BLUEPRINTSMEDICINESixth Edition

Vincent B. Young, MD, PhDAssociate ProfessorDepartments of Internal Medicine and Microbiology & ImmunologyUniversity of Michigan Medical SchoolAnn Arbor, Michigan

William A. Kormos, MD, MPHInstructor in MedicineHarvard Medical SchoolMassachusetts General HospitalBoston, Massachusetts

Davoren A. Chick, MD, FACPClinical Associate ProfessorDepartments of Internal Medicine and Learning Health SciencesUniversity of Michigan Medical SchoolAnn Arbor, Michigan

BLUEPRINTSMEDICINESixth Edition

Executive Editor: Shannon MageeProduct Development Editors: Lauren Pecarich and Amy WeintraubProduction Project Manager: Cynthia RudyMarketing Manager: Lisa ZoksCreative Director: Larry PezzatoManufacturing Coordinator: Margie O rzechPrepress Vendor: S4Carlisle Publishing Services

Sixth Edition

Copyright © 2016 Wolters Kluwer

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Library of Congress Cataloging-in-Publication DataYoung, Vincent B., author. Blueprints medicine / Vincent B. Young, William A. Kormos, Davoren A. Chick.—Sixth edition. p. ; cm. Includes bibliographical references and index. ISBN 978-1-4698-6415-0 I. Kormos, William A., author. II. Chick, Davoren A., author. III. Title. [DNLM: 1. Internal Medicine—Examination Q uestions. WB 18.2] RC59 616.0076—dc23

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Contents

Foreword ..............................................................................................................................................viiiPreface ....................................................................................................................................................ixAcknowledgments ...............................................................................................................................xAbbreviations .......................................................................................................................................xi

PART ONE: Cardiovascular .....................................................................................1

1 Chest Pain ....................................................................................................................2 2 Shock ............................................................................................................................ 6 3 Coronary Heart Disease and Chronic Angina .....................................................10 4 Acute Coronary Syndromes ...................................................................................17 5 Heart Failure ..............................................................................................................23 6 Bradyarrhythmias.....................................................................................................30 7 Tachyarrhythmias .....................................................................................................34 8 Hypertension ............................................................................................................41 9 Valvular Heart Disease ............................................................................................47 10 Vascular Disease .......................................................................................................53 11 Syncope ......................................................................................................................58

PART TWO: Respiratory ........................................................................................63

12 Dyspnea .....................................................................................................................64 13 Cough .........................................................................................................................68 14 Chronic Obstructive Pulmonary Disease .............................................................71 15 Asthma .......................................................................................................................76 16 Pulmonary Embolism ..............................................................................................81 17 Interstitial Lung Disease .........................................................................................86 18 Pleural Effusions .......................................................................................................90 19 Lung Cancer...............................................................................................................94

PART THREE: Renal ................................................................................................99

20 Acid–Base Disturbances ........................................................................................100 21 Fluid and Electrolytes ............................................................................................104

22 Acute Kidney Injury ...............................................................................................108 23 Chronic Kidney Disease .........................................................................................113 24 Glomerular Disease ................................................................................................117 25 Nephrolithiasis........................................................................................................120 26 Hematuria ................................................................................................................124

PART FOUR: Infectious Disease ......................................................................... 129

27 Fever and Rash ........................................................................................................130 28 Pneumonia ..............................................................................................................134 29 Sexually Transmitted Infections ..........................................................................140 30 Urinary Tract Infections .........................................................................................146 31 Tuberculosis ............................................................................................................149 32 Gastroenteritis ........................................................................................................154 33 Infective Endocarditis ............................................................................................159 34 Meningitis ................................................................................................................163 35 HIV Part I: Primary Care of the HIV-Infected Patient ........................................167 36 HIV Part II: Prophylaxis and Treatment of Opportunistic

Infections in HIV .....................................................................................................174

PART FIVE: Gastrointestinal .............................................................................. 179

37 Abdominal Pain ......................................................................................................180 38 Diarrhea ...................................................................................................................184 39 Dyspepsia ................................................................................................................187 40 Inflammatory Bowel Disease ...............................................................................191 41 Hepatitis ...................................................................................................................195 42 Cirrhosis ...................................................................................................................200 43 Cholestatic Liver Disease ......................................................................................205 44 Pancreatitis ..............................................................................................................208 45 Colorectal Cancer ...................................................................................................211

PART SIX: Endocrine .......................................................................................... 215

46 Weight Loss .............................................................................................................216 47 Hyperthyroidism ....................................................................................................219 48 Hypothyroidism ......................................................................................................223 49 Diabetes Mellitus ....................................................................................................226 50 Hypercalcemia ........................................................................................................233 51 Adrenal Insufficiency .............................................................................................237 52 Cushing Syndrome .................................................................................................240

vi • Blueprint s Medicine

53 Pituitary Disease .....................................................................................................244 54 Nutritional Disorders .............................................................................................248 55 Dyslipidemia ...........................................................................................................253

PART SEVEN: Rheumatology ............................................................................. 259

56 Acute Monoarticular Arthritis ..............................................................................260 57 Low Back Pain .........................................................................................................263 58 Rheumatoid Arthritis .............................................................................................266 59 Seronegative Spondylo arthropathies ...............................................................270 60 Connective Tissue Diseases ..................................................................................274 61 Vasculitis ..................................................................................................................279 62 Amyloidosis .............................................................................................................282

PART EIGHT: Hematology/Oncology ................................................................ 285

63 Anemia .....................................................................................................................286 64 Hemolytic Anemia ..................................................................................................291 65 Adenopathy .............................................................................................................294 66 Bleeding Disorders .................................................................................................296 67 Breast Cancer ..........................................................................................................300 68 Prostate Cancer .......................................................................................................306 69 Leukemia..................................................................................................................310 70 Lymphoma ...............................................................................................................313

PART NINE: Neurology ....................................................................................... 317

71 Headache .................................................................................................................318 72 Delirium ...................................................................................................................322 73 Dizziness ..................................................................................................................325 74 Dementia .................................................................................................................330 75 Stroke .......................................................................................................................334 76 Seizures ....................................................................................................................340

Questions ...........................................................................................................................................345Answers ..............................................................................................................................................368References/OnlineIndex ...................................................................................................................................................385

Contents • vii

viii

Foreword

It is now almost 20 years since one of my former medical students, during his early house staff training, approached me with his idea of a book series for medical students that

would encapsulate the knowledge base for each of the core clinical rotations. That was the origin of the Blueprints series, of which the Medicine offering has been among the most enduring and successful, now entering its sixth edition. As the chief editor of a major reference textbook (Primary Care Medicine), taking on another book project was beyond my capacity, but it was a great opportunity for our rising junior faculty, and I went about recruiting them. Serving as an early mentor to Drs. Kormos and Young, it is with great pride that I view what they and Dr. Chick have accomplished over the years with Blueprints Medicine. Although it does not replace the in-depth reading of a reference text, which is essential for foundational learning and subject mastery—all too often skipped over these days in search of the immediate “right answer”—Blueprints Medicine fulfills an important review function with thoughtful, clear, and concise chapters on key clinical topics likely to be encountered during the Core Medicine clerkship. This makes it an ideal companion to carry during the day, as well as when preparing for boards at the end of the year. The new edition is the best one yet, and I am very pleased to have the honor of writing this foreword and strongly recommending the book. It is a true accomplishment in the scholarship of synthesis.

Allan H. Goroll, MD, MACPProfessor of MedicineHarvard Medical SchoolMassachusetts General HospitalBoston, Massachusetts

ix

In 1997, the first five books in the Blueprints series were published as a board review for medical students, interns, and residents who wanted high-yield, accurate clinical content

for USMLE Steps 2 and 3. Eighteen years later, we are proud to report that the original books and the entire Blueprints brand of review materials have far exceeded our expectations.

The feedback we receive from our readers continues to be tremendously helpful and pivotal in deciding what direction each edition of the core books will take. To that end, this sixth edition includes updated material to reflect the latest developments in evidence-based medicine. We hope that this edition will continue to serve as a useful review for the USMLE, as well as a rapid reference during day-to-day activities in patient care.

What we have also learned from our readers is that Blueprints is more than just a board review for USMLE Steps 2 and 3. Students use the books during their clerkship rotations and subinternships. Residents studying for USMLE Step 3 often use the books for reviewing areas that were not their specialty. Students in physician assistant and nurse practitioner pro-grams use Blueprints either as a companion or in lieu of review materials written specifically for their areas.

However you use Blueprints, we hope that you find the books in the series informative and useful.

Preface

x

W e are grateful for the continued support we have received for Blueprints Medicine. We thank all of the people at Wolters Kluwer who helped us with the preparation

of this work. Finally, we thank our families for all their continuous encouragement during this project.

Vincent B. Young, MD, PhDWilliam H. Kormos, MD, MPHDavoren A. Chick, MD, FACP

Acknowledgm ents

Ab b reviations

5-ASA 5-aminosalicylic acidABGs arterial blood gasesACE angiotensin-converting enzymeACTH adrenocorticotropic hormoneADH antidiuretic hormoneAI aortic insufficiencyAIDS acquired immunodeficiency

syndromeALL acute lymphocytic leukemiaALT alanine transaminaseAML acute myelogenous leukemiaANA antinuclear antibodyARDS adult respiratory distress syndromeASD atrial septal defectASO antistreptolysin OAST aspartate transaminaseAV atrioventricularBE barium enemaBP blood pressureBUN blood urea nitrogenCALLA common acute lymphoblastic

leukemia antigenCBC complete blood countCHD coronary heart diseaseCHF congestive heart failureCK creatine kinaseCLL chronic lymphocytic leukemiaCML chronic myelogenous leukemiaCMV cytomegalovirusCNS central nervous systemCOPD chronic obstructive pulmonary diseaseCPK creatine phosphokinaseCSF cerebrospinal fluidCT computed tomographyCVA cerebrovascular accidentDHEA dehydroepiandrosteroneDIC disseminated intravascular

coagulationDKA diabetic ketoacidosisDM diabetes mellitusDTRs deep tendon reflexesDVT deep venous thrombosis

EBV Epstein–Barr virusECG electrocardiogramEF ejection fractionEGD esophagogastroduodenoscopyEMG electromyographyERCP endoscopic retrograde

cholangiopancreatographyESR erythrocyte sedimentation rateFEV forced expiratory volumeFNA fine-needle aspirationFTA-ABS fluorescent treponemal antibody

absorptionFVC forced vital capacityGFR glomerular filtration rateGH growth hormoneGI gastrointestinalGU genitourinaryHAV hepatitis A virusHbA1C glycosylated hemoglobinHCM hypertrophic cardiomyopathyHIV human immunodeficiency virusHLA human leukocyte antigenHR heart rateIFG impaired fasting glucoseIg immunoglobulinIM intramuscularINH isoniazidINR international normalized ratioIV intravenousJVP jugular venous pressureKUB kidneys/ureter/bladderLDH lactate dehydrogenaseLES lower esophageal sphincterLFTs liver function testsLP lumbar punctureLV left ventricularLVH left ventricular hypertrophylytes electrolytesMCHC mean corpuscular hemoglobin

concentrationMCV mean corpuscular volumeMEN multiple endocrine neoplasia

xi

MHC major histocompatibility complexMI myocardial infarctionMRI magnetic resonance imagingNHL non-Hodgkin lymphomaNPO nil per os (nothing by mouth)NSAID nonsteroidal anti-inflammatory drugNSTEMI non–ST-segment elevation

myocardial infarctionPA posteroanteriorPBS peripheral blood smearPCI percutaneous interventionPCP Pneumocystis jiroveci pneumoniaPE physical examinationPFTs pulmonary function testsPMI point of maximal intensityPMN polymorphonuclear leukocytePT prothrombin timePTH parathyroid hormonePTT partial thromboplastin timePUD peptic ulcer diseaseRBC red blood cellRPR rapid plasma reagin (test)RR respiratory rateRS Reed–Sternberg (cell)RV right ventricularRVH right ventricular hypertrophySBFT small bowel follow-throughSGOT serum glutamic-oxaloacetic

transaminase

SIADH syndrome of inappropriate secretion of ADH

SLE systemic lupus erythematosuss/p status postSTD sexually transmitted diseaseSTEMI ST-segment elevation myocardial

infarctionSVT supraventricular tachycardiaTFTs thyroid function testsTIA transient ischemic attackTIBC total iron-binding capacityTIPS transjugular intrahepatic

portosystemic shuntTMP-SMZ trimethoprim–sulfamethoxazoletPA tissue plasminogen activatorTPO thyroid peroxidaseTSH thyroid-stimulating hormoneTTP thrombotic thrombocytopenic

purpuraUA urinalysisUGI upper GIURI upper respiratory tract infectionUS ultrasoundVDRL Venereal Disease Research

LaboratoryVS vital signsVT ventricular tachycardiaWBC white blood cellWPW Wolff–Parkinson–White (syndrome)

xii • Blueprint s Medicine

1

Cardiovascular

Part 1

2

In diagnosing the patient with chest pain, it often helps to categorize the pain by its pathophysiology. Inflamma-tion of serous surfaces leads to pleuritic pain, charac-terized by sharp pain that increases with inspiration or cough. Pleuritic pain can be seen in pulmonary etiolo-gies, pulmonary embolism, pericarditis, and abdominal conditions that extend to the diaphragm and lower pul-monary serous surfaces. Musculoskeletal pain may also feel sharp and occur with inspiration or cough, but is more prominently positional with pain relating to the use of the affected musculoskeletal components. Vis-ceral pain, such as in myocardial ischemia, aortic dis-section, and esophageal disease, often produces poorly localized sensations that are not described as “pain” but rather as squeezing, pressure, dull ache, tightness, tear-ing/ripping, or sometimes a burning sensation.

The most important decision for the physician is to distinguish life-threatening causes, such as myocardial ischemia, pulmonary embolus, pneumothorax, and aortic dissection, from non–life-threatening causes.

RISK FACTORS

In evaluating patients with chest pain, certain risk factors may increase the suspicion for coronary heart disease (CHD) and other vascular etiologies, such as aortic dissection. Classic cardiovascular risk factors include:

• Diabetes mellitus• Smoking• Hypertension• Dyslipidemia• Family history of premature CHD

Chronic kidney disease also increases CHD risk. Abdominal (central) obesity is associated with

increased CHD risk and contributes to multiple other CHD risk factors. Patients with chest pain and cardio-vascular risk factors require further workup for CHD, even if the history is atypical. CHD is uncommon (but not unheard of) before 40 years of age, and men are at greater risk than women until approximately 65 years of age. Cocaine abuse is an important consid-eration, especially in younger patients with no other cardiac risk factors.

CLINICAL MANIFESTATIONS

HISTORY

In evaluating pleuritic pain, clinicians should seek historical clues for pulmonary, pericardial, and upper abdominal visceral pathologies. Pneumothorax has an acute onset of pleuritic pain associated with dyspnea. This occurs mostly in young patients (spontaneous) or those with underlying lung disease (secondary to blebs or bullae). Pulmonary embolism generally pres-ents with sudden shortness of breath, but the pleuritic pain may be of more gradual onset due to subsequent pulmonary tissue necrosis caused by vascular occlu-sion. Risk factors should be taken into account (see Chapter 16). The pain in pericarditis is classically pleuritic and positional, typically relieved by sitting forward. Substernal pain in pericarditis may radiate to the shoulder/ trapezius because of diaphragmatic/phrenic nerve irritation. Upper abdominal conditions such as cholecystitis or pancreatitis may cause sec-ondary pleuritic pain through diaphragmatic inflam-mation that extends to the pulmonary pleural spaces. Because diaphragmatic pain may be referred to the trapezius or scapular region, history of abdominal

Chapter

Chest Pain1

Chap ter 1 / Chest Pain • 3

be tempered by prior probability of cardiovascular disease on the basis of risk factors.

PHYSICAL EXAMINATION

Remember that a patient with ischemia may present (and often does) with a completely normal physical ex-amination. However, some physical findings may lead to the correct diagnosis.

• Unequal blood pressure between arms is an im-portant but uncommon feature for aortic dissec-tion. Hypotension or irregular rhythm suggests a life-threatening vascular etiology, large pulmonary embolus, or tension pneumothorax. Tachypnea is fairly nonspecific; it is seen in pulmonary causes such as pneumothorax or pulmonary embolism, but may also reflect anxiety or splinting due to pleurtic or musculoskeletal pain.

• Reproduction of the chest pain by palpation is a key feature of musculoskeletal causes. This is not the case in angina, pulmonary embolus, aortic dis-section, or true pleuritic disease. Superficial hy-peresthesia (not requiring firm palpation) suggests neuropathic pain such as herpes zoster.

• Cardiac findings to look for include a fourth heart sound (ischemia), an apical holosystolic murmur (ischemic mitral regurgitation), a blowing diastolic murmur (aortic regurgitation as a result of aortic dissection involving the valve root), and a pericar-dial rub (pericarditis).

• Pulmonary findings of a pneumothorax include hyperresonance to percussion, decreased fremi-tus, and tracheal deviation to the opposite side. A pleural rub may indicate pulmonary infarction or pneumonia. Rales and basilar dullness indicate congestive heart failure, which may reflect active cardiac ischemia.

• Abdominal findings of vascular disease include a pulsatile mass or tender abdominal aorta. Aor-tovascular bruits, including renal bruits, may also be detectable. Right upper quadrant tenderness suggests hepatic or gall bladder inflammation, and significant midepigastric tenderness increases suspicion of a wide spectrum of gastrointestinal diseases.

DIAGNOSTIC EVALUATION

The initial history and physical examination should guide the diagnostic workup, but neither history nor examination can reliably rule out coronary ischemia.

symptoms should be assessed for patients presenting with pleuritic pain near the shoulder.

Visceral pain, aching and poorly localized, suggests vascular or gastrointestinal pathologies. Patients with myocardial ischemia may present with a sensation of squeezing, pressure, or even a burning sensation. Classic myocardial ischemic discomfort is located substernally and radiates to the ulnar aspect of the left arm, but it may also be felt in the jaw, shoulder (right or left), epigastrium, or back. Brought on by ex-ertion or emotional stress, stable angina usually lasts only minutes and resolves with rest or resolution of stress. Associated symptoms may include diaphore-sis, nausea, dyspnea, palpitations, or light-headedness. Worrisome features include prolonged pain (more than 20 minutes) with myocardial infarction and rest pain with unstable angina. Aortic dissection presents with abrupt pain that is most intense at onset, which distinguishes this “must-not-miss” diagnosis. Pain is often described as ripping or tearing and radiates to the back. O cclusion of distal vessels may cause focal symptoms such as stroke, arm ischemia, back pain, or even simultaneous myocardial ischemic pain from ostial occlusion of a coronary artery. In gastrointes-tinal disease (such as reflux and esophageal spasm), symptoms may be relieved with antacids, are related to food intake, and are worsened in the supine posi-tion. Esophageal spasm may be difficult to differenti-ate from angina.

Musculoskeletal pain may be either dull and achy or sharp and pleuritic, but it is more easily localized and worsens with movement, specific positions, or palpation. Pain ranges from darting, lasting seconds, to a prolonged dull ache that lasts for days. In the neuropathic pain of herpes zoster, pain may precede rash by several days; a burning sensation in a derma-tomal distribution is a key feature. With anxiety, pain is often atypical and prolonged, and workup reveals no other cause.

The chest pain history is often used to categorize a patient’s pretest probability of ischemic chest pain. Three historical components differentiate nonanginal, atypical, or typical chest pain:

1. Substernal location of chest discomfort2. Provocation by physical exertion or emotional

distress3. Relief with rest or nitroglycerin

Typical pain of CHD meets all three criteria. Atypical pain meets two criteria, and nonanginal pain meets one or none. This historical categorization sys-tem is useful for risk stratification systems, but must

4 • Blueprint s Medicine

good choice for unstable patients. Either helical chest CT or a ventilation–perfusion (V/Q) scan is used in patients with pleuritic pain and normal chest radio-graph in whom pulmonary embolus is suspected. A helical chest CT is sensitive for small pulmonary em-boli and may detect other chest abnormalities leading to chest pain. A normal V/Q scan rules out the diag-nosis of pulmonary embolus, whereas a high-proba-bility scan confirms the diagnosis when accompanied by a high clinical suspicion. A d -dimer test may be useful in situations where clinical suspicion for aortic dissection and pulmonary embolism is low, as a low d -dimer further reduces posttest probability and can reduce the need for CT imaging. This is further de-tailed in Chapter 16.

In chest pain of esophageal origin, pain induced by esophageal reflux may be confirmed by 24-hour esophageal pH monitoring or by an empirical trial of antacids.

In the case of suspected musculoskeletal pain in the low-risk patient , a t rial of nonsteroidal anti-inflammatory drugs is appropriate both diagnostically and therapeutically. Pericarditis also responds to this intervention.

TREATMENT

When the differential diagnosis for chest pain includes a potentially life-threatening cause, treatment should be initiated during the diagnostic evaluation. Early emergent interventions generally include adminis-tration of oxygen and oral aspirin (chewed for more rapid absorption). Nitroglycerin may be administered if myocardial ischemia is suspected, but care should be taken to assess risk for aortic dissection or criti-cal aortic stenosis prior to administering nitroglycerin. Antacid therapy may be administered as a diagnostic and therapeutic trial. For suspected acute conditions, ready approximation of a defibrillator is advisable, as is rapid transfer to an emergency care center via an ambulance equipped with a defibrillator.

CONTINUED CARE

Patients with nonspecific chest pain following initial evaluation generally require continued observation in a monitored setting until their safety for outpatient care is established. Specific continuing care for pa-tients with chest pain will depend on the diagnosed cause and their overall risk for underlying CHD, but in all cases chest pain provides an opportunity to address

Therefore, if a cardiac cause is suspected, an electro-cardiogram (ECG) should be obtained. In patients with increased probability of underlying CHD (pa-tients over 50 years old, smokers, diabetics, etc.), an ECG should be checked even if the story is atypical. Table 1-1 lists some helpful findings. If active myo-cardial infarction or unstable angina is suspected, serial ECGs and ischemic biomarkers are indicated (see Chapter 3). If stable angina is suspected due to a chronic stable pattern of pain, an exercise stress test may be the appropriate next step, although if angina is suspected to be secondary to valvular disease, then an echocardiography should be performed prior to stress testing (see Chapter 3).

In patients with pleuritic pain and dyspnea as pre-dominant symptoms, a chest radiography should be the initial step to rule out pneumothorax, pulmonary infiltrates, and rib fractures. A widened mediastinum on the chest radiograph may be seen with aortic dis-section. Chest radiograph findings seen in pulmonary embolism are discussed in Chapter 16.

O ther important diagnostic tests include the chest computed tomography (CT), by which patients with worrisome histories for aortic dissection should be further evaluated regardless of chest radiograph or ECG results. Magnetic resonance imaging is a non-invasive diagnostic option for patients stable enough to be sent into the scanner. Transesophageal echocar-diography is a minimally invasive and rapid method of detecting aortic dissection at the bedside; so it is a

j TABLE 1 -1 Electroca rdiogra m• Q waves in two or more leads: previous myocardial

infarction

• ST depression > 1 mm: ischemia

• ST elevation: acute myocardial infarction or pericar-ditis (the latter often has involvement of all leads and associated PR depression)

• Left bundle branch block: suggests underlying heart disease (ischemic, hypertensive)

• Right bundle branch block: may be indicative of right heart strain (as in pulmonary embolus)

• T-wave inversions and nonspecific ST changes: seen both in healthy individuals and in many diseases (therefore, not useful)

Note: A norma l ECG does not rule out ischemia or serious disease, especia lly when recorded in the absence of pa in. Right bundle branch block and early repola riza tion may be seen in young, hea lthy, normal individua ls. O cclusion of the right corona ry a rtery by an aortic dissection may present with inferior ST eleva tion. This is a vita l distinction to make.

Chap ter 1 / Chest Pain • 5

addressed using a team care approach include diet and exercise (with nutritionists), medication adherence (in partnership with clinical pharmacologists), social stressors, and behavioral risks (with social workers, ad-diction counselors, and mental-health specialists).

modifiable cardiovascular risk factors. Smokers should be provided cessation counseling appropriate to their readiness to quit. Clinicians should optimize treat-ment recommendations for hypertension, diabetes, and hyperlipidemia. Psychosocial components to be

KEY PO INTS

• Patients with histories suggestive of serious causes of chest pain (e.g., ischemia, dissection, embolus) de-serve further evaluation even if physical examination, chest radiograph, and ECG results are normal.

• Certain chest pain syndromes have very typical pat-terns, such as the acute tearing pain of aortic dissec-tion, the dermatomal distribution of herpes zoster, or the positional pleuritic pain of pericarditis (relieved when the patient sits forward).

• Risk factors are important to determine the prob-ability of CHD in a patient with chest pain. These include older age, male gender, diabetes mellitus,

hypertension, dyslipidemia, smoking, obesity, prema-ture family history of CHD, and chronic kidney disease.

• The ECG is a key test in patients with a suspected car-diac origin of chest pain. The findings of Q waves, ST elevation, or ST depression all signify cardiac ischemia. A notable exception is pericarditis, which has diffuse ST elevation, often with associated PR depression.

• Independent of the final diagnosis, any chest pain pre-sentation provides an opportunity to optimize control of cardiovascular risk factors and to engage patients in team care management of psychosocial and behavioral risks.

6

Shock is a term used to describe decreased perfusion and oxygen delivery to the body. It presents with a decrease in blood pressure. Because pressure varies within each heartbeat between the systolic and the diastolic pressures, we monitor effective perfusion pressure using a calculated mean arterial pressure (MAP). More time is spent in diastole than in systole, so diastole is a greater determinant of MAP. A simple formula for MAP calculation is

MAP = Diastolic pressure + 13 Pulse pressure

Shock with a decreased MAP may result from ei-ther a decrease in cardiac output (CO ) or a decrease in systemic vascular resistance (SVR). This is best de-fined by the following equation:

MAP = CO × SVR

CO is the volume of blood pumped by the heart per minute and is calculated as

CO = Heart rate × Stroke volume

Stroke volume is determined by contractility and available blood volume. Therefore, any disturbance in available blood volume, cardiac contractility, heart rate, or SVR requires compensatory increases in the other determinants to maintain MAP. When compen-satory responses cannot sufficiently increase, MAP falls and the body is at risk for decreased perfusion with clinical presentation as shock.

There are three main shock syndromes: hypovo-lemic, cardiogenic, and distributive. A fourth syn-drome, obstructive shock, presents clinically much like cardiogenic shock, but is caused by obstruction of blood flow rather than by primary failure of the heart.

These shock syndromes differ in the underlying blood volume, CO, and SVR. O verall volume status is best assessed at the bedside by the jugular venous pressure (JVP) and in the intensive care unit by the pulmonary capillary wedge pressure (PCWP). Table 2-1 defines the syndromes and their features.

The low CO seen in cardiogenic shock may also be seen in obstructive shock syndromes that result in right heart failure (such as massive pulmonary embo-lism), decreased venous filling of the heart (tension pneumothorax) , and obstruction of outflow (cardiac tamponade) .

The low vascular resistance that occurs in distribu-tive shock is most commonly seen in sepsis, but may be mimicked by adrenal crisis (insufficiency) or ana-phylaxis. CO varies in these conditions, depending on severity and volume status.

Shock can occur when systolic blood pressure (BP) is < 90 or the MAP is < 70, but a low pressure alone does not indicate shock. Shock is a clinical syndrome defined by the effect of reduced perfusion on organ systems. O rgan failure is evidence of insufficient pres-sure for organ perfusion regardless of the actual MAP

Chapter

Shock2

j TABLE 2 -1 Cha ra cteristics of Shock Syndromes

CO SVRJVP/

PCWP

Hypovolemic Decrease Increase Decrease

Cardiogenic and obstructive

Decrease Increase Increase

Distributive Increase Decrease Decrease