What is the most supportive finding for the diagnosis in a patient with new-onset exertional dyspnea and palpitations, who had a viral upper respiratory infection a few weeks ago, and presents with tachycardia, tachypnea, and a gallop heart sound?

Gallop Heart Sound (S3) is the Most Supportive Diagnostic Finding

The gallop heart sound (S3) is the most supportive finding for diagnosing acute heart failure, likely representing viral myocarditis with left ventricular dysfunction, in this clinical scenario. 1

Diagnostic Superiority of S3 Gallop

The S3 gallop has the highest positive likelihood ratio (11; 95% CI, 4.9-25.0) for diagnosing heart failure among all physical examination findings, making it far more specific than tachycardia, tachypnea, or the viral history alone. 1 This means an S3 gallop increases the probability of heart failure 11-fold compared to baseline, representing the strongest objective physical finding available at the bedside. 1

The S3 gallop reflects rapid ventricular filling into a dysfunctional ventricle and is a pathologic finding in adults that indicates myocardial disease. 2 In the context of new-onset exertional dyspnea following a recent viral upper respiratory infection, the S3 strongly suggests acute myocarditis with left ventricular dysfunction. 2

Why Other Findings Are Less Supportive

Tachycardia (Option A)

• Tachycardia is a nonspecific compensatory response that occurs in numerous conditions including anxiety, fever, dehydration, anemia, hyperthyroidism, and pulmonary embolism. 1
• It occurs in >90% of patients with pulmonary embolism, making it highly sensitive but not specific. 2
• While present in heart failure, it provides minimal diagnostic discrimination. 1

Tachypnea (Option B)

• Tachypnea is similarly nonspecific and occurs in both cardiac and pulmonary conditions including pneumonia, pulmonary embolism, anxiety, and metabolic acidosis. 1
• It does not distinguish between cardiac and non-cardiac causes of dyspnea. 1

Viral History (Option C)

• Viral infection is an important etiologic clue for myocarditis, but it is not a diagnostic finding per se, and many patients have viral upper respiratory infections without developing myocarditis, making this history sensitive but not specific. 1
• The history provides context but lacks the diagnostic specificity of objective physical findings. 1

Clinical Significance in This Scenario

The S3 gallop was identified as one of the strongest independent predictors of life-threatening cardiac complications in the Original Cardiac Risk Index, with the most robust association with perioperative major adverse cardiac events. 1 In chronic aortic regurgitation studies, the S3 gallop consistently reflected left ventricular dysfunction rather than severity of the underlying lesion, confirming its role as a marker of myocardial decompensation. 3

The S3 gallop reflects left ventricular dysfunction with elevated filling pressures, not just increased flow or volume. 1 This distinguishes it from physiologic third heart sounds that may occur in high-output states. 4

Recommended Next Steps

• Obtain troponin and BNP/NT-proBNP levels to assess for myocardial injury and ventricular dysfunction in suspected myocarditis. 2
• Perform transthoracic echocardiography to evaluate for regional or global ventricular systolic dysfunction, which supports the diagnosis when combined with the S3 gallop. 2
• Obtain 12-lead ECG to look for ST-segment changes, T-wave abnormalities, or conduction abnormalities associated with myocarditis. 2
• Consider cardiac MRI >10 days from symptom onset if diagnosis remains uncertain, as it can identify myocardial edema, myocardial injury, and pericardial involvement. 2

Critical Pitfall to Avoid

Do not attribute all symptoms to the viral illness alone when a gallop sound is present, as this indicates cardiac involvement requiring specific evaluation. 2 The presence of an S3 gallop transforms a nonspecific presentation into one requiring urgent cardiac workup and potential advanced therapies. 1, 2