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The Knowledge Base for Key Clinical
Issues In Acute Myocardial Infraction
The clinical research investment in AMI is quite large and continues to
grow. Efficacy studies, when done properly, contribute immensely to the
knowledge base, although they cannot necessarily be applied across all the
major clinical questions and population groups. Two questions in selecting
key patient management topics for effectiveness studies are, therefore: what
unanswered questions remain, and are they suitable for projects outside the
realm of RCTs?
Several clinical subjects are briefly reviewed here because they provide
the context within which the committee's discussions took place. They
include diagnosis and management of myocardial infarction in five phases:
prehospital, emergency room, coronary care unit, hospital, and posthospital.
Other issues centered on treatment options whether pharmacologic, inva-
sive, or surgical—during the acute hospital phase. These particular sum
jects raised issues that influenced or led to specific patient management and
research recommendations that are discussed more fully later in this report.
This section, which is intended as an introduction for a general audience
and not as a detailed clinical text, was based on materials submitted by sev-
eral members of the committee who have special clinical expertise in car-
diovascular disease. In part it reflects information contained in the clinical
literature cited in the bibliography at the end of this report, which was cur-
rent as of the date of the workshop (May 1989~; advances in the knowledge
base as documented, for instance, in results of relevant RCTs released since
that time are not reflected here because they could not have been brought
into the workshop discussions. The clinical topics themselves were not
debated during the workshop.
9
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10
EFFECTlVE;NESS INITIATWE
The majority of clinical practice in the diagnosis and treatment of AMI is
based on studies performed on people under age 60. The body of informa-
tion on the elderly, particularly above age 70 or 75, is growing but remains
small. Although efforts are made in this section to note where relevant stud-
ies have included older patients, readers should assume that the following
knowledge base applies mainly to a younger population.
ETIOLOGY
An AMI commonly called a heart attack occurs when decreased
blood flow to the heart causes ischemia (damage or injury) of myocardial
(heart muscle) tissue. In most cases, an AMI is caused by occlusion (block-
age) of one or more coronary blood vessels by a thrombus (blood clot), and
it is accompanied by severe crushing chest pain. In a minority of AMIs, but
more commonly in the elderly, patients experience no pain. In some cases
the reduced blood flow is caused by a blood vessel problem other than a
thrombus. The underlying cause of most AMIs is atherosclerotic coronary
artery disease, which causes progressive obstruction of the arteries in the
heart, beginning in early adult life. Clinical research has established that
several risk factors influence the development of coronary disease, particu-
larly family history, diet, lack of exercise, obesity, serum fats (mainly
cholesterol), smoking, and presence of diabetes or high blood pressure.
EPIDEMIOLOGY
Coronary heart disease is present In about 1.S percent of adults ages 35 to
54, but it is estimated to be present in about ~ percent of people over age 65.
AMI occurs in more than 1.S million people in the United States annually
and leads to more than 500,000 deans, making it the nation's leading cause
of death. About 1.S percent of the adult population will sustain an AMI
each year. For those age 65 and over, these risks escalate considerably: 4
percent will have an AMI diagnosed yearly.
Me difference between sexes in these age groups is quite striking, with
the risk of AMI increasing more with age for women than for men.
Between ages 45 and 49, the annual incidence of AMI is 13 per 1,000 men
and 2 per 1,000 women; between ages 75 and 79, the difference narrows to
57 and 30 per 1,000 persons, respectively. Above age 80 the rates for men
and women are essentially equal.
Although AMI is the leading cause of dead in the United States, the
mortality rate differs considerably by age and sex; the general population
mortality rate and those frown more selective clinical teals also differ. Of
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ACUTE MYOCARDIAL INFARCTION
11
the approximately 500,000 deaths per year reported due to AMI, 49 percent
occur in women. About 81 percent of the AMI deaths occur in the
Medicare population age 65 and over; of these, 53 percent occur in women.
About 40 percent of AMI patients age 65 and over die within one year of
the AMI. These data are derived from carefully designed epidemiologic
studies in which unrecognized or "silent" MIs may be identified through
periodic electrocardiograms (ECGs); rates reported for the general popula-
tion are lower, which probably reflects the incidence of such unrecognized
. ~ .
m~arctlons.
The total cost to HCFA and to patients for diagnosis and treatment of
AMI in the hospital is estimated at $1.7 billion annually for Medicare
patients ages 65 and older. These costs do not include costs of hospital
admissions for chest pain or other conditions that prove not to be an AMI,
nor do they include the costs of extensive nonhospital services, including
post-AMI diagnostic and prognostic testing, physician visits, skilled nursing
facility (SNF) care, and home care.
These data about the incidence, mortality, and cost of AMI in the
Medicare population emphasize that AMI is an event in the natural history
of a common disease process that begins in early adult life, progresses with
age, and is influenced by well-established risk factors, some of which are
remediable or modifiable. Before an AMI, patients may have been severely
restricted by chest pain or seriously debilitated by complications of previous
episodes; alternatively, they may have been entirely free of symptoms, or
they may have had a previous AW without complication. For many, life
after an AMI is uneventful; others suffer major complications, including
heart failure, angina, recurrent infarction, arrhythmias (heart rhy hm distur-
bances), and sudden death. Many of the elderly who survive an AMI have
substantial limitations in functional capacity and general quality of life, in
part because of other chronic conditions.
Measuring the effectiveness of diagnosis and treatment of AMI must rec-
ognize, therefore, the multiplicity of factors contributing to the outcome of
an AMI, both immediate and long term. Not all controlled clinical trials
include patients from the Medicare age group, particularly those over age
75. Measures found to improve outcomes in these trials may not be effective
in Medicare patients, especially women, because they may be in a more
advanced stage of coronary disease and frequently have other significant
complicating illnesses.
1h the past decade, dramatic "high-tech" therapies for AMI have become
routine. They include use of clot-dissolving medications (thrombolytics),
breakup or compression of atherosclerotic plaques and clots by means of
catheters threaded into the heart (percutaneous transluminal coronary angio-
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2
EFFECTIVENESS INITIATWE
plasty or PI CA), and surgical implant of blood vessels from other parts of
the body to bypass those that are clogged (coronary artery bypass graft
[CABG]). In certain patients, these procedures can save lives and improve
the quality of life for many patients with AMI and its complications. RCTs
have shown, however, that these procedures do not always improve patient
outcomes following an AMI and, in fact, may be harmful and costly.
Clouding this clinical picture for Medicare patients is the fact that the
majority of patients included in the critical RCTs are under age 75.
Therefore, regardless of proved efficacy in younger patients, the effective-
ness and outcomes of these invasive and costly therapies must be better doc-
umented in those over age 75.
DIAGNOSIS AND MANAGEMENT
Although substantial attention has been focused in recent years on the
newer treatments of AMI, early diagnosis and management have been the
focus of much research during the previous decades. Thus, identifying
patients with possible AMI as early as possible in the community, getting
them to emergency medical care, and continuing their diagnostic evaluation
and subsequent treatment in a coronary care unit (CCU) have been major
contributors to the almost 40-percent decrease in mortality from AMI over
the last 20 years.
The speedy and accurate diagnosis of AMI is critical for several reasons.
First, the greatest danger of death is within the first several hours. Correct
early identification of an AMI and rapid initiation of cardiac monitoring can
result in effective treatment of life-threatening arrhythmias during the initial
hours. Second, intravenous thrombolytic drugs are probably successful in
preventing or mitigating damage in an AMI primarily in the first few hours.
When given in the first four hours, such drugs may reduce the risk of death
by 50 percent, whereas six or more hours later, the benefit is probably less.
Third, for patients with extensive AMIs that lead to serious complications
such as shock or heart failure, early monitoring makes potentially life-sav-
ing evaluation and therapy possible. Fourth, in addition to assuring rapid
diagnosis of patients with an AMI, it is also important to diagnose those
patients who are not having an AMI. Unnecessary CCU admission may
have adverse medical and psychological consequences for the patient, ties
up critical hospital CCU resources, and generates appreciable costs each
year. However, many patients admitted to the CCU who have not had an
AMI are still appropriate for CCU care because of other clinical conditions
that require close monitoring, such as patients with syncope or arrhythmia
win chest pain.
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ACUTE MYOCARDIAL INFARCTION
13
Prehospital Care
The average delay for patients of all ages presenting to the hospital after
the onset of symptoms of a AMI is three hours or more. For the elderly,
times may differ as a function of whether patients come from the communi-
ty or from a custodial setting. More than 60 percent of the deaths from
AMI, amounting to more than 300,000 annually, occur before arrival at a
hospital. ~ many communities, emergency medical services (EMS) have
been established in the past 20 years that are capable of the prehospital diag-
nosis and initial treatment of several life-threatening conditions, including
AMI. In most of these communities, however, 50 percent or more of
patients with "heart attack" symptoms do not call for emergency help before
coming to the hospital, thereby exposing themselves to enormous risk at this
most critical phase.
The goals of optimal prehospital care are to improve early diagnosis and
maximize early treatment through emergency services, thus reducing the
delay from onset of chest pain to initiation of definitive treatment.
Prehospital electrocardiography, done by EMS personnel, is now feasible
and has been shown to affect early triage of the patient with heart attack
symptoms. ECGs can be sent by telephone or radio and interpreted by a
physician in a remote emergency room; that practitioner can, then, decide to
initiate therapy before the patient arrives at the hospital or make arrange-
ments for rapid hospital treatment after arrival.
The major prehospital delays in treatment are caused by lack of patient
recognition or admission of Me problem and delay in self-transportation to
the hospital. Additional delay can occur at the hospital if emergency room
medical and nursing personnel do not have well-defined protocols to assess
patients rapidly and identify those subsets appropriate for specific treat-
ments. With earlier recognition by the patient of Me potential seriousness of
symptoms, state-of-the-art EMS intervention can effectively extend the
capabilities of the hospital into the community, for example by routinely ini-
iiating thrombolytic treannent of appropriate patients in their homes or dur-
ing transport. A time saving of one to one and one-half hours could result in
less damage and fewer deans from AMI.
Emergency Room Care
The development of new tests and computer-assisted diagnostic aids
notwithstanding, the practice of diagnosing AMI in the emergency room
(ER) has changed little in decades. At that stage, diagnosing AMI is still
based primarily on the physician's evaluation of presenting symptoms,
physical examination, and ECG results.
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14
EFFECI~E~ESS INITIATIVE
In evaluating the patient's presenting complaints, both the past history
and the character of the current symptoms are important. A patient with a
past history of coronary disease is more likely to be having an AMI than a
patient with prior evaluation for similar symptoms who demonstrated no
coronary disease. Similarly, a complaint of heavy crushing chest pain radi-
ating into the left arm is strongly suggestive of AMI, whereas chest pain that
is clearly made better or worse by moving or taking a deep breath or that
can be related to recent trauma is not suggestive of AMI. Other presenting
symptoms, such as sudden collapse and loss of consciousness, can be
strongly suggestive, but more often the presenting complaints are not clear
or specific. Atypical presenting symptoms of AMI, such as confusion or
agitation, or strokes are more frequent in the elderly.
The physical examination can reveal telling changes in blood pressure
and pulse, but these usually are not clearly abnormal until some time after
the presenting symptoms or ECG are strongly suggestive of an AMI. Thus,
physical examination may play only a minor role in diagnosis, except by
identifying alternative causes for chest pain such as a broken rib or pneumo-
nia.
In the ER, the ECG, interpreted in conjunction with the presenting com-
plaint, may provide the critical information. Specific changes in the ECG,
(referred to clinically as new Q waves, ST elevation or depression, T wave
elevation or inversion) strongly suggest an impending or ongoing AMI.
Many ECG changes, however, are equivocal and not diagnostic, and the
physician must integrate the ECG with the symptoms and examination; in
the face of a normal or equivocal ECG, patients with strongly suggestive
history or symptoms and examination will be admitted, and those without
will be sent home. In the elderly, this decision is complicated by the
increased incidence of AMI without specific ECG changes.
Other diagnostic tests have not proved as useful in diagnosing AMI in
the ER. Creatine kinase, an enzyme released by damaged heart muscle, is
very helpful in establishing the diagnosis of AMI over 12 to 24 hours, but it
has not proved valuable in the early ER diagnosis because up to one-half of
AMI patients will have normal values on a blood sample taken in the emer-
gency room. Likewise, high-technology tests such as echocardiography and
scintigraphy are not useful in He ER. A promising assist to the ER diagnos-
tic process is the use of computer-supported mathematical modeling, which
predicts acute ischemic disease based on the presenting symptoms and
ECG. In one trial, this instrument decreased CCU admission for those who
did not have an AMI by 30 percent and did not increase the number of
patients inappropriately sent home with an AMI.
Of the 1.5 million patients admitted from an ER into Me CCU each year
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ACUTE MYOCARDIAL INFARCTION
15
for a suspected AMI, only about one-third actually prove to be having an
AMI. The diagnostic error in the ER is 10 times more likely to be a false-
positive admission of those without an AMI than a false-negative decision
to send home the patient with an AMI. This ratio of false-positives to false-
negatives is prudent, and some of those admitted without a diagnosis of
AMI are properly hospitalized for conditions such as acute myocardial
ischemia or unstable angina. Nonetheless, the high rate of false-positives
implies considerable unnecessary cost, poor allocation of high technology
resources, and dislocation for many of the patients so treated. Thus, a major
goal in improving care for patients with possible AMI is to improve imme-
diate diagnostic labeling.
Coronary Care Unit
Most hospitalized patients with AMI are managed initially in a critical
care unit. Larger hospitals will have two types of units; a coronary care unit
(CCU) that cares only for patients with AM and related heart problems, and
an intensive care unit (ICU) that cares for all other types of critically ill
patients. Smaller hospitals may have only an ICU. While undergoing either
diagnostic tests or medical therapy, the AMI patient is monitored electroni-
cally at all times (pulse and ECG) to allow immediate detection of life-
threatening complications. The risk of sudden death or serious arrhythmia
is highest in the first few hours after an AMI and diminishes greatly after 24
hours. In patients with evidence of hemodynamic instability (high or low
blood pressure, shock, or heart failure), invasive hemodynamic monitoring
(such as with a Swan catheter or other techniques) may be appropriate. The
availability of specially trained physicians and nurses in the CCU offers
rapid treatment, including cardioversion or defibrillation (electrically
restarting a heart beat or converting an arrhythmia to normal heart rhythm),
emergency medications (for instance antiarrhythmic drugs), and insertion of
pacemakers to maintain effective cardiac rate and rhythm. Routine pharma-
cologic therapy during CCU stay is summarized below.
Length of stay in CCUs or ICUs for AMI patients has progressively
shortened over the 25 years that these units have been in use. This has
resulted from the recognition and stratification of risk of complications, the
development of continued monitoring in less intensive care units (so-called
step-down or intermediate care units), and remote monitoring of patients in
routine hospital rooms. However, Me criteria for caring for an AMI patient
outside the CCU are not fully agreed upon. Certain low-risk patients may
derive little benefit from CCU care, particularly after 72 hours from onset of
AMI, and there is concern that odlers including very elderly patients may be
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16
EFFECTIVENESS INITIATIVE
harmed by the isolation and psychological stress. For example, many elder-
ly patients with uncomplicated AMI remain in the CCU after the initial 48
hours for monitored observation on lidocaine to suppress ventricular ectopy.
Recent studies strongly suggest that such treatment is not effective, except
in certain high-risk patients.
Hospital Care
Several diagnostic procedures are often used during the hospital stay to
assess complications and stratify risk. Echocardiography (computer-simu-
lated pictures of the heart made with sound waves) and radionuclide imag-
ing or scintigraphy (pictures of the heart made with radioactive materials)
are useful for evaluating the patient with structural damage, such as mitral
regurgitation (damage to one of the heart valves), septal defect (a hole
between the major heart chambers), or pericardial effusion (fluid collected
around the heart). For patients who develop heart failure or dysfunction
without clinical evidence of structural abnormalities, scintigraphy can be of
substantial value in evaluating the functioning of the heart's major cham-
bers. Recognition of how such ventricular dysfunction contributes to heart
failure in the AMI patient can lead to additions to or modifications of thera-
py that may reduce morbidity and mortality. Other diagnostic methods have
been used less frequently during the in-hospital phase (for example,
radionuclide myocardial infarction imaging with technetium-99m [Tc99m]
pyrophosphate or radiolabeled antibody to cardiac myosin to visualize dam-
aged heart muscle directly; myocardial perfusion imaging with thallium-201
LT1-201] chloride and Tc99m isonitrites).
Evaluation of AMI patients before discharge from the hospital is useful
for prognostic risk stratification and thus for planning appropriate therapy.
An excellent method of risk stratification is "submaximal" exercise testing
alone or with myocardial perfusion imaging with T1-201 (a picture of blood
flow to the heart muscle). Numerous published reports have documented
that this approach can effectively classify patients into those with low, inter-
mediate, and high risk. Several other methods to stratify risk (computerized
thallium clearance rates, single photon emission computed tomography,
photon emission tomography, and rest and submaximal exercise radionu-
clide scintigraphy) have not proved to be more advantageous. Of particular
note is positron emission tomography, or PET scanning. This method gives
a cross-sectional image of He heart showing biochemical activity as well as
anatomy and may be superior to T1-201 perfusion study for demonstrating
surviving myocardium. Although it is not considered cost-effective in com-
parison to other methods for routine use, PET scanning has great potential
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ACUTE MYOCARDIAL INFARCTION
17
value as a research tool. Ambulatory ECG monitoring provides a means to
detect potentially life-threatening arrhythmias, but it is of no proven value
for risk stratification compared with submaximal exercise testing alone or
with radioactive T1-201 imaging.
Some centers use other diagnostic methods. For instance, high-speed
computerized axial tomography (CAT scan) and magnetic resonance imag-
ing (WRY provide higher resolution images than standard CAT scanning or
radionuclide imaging, but they are more expensive and complicated. In
addition to a detailed picture of the heart and its function, MRI can assess
the extent of heart muscle damage. However, it is much more expensive
and often presents substantial logistical problems; hence, the cost-effective-
ness of MRI must be evaluated further before it is used routinely after an
AMI. Other diagnostic techniques including continuous 12-lead ECG moni-
toring or specialized heart enzyme studies are used in some institutions, par-
ticularly in conjunction with thrombolytic techniques.
Posthospital Care
The ambulatory management of the AMI patient after acute hospitaliza-
tion represents a continuum from the hospital period. Much less is known,
however, about the effectiveness of the variety of diagnostic tests routinely
used to define further the clinical status of patients with coronary disease.
The physician is presented with the dilemma of balancing risks, costs, and
discomfort to the patient in an attempt to estimate the future risk for the
patient and to identify appropriate treatment such as rhythm-controlling
drugs or revascularization procedures. These decisions are particularly dif-
ficult for patients over 75 years old, because there is less documentation of
the effectiveness of these tests and therapies in this age group, particularly
on their quality of life. For many elderly patients the risk of the diagnostic
procedure itself must be weighed against the risks of further myocardial
damage and reduction of functional ability if no other interventions are
attempted.
Ambulatory diagnostic testing falls into four general categories: (1) rou-
tine office tests, such as ECG, echocardiography, and serum lipids, to follow
changes in myocardial ischemia and risk factors; (2) exercise testing, to
measure residual myocardial ischemia; (3) ambulatory ECG monitoring, to
detect arrhythmias; and (4) catheterization and coronary angiography, to
assess the coronary anatomy and ventricular function, the primary determi-
nants of outcome.
Patients with established coronary artery disease after an AMI are routine-
ly tested with repeat ECGs and various blood tests, including blood glucose
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18
EFFEC17VE0NESS INITIATIVE
and serum lipids, particularly cholesterol. Although serial ECGs have been
shown to provide valuable information for future prognostication, there are
no established norms for the value or frequency of blood tests, nor is there
documentation that additional therapy based on these tests will in any way
improve the patient's health status. For example, it is currently unclear
whether careful monitoring of cholesterol, with aggressive dietary or phar-
macologic treatment, will improve outcomes in the elderly patient after
AMI. Furthermore, cholesterol values are notoriously unreliably low until
six to eight weeks after an infarction, so they should not be obtained until
after that time. Some experts believe that a lipoprotein profile, not just
cholesterol, can be supported as superior at the six-to-eight week point.
Exercise testing is often performed in the AMI patient four to six weeks
after hospital discharge to evaluate myocardial function and ischemia even
though "submaximal" testing was performed during hospitalization. This
procedure can be most valuable in identifying conditions not present during
hospitalization and in identifying patients who have a high risk of death
from coronary artery disease. This information may, in turn, determine the
need for furler evaluation or changes in management, although the effect
of early revascularization on longevity in these patients is not known.
Exercise testing in the Medicare age patient may be constrained by many
patients' limited capacity to undergo the test because of other noncardiac ill-
nesses. Most patients ages 65 to 75, however, can exercise adequately or can
be tested with a different activity such as arm exercise.
Patients who continue to have chest pain, demonstrate myocardial
ischemia on exercise testing, or give evidence of heart failure after AMI by
the need for medication, cardiomegaly, or restricted activity due to shortness
of breath or fatigue are often considered candidates for invasive diagnostic
studies. In some cases, they may be candidates for revascularization proce-
dures. The effect of these invasive procedures- on longevity or functional
status in the elderly, particularly those over 75 years of age, remains unclear.
Sudden death from an arrhythmia is the most frequent serious late com-
plication of an AMI, occurring in patients under age 65 with a peak inci-
dence at six weeks after the AMI. Although ambulatory ECG monitoring in
this period may be effective in identifying potentially threatening abnormal
activity, the effects of its routine use are unknown. Moreover, *miner elec-
trophysiologic testing to evaluate these arrhythmias or their prophylactic
treannent have not been shown to reduce mortality, particularly in view of
the potentially increased mortality and morbidity of these procedures them-
selves in the elderly.
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ACUTE MYOCARDIAL INFARCTION
19
THERAPEUTIC OPTIONS
Treatment of AMI begins with emergency procedures in the community
and continues through all phases of hospital and posthospital care. All AMI
patients should be considered candidates for emergency care, including car-
diopulmonary resuscitation (CPR), rapid transport to a fully staffed ER, hos-
pitalization, CCU care with careful monitoring for complications, support-
ive nursing care, and education and rehabilitation to reduce risk of further
myocardial injury or complications upon return to family and community.
Special considerations may apply, however, in selected situations; (such as
when "do not resuscitate" orders have been written for extremely ill
patients).
Two major categories of therapeutic intervention can be employed at the
appropriate time during the course of an AMI: pharmacologic therapies and
surgical or other invasive procedures. The choice of one or more of the
options under these categories is concurrent with the diagnostic efforts
described above. They may be initiated to prevent immediate or late death,
to reduce the risk of complications, to reduce symptoms or increase func-
tion, and to reach or improve "expected" outcomes predicted by diagnostic
risk stratification.
Pharmacologic Therapy
Choosing appropriate pharmacologic therapies is predicated on many dif-
ferent clinical factors, including the extent of damage to the heart muscle,
recurrence of symptoms, coexisting conditions, and complications of the
AMI. These factors can interact in many ways, making the clinical deci-
sions even more complex. Further difficulties are presented by uncertainty
about the effectiveness of particular drugs for some patients (especially the
elderly), about new medications, and about new or different ways to admin-
ister established drugs. Other controversies involve the routine versus
selective use of some pharmacologic agents and the use of certain agents in
ambulatory rather than inpatient settings.
Patients with chest pain suggestive of AMI can be divided quickly into
three therapeutic groups: (1) patients with early transmural injury, which
refers to damage to the full thickness (more than two-thirds) of the cardiac
muscle and is often denoted "Q wave" infarction; (2) patients with late
transmural or Q wave injury; and (3) patients with nontransmural injury,
which refers to damage only to partial thickness Hess than two-~irds)-of the
cardiac muscle and is often denoted "none wave" infarction.
Group 1 patients are admitted to the hospital with specific ECG changes
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20
EFFECTIVENESS INITIATWE
(e.g., ST elevation) and with no more than four to six hours having passed
since the onset of chest pain. Usual practice would include the use of intra-
venous morphine, nasal oxygen, and nitroglycerin either orally or intra-
venously. Intravenous lidocaine has often been recommended to suppress
cardiac arrhythmias for 12 to 24 hours, but this approach is used only with
great caution in the elderly. Immediate administration of a thrombolytic
agent is indicated, except when explicit contraindications are present.
Aspirin should be given orally. If the thrombolytic drug is tissue plasmino-
gen activator (tPA), it should be followed by intravenous heparin; if the
thrombolytic agent is streptokinase, heparin is probably unnecessary and
possibly risky; and if urokinase is the drug of choice, the heparin issue has
not been decided. (Both aspirin and heparin act to prevent clotting of
blood.) Given evidence of continued ischemia and no contraindications,
most physicians would add drugs that can reduce myocardial ischemia, such
as beta blocker, a calcium channel blocker, or both. Intravenous nitroglyc-
erine, angiotensin-converting enzyme (ACE) inhibitors, and vasodilators
(blood vessel dilators) are examples of other drugs currently being used in
AMI.
Group 2 patients with transmural infarction have specific ECG changes
(ST elevation with Q waves) but are diagnosed more than six hours after the
onset of their symptoms. Use of thrombolytic agents for this group remains
controversial. Research data suggest mixed benefits from thrombolytics
after four to six hours, but recent studies indicate that streptokinase may be
helpful for up to 24 hours. Otherwise, management is similar to early trans-
mural AMI.
Group 3 patients may not have specific ECG changes, but they do have
nonspecific ECG abnormalities and a history strongly suggesting AMI.
Thrombolytic agents are not routinely used but are under investigation.
Aspirin should be begun immediately, and in most cases heparin is given for
one to four days. Anti-ischemic agents (nitrates, beta blockers, and calcium
channel blockers) and narcotics may be used for appropriate indications,
such as chest pain or congestive heart failure.
Patients with recurring symptoms including specific ECG changes (ST
elevation) may be catheterized and may benefit from repeat administration
of the thrombolytic agent. Chest pain alone is treated by intensification of
other treatments and by catheterization in some cases.
Patients manifesting clinical signs of congestive heart failure as a compli-
cation of AMI are appropriately managed initially with diuretics. Some
centers add digitalis glycosides to this regimen, whereas others avoid them
and instead use ACE inhibitors (in the inpatient setting).
Patients win major damage to the left ventncle of the heart (the chamber
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ACllTE MYOCARDIAL INFARCTION
21
that pumps blood to the rest of the body) warrant more intensive and pro-
longed anticoagulation with heparin and aspirin or warfarin. This strategy
aims to prevent blood clots from breaking off and moving to the brain or
limbs (thromboembolism).
During the hospital stay, while beginning to wale around and undergoing
further tests, most patients with Q wave AMI should be placed on beta
blockers. This is particularly true for those with extensive AMI or chest
pain even at low exercise levels. Recurrent episodes of pain are usually an
indication for catheterization and possibly for coronary angioplasty or
revascularization.
The only medications shown to reduce short-term mortality in Group 1
AMI patients are thrombolytic agents, aspirin, and early beta blockers.
Thrombolytic agents should be administered within one to two hours after
the onset of symptoms, if possible, but some benefit extends to as long as 24
hours after the onset of symptoms. In some patients the time of onset of
symptoms is uncertain, and so it is not unreasonable to administer the agent
even if the time since onset may exceed four to six hours.
Invasive Procedures
The uncertainties and controversies about invasive procedures are as
great as those concerning drugs. The issues arise for patients who have sur-
vived the acute event, for those who have never suffered an AMI but who
are believed to be at some (or high) risk for one, and for those who are in
the middle of an evolving AMI or are only a few hours post-AMI.
For patients who have recurrent or persistent chest pain or evidence of
further cardiac damage even after use of thrombolytic agents, PICA or
CABG may be helpful. Performed after diagnostic catherization, INCA
involves threading a small tube into the obstructed coronary blood vessel
and dilating the atherosclerotic narrowing. Conventionally, this is done by
inflating a tiny balloon; new research is testing the efficacy of lasers or other
devices for this purpose. The use of PICA in patients who arrive at the hos-
pital too late to receive thrombolytic therapy (e.g., after four to six hours)
has been advocated. The mortality rate is high in such cases, however, and
this approach is not used routinely in the elderly. Much research must be
done to identify patients most likely to benefit from the procedure. A recent
series of RCrs showed that performing PI CA immediately on patients who
had received thrombolytics did not improve their survival or cardiac func-
tion, and these reports established that such procedures can be correlated
with more bleeding complications.
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EFFECT7VENESS INITIATE
CABG is performed most frequently as an elective procedure for symbol
somatic patients with advanced obstruction of several coronary vessels.
Although it is not routinely done during an AMI, in selected unstable
patients it can be life-saving within hours or days of an AMI. In some cases
CABG may be the first choice when catheterization reveals obstructions in
multiple coronary vessels that are not amenable to PICA. CABG is also
performed as a backup to PICA, either following complications with the
latter procedure or when critically narrowed or clot-obstructed vessels can-
not be dilated. Although CABG can be performed in the early hours follow-
ing AMI with comparatively low risk and successful outcome in selected
patients, no adequately sized, prospective controlled trials have been con-
ducted and its use in this setting is highly individualized or uncertain.
The effectiveness of these potentially life-saving therapies needs to be
documented in the Medicare age group, because most clinical studies have
been done with patients under age 75. Mortality rates from subsequent AMI
are substantially higher among elderly than younger patients; surgery in
these patients also has a greater risk of complications. Nevertheless, the
survival rate in the elderly group over age 70 may be better with surgery
than with medical treatment.
Rehabilitation
Rehabilitative care after myocardial infarction should help restore the
patient to the pre-illness lifestyle and level of function. It should, addition-
ally, favorably modify conventional coronary risk factors, limit psychosocial
disability, and reduce the increased complications of immobility in the
elderly.
Elderly patients are more likely than younger patients to experience a
severe and complicated AMI and a longer hospital stay. Prescriptive exer-
cise rehabilitation which is gradually progressive, predominantly- aerobic,
low-impact, modest-intensity physical activity (for example, walking)
can enhance functional capacity and reduce symptoms brought on by activi-
ty. Thus, it often enables patients to maintain independent living. An
increase of exercise tolerance to a level designed for return to gainful
employment is less frequent. Exercise test (treadmill or bicycle) results are
used to prescribe safe and appropriate levels of exercise training and to mea-
sure the resulting improvement in exercise tolerance.
The life expectancy of a woman in the United States who has reached age
65 is almost 19 additional years; for a man of that age, it is about 15 addi-
tional years. These figures may well justify the delivery of education and
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ACUTE MYOCARDIAL INFARCT70N
23
counseling designed to modify conventional coronary risk factors, even
though the effects modifying most risk factors after an AMI in elderly
patients are not definitively known.
Coronary risk modification, which is designed to retard the progression
or effect regression of atherosclerosis, has proved feasible in elderly popula-
tions; selected components of risk reduction can significantly improve sur-
vival in some elderly patient groups. The American Heart Association has
removed the term"premature" from its mission statement of "reducing
death and disability from heart disease" and indeed has reversed the priority
order for "death" and "disability"; both steps emphasize the advocacy for
coronary risk reduction, including in the elderly. Smoking cessation, con-
trol of hypertension by diet and drugs, weight reduction or weight control,
control of hyperlipidemia predominantly by diet, and regular exercise are
the recommended interventions. Teaching elderly patients how to simplify
work and consene energy can further extend the duration of independent
living for coronary patients win limited residual function.
By age 80, as many women as men have AMIs. Attention is thus
required to maintain and enhance exercise capacity in elderly women, who
generally decrease their habitual activity level with aging more than men do
even before infarction. Additional benefits of exercise training include lim-
iting bone loss and osteoporosis and maintaining joint stability and muscle
and tendon strength, both of which can limit falls and the resultant impair-
ment. These points were also emphasized by the IOM committee that con-
sidered hip fracture another of the three conditions included in the
Effectiveness Initiative project.
The psychosocial complications of myocardial infarction particularly
fear, depression, and dependency can be decreased by exercise rehabilita-
tion and by the social support offered by a peer group in supervised exercise
settings. Psychosocial counseling, based on prognostic information
obtained from exercise testing approaches and from risk reduction, can fur-
ther improve psychosocial status. The perception of personal health status
can be improved by education and counseling. Perceived health status often
correlates with the outcome of illness, thus perhaps affecting the outcome.
The threatened loss of independence that commonly accentuates most psy-
chosocial complications can be retarded or reversed by the rehabilitative
approach to care.
Restoration of physical capacity, decrease in symptoms, and resultant
improvement in function and comfort are measurable outcomes of health
care that are valued by AMI patients including the elderly; these can be
assessed by a number of quality-of-life measures. Patient awareness that
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EFFECTIVENESS INITIATWE
lifestyle components can favorably influence the course of coronary illness
has provided further incentive for secondary preventive interventions.
Provision of rehabilitative services to elderly coronary patients recovering
from an AMI may prove the most economical approach to limiting or delay-
ing the need for costly custodial care. The challenge to the clinical commu-
nity is to deliver these rehabilitative services in a cost-effective manner.
Representative terms from entire chapter:
myocardial infarction
