Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 9
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 surgicalóduring 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
OCR for page 10
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
OCR for page 11
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-
OCR for page 12
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.
OCR for page 13
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.
OCR for page 14
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
OCR for page 15
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
OCR for page 16
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
OCR for page 17
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
OCR for page 18
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.
OCR for page 19
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
OCR for page 20
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
OCR for page 21
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.
OCR for page 22
22 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
OCR for page 23
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
OCR for page 24
24 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: