The Significance of a Third Heart Sound During Blood Pressure Check
A third heart sound (S3) during blood pressure check is a significant clinical finding that often indicates left ventricular dysfunction and may represent heart failure, particularly when accompanied by other signs of cardiac compromise. 1, 2
Understanding the Third Heart Sound
- The third heart sound occurs in early diastole and is caused by the abrupt deceleration of left ventricular inflow, increased left ventricular filling pressures, and decreased left ventricular compliance 2
- S3 is typically heard as a low-frequency "lub-dub-dub" sound, with the third sound following shortly after the second heart sound 1
- During blood pressure measurement using the auscultatory method, the third heart sound may be detected when listening for Korotkoff sounds 1
- The third heart sound is best appreciated at the apex of the heart with the patient in the left lateral decubitus position 1
Clinical Significance of S3
- In adults, a third heart sound is often pathological and associated with heart failure, indicating critically deteriorated hemodynamics 3, 4
- S3 is strongly associated with left ventricular dysfunction, with studies showing significantly lower ejection fraction in patients with S3 compared to those without (particularly in aortic stenosis patients) 5
- The presence of S3 is independently associated with adverse outcomes in heart failure patients, including increased risk of hospitalization and death from pump failure 4
- S3 correlates with elevated E/E' ratio (ratio of early mitral inflow velocity to diastolic velocity of the mitral annulus), which is a marker of elevated left ventricular filling pressures 2
Exceptions and Normal Variants
- In normal pregnancy, third heart sounds are present in most patients and do not necessarily indicate pathology 1
- In young, healthy individuals (especially athletes), S3 may be a normal finding and not indicative of heart disease 1
- In patients with mitral regurgitation, S3 is common (present in 46% of cases) and does not necessarily reflect left ventricular systolic dysfunction or increased filling pressure 5
Diagnostic Approach When S3 is Detected
- When a third heart sound is detected during blood pressure measurement, a complete cardiovascular assessment is warranted 1
- Echocardiography is indicated to assess left ventricular function, chamber dimensions, and valvular function 1
- Additional evaluation should include assessment for other signs of heart failure, including:
Pitfalls in S3 Detection
- There is significant interobserver variability in detecting S3, with agreement between pairs of observers varying between 48% and 73% 7
- The kappa statistic for interobserver agreement on S3 detection ranges from slight (0.10-0.30) to moderate (0.40-0.50) at best 7
- During blood pressure measurement, S3 may be confused with Korotkoff sounds, particularly phase II and III sounds, which become softer and longer, then crisper and louder 1
- The auscultatory gap phenomenon (where Korotkoff sounds become inaudible between systolic and diastolic pressure) may complicate the detection of heart sounds during blood pressure measurement 1
Clinical Implications and Management
- When S3 is detected in a non-pregnant adult during blood pressure check, further cardiac evaluation is warranted, particularly if accompanied by other signs of heart failure 1, 4
- The presence of S3 in patients with heart failure is associated with more severe disease and worse prognosis 4
- In patients with aortic stenosis, S3 is uncommon (11% prevalence) but usually indicates systolic dysfunction and elevated filling pressure 5
- Treatment should be directed at the underlying cause, with heart failure therapy including diuretics, ACE inhibitors, and other appropriate medications based on the specific diagnosis 6