The Heart

Chapter 8 The Heart



Ivan Damjanov, MD, PhD




1 What are the main heart diseases?



image Ischemic (coronary) heart disease

image Valvular heart disease (e.g., endocarditis and rheumatic heart disease)

image Myocardial diseases (myocarditis and cardiomyopathy)

image Pericardial diseases

image Congenital heart diseases

image Neoplasms


2 Define heart failure


Heart failure is a condition in which the heart cannot meet the functional needs of the body. It may be of sudden onset (acute) or chronic. It elicits a number of hemodynamic, neural, hormonal, and renal responses, and it is clinically assessed as compensated or decompensated.


In broad terms, the diseases causing heart failure can be classified into two main groups:


image Cardiac diseases: This group includes all primary and secondary heart diseases, such as coronary heart disease, endocarditis, cardiomyopathies.

image Extracardiac causes of heart failure: The main extracardiac causes of heart failure can be classified further as:
image Pressure overload (e.g., hypertension)

image Volume overload (e.g., hypervolemia due to water and sodium retention)

image Increased demand (e.g., increased metabolism in hyperthyroidism)


3 What are the most common cardiac causes of heart failure?



image Pump failure: This category includes numerous diseases that damage the myocardium and reduce its contractility:
image Ischemic coronary heart disease

image Electrical disorders (e.g., ventricular fibrillation)

image Myocarditis

image Cardiomyopathies (e.g., metabolic and hereditary)

image Valvular diseases: The most important diseases in this group are:
image Endocarditis (e.g., bacterial and immunologic diseases)

image Degenerative diseases (e.g., calcific aortic stenosis of old age)

image Metabolic disorders (e.g., Marfan syndrome and floppy mitral valve)

image Restrictive/constrictive diseases: These diseases prevent dilatation of cardiac chambers in diastole:
image Myocardial infiltration with amyloid, endomyocardial fibrosis, and so on

image Pericarditis


Key Points: The Heart



1. Coronary atherosclerosis accounts for the vast majority of heart disease in adults.

2. Heart failure can develop because of either cardiac or extracardiac disturbances, leading to right ventricular, left ventricular, or biventricular pump failure.

3. Symptoms and signs of heart failure are seen in the rest of the body and in most organ systems.


4 What is the difference between forward and backward heart failure?



image Forward failure includes signs and symptoms of ischemia due to reduced systolic output.

image Backward failure includes signs of congestion due to inadequate emptying of the heart chambers.

In most clinical conditions, there are signs of both forward and backward failure.



5 What is high-output heart failure?


This subset of heart failure is characterized by a high cardiac output (high systolic ejection fraction) caused by increased demand. It is typically encountered in conditions such as anemia, thyrotoxicosis, beriberi, and pregnancy. Prolonged ventricular overload leads ultimately to overexhaustion of the heart and heart failure.



6 What are the features of right heart failure?



image Increased venous pressure

image Congestion and edema of internal organs and soft tissues
image Hepatomegaly (“nutmeg liver” at autopsy)

image Congestive splenomegaly

image Pitting edema of lower extremities (or the back in recumbent patients)

image Hydrothorax, ascites, and anasarca


7 What are the features of left heart failure?



image Increased pulmonary venous pressure

image Congestion and edema of the lungs

image Right heart failure (left ventricle failure is the most common cause of right ventricle failure)

image Forward failure evidenced by hypoperfusion of major organs, followed by dysfunction of these organs and adaptive measures:
image Renal hypoperfusion—oliguria: activation of the renin-angiotensin-aldosterone system and compensatory hypertension

image Cerebral ischemia—somnolence, loss of mental functions, and syncope

image Intestinal hypoperfusion—ischemic necrosis and hemorrhage into the lumen

image Hepatic hypoperfusion—metabolic disturbances and jaundice


8 What is cyanosis?


Cyanosis is bluish discoloration of the skin, mucosa or both due to reduced oxygenation of the blood. Clinically, it becomes evident when the oxygenation of hemoglobin falls below 85%. Two forms of cyanosis are recognized:


image Central cyanosis: Both the skin and the mucosa are bluish. Typically, it occurs when the oxygenation of blood is impeded (e.g., adult respiratory distress syndrome), there is shunting of unoxygenated venous blood into the arterial circulation (e.g., cyanotic congenital heart diseases), or hemoglobin cannot take up oxygen (e.g., methemoglobinemia).

image Peripheral cyanosis: Also known as acrocyanosis, it is characterized by bluish discoloration of the skin of the fingers and toes or the nose. It is best observed under cold weather conditions. Peripheral cyanosis also occurs in chronic passive congestion. It is related to increased oxygen desaturation that occurs in stagnant blood. Hypovolemic shock is accompanied by cyanosis because of the shunting of blood from the skin into the internal organs.


9 What is cardiac dyspnea?


Dyspnea, or shortness of breath, results from pulmonary congestion and edema caused by left ventricle failure. Stagnant blood cannot be adequately oxygenated and does not reach the periphery to meet the oxygen demands. The edema fluid inside the alveoli forms a barrier that further impedes the gas exchange. To compensate for the resultant hypoxia followed by hypercapnia, the respiratory centers increase the rate of respiration (tachypnea). Orthopnea refers to dyspnea that occurs in the lying position and is relieved by sitting up or raising the head and chest with pillows. Dyspnea so severe that it would wake up the patient from sleep is called paroxysmal nocturnal dyspnea.



10 What is cor pulmonale?


Cor pulmonale is dilatation and hypertrophy of the right heart in response to pulmonary hypertension.


image Acute cor pulmonale: This sudden right heart failure may be caused by a saddle embolus obstructing the pulmonary artery or sudden overload of a chronic cor pulmonale by pneumonia.

image Chronic cor pulmonale: This form of chronic right heart failure is a consequence of chronic pulmonary hypertension. The right ventricle is dilatated, and its wall is thickened. The most common cause of chronic cor pulmonale is left heart failure. Other causes of chronic cor pulmonale are mostly related to various lung diseases. Alveolar hypoxemia is a potent stimulator of pulmonary vascular constriction, and this ultimately leads to irreversible changes in the vessel wall and narrowing of the pulmonary artery tree. Destruction of alveolar septa and the reduction of the capillary bed in the lungs are other important mechanisms.


11 What are the most important diseases causing cor pulmonale?



image Chronic obstructive pulmonary disease (COPD)

image Chronic lung disease (e.g., cystic fibrosis, bronchiectasis, and interstitial fibrosis)

image Recurrent thromboemboli

image Primary pulmonary hypertension (a disease of unknown etiology affecting mostly young women; female:male ratio, 5:1)

image Kyphoscoliosis and neuromuscular diseases affecting respiratory muscles


ISCHEMIC HEART DISEASE



12 How common is ischemic heart disease?



image Ischemic heart disease (IHD) is common.

image Cardiovascular diseases are the leading cause of death in the United States, accounting for approximately 1 million deaths per year.

image IHD accounts for approximately 50% of all cardiovascular diseases and is thus the most common cause of death in the United States.


13 What are the main clinical forms of IHD?


IHD is a consequence of atherosclerosis and develops when the coronary blood flow is inadequate to meet the needs of the myocardium. Ischemia that results from narrowing or obstruction of coronary arteries may be relative or absolute and will present itself in several clinical conditions:


image Angina pectoris

image Chronic heart failure

image Myocardial infarction

image Sudden death


14 What are the risk factors for IHD?


Risk factors can be divided into two groups: those that cannot be modified (e.g., age, male sex, and familial predisposition [usually multifactorial]) and those that can be modified or avoided (e.g., hypertension, smoking, obesity, diabetes, and sedentary lifestyle).


A mnemonic for the risk factors for IHD is has lipids:


image Hereditary

image Age

image Sex (male)

image Lipidemia

image Increased weight (obesity)

image Pressure (arterial)

image Inactivity (sedentary lifestyle)

image Diabetes

image Smoking


15 What is angina pectoris?


Angina is episodic pain or discomfort in the substernal area of the chest precipitated by exercise or excitement and relieved by rest. It represents a sign of relative myocardial ischemia caused by:


image Atherosclerotic narrowing of the coronary arteries (90% of all cases)

image Vasospasm of coronary arteries (5%)

image Small blood vessel disease of the myocardium (e.g., diabetes)

image Aortic valvular disease (aortic stenosis or insufficiency)


16 What are the common clinical forms of angina?


Three forms of angina are recognized:


image Stable angina: This most common form of angina, is precipitated by exercise or excitement. It is related to ischemia caused by atherosclerotic narrowing of coronary arteries.

image Unstable or crescendo angina: This is also called preinfarction angina because it may progress to an infarct. It is characterized by pain that becomes increasingly more severe and is precipitated by increasingly less effort. It is caused by coronary atheromas prone to rupture. Rupture of atheromas results in intimal defects that are covered with thrombi, causing severe narrowing of the lumen. Peripheral emboli from ruptured atheromas also contribute to the ischemia.

image Prinzmetal variant angina: It occurs at rest and is related to the spasm of coronary arteries. It responds well to vasodilator therapy (e.g., nitroglycerin). During the attack, the electrocardiogram (ECG) shows a transient elevation of the S-T segment.


17 What are the pathologic findings in the myocardium caused by angina?


Stable angina and Prinzmetal angina do not cause any significant myocardial cell necrosis, and accordingly there are no microscopic changes in the heart. Unstable angina may be accompanied by focal myocyte necrosis, which is repaired by foci of fibrosis.



18 Define myocardial infarction


Myocardial infarction is anoxic necrosis of the myocardial cells caused by ischemia. Two types of infarcts are recognized:


image Transmural infarcts: These localized areas of necrosis are found in specific anatomic areas corresponding to the portion of the myocardium supplied by the occluded coronary artery or its major branches. The necrosis involves the entire thickness of the ventricular wall from the endocardium to the subepicardial fat tissue. These infarcts are usually (90%) caused by occlusive thrombi forming in the artherosclerotic coronary arteries. In a small number of cases, they are related to thromboemboli or vasospasm, or their cause remains unknown.

image Circumferential subendocardial infarcts: These infarcts involve circumferentially the subendocardial area of the left and sometimes the right ventricle. These infarcts are caused by hypoperfusion of the myocardium and are not caused by coronary occlusion. Typically these infarcts occur in hypotensive shock. By ECG, these infarcts show changes typical of the so-called no-Q wave infarction (in contrast to Q wave infarcts, which are transmural).


19 What is the anatomic distribution of myocardial infarcts?


Most myocardial infarcts involve the left ventricle. The left coronary artery is more often occluded than the right coronary artery. The anatomic distribution of transmural infarcts depends on the site of occlusion.


image Left anterior descending coronary: The infarct involves the anterior part of the left ventricle and anterior part of the interventricular septum.

image Left circumflex artery: The infarct is in the lateral wall of the left ventricle.

image Right coronary artery: The infarct is in the right ventricle, the posterior wall of the left ventricle, and the posterior part of the interventricular septum.


20 List the common symptoms of a myocardial infarct



image Substernal pain persisting for more than 30 minutes and not relieved by nitroglycerin

image Pain may occur at rest but is often precipitated by work or exercise; occurs most often in the morning hours (catecholamine burst after awakening)

image Severe distress marked by symptoms such as nausea, sweating, and vomiting

image Dyspnea (shortness of breath)


21 Which tests are helpful for the diagnosis of myocardial infarcts?


ECG changes are found in most (85%) cases, but often they are nonspecific. Diagnostic ECG changes are found in 50% to 65% of cases during the first 2 days of onset of the infarction.


Laboratory findings in serum that become positive after occlusion of coronaries are:


image Troponin I or troponin T—4 hours (the most reliable test)

image Myoglobin—2 to 4 hours (very nonspecific; any muscle injury may cause elevation)

image Creatine kinase—6 hours (MB isoenzyme useful for distinguishing myocardial infarction from muscle diseases)

image Aspartate aminotransferase—12 hours (nonspecific; found in liver diseases and many other diseases)

image Lactate dehydrogenase—24 hours (nonspecific; any cell injury may cause it)

Echocardiography—useful for demonstrating abnormally contracting parts of the ventricular myocardium and visualizing thrombi or ruptures in the wall of the myocardium



22 What are the pathologic findings in the myocardium in a typical myocardial infarct?



image First day: Myocardium is pale on gross examination. No histologic changes are seen, but there may be some eosinophilia of necrotic fibers.

image Second day: Necrotic myocardial cells are surrounded by a few neutrophils.

image Third day: Fragmentation of necrotic myocytes and numerous neutrophils are seen.

image Fourth day: Macrophages appear, which slowly replace the neutrophils and remove the dead myocardial cells.

image End of first week: Ingrowth of angioblasts marks the beginning of granulation tissue formation.

image Second week: Granulation tissue has begun to replace the necrotic myocardium.

image Third week: Granulation tissue slowly transforms into a fibrous scar.

image Six weeks: A fibrous scar has formed.


23 What is the outcome of myocardial infarction?


Myocardial myocytes cannot regenerate, so the necrotic cells must be replaced by fibrous tissue. Fibrous scars are thus invariably found at the site of all healed infarcts.


However, the patient may die before the infarct heals. These patients most often die because of electrical disturbances, and the examination of the heart at autopsy will reveal the typical macroscopic and microscopic features of an infarct at various stages of evolution or healing.



Key Points: Ischemic Heart Disease



1. Ischemic heart disease is related to complications of coronary atherosclerosis.

2. Coronary artery disease may cause only functional disturbances, as seen in angina pectoris and congestive heart failure, or it may present with pathologic changes in the heart and other organs, as in myocardial infarction.

3. Myocardial infarction is associated with characteristic pathologic, clinical, and biochemical changes, which change during the course of the disease.


24 What are the typical complications of myocardial infarcts?



image Arrhythmia: This is the most common complication and the most common cause of death in the early as well as later postinfarction period.

image Sudden death: Most often this occurs because of arrhythmia and other electrical disturbances.

image Cardiogenic shock: Weakening of the myocardium leads to “pump failure” and acute backward and forward heart failure.

image Rupture of the myocardium: This complication occurs during the first week postocclusion of coronary artery. During that time, the necrotic myocardium is very soft (because of the action of neutrophils infiltrating the area).

image Rupture of the free wall of the left ventricle: The hole in the wall of the ventricle allows the blood to escape from the left ventricle into the pericardial cavity. The high pressure in the left ventricle will “blow out” the surrounding necrotic myocardium and enlarge the hole. Massive bleeding into the pericardial sac is called hemopericardium. The patient dies of cardiac tamponade.

image Rupture of the papillary muscles: Because the damaged papillary muscle cannot contract, it will typically cause mitral insufficiency.

image Rupture of the interventricular septum: The hole in the septum allows the blood from the left ventricle to enter the right ventricle. This shunt will overburden the right ventricle and cause acute right ventricular failure and pulmonary hypertension.

image Mural thrombosis: It forms in the ventricle.
image Ventricular thrombi: These thrombi are attached to the endocardium overlying the infarcted area of the ventricle.

image Atrial thrombi: These thrombi develop usually because of irregular blood flow inside the dilatated and irregularly contracting left atrium (atrial fibrillation and atrial flutter).

image Extension or reinfarction: They are found adjacent to the original infarct.

image Pericarditis: Subepicardial necrosis of the myocardium leads to a sterile inflammation of the epicardium and exudation of fibrin. Rubbing of the epicardium and the pericardium further promotes the inflammation, which may lead to obliteration of the pericardial cavity and formation of fibrous adhesions in the healing stage of the disease.

image Ventricular aneurysm: This complication develops several weeks and months after the infarction. Typically it develops at the site of large myocardial scars. The connective tissue of the scar does not contract and actually bulges out little by little during each systole until an aneurysm is formed. The lumen of these aneurysms often contains mural thrombi.

A convenient mnemonic to remember the most important complications of myocardial infarct is appear:


image Arrhythmia (e.g., atrial or ventricular fibrillation, cardiac block, asystole)

image Pump failure

image Pericarditis

image Emboli (from mural thrombi in ventricle or atria)

image Aneurysm of the ventricle

image Rupture (free wall of the ventricle, septum, or papillary muscle)


25 What is Dressler syndrome?


Dressler syndrome is a complication of transmural myocardial infarcts clinically presenting with pericardial pain associated with pericardial friction rub. Although the pathogenesis of this complication is not known, it is thought to be immunologically mediated. Pericarditis is presumably caused by the development of antibodies to proteins released from the necrotic myocardial cells. These patients have fever, pleural effusion, and joint pains (i.e., symptoms suggestive of serum sickness), all of which may also be caused by autoantibodies. Cortisone treatment is beneficial, also supporting an immunologic explanation.



26 What is the pathogenesis of chronic IHD after an infarction?


Myocardial infarctions typically develop in people who usually have generalized atherosclerosis. Accordingly, one can expect that the occluded coronary artery is not the only abnormal vessel and that other coronary arteries are also narrowed to some extent. Loss of myocardium in the infarcted area is accompanied by increased demand for work by the remaining uninfarcted myocardium. Because the blood to this normal myocardium flows through narrowed and calcified arteries, which cannot dilatate, the increased demand generates relative ischemia. Chronic pump failure develops over time.



27 What are the pathologic findings in sudden cardiac death?


The most common finding is thrombosis of coronary arteries. Typically, it develops over a ruptured “soft” atheroma—that is, an atheroma that has a soft central core (composed of semiliquid lipid-rich debris) covered with a fibrous cap. The rupture of the fibrous cap will release the atheromatous material into the coronary vessel. Because this material acts as thromboplastin, it will initiate local coagulation of the blood and result in the formation of thrombus. Other causes of sudden cardiac death are coronary diseases (e.g., vasculitis and coronary artery aneurysm), cardiac diseases not clinically recognized (e.g., cardiomyopathies and myocarditis), and valvular disease (e.g., mitral valve prolapse and aortic stenosis).



28 Describe a hypertrophic heart


The hypertrophic heart appears enlarged. At autopsy, such hearts weigh 500 g or more. The walls of the left and the right ventricle is thickened. Extremely enlarged hearts weighing more than 600 g are colloquially called “cor bovinum” because they resemble bovine hearts.


Histologically, the cardiac myocytes are hypertrophic (i.e., in longitudinal sections they have a “boxcar” appearance). The nuclei are enlarged and are polypoid.



29 What are the most common causes of cardiac hypertrophy?


The most common causes are:


image Hypertension

image Aortic valvular disease (stenosis > insufficiency)

image Mitral insufficiency

image Cardiomyopathy
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Jul 23, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on The Heart

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