Extracardiac murmurs and functional murmurs

Functional murmurs: mechanisms and criteria

Unlike organic lesions, which are caused by anatomical defects of the valves themselves, functional murmurs occur with an intact valve apparatus.

The main cause of their appearance is an acceleration of blood flow, which is often observed against the background of reduced blood viscosity (e.g., in severe anemia). Due to turbulent eddies inside the heart, the intracardiac structures — chordae tendineae and papillary muscles — begin to vibrate, creating a sound phenomenon even in the absence of actual narrowing (stenosis).

Key diagnostic criteria for functional murmurs:

• Variability (lability): sound loudness strongly depends on the patient's body position and phases of respiration.
• Soft character: they are usually soft (grades 2–3) and are never harsh or rasping.
• Patient cohort: very often detected in completely healthy children and young adults.
• Lack of association with valvular disease: the valve apparatus remains undamaged.

In the vast majority of cases, such murmurs are auscultated during systole. Diastolic functional murmurs are extremely rare (one example is auscultation in the second intercostal space to the left in patients with renal failure against the background of severe anemia).

Extra-cardiac phenomena: pericardial friction rub

A pericardial friction rub indicates pathology of the serous layers of the pericardium, most commonly of an inflammatory nature (acute or constrictive pericarditis).

Classically, this sound phenomenon is triphasic, meaning it coincides with three phases of cardiac motion: atrial systole, ventricular systole, and ventricular diastole. However, the auscultatory pattern is highly variable. Physicians more often hear only two ventricular components, and sometimes only a single systolic one.

Characteristic features of a pericardial friction rub:

• Localization: auscultated over the sternum or along its left border, predominantly in the zone of absolute cardiac dullness.
• Radiation: the murmur is strictly localized. As soon as the stethoscope moves away from the sternum, the sound intensity drops sharply (it radiates poorly to other points).
• Dependence on loudness: a loud, rasping sound can be heard in any posture. A weak (quiet, soft, scratching) one requires special conditions for detection: the patient needs to be placed in an upright position, asked to lean the torso forward, and the stethoscope bell/diaphragm pressed more firmly against the chest wall.

Systolic-diastolic (continuous) murmurs

Continuous murmurs are heard for a prolonged duration: they sound both in systole and diastole, without interruption between the phases of the cardiac cycle.

Their main causes are the presence of an arteriovenous fistula or patent ductus arteriosus (Botallo's duct). In patent ductus arteriosus, the zone of maximum intensity (punctum maximum) is located in the second intercostal space to the left of the sternum. Upon palpation in the same area, a chest wall thrill described as a 'cat's purr' can often be felt.

Effect of dynamic tests on auscultation

For the differential diagnosis of organic and functional phenomena, tests that alter hemodynamics are used:

1. Deep inspiration test: increases venous return to the right side of the heart. As a result, all murmurs generated in the right half of the heart intensify (splitting of the second heart sound is often detected).
2. Valsalva maneuver (straining against a closed glottis): increases intrathoracic pressure, lowering blood pressure and venous return. This helps distinguish hypertrophic obstructive cardiomyopathy (its murmur intensifies due to a drop in ventricular filling and increased obstruction) from valvular aortic stenosis and mitral regurgitation (their murmurs diminish).
3. Orthostatic test (rapid transition to a standing position): decreases venous return, leading to a weakening of murmurs of aortic and pulmonary trunk stenosis.
4. Nitroglycerin test: causes vasodilation and a drop in blood pressure, which compensatorily increases cardiac output. This leads to an intensification of ejection murmurs (characteristic of aortic stenosis and obstructive cardiomyopathy).

Special auscultation positions and multiple valve lesions

Special positions are used to bring certain heart structures closer to the chest wall. For example, the left lateral decubitus position shifts the left ventricle forward. In this posture, using the stethoscope bell (without the diaphragm, to capture low frequencies) is best for searching for mitral valve pathology, including the diastolic murmur of mitral stenosis, as well as the third and fourth heart sounds. Leaning the torso forward on a full exhalation with breath-holding is used when searching for aortic valve pathologies (auscultated with a diaphragmatic stethoscope).

The situation becomes more complex with multiple lesions (combined lesions of different valves or combined lesion of a single valve). Identification is hindered by an abundance of sounds. Thus, the 'double murmur' phenomenon (systolic and diastolic) over a single orifice most often indicates stenosis and regurgitation. However, it is important to remember that the second murmur in such a combination is not always organic and may well turn out to be functional.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Methodology and algorithm for sequential cardiac auscultation
• Assessment of the first and second heart sounds: intensity and splitting
• Detection and interpretation of additional heart sounds (third and fourth)
• Palpatory detection of a thrill («cat's purr») in valvular heart disease
• Combined and mixed heart defects: differential diagnosis

Other topics in the "Cardiovascular system" section

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