Step-Up to Medicine

1259 Pages·2004·11.77 MB·English

by  Steven S. Agabegi

Chapter 1- Diseases of the cardiovascular system.
Chapter 2- Diseases of the Pulmonary System.
Chapter 3- Diseases of the Gastrointestinal system.
Chapter 4- Endocrine and Metabolic Diseases.
Chapter 5- Diseases of the Central and Peripheral
Nervous Systems.
Chapter 6- Connective Tissue and Joint Diseases.
Chapter 7- Diseases of the Renal and Genitourinary
System.
Chapter 8- Fluids, Electrolytes, and Acid-Base
Disorders.
Chapter 9- Hematologic Diseases and Neoplasms.
Chapter 10- Infectious Diseases.
Chapter 11- Diseases of the skin and Hypersensitivity
Disorders.
Chapter 12- Ambulatory Medicine.
CHAPTER 1
Diseases of the Cardiovascular System
ISCHEMIC HEART DISEASE
Stable Angina Pectoris
A. General characteristics
Stable angina pectoris is due to fixed atherosclerotic lesions that narrow the major
coronary arteries. Coronary ischemia is due to an imbalance between blood supply and
oxygen demand, leading to inadequate perfusion. Stable angina occurs when oxygen
demand exceeds available blood supply.
Risk factors
o Diabetes mellitus (DM)
o Hyperlipidemia—elevated LDL
o Hypertension (HTN)
o Cigarette smoking
o Age (men >45 years; women >55 years)
o Family history of premature coronary artery disease (CAD) or myocardial
infarction (MI) in first-degree relative: men <45 years; women <55 years
o Low levels of high-density lipoprotein (HDL)
o Elevated homocysteine levels
Prognostic indicators of CAD
o Left ventricular function (ejection fraction [EF])
 Normal >50%
 If <50%, associated with increased mortality
o Vessel(s) involved (severity/extent of ischemia)
 Left main coronary artery–poor prognosis because it covers
approximately two thirds of the heart.
 Two- or three-vessel CAD–worse prognosis.
Coronary artery disease (CAD) can have the following clinical presentations:
Asymptomatic
Stable angina pectoris
Unstable angina pectoris (USA)
Myocardial infarction (MI)
Sudden cardiac death
B. Clinical features
Chest pain or substernal pressure sensation
o Lasts less than 10 to 15 minutes (usually 1 to 5 minutes)
o Frightening chest discomfort, usually described as heaviness, pressure,
squeezing; rarely described as frank pain
Brought on by exertion or emotion
Relieved with rest or nitroglycerin
Stress ECG (exercise testing) is used in the following situations:
To confirm diagnosis of angina
To evaluate response of therapy in patients with documented CAD
To identify patients with CAD who may have a high risk of acute coronary events
C. Diagnosis (of CAD)
Resting ECG
o Usually normal in patients with stable angina
o Q waves are consistent with a prior myocardial infarction.
P.2

o If ST segment or T wave abnormalities are present during an episode of chest
pain, then treat as for unstable angina.
For patients with normal resting ECG, determine whether the patient is capable of
performing treadmill exercise. If so, proceed to an exercise stress test.
o Stress ECG
 Test involves recording ECG before, during, and after exercise on a
treadmill.
 75% sensitive if patients are able to exercise sufficiently to increase
heart rate to 85% of maximum predicted value for age.
 Exercise-induced ischemia results in subendocardial ischemia, producing
ST segment depression.
 Other positive findings include onset of heart failure or ventricular
arrhythmia during exercise or hypotension.
 Patients with a positive stress test result should undergo cardiac
catheterization.
o Stress echocardiography
 Performed before and immediately after exercise. Exercise-induced
ischemia is evidenced by wall motion abnormalities (e.g., akinesis or
dyskinesis) not present at rest.
 Favored by many cardiologists over stress ECG. It is more sensitive in
detecting ischemia, can assess LV size and function, and can diagnose
valvular disease.
 Again, patients with a positive test result should undergo cardiac
catheterization.
P.3

o Information gained from a stress test can be enhanced by stress myocardial
perfusion imaging after IV administration of a radioisotope such as thallium 201
during exercise.
 Viable myocardial cells extract the radioisotope from the blood. No
radioisotope uptake means no blood flow to an area of the myocardium.
 It is important to determine whether the ischemia is reversible, i.e.,
whether areas of hypoperfusion are perfused over time as blood flow
eventually equalizes. Areas of reversible ischemia may be rescued with
percutaneous transluminal coronary angioplasty (PTCA) or coronary
artery bypass graft (CABG). Irreversible ischemia, however, indicates
infarcted tissue that cannot be salvaged.
 Perfusion imaging increases the sensitivity and specificity of exercise
stress tests, but is also more expensive.
If the patient cannot exercise, perform a pharmacologic stress test.
o IV adenosine, dipyramidole, or dobutamine can be used. The cardiac stress
induced by these agents takes the place of exercise. This can be combined with
an ECG, an echocardiogram, or nuclear perfusion imaging.
o IV adenosine and dipyramidole cause generalized coronary vasodilation.
Because diseased coronary arteries are already maximally dilated at rest to
increase blood flow, they receive relatively less blood flow when the entire
coronary system is pharmacologically vasodilated.
o Dobutamine increases myocardial oxygen demand by increasing heart rate,
blood pressure, and cardiac contractility.
Holter monitoring (ambulatory ECG) can be useful in detecting silent ischemia (i.e.,
ECG changes not accompanied by symptoms).
Cardiac catheterization with coronary angiography (see Box 1-2)
o Coronary angiography–definitive test for CAD. Indicated for patients being
considered for revascularization (PTCA or CABG).
o Contrast is injected into coronary vessels to visualize any stenotic lesions. This
defines the location and extent of coronary disease.
o If coronary artery disease is severe (e.g., left main or three-vessel disease),
refer patient for surgical revascularization (CABG).
Box 1-1 There Are Two Conditions Termed Syndrome X
Metabolic Syndrome X
o Any combination of hypercholesterolemia, hypertriglyceridemia, impaired
glucose tolerance, diabetes, hyperuricemia, HTN
o Key underlying factor is insulin resistance (due to obesity)
Syndrome X
o Exertional angina with normal coronary arteriogram: Patients present with chest
pain after exertion but have no coronary stenoses at cardiac catheterization.
o Exercise testing and nuclear imaging show evidence of myocardial ischemia.
o Prognosis is excellent.
Box 1-2
Cardiac Catheterization
Most accurate method of determining a specific cardiac diagnosis
Provides information on hemodynamics, intracardiac pressure measurements, cardiac
output, oxygen saturation, etc.
Coronary angiography (see below) is almost always performed as well for
visualization of coronary arteries.
There are many indications for cardiac catheterization (generally performed when
revascularization or other surgical intervention are being considered):
o After a positive stress test
o In a patient with angina in any of the following situations: when noninvasive
tests are nondiagnostic, angina that occurs despite medical therapy, angina that
occurs soon after MI, and any angina that is a diagnostic dilemma.
o If patient is severely symptomatic and urgent diagnosis and management are
necessary
o For evaluation of valvular disease, and to determine the need for surgical
intervention
Coronary Arteriography (Angiography)
Most accurate method of identifying the presence and severity of CAD; the standard
test for delineating coronary anatomy
Main purpose is to identify patients with severe coronary disease to determine whether
revascularization is needed
Coronary stenosis >70% may be significant (i.e., it can produce angina)
A stress test is generally considered positive if the patient develops any of the following during
exercise: S-T segment depression, chest pain, hypotension, or significant arrhythmias.
D. Treatment
Risk factor modification
o Smoking cessation cuts coronary heart disease (CHD) risk in half by 1 year after
quitting.
o HTN—vigorous BP control reduces the risk of CHD, especially in diabetic
patients.
o Hyperlipidemia—reduction in serum cholesterol with lifestyle modifications and
HMG-CoA reductase inhibitors reduces CHD risk.
o DM—strict glycemic control is thought to have less effect on macrovascular
disease risk than microvascular disease risk but should still be emphasized.
o Obesity—weight loss modifies other risk factors (diabetes, HTN, and
hyperlipidemia) and provides other health benefits.
o Exercise is critical; it minimizes emotional stress, promotes weight loss, and
helps reduce other risk factors.
o Diet: Reduce intake of saturated fat (<7% total calories) and cholesterol (<200
mg/day).
o Hyperhomocystinemia–value of treating yet to be established.
Medical therapy
o Aspirin
 Indicated in all patients with CAD
 Decreases morbidity—reduces risk of MI
o β-Blockers—block sympathetic stimulation of heart
 Reduce HR, BP, and contractility, thereby decreasing cardiac work (i.e.,
β-blockers lower myocardial oxygen consumption)
 Have been shown to reduce the frequency of coronary events
P.4
FIGURE 1-1 Coronary angiogram.
injection of the right coronary artery
shows a stenosis in the midportion of the
vessel, indicated by the arrow.
(From Lilly LS. Pathophysiology of Heart
Disease. 3rd Ed. Philadelphia: Lippincott
Williams & Wilkins, 2003:148, Figure 6.8.
Courtesy of Dr. William Daley.)

View Figure

o Nitrates—cause generalized vasodilation
 Relieve angina; reduce preload, therefore the load and oxygen demand.
 May prevent angina when taken before exertion
 Effect on prognosis is unknown; main benefit is symptomatic relief
 Can be administered orally, sublingually, transdermally, or intravenously
o Calcium channel blockers
 Cause coronary vasodilation and afterload reduction
 Now considered a secondary treatment when β-blockers and/or nitrates
are not fully effective.
o If CHF is also present, treatment with ACE inhibitors and/or diuretics may be
indicated as well.
Revascularization
o May be preferred for high-risk patients, although there is some controversy
whether revascularization is superior to medical management for a patient with
stable angina and stenosis >70%.
o Two methods—PTCA and CABG—see Box 1-3
P.5

o Revascularization does not reduce incidence of MI, but does result in significant
improvement in symptoms.
Management decisions (general guidelines)—Risk factor modification and aspirin are
indicated in all patients. Manage patients according to overall risk:
o Mild disease (normal EF, mild angina, single-vessel disease)
 Nitrates (for symptoms and as prophylaxis) and a β-blocker are
appropriate.
 Consider calcium channel blockers if symptoms continue despite nitrates
and β-blockers.
o Moderate disease (normal EF, moderate angina, two-vessel disease)
 If the above regimen does not control symptoms, consider coronary
angiography to assess suitability for revascularization (either PTCA or
CABG).
o Severe disease (decreased EF, severe angina, and three-vessel/left main or left
anterior descending disease)
 Coronary angiography and consider for CABG
Box 1-3
Percutaneous Transluminal Coronary Angioplasty (PTCA)
Should be considered in patients with one- or two-vessel disease
Best if used for proximal lesions
Restenosis is a significant problem (up to 40% within first 6 months); however, if there
is no evidence of restenosis at 6 months, it usually does not occur.
Stents significantly reduce the rate of restenosis.
Coronary Artery Bypass Grafting (CABG)
Treatment of choice in patients with high-risk disease
Indicated in patients with left main disease, three-vessel disease with reduced left
ventricular function, two-vessel disease with proximal LAD stenosis, or severe ischemia
for palliation of symptoms
Side effects of nitrates
Headache
Orthostatic hypotension
Tolerance
Syncope
Unstable Angina Pectoris
A. General characteristics
Pathophysiology
o With unstable angina (USA), oxygen demand is unchanged. Supply is decreased
secondary to reduced resting coronary flow. This is in contrast to stable
angina, which is due to increased demand.
o USA is significant because it indicates stenosis that has enlarged via
thrombosis, hemorrhage, or plaque rupture. It may lead to total occlusion of a
coronary vessel.
The following patients may be said to have USA:
o Patients with chronic angina with increasing frequency, duration, or intensity of
chest pain
o Patients with new-onset angina that is severe and worsening
o Patients with angina at rest
Acute coronary syndrome
The clinical manifestations of atherosclerotic plaque rupture and coronary occlusion
Term generally refers to unstable angina or acute MI
B. Diagnosis (see stable angina)
Perform a diagnostic workup to exclude MI in all patients.
Patients with USA have a higher risk of adverse events during stress testing. These
patients should be stabilized with medical management before stress testing or should
undergo cardiac catheterization initially.
USA and non-ST-segment elevation MI are often considered together because it is very
difficult to distinguish the two based on patient presentation. If cardiac enzymes are elevated,
then the patient has non-ST segment elevation MI.
The ESSENCE trial showed that in USA and non-ST segment-elevation MI, risk of death, MI, or
recurrent angina was lower in the enoxaparin group than in the heparin group at 14 days, 30
days, and 1 year. The need for revascularization was also lower in the enoxaparin group.
Thrombolytic therapy and calcium channel blockers have not been proven to be beneficial in
unstable angina.
C. Treatment
Hospital admission on a floor with continuous cardiac monitoring. Establish IV access
and give supplemental oxygen. Provide pain control with nitrates (below) and morphine.