Pharmacological Stress Testing and Noninvasive Imaging

Graded exercise electrocardiography has its limitations in patients who have baseline ECG abnormalities or who are unable to ambulate. Additionally, rest MPI cannot be performed in patients with previous AMI. In these patients, stress testing with echocardiography or nuclear scintigraphy can be alternative solutions. Similarly, for patients who are unable to exercise, pharmacological methods are available. These techniques offer more diagnostic information than exercise ECG testing but may be offset by higher costs, especially when applied to the low-risk patient population (64). Because there are few studies evaluating stress nuclear scintigraphy and stress echocardiography in the ED setting, it is unclear whether or not the increased diagnostic accuracy will offset the cost of these tests in the low-risk patient population.

Dobutamine Stress Echocardiography

Dobutamine stress echocardiography (DSE) is an alternative for patients who are unable to perform graded exercise testing. The incidence of AMI or ventricular dysrhythmia is approx 1/2000, but no deaths have been reported. Bholasingh et al. (65) studied 404 low-risk patients who underwent DSE after negative cTnT measurements 12 h after the onset of symptoms. Patients with previous CAD were included in this analysis. Twenty-three (5.7%) patients were removed from the study because of poor echocardiographic images.

Delta Two-Hour Cardiac Biomarkers, Automated Serial ECG Monitoring
Fig. 4. Erlanger Chest Pain Protocol using nuclear stress testing (From ref. 47.)

Thirty-nine patients (10.3%) could not finish the study because of intolerable side effects, which were defined as dysrhythmia and severe hypotension or hypertension. Patients with positive DSE had a sevenfold increased risk of cardiac death, AMI, rehospitalization for unstable angina, or revascularization within 6 mo. In those patients with a negative DSE, one cardiac death was reported (0.3%) and seven patients underwent revascularizations (2%). No patients with AMI, however, were observed at 6-mo follow-up (65). Although DSE appears to be an effective means for risk stratification, its cost-effectiveness in the ED setting is not known. It is also important for the institution to have on staff physicians who are interested in DSE and have expertise in this methodology.

Erlanger Chest Pain Protocol

Fesmire et al. (47) have developed a novel chest pain protocol incorporating 2-h changes in CK-MB and cTnI with stress nuclear imaging (Fig. 4). In their protocol, patients with chest pain are initially stratified into five categories based on initial history, physical examination, and 12-lead ECG (Table 3). Category I and II patients are considered to be at high risk of ACS and are treated according to published American College of Cardiology/ American Heart Association (ACC/AHA) guidelines. Any treatment decisions for patients in categories III and IV are left up to the treating physician.

Patients not undergoing emergency reperfusion therapy are then evaluated for 2 h, which includes ST-segment monitoring with serial ECGs, and baseline and 2-h CK-MB/ cardiac troponin levels. After 2 h, these patients are recategorized to one of three risk categories (Table 4). Patients with a positive delta CK-MB, defined as an increase of 1.5 ng/mL or greater, or a positive delta cTnI, defined as an increase of 0.2 ng/mL or greater, are placed in category II. Patients without significant increases in CK-MB and cTnI are placed in categories III and IV. Patients reassigned to category III have nuclear stress

Table 3

Initial Risk Stratification into Five Categories Using Erlanger Chest Pain Protocol

Table 3

Initial Risk Stratification into Five Categories Using Erlanger Chest Pain Protocol

Category

Presence of ACS

ECG Treatment

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