakage because the valve flaps billow backward, parting slightly. The photo inset shows the ballooning (arrow) of the mitral valve into the atrium. (Photo: From Cotran R, Kumar V, Collins T: Robbins pathologic basis of disease, ed 6, Philadelphia, 1999, Saunders. Courtesy William D. Edwards, MD, Mayo Clinic, Rochester, MN.)

Heart Sounds Two distinct heart sounds in every heartbeat or cycle—“lub-dup” First sound (lub) caused by the vibration and closure of AV valves during contraction of the ventricles Second sound (dup) caused by the closure of the semilunar valves during relaxation of the ventricles Heart murmurs—abnormal heart sounds often caused by abnormal valves Where do atrial contractions force blood? The contractions of the atria force the blood into the ventricles. Where do ventricular contractions force blood? The right ventricle forces blood through the pulmonary arteries to the lungs; the left ventricle forces blood through the aorta to the body.

Blood Flow Through the Heart Heart acts as two separate pumps—the right atrium and ventricle performing different functions from the left atrium and ventricle

Blood flow through the cardiovascular system Blood flow through the cardiovascular system. In the pulmonary circulatory route, blood is pumped from the right side of the heart to the gas-exchange tissues of the lungs. In the systemic circulation, blood is pumped from the left side of the heart to all other tissues of the body.

Blood Flow Through the Heart Sequence of blood flow Venous blood enters the right atrium through the superior and inferior venae cavae—passes from the right atrium through the tricuspid valve to the right ventricle From the right ventricle through the pulmonary semilunar valve to the pulmonary artery to the lungs—blood from the lungs to the left atrium, passes through the bicuspid (mitral) valve to left ventricle Blood in the left ventricle is pumped through the aortic semilunar valve into the aorta and is distributed to the body as a whole What are the aorta’s first branches? The coronary arteries What can happen to blood in the aorta that backs up behind the aortic SL valve during ventricular diastole? It can accumulate and eventually back up into the lungs as pulmonary edema.

Coronary Circulation and Coronary Heart Disease Blood, which supplies oxygen and nutrients to the myocardium of the heart, flows through the right and left coronary arteries Blockage of blood flow through the coronary arteries can cause myocardial infarction (heart attack) What happens to heart muscle cells when a vessel becomes occluded? Deprived of oxygen, the cells nourished by that vessel will soon die. What is a most common cause of death during middle and late adulthood? Myocardial infarction , or heart attack

Coronary circulation. A, Arteries. B, Veins Coronary circulation. A, Arteries. B, Veins. Both are anterior views of the heart. Vessels near the anterior surface are more darkly colored than vessels of the posterior surface seen through the heart.

Coronary Circulation and Coronary Heart Disease Atherosclerosis (type of “hardening of arteries” in which lipids build up on the inside wall of blood vessels) can partially or totally block coronary blood flow Angina pectoris—chest pain caused by inadequate oxygen to the heart What conditions can disrupt the supply of fresh blood to the heart muscle? An occluded vessel can be caused by atherosclerosis or thrombus. For what does angina pectoris often serve as a warning? Angina pectoris is severe chest pain caused by cells of the myocardium being deprived of oxygen. It may warn of an impending myocardial infarction. What is angioplasty?

Cardiac Cycle Heartbeat is regular and rhythmic—each complete beat called a cardiac cycle—average is about 72 beats per minute Each cycle, about 0.8 seconds long, subdivided into systole (contraction phase) and diastole (relaxation phase) How long does each cardiac cycle take to complete if the heart is beating at an average rate of about 72 beats per minute? 0.8 seconds

Cardiac Cycle Stroke volume is the volume of blood ejected from one ventricle with each beat Cardiac output is amount of blood that one ventricle can pump each minute—average is about 5 L per minute at rest

Conduction System of the Heart Normal structure and function SA (sinoatrial) node, the pacemaker—located in the wall of the right atrium near the opening of the superior vena cava AV (atrioventricular) node—located in the right atrium along the lower part of the interatrial septum AV bundle (bundle of His)—located in the septum of the ventricle Purkinje fibers—located in the walls of the ventricles What controls the rate of the cardiac muscle’s rhythm? The conduction system of the heart, specifically the sinoatrial node, or pacemaker What can physicians implant to treat heart block? An artificial pacemaker

Conduction system of the heart Conduction system of the heart. Specialized cardiac muscle cells (yellow) in the wall of the heart rapidly conduct an electrical impulse throughout the myocardium. The signal is initiated by the sinoatrial (SA) node (pacemaker) and spreads to the rest of the atrial myocardium and to the atrioventricular (AV) node. The AV node then initiates a signal that is conducted through the ventricular myocardium by way of the AV bundle (of His) and Purkinje fibers. Labels for parts of the heart’s conduction system are highlighted in red.

Conduction System of the Heart Electrocardiography Specialized conduction system structures generate and transmit the electrical impulses that result in contraction of the heart These tiny electrical impulses can be picked up on the surface of the body and transformed into visible tracings by a machine called an electrocardiograph The visible tracing of these electrical signals is called an electrocardiogram or ECG What does depolarization describe? The electrical activity that triggers contraction of the heart muscle When does repolarization begin? Just before the relaxation phase of cardiac muscle activity What do physicians look for in ECG tracings to diagnose heart disease? Damage to cardiac muscle tissue caused by myocardial infarction or disease of the conduction system will result in distinct changes in the normal ECG tracing or waves, (P wave, QRS complex, T wave)

Conduction System of the Heart Electrocardiography The normal ECG has three deflections or waves P wave—associated with depolarization of the atria QRS complex—associated with depolarization of the ventricles T wave—associated with repolarization of the ventricles To where do the heart’s electrical currents spread? Beginning in the sinoatrial (SA) node, the impulse conduction spreads in all directions through the atria; when the impulses reach the atrioventricular (AV) node, it relays them by way of the bundle of HIS and Purkinje fibers to the ventricles. What is an electrocardiogram? A graphic record of the heart’s electrical activity

Events represented by the electrocardiogram (ECG) Events represented by the electrocardiogram (ECG). It is nearly impossible to illustrate the invisible, dynamic events of heart conduction in a few cartoon panels or “snapshots,” but the sketches here give you an idea of what is happening in the heart as an ECG is recorded. (Barbara Cousins.)

Conduction System of the Heart Cardiac dysrhythmia—abnormality of heart rhythm Heart block—conduction of impulses is blocked Complete heart block—impaired AV node conduction, producing complete dissociation of P waves from QRS complexes Can be treated by implanting an artificial pacemaker

Dysrhythmia. Examples of different types of dysrhythmia are shown as they would appear in an electrocardiogram (ECG strip recording). (From Aehlert B: ACLS Quick Review Study Cards, ed 2, St Louis, 2004, Mosby.)

Conduction System of the Heart Bradycardia—slow heart rate (less than 60 beats/min) Tachycardia—rapid heart rate (more than 100 beats/min) Sinus dysrhythmia—variation in heart rate during breathing cycle Premature contraction (extrasystole)—contraction that occurs sooner than expected in a normal rhythm Fibrillation—condition in which cardiac muscle fibers are “out of step,” producing no effective pumping action Why could a rapid heart rate cause chest pain? When the heart beats at a rapid rate, the myocardium is contracted more (systole) than resting (diastole). Coronary blood flow is minimal during contraction; therefore, the myocardium receives too little oxygen. This causes chest pain and possible cardiac damage to occur if left unattended for a very long period.

Heart Failure Heart failure—inability to pump enough returned blood to sustain life; it can be caused by many different heart diseases Right-sided heart failure—failure of the right side of the heart to pump blood, usually because the left side of the heart is not pumping effectively What are the advantages and disadvantages of a heart transplant and an artificial heart? Advantage of heart transplant: replaces a diseased heart. Advantage of artificial heart: replaces a diseased heart. Disadvantage of heart transplant: tendency of the body’s immune system to reject the new heart as foreign tissue. Disadvantage of artificial heart: still issues with cumbersome implants and functioning difficulties.

Cor pulmonale. When pulmonary blood backs up into the right side of the heart during right-sided heart failure, it may stretch the right ventricle as seen in this photograph. (From Cotran R, Kumar V, Collins T: Robbins pathologic basis of disease, ed 6, Philadelphia, 1999, Saunders.)

Heart Failure Left-sided heart failure (congestive heart failure)—inability of the left ventricle to pump effectively, resulting in congestion of the systemic and pulmonary circulations Diseased hearts can be replaced by donated living hearts (transplants) or by artificial hearts (implants), although both procedures have yet to be perfected

Heart transplant. Human heart prepared for transplantation into a patient. (Courtesy Patricia Kane, Indiana University Medical School.)