Mechanisms of intracardiac murmurs
The appearance of murmurs is associated with a disturbance of normal (laminar) hemodynamics. For a murmur to become audible, a combination of an anatomical obstacle and sufficient blood flow velocity is required. At low blood velocities, even severe valve lesions can be silent (so-called "silent" valve diseases).
Main anatomical causes of turbulence:
- Stenosis (narrowing): valve leaflets fuse, preventing the orifice from opening fully. Blood forcefully passes through the narrow segment.
- Valve regurgitation (insufficiency): leaflets become deformed (shrunken) or the fibrous ring dilates. Upon closure, a gap remains through which blood flows backward—regurgitation. This gap acts as a functional narrowing.
- Shunts (abnormal communications): pathological openings in the interventricular or interatrial septum.
Classification of murmurs
Depending on the location of the source, there are intracardiac (endocardial) murmurs associated with septal and valvular defects, and extracardiac (extraventricular) murmurs. The latter include pericardial friction rubs and pleuropericardial murmurs.
Intracardiac murmurs are classified according to several qualitative characteristics:
- By cardiac cycle phase: systolic and diastolic.
- By timbre: blowing, sawing, rasping, musical (high-frequency).
- By shape (configuration): crescendo and decrescendo.
Topographic diagnostics and radiation
The point of maximum murmur loudness (punctum maximum) usually coincides with the auscultation site of the valve whose lesion caused the sound phenomenon.
Main auscultation points and characteristic valve defects:
- Apex of the heart (mitral valve): a systolic murmur indicates valve regurgitation, while a diastolic murmur indicates orifice stenosis. Radiates to the left (into the axillary region in regurgitation).
- Right 2nd intercostal space (aortic valve): a harsh systolic murmur is characteristic of aortic stenosis (transmitted to the neck vessels), and a diastolic murmur is characteristic of aortic regurgitation. An additional auscultation point for aortic regurgitation is Botkin-Erb's point (left 3rd intercostal space at the sternal border).
- Left 2nd intercostal space (pulmonary valve): murmurs are similar to aortic ones but reflect right-heart pathology.
- Base of the xiphoid process (tricuspid valve): murmurs are heard in tricuspid valve disease.
Murmur loudness scale
A 6-point system is used to objectively assess sound intensity:
- Grade 1: Very faint. Heard with difficulty, not in all positions.
- Grade 2: Faint, but constant. Heard immediately upon applying the stethoscope.
- Grade 3: Moderately loud. Palpable thrill of the chest wall is absent.
- Grade 4: Loud. Accompanied by a thrill ("cat's purr" / systolic or diastolic thrill).
- Grade 5: Very loud. Heard with partial stethoscope contact with the skin and over the entire precordial area.
- Grade 6: Extremely loud. Heard at a distance (without skin contact) or from other parts of the body (e.g., the shoulder).
Briefly: answers to topical questions
What types of extracardiac murmurs exist?
Sources classify extracardiac murmurs as:
- Pericardial friction rub — associated with alterations of the pericardial layers.
- Pleuropericardial murmurs — associated with the involvement of the pleura in contact with the heart.
- Cardiopulmonary murmur — listed among extracardiac murmurs.
What types of murmurs (systolic or diastolic) are characteristic of tricuspid regurgitation and stenosis?
The phase of the auscultated murmur in tricuspid valve disease depends on the hemodynamic variant of the defect.
| Type of defect | Cardiac cycle phase | Murmur characteristics |
|---|---|---|
| Right atrioventricular orifice stenosis | Diastolic | Protodiastolic (accentuated at the beginning of diastole) and presystolic (accentuated before systole) |
| Tricuspid regurgitation | Systolic | Maximum auscultation point is in the 5th intercostal space to the left of the sternum |
The main rule of radiation: "Where the blood flows, the murmur goes." In aortic stenosis, blood is ejected upward—the murmur is transmitted to the neck. In mitral regurgitation, blood flows back into the atrium—the murmur is transmitted to the axilla.
Class and exam questions
Why might a murmur be inaudible despite severe valve disease?
Murmur loudness directly depends on blood flow velocity. If blood flow velocity is low (e.g., in severe heart failure), turbulence is insufficient to generate sound waves. This is termed a "silent" valve defect.
What does the term "cat's purr" mean?
This is a palpable sensation of chest wall vibration (thrill) that occurs with loud intracardiac murmurs graded 4 and above.
What is the functional difference between valve regurgitation and stenosis?
In stenosis, blood has difficulty passing through a narrowed, fused orifice. In regurgitation, the valve does not close completely, leaving a gap through which blood flows backward (regurgitation). This gap also functions as a narrowed space, creating eddies.
What is the Botkin-Erb point for?
This is an additional auscultation point for the aortic valve, located in the 3rd intercostal space to the left of the sternum. The diastolic murmur of aortic regurgitation is best heard here, as the sound is well transmitted along the current of blood returning to the ventricle.
What else to study on this topic
- Mechanism of the pericardial friction rub
- Differences between pleuropericardial and intracardiac murmurs
- Hemodynamics in ventricular septal defect
- Characteristics of auscultating musical murmurs
- Detailed features of murmur shapes (crescendo and decrescendo)
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