Functional murmurs and anatomy of the valvular apparatus
Functional murmurs in children have various origins and are fundamentally unrelated to organic lesions of the valvular apparatus. They are generally divided into four main groups depending on the mechanism of occurrence:
- Hemodynamic (dynamic) murmurs. They occur due to a hyperkinetic type of circulation when blood flow velocity increases. Causes may include fever, thyrotoxicosis, neuroses, as well as physical or emotional stress. Anemic murmur is distinguished separately: it is caused by the combined effect of reduced blood viscosity, tachycardia, and accelerated blood flow.
- Muscular-tonic murmurs. Their basis is a disturbance in the tone of the myocardium, papillary muscles, or blood vessels. Because of this, the cusps do not close completely, forming relative valve insufficiency (regurgitation). This is caused by myocardial dystrophy and autonomic dysfunction syndrome (ADS).
- Murmurs of heterochronia (growth-related disproportion). They are exclusively transient in nature. They occur due to the uneven development of structures: a mismatch between the sizes of the chambers and great vessels, and asynchronous growth of the cusps and chordae. This causes temporary valve dysfunction and a change in the resonance properties of the tissues.
- Murmurs in minor heart anomalies (MHA). They are auscultated against the background of completely normal hemodynamics and preserved myocardial contractility. The causes lie in the anatomy: the presence of false (additional) chordae, their atypical attachment, or anatomical features of the papillary muscles.
Extracardiac acoustic phenomena
During auscultation, it is important to differentiate intracardiac processes from murmurs arising in adjacent anatomical structures. Differential diagnosis is carried out with two main extracardiac murmurs:
- Pericardial friction rub. It has a very clear localization and never radiates to other areas. Its most characteristic sign is a noticeable increase in sound intensity when pressing the stethoscope chestpiece against the patient's chest wall.
- Pleuropericardial rub. It is auscultated strictly along the left border of relative cardiac dullness. It has a clear connection with the act of breathing: the sound is maximally amplified at the peak of inspiration and completely disappears during breath-holding (apnea).
Auscultation of great vessels and instrumental diagnostics
In physiological norm, two heart sounds are auscultated over the carotid and subclavian arteries. Only the 1st sound is inconsistently auscultated over the femoral artery. All other peripheral arteries normally remain "silent". Pathological vascular murmurs can be local (occurring during dilation or stenosis of the vessel itself) or conducted (representing the radiation of a murmur from the aorta or heart valves).
Instrumental diagnostics of the cardiovascular system is divided into two groups depending on the purpose of the study:
- Assessment of morphology (exact dimensions of chambers and vessels). Echocardiography (EchoCG), chest X-ray (which is mandatory in 3 projections), computed tomography and magnetic resonance imaging (CT and MRI), as well as angiography are used.
- Assessment of functional reserve. Stress tests with metered physical exertion are used.
Age-related ECG features in children
An ECG is a basic research method; however, its interpretation in children requires mandatory consideration of age-related evolutionary changes. The specifics of a pediatric ECG are determined by three main factors: the gradual change in the mass ratio of the right and left ventricles as the child grows older, the change in the anatomical position of the heart in the thoracic cavity, and the age dynamics of heart rate (HR).
The key differences between a healthy child's ECG and an adult's ECG are as follows:
- Shortening of time intervals and waves. This is a direct consequence of the higher conduction velocity of the electrical impulse through the myocardium and conduction system.
- High lability of parameters. The width of the waves and the duration of the intervals directly depend on the child's age and current heart rate.
- Presence of sinus respiratory arrhythmia. In childhood, this condition is considered exclusively as a variant of physiological norm.
To remember the difference between a pleuropericardial rub and a pericardial friction rub, use the "Breath and Pressure" rule: the former depends on breathing (disappears during apnea), while the latter depends on pressure (amplifies when pressed with a stethoscope).
Class and exam questions
Why does an anemic murmur occur?
It forms due to the combined effect of three factors at once: a decrease in blood viscosity, compensatory tachycardia, and an increase in blood flow velocity.
What are heterochronia murmurs?
These are transient acoustic phenomena caused by the uneven growth of heart structures. For example, when chamber sizes temporarily do not match the great vessels or chordae grow asynchronously with valve cusps.
Is sinus respiratory arrhythmia on an ECG considered a pathology in a child?
No, in childhood, the presence of sinus respiratory arrhythmia is considered an absolute variant of physiological norm.
What methods are used to assess heart morphology?
EchoCG, chest radiography (strictly in 3 projections), CT, MRI, and angiography are used to assess the size of chambers and vessels.
What else to study on this topic
- Mechanisms of formation of the hyperkinetic type of circulation
- Autonomic dysfunction syndrome and its effect on myocardial tone
- Minor heart anomalies (MHA): types and location of false chordae
- Conduction system of the heart and impulse conduction velocity
- Stress tests: criteria for assessing functional reserve
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