Cardiac murmur is the abnormal or unusual heart sound. It is also called abnormal heart sound or cardiac bruit.
The "murmur" is the sound of blood flowing. It may be passing through a problem heart valve, for instance.
Cause of Murmur-
Cardiac murmur is produced because of change in the pattern of blood flow. Normally, blood flows
in streamline through the heart and blood vessels. During abnormal conditions like valvular diseases, the blood flow becomes turbulent. It produces the cardiac murmur. Murmur is produced because of valvular diseases, septal defects and vascular defects.
Valvular Diseases Valvular diseases are of two types
- Stenosis -Stenosis means narrowing of heart valve. Blood flows rapidly with turbulence through the narrow orifice of the valve, resulting in murmur.
- Incompetence-Incompetence refers to weakening of the heart valve. When the valve becomes weak, it cannot close properly. It causes back flow of blood, resulting in turbulence. This disease is also called regurgitation or valvular insufficiency.
Classification of Murmur- Three types-
- Systolic murmur
- Diastolic murmur
- Continuous murmur.
A. Systolic murmur –
- Incompetence of Atrioventricular Valves- It causes regurgitation of blood from ventricles to the atria during ventricular systole, producing the murmur. It is a harsh blowing sound with high frequency.
- Coarctation of Aorta- Coarctation of aorta is a congenital disorder, characterized by the narrowing of a part of systemic aorta
- Stenosis of Semilunar Valves- During stenosis of aortic valve, the left ventricular pressure raises up to 300 mm Hg during systole. It causes a greater turbulence in the blood flow. The vibrations of this sound can be felt as ‘thrills’ by palpation over lower neck region and upper chest.
- Septal Defect- During interventricular septal defect, blood flows from left ventricle to right ventricle during systole. It produces a systolic murmur.
- Murmur due to Anaemia- A systolic murmur is heard in severe anemia because of reduced viscosity and accelerated flow of blood.
B. Diastolic murmur-
Diastolic murmur is the murmur that is produced during diastole.
- Incompetence of Semilunar Valves- Murmur is produced during the regurgitation of blood from aorta into the ventricle, through incompetent semilunar valve during diastole. It is like a blowing sound with low frequency.
- Stenosis of Atrioventricular Valves- Murmur due to stenosis of tricuspid valve is heard best at tricuspid area. It is a weak sound with low frequency.
Sometimes, murmur due to mitral stenosis cannot be heard by stethoscope, due to low frequency. But it can be felt as a mild thrill over mitral area of the chest.
C. Continuous murmur-
Continuous murmur is the murmur that is heard in conditions such as patent ductus arteriosus.
Patent Ductus-Arteriosus Intact ductus arteriosus is called patent ductus arteriosus. A continuous murmur is heard in this condition. However, intensity of the sound is more during systole and less during diastole. Because of this, it is also called machinery murmur.