What is the differential diagnosis for S3 and S4 heart gallops?

Differential Diagnosis of S3 and S4 Heart Gallops

S3 Gallop (Third Heart Sound)

An S3 gallop is a reliable indicator of cardiac decompensation and left ventricular dysfunction, occurring during rapid ventricular filling in mid-diastole. 1, 2

Primary Causes of S3

Heart Failure with Reduced Ejection Fraction:

• Most common cause in adults, indicating elevated left ventricular filling pressures and volume overload 1, 2
• Associated with systolic dysfunction and depressed contractile state 3, 4
• Sensitivity for detecting elevated LVEDP is only 41%, but specificity reaches 92% 4

Acute Myocardial Infarction:

• Part of Killip Stage II classification, indicating heart failure complicating MI 1
• Accompanied by pulmonary rales and pulmonary venous hypertension 1

Valvular Heart Disease:

• Chronic aortic regurgitation: S3 reflects left ventricular dysfunction rather than severity of regurgitation itself 3
• Severe mitral regurgitation with volume overload 1

Cardiomyopathies:

• Dilated cardiomyopathy with ventricular dilation and reduced ejection fraction 1, 5
• Restrictive cardiomyopathy (though less common than S4 in this condition) 1

Right Ventricular Failure:

• S3 heard over tricuspid area (left lower sternal border) indicates right ventricular dysfunction 6
• Associated with pulmonary hypertension, chronic thromboembolic disease 1, 6
• Accompanied by jugular venous distension, hepatomegaly, peripheral edema 1

Physiologic S3 (Normal Variant):

• Young healthy individuals with hyperdynamic circulation 2
• Rapid early filling velocity without underlying cardiac disease 2
• Critical distinction: disappears with age and is never pathologic in children/young adults 2

Location Matters for S3

• Mitral area (apex): Left ventricular dysfunction 6
• Tricuspid area (left lower sternal border/xiphoid): Right ventricular dysfunction 6, 5

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S4 Gallop (Fourth Heart Sound)

An S4 occurs during late diastole with atrial contraction and is most frequently associated with coronary heart disease and conditions causing decreased ventricular compliance. 5, 2

Primary Causes of S4

Coronary Artery Disease:

• Most common cause, constant finding in patients with ischemic heart disease 5
• Does NOT indicate heart failure, unlike S3 5

Hypertensive Heart Disease:

• Constant finding in patients with hypertension 5
• Associated with left ventricular hypertrophy and diastolic dysfunction 2

Left Ventricular Hypertrophy (any cause):

• Aortic stenosis with concentric hypertrophy 1
• Hypertrophic cardiomyopathy 1
• Chronic hypertension 2, 5

Acute Myocardial Ischemia/Infarction:

• Reflects decreased ventricular compliance 1
• May occur with or without S3 5

Restrictive Cardiomyopathy:

• Infiltrative diseases (amyloidosis, sarcoidosis) 1
• Impaired ventricular relaxation requiring forceful atrial contraction 1

Diastolic Dysfunction (HFpEF):

• Heart failure with preserved ejection fraction 1, 2
• Elevated filling pressures despite normal systolic function 1

Key Clinical Distinction

S4 does NOT independently predict heart failure or indicate cardiac decompensation, unlike S3 2, 5

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Summation Gallop

When both S3 and S4 occur simultaneously or in close proximity, a summation gallop results, often louder than either S1 or S2. 5

Causes:

• Severe cardiac decompensation with tachycardia 5
• Dilated cardiomyopathy with both systolic and diastolic dysfunction 5
• Advanced coronary heart disease 5
• Hypertensive heart disease with decompensation 5

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Critical Diagnostic Pitfalls

Detection Challenges:

• S3 and S4 may be missed in patients with emphysematous chest or increased anteroposterior diameter if listening only over standard precordial areas 5
• Solution: Listen over xiphoid or epigastric area where gallops are often more easily detected 5

Distinguishing S4 from Other Sounds:

• S4 disappears with firm pressure on stethoscope, while ejection sounds and split S1 do not 5
• Use "inching" technique: move stethoscope from aortic area to apex while keeping S2 as reference 5

Body Habitus Considerations:

• Obesity significantly reduces sensitivity of auscultation for S3 7
• Acoustic cardiography improves detection in obese patients 7

BNP "Gray Zone" (100-499 pg/mL):

• S3 detection increases diagnostic accuracy for acute heart failure from 47% to 69% 7
• Low BNP does not exclude HFpEF, especially in obese patients 8

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Recommended Diagnostic Workup

For Any Patient with S3 or S4:

1. Echocardiography (first-line): Assess ventricular function, wall thickness, valvular disease, and diastolic parameters 2, 6
2. ECG: Evaluate for ischemia, hypertrophy, conduction abnormalities 1
3. BNP/NT-proBNP: Particularly useful when S3 present with BNP >100 pg/mL indicating likely heart failure 8
4. Chest X-ray: Assess for pulmonary congestion, cardiomegaly 1

For S3 Specifically:

• Cardiac catheterization if non-invasive methods don't provide definitive diagnosis 1
• Consider cardiac MRI for infiltrative processes or myocardial fibrosis 2

For S4 Specifically:

• Blood pressure monitoring and assessment for hypertensive target organ damage 2
• Stress testing if coronary disease suspected 5

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Prognostic Implications

S3 carries significant prognostic weight:

• Substantially increases perioperative risk during noncardiac surgery 2
• Independent predictor of death and readmission in heart failure 7
• In aortic regurgitation, signals need for cardiac catheterization and possible valve replacement 3

S4 has limited prognostic value:

• Does not independently predict heart failure development 2
• May resolve with improved blood pressure control 2