Gallop Heart Sound is Most Supportive of Myocarditis
The gallop heart sound (S3) is the most supportive finding for the diagnosis of acute myocarditis in this clinical scenario, as it specifically indicates ventricular dysfunction and myocardial injury rather than simply reflecting the physiologic response to illness. 1
Why the Gallop Sound is Most Specific
The presence of an S3 gallop in the context of new-onset exertional dyspnea following a recent viral upper respiratory infection strongly suggests acute myocarditis with left ventricular dysfunction. 1
- An S3 gallop reflects rapid ventricular filling into a dysfunctional ventricle and is a pathologic finding in adults that indicates myocardial disease. 1
- The 2020 JACC guidelines on COVID-19 myocarditis specifically identify S3 as a supportive finding for myocarditis diagnosis, along with fever, chest pain, and heart failure symptoms. 1
- The 2021 ACC/AHA chest pain guidelines note that myocarditis presents with fever, chest pain, heart failure, and S3 gallop. 1
Why Other Findings Are Less Specific
Tachycardia and tachypnea are nonspecific physiologic responses that occur with numerous conditions including infection, anxiety, dehydration, anemia, and pulmonary disease. 1
- Tachycardia occurs in >90% of patients with pulmonary embolism, making it highly sensitive but not specific. 1
- Sinus tachycardia requires investigation of reversible causes including infection, hyperthyroidism, dehydration, and anxiety before being considered pathologic. 2
- Both tachycardia and tachypnea are expected compensatory responses to any acute illness and do not localize the pathology to the myocardium. 1
The history of recent viral illness, while important for establishing temporal relationship, is also nonspecific as viral upper respiratory infections are extremely common and most do not lead to myocarditis. 1
Diagnostic Approach for Suspected Myocarditis
When a gallop sound is present in this clinical context, the following evaluation is indicated:
- Obtain troponin and BNP/NT-proBNP levels to assess for myocardial injury and ventricular dysfunction. 1, 3
- Perform transthoracic echocardiography to evaluate for regional or global ventricular systolic dysfunction, which supports the diagnosis when combined with the S3 gallop. 1, 3
- Obtain 12-lead ECG to look for ST-segment changes, T-wave abnormalities, or conduction abnormalities associated with myocarditis. 1, 2
- Consider cardiac MRI >10 days from symptom onset if diagnosis remains uncertain, as it can identify myocardial edema (elevated T2), myocardial injury (elevated native T1, ECV >30%, or late gadolinium enhancement), and pericardial involvement. 1
Critical Clinical Pitfalls
- Do not dismiss the gallop sound as simply reflecting tachycardia or volume overload without investigating for underlying myocardial dysfunction. 4
- Do not attribute all symptoms to the viral illness alone when a gallop sound is present, as this indicates cardiac involvement requiring specific evaluation. 1
- Avoid performing cardiac MRI during the acute febrile phase to reduce exposure risk to healthcare staff; wait >10 days from initial diagnosis. 1
- Recognize that examination may be completely normal in uncomplicated acute coronary syndrome, so the presence of positive findings like S3 gallop carries significant diagnostic weight. 1
Hemodynamic Significance of S3 Gallop
The S3 gallop in this patient indicates left ventricular dysfunction with elevated filling pressures. 1, 4
- Studies in aortic regurgitation demonstrate that S3 gallop reflects left ventricular dysfunction with increased residual volume and depressed contractile state, rather than simply reflecting volume overload. 4
- The S3 is coincident with the rapid filling wave and indicates impaired ventricular compliance or systolic dysfunction. 5
- Left ventricular gallop sounds commonly transmit to the right supraclavicular fossa, which can aid in detection during physical examination. 5