What are the different types of heart murmurs and how are they classified?

Classification of Heart Murmurs

Heart murmurs are classified primarily by their timing in the cardiac cycle (systolic, diastolic, or continuous), with systolic murmurs further subdivided into holosystolic, midsystolic, early systolic, and late systolic types based on their onset, duration, and configuration. 1

Primary Classification Framework

Heart murmurs are produced by three main mechanisms 1:

• High blood flow rate through normal or abnormal orifices
• Forward flow through a narrowed or irregular orifice into a dilated vessel or chamber
• Backward or regurgitant flow through an incompetent valve

Systolic Murmurs

Holosystolic (Pansystolic) Murmurs

These murmurs span the entire systolic period from S1 to S2 and virtually always indicate pathological conditions requiring echocardiographic evaluation. 1, 2

• Generated when blood flows between chambers with widely different pressures throughout systole (left ventricle to left atrium or right ventricle) 1
• The pressure gradient begins early in contraction and persists until relaxation is nearly complete 1
• Three primary causes: mitral regurgitation, tricuspid regurgitation, and ventricular septal defect 2
• Plateau-shaped configuration distinguishes them from other systolic murmurs 2

Midsystolic (Systolic Ejection) Murmurs

These are the most common murmurs in clinical practice and frequently represent benign flow states, though they can indicate valvular stenosis. 1

• Typically crescendo-decrescendo (diamond-shaped) configuration 1
• Begin shortly after S1 when ventricular pressure opens the semilunar valve 1
• Most innocent murmurs in children and young adults are midsystolic, originating from aortic or pulmonic outflow tracts 1
• Can be caused by increased flow states (pregnancy, thyrotoxicosis, anemia, arteriovenous fistula) in the presence of normal valves 1
• Echocardiography is often necessary to distinguish a prominent grade 3 benign midsystolic murmur from valvular aortic stenosis 1

Early Systolic Murmurs

These less common murmurs begin with S1 and end in midsystole. 1, 2

• Often due to tricuspid regurgitation without pulmonary hypertension 1, 2
• Also occur in acute mitral regurgitation 1
• In large ventricular septal defects with pulmonary hypertension, pressure equalization at end-systole eliminates the shunt, limiting the murmur to early systole 1, 2

Late Systolic Murmurs

These murmurs start well after ejection begins and end before or at S2, classically associated with mitral valve prolapse. 1, 2

• Soft to moderately loud, high-pitched at the left ventricular apex 1
• Often due to apical tethering and malcoaptation of mitral leaflets from anatomic and functional changes 1
• In mitral valve prolapse, preceded by a midsystolic click 3
• Can occur with or without clicks 1

Diastolic Murmurs

Diastolic murmurs virtually always represent pathological conditions and require further cardiac evaluation with echocardiography. 1

Early Diastolic Murmurs

• Begin with or shortly after S2 when ventricular pressure drops below aortic or pulmonary artery pressure 1, 2
• High-pitched and decrescendo in character 2
• Indicate aortic regurgitation or pulmonic regurgitation 2

Middiastolic Murmurs

• Occur during early ventricular filling due to disproportion between valve orifice size and diastolic blood flow volume 2
• Usually originate from mitral and tricuspid valves 2
• Mitral stenosis produces a low-pitched, rumbling, apical diastolic murmur best heard with the bell of the stethoscope 2

Presystolic Murmurs

• Begin during ventricular filling that follows atrial contraction 2
• Evaluated for mitral or tricuspid stenosis 2

Continuous Murmurs

Most continuous murmurs require further evaluation, with two important exceptions. 1

• Innocent continuous murmurs: venous hums and mammary souffles 1
• All other continuous murmurs warrant cardiac evaluation 1

Dynamic Auscultation for Differentiation

Respiratory Maneuvers

• Right-sided murmurs increase with inspiration due to increased venous return 1, 2
• Left-sided murmurs are louder during expiration 1, 2

Valsalva Maneuver

• Most murmurs decrease in length and intensity 1
• Two critical exceptions: hypertrophic cardiomyopathy (becomes much louder) and mitral valve prolapse (becomes longer and often louder) 1, 2
• After release, right-sided murmurs return to baseline earlier than left-sided murmurs 1

Positional Changes

• Standing: most murmurs diminish except hypertrophic cardiomyopathy (louder) and mitral valve prolapse (lengthens and intensifies) 1, 2
• Squatting: most murmurs become louder, but hypertrophic cardiomyopathy and mitral valve prolapse usually soften and may disappear 1, 2
• In mitral valve prolapse specifically: standing shifts the click-murmur complex earlier (closer to S1), while squatting shifts it later (closer to S2) 3

Post-Premature Beat or Atrial Fibrillation

• Murmurs from normal or stenotic semilunar valves increase in intensity after a ventricular premature beat or during long cycle lengths in atrial fibrillation 1
• Systolic murmurs from atrioventricular valve regurgitation do not change, diminish, or become shorter 1

Assessment Characteristics

Traditional auscultation assessment includes 1:

• Timing in the cardiac cycle (systolic, diastolic, continuous)
• Configuration (crescendo, decrescendo, crescendo-decrescendo/diamond-shaped, plateau)
• Location and radiation
• Pitch (high, medium, low)
• Intensity (graded 1 through 6)
• Duration

Critical Clinical Pitfalls

• Most systolic heart murmurs do not signify cardiac disease and many relate to physiological increases in blood flow velocity 1
• Diastolic murmurs are the exception—they almost always indicate pathology 1
• The murmur may be inaudible in patients with low cardiac output, obesity, chest-wall deformities, or emphysema despite hemodynamically significant disease 2
• Echocardiography is the gold standard for confirming the cause of murmurs and should be performed in all patients with pansystolic murmurs of unknown cause, all diastolic murmurs, and when clinical uncertainty exists 1, 2