What is the appropriate evaluation and management for chest pain in a patient 3 weeks after a bout of influenza?

Evaluation and Management of Chest Pain 3 Weeks Post-Influenza

In a patient presenting with chest pain 3 weeks after influenza, immediately obtain an ECG within 10 minutes and consider post-viral myocarditis or pericarditis as the primary cardiac complications, while systematically excluding acute coronary syndrome, pulmonary embolism, and other life-threatening causes. 1, 2

Immediate Diagnostic Workup

Essential First Steps

• Obtain a 12-lead ECG within 10 minutes of presentation to identify ST-segment elevation (myocardial infarction), widespread ST-elevation with PR depression (pericarditis), or low-voltage QRS with electrical alternans (pericardial effusion with tamponade). 3, 1, 4
• Measure cardiac troponin immediately as myocarditis following influenza can present with troponin elevation mimicking acute coronary syndrome. 1, 5
• Order chest radiography to evaluate for pneumonia, pleural effusion, pneumothorax, or cardiomegaly suggesting pericardial effusion. 1, 6

Critical Physical Examination Findings

• Assess vital signs for tachycardia and tachypnea (present in >90% of pulmonary embolism cases), fever (suggesting ongoing infection or pericarditis), and hypotension (suggesting tamponade or massive PE). 1, 4
• Listen for pericardial friction rub (biphasic sound indicating pericarditis) and distant heart sounds (suggesting pericardial effusion). 1, 4
• Check for pulsus paradoxus >10 mmHg which indicates hemodynamically significant pericardial effusion or tamponade. 4
• Examine for chest wall tenderness, though 7% of patients with reproducible chest wall pain still have acute coronary syndrome, so this does not exclude cardiac pathology. 1

Post-Influenza Cardiac Complications

Myocarditis

• Influenza-associated myocarditis can present with chest pain, ST-segment elevation, and troponin elevation mimicking acute coronary syndrome, even with normal coronary angiography. 5
• The mechanism involves endothelial impairment and microcirculatory disturbance rather than direct myocyte injury. 5
• Physical examination may reveal fever, signs of heart failure, and S3 gallop. 1, 2

Pericarditis/Pericardial Effusion

• Sharp, pleuritic chest pain that improves when sitting forward and worsens when supine is characteristic of pericarditis. 1, 2
• ECG shows widespread ST-elevation with PR depression (distinguishing it from STEMI which has regional ST changes). 1
• Cardiac tamponade is a rare but life-threatening complication presenting with hypotension, tachycardia, distant heart sounds, and pulsus paradoxus. 4
• One case report documented acute influenza complicated by pericardial effusion requiring emergent pericardiocentesis with removal of 250 mL fluid. 4

Systematic Exclusion of Life-Threatening Causes

Acute Coronary Syndrome

• Do not assume chest pain is benign simply because it occurs post-influenza—influenza can exacerbate preexisting cardiovascular disease. 4
• Retrosternal pressure-type discomfort radiating to left arm/jaw/neck with diaphoresis, dyspnea, or nausea suggests ACS. 2
• Sharp, pleuritic pain makes ischemic heart disease less likely but does not completely rule it out, as 13% of ACS patients present with pleuritic pain. 1

Pulmonary Embolism

• Presents with acute dyspnea, pleuritic chest pain, tachycardia, and tachypnea. 1, 2
• Use validated clinical decision rules (Wells score, PERC rule) to determine pretest probability and guide D-dimer testing. 1

Pneumonia

• Localized pleuritic pain with fever, productive cough, regional dullness to percussion, and egophony. 1
• Chest X-ray will show infiltrate. 1

Advanced Imaging When Indicated

Echocardiography

• Obtain transthoracic echocardiography (TTE) to assess for pericardial effusion, ventricular wall motion abnormalities, or restrictive physiology in patients with suspected pericarditis or myocarditis. 1
• Bedside echocardiogram can rapidly identify pericardial effusion with right ventricular diastolic collapse indicating tamponade physiology. 4

Cardiac MRI

• CMR with gadolinium contrast distinguishes myopericarditis from other causes including myocardial infarction with nonobstructive coronary arteries (MINOCA) when myocardial injury is present. 1
• Useful when diagnostic uncertainty exists or to determine extent of pericardial inflammation and fibrosis. 1

Coronary Angiography

• Consider if troponin is elevated and ECG suggests ischemia, as influenza-associated myocarditis can mimic ACS with normal coronary arteries on angiography. 5

Critical Pitfalls to Avoid

• Never use nitroglycerin response as a diagnostic criterion—esophageal spasm and other noncardiac conditions also respond to nitroglycerin. 1, 2
• Do not assume reproducible chest wall tenderness excludes serious pathology, as 7% of patients with palpable tenderness have acute coronary syndrome. 1
• Do not delay transfer to the emergency department for troponin testing in office settings—patients with suspected ACS should be transported urgently by EMS. 1, 2
• Consider recent viral illness in the differential diagnosis when evaluating chest pain, as post-viral cardiac complications are underreported. 4, 7

Disposition and Management

• If ECG shows ST elevation, new ischemic changes, or signs of tamponade, arrange immediate transfer by EMS to the emergency department. 2, 8
• If initial workup suggests myocarditis or pericarditis without hemodynamic compromise, admit for monitoring, serial troponins, and echocardiography. 5, 4
• For confirmed pericarditis, treatment includes NSAIDs and colchicine; steroids may be needed for refractory cases. 4, 7
• If all cardiac causes are excluded and symptoms persist, consider musculoskeletal causes (costochondritis) or gastroesophageal reflux, but only after thorough cardiac evaluation. 3, 2