Original Article
Assessing risk in acute chest pain: The value of stress myocardial perfusion imaging in patients admitted through the emergency department

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Background

To prospectively assess the clinical value of stress-gated myocardial single photon emission computed tomography (SPECT) for triaging patients admitted through the emergency department (ED) with acute chest pain (ACP).

Methods

Prospective, observational cohort study in 1,576 consecutive patients who were evaluated for ACP over a 29-month period. Stress SPECT was performed within 24 hours of admission from the ED. Analysis included quantification of total and ischemic left ventricular perfusion defect size (PDS). Cardiac events were defined as an acute coronary syndrome during the index hospitalization or in follow-up over 7.3 ± 2.8 months.

Results

Eighty-five cardiac events occurred in 77 patients (4.9%). SPECT was abnormal in 135 patients (8.6%) of whom 83 (61.5%) had a reversible defect. Event rates were significantly higher in patients with an abnormal (40%) versus a normal (1.6%) SPECT (P < .0001); and in those with a (1) large (>15%) versus small (≤15%) PDS (50.0% vs 33.7%, P = .05) and (2) large (>10%) versus small (≤10%) ischemic PDS (87.5% vs 42.4%, P < .0001, respectively). SPECT best predicted cardiac events by multivariate analysis. The addition of SPECT to clinical variables significantly improved overall risk prediction (global χ2 103.6 vs 207.1, P < .001).

Conclusions

Stress SPECT can accurately assess risk in a heterogeneous group of patients with ACP of unclear cardiac etiology, and beyond that provided by a clinical risk assessment alone. Our results support the use of stress SPECT for identifying very low-risk ACP patients with normal study results who can be safely discharged home.

Introduction

Each year in the United States more than 6 million patients present to an emergency department (ED) with chest pain or other symptoms suggestive of acute cardiac ischemia. The majority of these patients are hospitalized or admitted to an observation unit because initial clinical examination, electrocardiogram (ECG) results, and cardiac biomarkers are insufficient to exclude an acute coronary syndrome (ACS).1

Recent guidelines have endorsed stress-gated myocardial single photon emission computed tomography (SPECT) as an appropriate test for evaluating patients with acute chest pain (ACP) and possible ACS.2, 3, 4 These recommendations are based in part on previous studies performed over a decade ago in patients presenting with unstable angina pectoris (UAP).5, 6, 7, 8, 9, 10 More recently, the Adenosine Post Infarction Evaluation Trial (INSPIRE) demonstrated the value of adenosine SPECT for assessing risk in stabilized patients with acute myocardial infarction (AMI).11 However, there is limited information regarding the use of stress SPECT in low to intermediate risk patients admitted through the ED with ACP.12, 13, 14, 15 Therefore, the purpose of this study was to evaluate the role of stress SPECT for evaluating risk and guiding therapeutic decision making in this contemporary patient population.

Section snippets

Study Population

This was a prospective observational cohort study in 1,576 patients >18 years of age who had ACP of uncertain cardiac etiology and who were hospitalized under observational status pending further evaluation with SPECT. During the 29-month enrollment period, 5,066 patients with ACP were evaluated in the ED of whom 1,317 (26%) were discharged home with a diagnosis of non-cardiac chest pain. Of the remaining 3,749 admitted patients, 2,173 had ACP consistent with or highly suggestive of ACS and

Baseline Characteristics (Table 2)

For the entire cohort of 1,576 subjects, mean patient age was 55.5 ± 13.8 (range 21 to 100) years and 58% of enrolled subjects were women. Cardiac risk factors were prevalent with a mean of 1.9 ± 1.0 risk factors per patient. The mean BMI of the cohort was 30.7 ± 7.3. The mean TIMI risk score was 1.7 ± 1.0 with 1,254 (80%) patients having a low (i.e., 0-2) risk score and 322 (20%) an intermediate (i.e., 3-5) risk score. No patient had a high TIMI risk score (i.e., >5) due to exclusion criteria.

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Discussion

The current study demonstrates the value of stress SPECT for evaluating a heterogenous group of patients who were admitted through the ED with ACP of uncertain cardiac etiology. Although it is generally recognized that stress SPECT can accurately risk stratify stable patients with chest pain,23 there is limited information of its potential diagnostic and prognostic role in low to intermediate risk chest pain patients in the contemporary ED setting.12, 13, 14, 15 Previous studies have primarily

Study Limitations

This was a single center study; however, our patients had a similar clinical risk profile as observed in multi-center trials evaluating patients in the ED setting and with a comparable overall event rate.12, 13, 14, 15 Second, coronary angiography was not performed in all patients and, therefore, the diagnostic accuracy of SPECT could not be ascertained. Instead, we focused on the prognostic importance of SPECT for identifying high- and low-risk groups. Third, our definition of UAP required the

Conclusion

Stress SPECT can accurately assess risk in ED patients admitted with chest pain of uncertain cardiac etiology and beyond that provided by clinical assessment alone. Our results support the use of stress SPECT for identifying very low-risk ACP patients with normal study results who can be safely discharged home.

References (27)

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