Hemodynamic mechanisms
Systolic murmurs always coincide with the ventricular contraction phase. Depending on the direction of blood flow, there are two main mechanisms of sound formation:
- Natural pathway (ejection murmurs): blood forcibly overcomes a narrowing in the outflow tracts. This is typical for aortic stenosis or pulmonary stenosis.
- Alternative pathway (regurgitant murmurs): blood flows in the reverse direction due to incomplete closure of the atrioventricular valve leaflets. It occurs in mitral or tricuspid regurgitation, ultimately leading to volume overload of the respective atria.
Ejection murmurs (mesosystolic)
Such murmurs have a crescendo-decrescendo (crescendo-decrescendo) pattern. Loudness peaks in mid-systole. A critical diagnostic sign is the presence of a pause between the end of the murmur and the second heart sound.
By etiology, they are divided into physiological (in hyperdynamic circulation: anemia, fever, pregnancy, thyrotoxicosis), functional (accelerated flow through normal valves), and pathological.
Clinical variants of pathological ejection murmurs:
- Aortic stenosis (Stenosis ostii aortae): a harsh murmur best heard in the second right intercostal space. Radiates to the carotid arteries and along the left sternal border. Accompanied by a systolic thrill ("cat's purr"), an ejection click, and attenuation of the second heart sound. With decreased left ventricular contractility, the murmur may become softer and fainter.
- Pulmonary stenosis (Stenosis arteriae pulmonalis): acoustically similar to aortic stenosis, but heard in the second to third left intercostal spaces and radiates to the left shoulder.
- Hypertrophic cardiomyopathy (HCM): caused by powerful contraction of the hypertrophied myocardium and dynamic obstruction of the left ventricular outflow tract.
- Atrial septal defect (ASD): the murmur arises not from the defect itself (due to low pressure gradient), but from right-sided volume overload and relative pulmonary stenosis.
Pansystolic and late murmurs
Pansystolic (holosystolic) murmurs occupy the entire systole. They start with the first sound and continue up to the second sound without pauses. They are always a sign of pathology.
- Mitral regurgitation: a classic "blowing" murmur at the apex of the heart (apex cordis), radiating to the axilla (axilla). May be accompanied by a muffled first sound and the presence of a third heart sound.
- Tricuspid regurgitation: heard over the right ventricle at the lower sternal border. Unlike mitral valve disease, it does not radiate to the axilla and intensifies on inspiration.
- Ventricular septal defect (VSD): a loud, very harsh shunt murmur at the left sternal border, accompanied by a palpable thrill.
Late systolic murmurs occur in the second half of systole. A typical example is mitral valve prolapse, where elongated chordae tendineae allow the leaflets to prolapse into the atrium. Auscultatatorily, this manifests as a systolic click followed by a late regurgitant murmur.
Functional tests
Physical maneuvers that alter hemodynamics are used to clarify the origin of the murmur:
- Respiratory maneuvers: inspiration increases venous return, intensifying right-sided murmurs (e.g., tricuspid regurgitation).
- Isometric exercise (handgrip): increases peripheral vascular resistance. This intensifies the murmur of mitral regurgitation and VSD.
- Valsalva maneuver and standing: decrease venous return and ventricular filling. Specifically intensify the murmur in hypertrophic cardiomyopathy.
- Squatting: increases venous return and afterload, causing the murmur of HCM to soften.
Briefly: answers to topical questions
What are the main causes of mitral regurgitation?
Mitral regurgitation occurs when any element of the valve apparatus is damaged: leaflets, chordae, papillary muscles, fibrous ring, or left ventricular myocardium.
The main causes include:
- Leaflet involvement — rheumatic heart disease (most common cause) and mitral valve prolapse.
- Chordae involvement — rupture due to chest trauma or secondary to infective endocarditis.
- Papillary muscle involvement — coronary artery disease (muscle dysfunction) and myocardial infarction (risk of rupture).
- Changes in the fibrous ring and left ventricle — dilation (in Marfan syndrome, dilated cardiomyopathy) and calcification in the elderly.
How does the loudness of various systolic murmurs change during the Valsalva maneuver?
The Valsalva maneuver decreases venous return and ventricular filling, leading to changes in murmur loudness.
- The murmur intensifies in obstructive hypertrophic cardiomyopathy (subaortic stenosis) due to decreased ventricular filling and increased outflow tract obstruction.
- Murmurs in valvular aortic stenosis and mitral regurgitation soften due to reduced blood flow.
What types of systolic murmurs are distinguished by their shape on a phonocardiogram?
The following shapes of systolic murmurs are described on a phonocardiogram:
- Spindle-shaped (diamond-shaped), or crescendo-decrescendo, — characteristic of mesosystolic ejection murmurs, such as in aortic stenosis and hypertrophic cardiomyopathy.
- Holosystolic (pansystolic, plateau-shaped) — characteristic of mitral regurgitation.
- In tricuspid regurgitation, the pansystolic murmur occupies the entire systole and has a ribbon-like shape.
- In ventricular septal defect, a high-amplitude pansystolic murmur is described, occupying the entire space between the first and second heart sounds.
For differential diagnosis of HCM: maneuvers that decrease cardiac blood volume (Valsalva maneuver, standing) paradoxically intensify this murmur, while squatting (increased preload) softens it.
Class and exam questions
How to distinguish a mesosystolic ejection murmur from a pansystolic murmur?
The key difference is the relationship to the second heart sound. In ejection murmurs, there is always a short pause before the second sound occurs. Pansystolic murmurs continuously merge with the second sound.
Why is a systolic murmur heard in an atrial septal defect (ASD)?
The murmur arises not from blood flow through the defect itself, but from right heart chamber overload. The excess volume creates relative pulmonary stenosis during blood ejection.
Is a systolic murmur at the apex specific only for mitral regurgitation?
No. Modern evidence shows that a systolic murmur at the apex can also occur in pure mitral stenosis, which was previously mistakenly considered concomitant regurgitation.
What else to study on this topic
- Features of phonocardiography in various heart defects
- Differential diagnosis of physiological and functional murmurs
- Auscultatory syndrome in mitral valve prolapse
- Impact of heart failure on valve murmur characteristics
- Evaluation of systolic thrills ("cat's purr")
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