What is the significance and evaluation of heart sounds in cardiac assessment?

Heart Sounds in Cardiac Assessment

Fundamental Principles

Cardiac auscultation remains the most widely used screening method for valvular heart disease and structural cardiac abnormalities, with heart sounds produced by high blood flow through normal or abnormal orifices, forward flow through narrowed openings, or regurgitant flow through incompetent valves 1.

Normal Heart Sounds

• S1 (First Heart Sound): Marks the beginning of systole, produced by closure of mitral and tricuspid valves 1
• S2 (Second Heart Sound): Marks the end of systole, produced by closure of aortic and pulmonic valves; physiologic splitting during inspiration is normal 1
• S3 (Third Heart Sound): May be normal in young adults, pregnant women, and high-output states; pathologic when present in older adults with heart failure 2
• S4 (Fourth Heart Sound): Always pathologic in adults, indicates decreased ventricular compliance 3

Pathologic Heart Sounds

Diastolic murmurs virtually always represent pathological conditions and require immediate cardiac evaluation with echocardiography, as do most continuous murmurs except venous hums and mammary souffles 1.

Systematic Auscultation Approach

Murmur Characterization

Assess every murmur using these parameters 1:

• Timing: Systolic, diastolic, or continuous in the cardiac cycle
• Configuration: Crescendo, decrescendo, crescendo-decrescendo (diamond-shaped), or plateau
• Location: Where the murmur is loudest (aortic area, pulmonic area, tricuspid area, apex)
• Radiation: Where the sound travels (carotids, axilla, back)
• Pitch: High, medium, or low frequency
• Intensity: Graded 1-6, with grade 3 or greater requiring echocardiography 1
• Duration: Throughout systole (holosystolic), early, mid, or late

Dynamic Cardiac Auscultation

Dynamic maneuvers during auscultation enable accurate deduction of murmur origin and significance 1:

• Respiration: Right-sided murmurs increase with inspiration; left-sided murmurs louder during expiration 1
• Valsalva maneuver: Most murmurs decrease, except hypertrophic cardiomyopathy (becomes louder) and mitral valve prolapse (becomes longer and louder) 1
• Exercise/Handgrip: Murmurs from flow across stenotic valves become louder; mitral regurgitation, ventricular septal defect, and aortic regurgitation also increase 1
• Positional changes: Standing decreases most murmurs except hypertrophic cardiomyopathy and mitral valve prolapse; squatting increases most murmurs but softens hypertrophic cardiomyopathy and mitral valve prolapse 1

Clinical Integration with Physical Findings

Associated Cardiac Findings

The presence of specific physical findings provides critical diagnostic clues 1:

• Fixed splitting of S2: Suggests atrial septal defect when combined with midsystolic murmur 1
• Soft or absent A2 or reversed splitting of S2: Indicates severe aortic stenosis 1
• Early systolic ejection sound: Suggests bicuspid aortic valve if heard during both inspiration and expiration 1
• Pulsus parvus et tardus (slow-rising, diminished arterial pulse): Indicates severe aortic stenosis, though may be absent in elderly due to vascular aging 1
• LV dilatation on palpation with bibasilar rales: Favors severe chronic mitral regurgitation 1

Noncardiac Findings

Systemic findings guide diagnosis 1, 4:

• Fever, petechiae, Osler's nodes, Janeway lesions: Suggest infective endocarditis in patient with new murmur 1, 4
• Recent trauma with new murmur: Mandates immediate echocardiography for traumatic valvular injury 5

Indications for Echocardiography

Echocardiography is the definitive diagnostic test following auscultation and should be performed for 1:

• Any diastolic murmur (except innocent continuous murmurs) 1
• Any continuous murmur not due to venous hum or mammary souffle 1
• Holosystolic or late systolic murmurs at apex or left sternal edge 1
• Midsystolic murmurs grade 3 or greater intensity 1
• Softer systolic murmurs when dynamic auscultation suggests definite pathology 1
• Any symptomatic patient with a murmur, regardless of grade 4, 5
• New murmur after trauma 5
• New murmur with chest discomfort (requires urgent same-day echocardiography) 4

Emergency and Critical Care Applications

Focused Cardiac Ultrasound Protocols

Basic focused echocardiography can be performed by non-cardiologists after minimal training (12-hour course) to identify life-threatening cardiac pathology 1:

• FEEL (Focused Echocardiography in Emergency Life Support): Identifies true asystole, tamponade, and catastrophic states during resuscitation 1
• FATE (Focused Assessed Transthoracic Echocardiography): Assesses cardiac pathology, ventricular function, and volume status in critically ill patients 1
• FAST (Focused Assessment with Sonography for Trauma): Detects hemopericardium in trauma patients 1

Bedside Cardiac Ultrasound in ICU

Strong recommendations exist for bedside cardiac ultrasound in critical care 1:

• Assess preload responsiveness in mechanically ventilated patients (Class 1B recommendation) 1
• Evaluate left ventricular systolic (1C) and diastolic (2C) function 1
• Identify acute cor pulmonale (1C), pulmonary hypertension (1B), and symptomatic pulmonary embolism (1C) 1
• Detect pericardial effusion (1C) and cardiac tamponade (1B) 1
• Guide cardiopulmonary resuscitation decisions (1B-2C depending on rhythm) 1

Common Pitfalls and Caveats

Critical Errors to Avoid

• Never dismiss an ejection systolic murmur as "innocent" in a symptomatic patient—presence of symptoms fundamentally changes diagnostic urgency 4
• Never delay echocardiography to obtain chest X-ray or other tests when a symptomatic murmur is present 4
• Never assume a soft murmur is benign in elderly patients—the typical parvus et tardus pulse may be absent in severe aortic stenosis due to vascular aging 1
• Never attribute all murmurs in pregnancy to physiologic changes—diastolic murmurs are always pathologic even in pregnancy 2

Special Populations

Pregnancy 2:

• Grade 1-2 midsystolic murmurs at mid-to-upper left sternal edge are normal
• Louder S1 with prominent splitting, S3, and continuous murmurs (venous hum, mammary souffle) are physiologic
• Any diastolic murmur requires evaluation despite pregnancy

Elderly patients 1:

• Aortic sclerosis is common and may produce murmurs without significant stenosis
• Vascular changes may mask typical pulse findings in severe aortic stenosis
• Lower threshold for echocardiography given higher prevalence of significant disease

Advanced Diagnostic Technologies

Acoustic cardiography synchronizes cardiac auscultation with ECG recording, providing comprehensive assessment of both mechanical and electronic cardiac function beyond traditional auscultation 6. This technology generates parameters correlating with gold standards in heart failure diagnosis and ischemic heart disease detection 6.

Phonocardiography with digital signal processing techniques improves diagnostic efficiency and accuracy by converting heart sounds into electrical signals and analyzing the four cardiac sounds (S1, S2, S3, S4) using spectro-temporal analysis 3, 7.