What's the next step for a patient with chest pain and an EKG showing atrial flutter at a normal heart rate on metoprolol (beta-blocker) 25 mg Extended Release (XR), with a recently negative Cardiolite (technetium-99m sestamibi) stress test?

Next Step: Obtain Serial Cardiac Troponins and Repeat ECG Immediately

Despite the recent negative stress test, this patient requires immediate serial high-sensitivity cardiac troponin measurements and repeat ECG, as a single normal or nondiagnostic ECG is insufficient to exclude acute coronary syndrome (ACS), and up to 6% of patients with evolving ACS are inappropriately discharged with a normal initial ECG. 1, 2, 3

Critical Context: Why the Negative Stress Test Doesn't Rule Out ACS

• A negative stress test within the past few months does not exclude acute coronary syndrome in a patient presenting with new chest pain. 4
• Stress tests have incomplete sensitivity and specificity for coronary artery disease (CAD), with studies showing that 20.7% of patients with recent negative stress tests who present to the ED with chest pain are ultimately diagnosed with CAD. 5
• The atrial flutter itself is a new finding that warrants investigation, as it may represent a manifestation of underlying cardiac pathology or ischemia. 1

Immediate Diagnostic Steps

Serial Troponin Measurements (Class I)

• Obtain high-sensitivity cardiac troponin immediately if not already done, as troponin is the most sensitive test for diagnosing acute myocardial injury. 1, 2, 3
• Repeat troponin measurement at 6-12 hours from symptom onset to detect rising or falling patterns that indicate myocardial injury. 2, 3
• A single troponin measurement drawn less than 6 hours from symptom onset may miss myocardial injury and should never be used alone to exclude ACS. 2

Serial ECG Monitoring

• Perform repeat ECG immediately if chest pain recurs, persists, or if the clinical condition deteriorates, as ongoing symptoms increase the likelihood of capturing evolving ischemic changes. 1, 3
• Continue serial ECGs every 15-30 minutes during the first hour if symptoms persist, even if the patient is currently pain-free. 3
• Always compare the current ECG with previous ECGs if available, as a normal but changed ECG may reveal subtle new abnormalities. 1
• Consider posterior leads (V7-V9) if clinical suspicion remains intermediate-to-high, as left circumflex or right coronary artery occlusions causing posterior wall ischemia are often "electrically silent" on standard 12-lead ECG. 1

Risk Stratification for Disposition

High-Risk Features Requiring Admission 2, 3

• Recurrent or persistent ischemic chest pain despite medical therapy
• Dynamic ECG changes on serial tracings
• Positive second troponin measurement or rising pattern
• Hemodynamic instability
• Life-threatening arrhythmias (the atrial flutter at 78 bpm is controlled but warrants monitoring)
• New or worsening heart failure

Low-Risk Criteria Allowing Potential Discharge 2, 3

• No recurrent chest pain after 6-12 hours of observation
• Normal or unchanged ECG on serial testing
• Two negative troponin measurements (at presentation and 6-12 hours)
• No high-risk features present

Management of the Atrial Flutter

Rate Control Assessment

• The patient is currently rate-controlled at 78 bpm on metoprolol 25 mg XR, which is appropriate. 6
• Do not abruptly discontinue metoprolol, as severe exacerbation of angina, myocardial infarction, and ventricular arrhythmias have been reported in patients with coronary artery disease following abrupt discontinuation of beta-blockers. 7
• Continue continuous cardiac monitoring to detect any changes in rhythm or rate. 4

Beta-Blocker Considerations

• Metoprolol may mask tachycardia occurring with hypoglycemia or hyperthyroidism, but other manifestations such as dizziness and sweating may not be significantly affected. 7
• Monitor for bradycardia, including sinus pause, heart block, and cardiac arrest, which have occurred with metoprolol use. 7

Disposition Algorithm

If High-Risk Features Present

• Admit to inpatient unit with continuous cardiac monitoring. 4, 3
• Consider urgent coronary angiography if recurrent ischemia, elevated troponin, or hemodynamic instability develops. 4
• Initiate aspirin 75-325 mg daily immediately if ACS is suspected and no contraindications exist. 2
• Administer low molecular weight heparin or unfractionated heparin. 2

If Intermediate-Risk

• Continue observation in chest pain unit or ED with serial ECGs and troponins until the 6-12 hour mark. 3
• Consider anatomic or functional testing before discharge (though the recent negative stress test may influence this decision). 4

If Low-Risk After Serial Testing

• Consider early stress test to provoke ischemia before discharge, with outpatient follow-up within 72 hours. 4, 3
• Recent meta-analysis shows patients with negative stress testing in the past 12 months and reassuring ECG/troponin have low major adverse cardiac events (MACE) rates: 0.09-0.23% at 1 month. 8

Critical Pitfalls to Avoid

• Never rely on a single normal ECG to discharge a patient with ongoing chest pain or high clinical suspicion for ACS—this is the most dangerous error in chest pain evaluation. 1
• Do not delay repeat ECGs waiting for scheduled intervals if symptoms change; symptom-driven timing takes priority. 1
• Do not assume the negative stress test from "a few months ago" excludes current ACS, as 20.7% of such patients ultimately have CAD. 5
• Patients in whom ACS has been excluded should be reassessed for other potentially serious medical conditions that may mimic ACS symptomatology (e.g., pulmonary embolism, aortic dissection). 4

Follow-Up Considerations

• If discharged after negative serial testing, the patient should be seen by a physician within 72 hours for further investigation into the cause of symptoms and management of the atrial flutter. 4
• The primary physician should be notified of the evaluation results and receive a copy of relevant test results. 4