Chest Pain and Acute Coronary Syndromes, and Acute Myocardial Infarction

Chest pain accounts for approximately 6 million annual visits to emergency departments in the United States, making chest pain the second most common complaint in the emergency department.¹⁰ ACS are life-threatening causes of chest pain seen in the emergency department and include unstable angina, non–ST segment elevation MI (NSTEMI), and acute MI or ST segment elevation MI. Less than 15% to 30% of patients who present to the emergency department with nontraumatic chest pain have ACS, however.^11,12 An important challenge is to identify patients with ACS appropriately and admit them to the appropriate setting for further care. For the evaluation and management of patients with acute chest pain, prediction models have markedly improved our ability to estimate risk, and cost-effectiveness analyses have helped guide the development of new paradigms and the incorporation of new technologies.¹³

In addition to treating patients with ACS, the CICU has traditionally been considered appropriate for monitoring patients with acute chest pain until ACS is diagnosed or excluded. Increasing health care costs have created pressures, however, to increase the efficiency of CICUs. Possible strategies seek to decrease resource use by identifying low-risk patients for initial triage or early transfer to lower levels of care. The application of management algorithms and the development of intermediate care units are allowing for a distinction between intensive coronary care and careful coronary observation.¹⁴ The development of chest pain units located in the emergency department is an another alternative to CICU admission. These units are safe, effective, and a cost-saving means of ensuring that patients with unstable angina who are considered to be at intermediate risk of cardiovascular events receive appropriate care.¹⁵ Patients at low clinical risk can receive immediate exercise testing in the chest pain unit if the appropriate diagnostic modalities are available. This approach is accurate for discriminating low-risk patients who require admission from patients who can be discharged to further outpatient evaluation.¹⁶

Several reports have detailed strategies to identify high-risk patients early. To achieve more appropriate triage to the CICU of patients presenting with acute chest pain, Goldman and coworkers¹⁷ used clinical data on 1379 patients at two hospitals to construct a computer protocol to predict the presence of MI. This protocol was tested prospectively, and it had a significantly higher specificity (74% versus 71%) in predicting the absence of infarction than physicians deciding whether to admit patients to the CICU, and it had a similar sensitivity in detecting the presence of infarction (88% versus 87.8%). Decisions based solely on the computer protocol would have reduced the admission of patients without infarction to the CICU by 11.5% without adversely affecting the admission of patients in whom emergent complications developed that required intensive care.

In another study,¹⁸ the acute cardiac ischemia time-insensitive predictive instrument (ACI-TIPI) was used to triage patients with symptoms suggestive of acute cardiac ischemia to the CICU, telemetry unit, ward, or home. Use of ACI-TIPI was associated with reduced hospitalization among emergency department patients without acute cardiac ischemia. Appropriate admission for unstable angina or acute infarction was not affected. If ACI-TIPI is used widely in the United States, its potential incremental impact is estimated to be more than 200,000 fewer unnecessary hospitalizations and more than 100,000 fewer unnecessary CICU admissions.¹⁸

In a cost-effectiveness analysis, Fineberg and colleagues¹⁹ found that for patients with a 5% probability of infarction, admission to a CICU would cost $2.04 million per life saved and $139,000 per year of life saved compared with intermediate care. For the expected number of such patients annually in the United States, the cost would be $297 million to save 145 lives.

In another study by Goldman and associates,²⁰ a set of clinical features was defined; if these features were present in the emergency department, they were associated with an increased risk of complications. These clinical features included ST segment elevation or Q waves on the electrocardiogram (ECG) thought to indicate acute MI, other ECG changes indicating myocardial ischemia, low systolic blood pressure, pulmonary rales above the bases, or an exacerbation of known ischemic heart disease. The risk of major complications in patients with acute chest pain can be estimated on the basis of the clinical presentation and new clinical observations made during the hospital course. These estimates of risk help in making rational decisions about the appropriate level of medical care for patients with acute chest pain.

Despite these findings, the implementation of these algorithms in clinical practice by physicians without specific training in their use has been minimal.^21,22 This situation may relate to physicians’ reporting that they are too busy, are unsure of the value of the algorithms, and are concerned about the consequences of inappropriately discharging patients who are later found to have had MI.²³

A more recent analysis by Tosteson and colleagues²⁴ indicates that the CICU usually should be reserved for patients with a moderate (≥21%, depending on the patient’s age) probability of acute MI, unless patients need intensive care for other reasons. Clinical data suggest that only patients with ECG changes of ischemia or infarction not known to be old have a probability of acute MI this high. A summary has been developed that outlines the location to which chest pain patients should be admitted (Table 3-2).²⁵

Table 3–2 Indications to Guide Where to Admit Patients with Acute Chest Pain

Another important issue to consider is the length of stay in the CICU after patients are admitted. If patients are initially triaged to the CICU, the lack of cardiac enzyme abnormalities or recurrent chest pain during the first 12 hours of hospitalization are parameters that can be used to identify patients for whom a 12-hour period of CICU observation is sufficient to exclude acute MI.²⁶ In a study by Weingarten and colleagues,²⁷ physicians caring for patients with chest pain who were at low risk for complications received personalized written and verbal reminders regarding a guideline that recommended a 2-day hospital stay. Use of the practice guideline recommendation with concurrent reminders was associated with a decrease in length of stay from 3.54 ± 4.1 days to 2.63 ± 3 days and a total cost reduction of $1397 per patient. No significant difference was noted in complications, patient health status, or patient satisfaction when measured 1 month after hospital discharge.

The European Society of Cardiology and American College of Cardiology restructured the definition of acute MI in 2000 (Table 3-3).²⁸ The principal revision compared with the previous World Health Organization definition²⁹ is the inclusion of biomarkers, specifically troponin, as a necessary component. There have been some attempts to assess the new definition and the widespread introduction of troponin measurement on CICU admitting practices. One study by Amit and colleagues³⁰ was a retrospective cohort study in which all admissions to the CICU the year before and after the introduction of troponin measurement and the updated MI definition were examined. There was a 20% increase in the number of CICU admissions, driven by a 141% increase in the number of NSTEMIs. Length of stay in the CICU decreased by 1 day for all ACS patients, and the 30-day mortality for acute MI did not change significantly. In another study by Zahger and associates,³¹ the number of NSTEMI patients increased by 33% after the definition change, whereas the number of patients with ST segment elevation MI remained the same. There was no change in the number of CICU beds at the participating institutions. The proportion of patients given the diagnosis of NSTEMI increased significantly more in centers with high use of troponin. These changes have a significant impact on resource use.

Table 3–3 European Society of Cardiology/American College of Cardiology Definition of Acute, Evolving, or Recent Myocardial Infarction

Given this increased demand for a relatively fixed resource, the question of whether all NSTEMI patients need to be admitted to the CICU arises. The CRUSADE registry³² showed that patients with NSTEMI often receive excess doses of antithrombotic therapy, and that dosing errors occur more often in vulnerable populations and predict an increased risk of major bleeding. Some institutions have interpreted these data to indicate that all NSTEMI patients should be admitted to the CICU because a maximally observed setting may limit excess dosing and bleeding complications.

At our institution, it is practice for only NSTEMI patients who are high risk by the TIMI risk score³³ to be admitted to the CICU. The lower risk NSTEMI patients are admitted to a telemetry unit with cardiac nurses. There is preliminary evidence that admission of patients with initially uncomplicated chest pain with a relatively low probability of acute MI to a stepdown unit does not place at increased risk those who eventually “rule in” for MI.³⁴ Regardless of specific setting, the adherence to clinical pathways offers the potential to improve the care of patients with ACS while reducing the cost of care.³⁵

Heart Failure

It is estimated that 5.2 million people in the United States are being treated for heart failure.¹ Hospital discharges for heart failure increased from 402,000 in 1979 to 1,101,000 in 2004.³⁶ Interventions to improve adherence, the control of hypertension, and the appropriate use of angiotensin-converting enzyme inhibitors may prevent many hospitalizations of heart failure patients.³⁷ Device therapy, including biventricular pacemakers and implantable cardioverter-defibrillators, has also led to significant improvements in outcomes for certain heart failure patient populations.^38,39 Nonetheless, some patients admitted to the hospital with heart failure require advanced cardiac care in the CICU. Standard criteria for management of acute decompensated heart failure (ADHF) in the CICU are not clearly established. Management usually involves invasive hemodynamic monitoring and inotropic or vasopressor support that cannot be done outside the CICU in most institutions.

Admission for heart failure is a high-risk event for patients, particularly patients admitted to an intensive care unit (ICU) setting.⁴⁰ Table 3-4 shows the events and procedures that occurred during hospitalization of patients with congestive heart failure (CHF) in the ADHERE registry.

Table 3–4 Events and Procedures for Congestive Heart Failure Patients during Hospital Stay

Weingarten and associates⁴¹ found that nearly one third of patients with CHF hospitalized in either the CICU or intermediate care unit are lower risk and potentially suitable for transfer 24 hours after admission. In this study, low risk is defined as patients without acute MI or ischemia, active or planned cardiac interventions, unstable comorbidity, worsening clinical status, or lack of response to diuretic therapy. A more common planned cardiac intervention for heart failure patients is the use of the pulmonary artery catheter. Although addition of the pulmonary artery catheter to careful clinical assessment increases anticipated adverse events, it does not affect overall mortality and hospitalization in patients with severe symptomatic and recurrent heart failure.⁴²

In most hospitals, certain medical therapies used in the treatment for decompensated heart failure are delivered in the CICU setting. The need for pronounced afterload reduction is an indication for intravenous nitroprusside.⁴³ This therapy is commonly delivered in the CICU because it requires continuous blood pressure monitoring. The major limitation to the use of nitroprusside is its metabolism to cyanide, possibly leading to development of cyanide toxicity or rarely thiocyanate toxicity that may be fatal.⁴⁴

Patients with systolic dysfunction who remain volume-overloaded despite vasodilator and diuretic therapy may require intravenous inotropic support to improve systemic perfusion. The β agonist dobutamine is a useful inotropic agent for ADHF.⁴⁵ In patients with severe CHF, short-term administration of dobutamine selectively improves vascular endothelial function.⁴⁶ Another class of inotropic agents commonly used is the phosphodiesterase inhibitors. In addition to being given in the acute setting, prolonged outpatient therapy with milrinone, a phosphodiesterase inhibitor, has been employed.⁴⁷ The use of intravenous continuous infusion of inotropes, including dobutamine and milrinone, has not been shown to have a benefit in mortality.⁴⁸

Another treatment modality that has been used in the CICU or cardiac stepdown unit is the exogenous administration of nesiritide, recombinant human brain natriuretic peptide. In patients hospitalized with ADHF, nesiritide improves hemodynamic function.⁴⁹ More recent independent analyses have questioned the safety of nesiritide, however. Compared with non–inotrope-based control therapy, nesiritide may be associated with an increased risk of worsening renal function⁵⁰ and death⁵¹ after treatment for ADHF. If used, these treatments are best used in the CICU or cardiac stepdown unit to achieve hemodynamic targets.

Certain causes of heart failure require specific therapies. Patients with giant cell myocarditis have improved outcomes if they receive immunosuppressive treatment.⁵² Patients with a fulminant presentation from giant cell myocarditis, or more rarely from other etiologies such as lymphocytic or viral myocarditis, require an intensive level of hemodynamic support with inotropes and vasopressors in the CICU.⁵³

Patients receiving inotropic therapy can go on to have improved outcomes with the use of mechanical circulatory support, specifically left ventricular assist devices (LVADs), as destination therapy.⁵⁴ Although cellular recovery and improvement in ventricular function are observed, the degree of clinical recovery is insufficient for device explantation in most patients with chronic heart failure.⁵⁵ If not used as destination therapy, the LVAD may serve as a bridge to heart transplantation, and these patients are cared for in the cardiothoracic surgery ICU after surgery. Also, at cardiac transplantation centers, some advanced CHF patients require continuous infusion of a single high-dose intravenous inotrope (e.g., dobutamine, ≥7.5 μg/kg/min, or milrinone, ≥0.50 μg/kg/min), or multiple intravenous inotropes, in addition to continuous hemodynamic monitoring of left ventricle filling pressures, which satisfies criteria for listing as Status 1A by the United Network of Organ Sharing.⁵⁶ Additionally, patients undergoing new advanced cardiac care procedures, such as percutaneous mechanical devices,⁵⁷ require management in the CICU.

Multiorgan dysfunction in the setting of heart failure requires admission to the CICU. A reduced glomerular filtration rate is associated with an increased mortality in patients with heart failure.⁵⁸ Because many patients with ADHF and renal failure have compromised hemodynamics, a form of renal replacement therapy, such as continuous venovenous hemofiltration or hemodialysis, in the intensive care setting is commonly required. Other volume management techniques for heart failure treatment, such as ultrafiltration,⁵⁹ may necessitate care in the CICU or stepdown unit.

While the patient is hospitalized, careful attention to certain laboratory values such as serum sodium and blood urea nitrogen is reasonable because both values have been shown to be independent predictors of subsequent mortality.^60,61 Treatment with tolvaptan, a vasopressin V2 receptor blocker, has been shown to increase serum sodium concentrations effectively in patients with euvolemic or hypervolemic hyponatremia,⁶² but has no effect on long-term mortality or heart failure–related morbidity.⁶³

Pulmonary Hypertension

Several treatments for pulmonary arterial hypertension are approved in the United States, including epoprostenol, treprostinil, bosentan, and sildenafil. Because limited data are available from head-to-head comparisons of approved therapies, the choice of treatment is dictated by clinical experience and by patients’ preferences.⁶⁴ There are no evidence-based guidelines on when to admit patients with pulmonary hypertension to the CICU. Generally, patients with New York Heart Association or World Health Organization functional class IV may require an intensive care setting for management. Intravenous epoprostenol is an advanced pulmonary hypertension therapy that has been shown to improve functional capacity and survival in patients with idiopathic pulmonary arterial hypertension.⁶⁵

Related posts:

Elevated Cardiac Troponin in the Absence of Acute Coronary Syndromes: Mechanism, Significance, and Prognosis Hemodynamically Unstable Presentations of Congenital Heart Disease in Adults Vascular Complications after Percutaneous Coronary Intervention Diagnosis and Treatment of Complications of Coronary and Valvular Interventions Pharmacologic Interactions in the CICU Acute Aortic Syndromes: Diagnosis and Management

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