Cardiac murmurs are initially classified into systolic, diastolic and continuous. They can be timed in relation to the carotid pulse. A systolic murmur starts with or after the first heart sound and ends at or before the second heart sound. Clinically, systole can be timed with the onset of carotid pulse. Diastolic murmurs start with or after the second heart sound. By definition, a continuous murmur starts in systole, persists through the second heart sound, into the diastole. When the pressure gradient is high between the two chambers across which the murmur is generated is high, the murmur is high pitched.
Levine’s grading of murmurs: The initial grading was based on the intensity of the murmur alone. Later presence of thrill was added, with thrill being appreciated in murmurs of grade IV and above. Conventionally, grading is considered for systolic murmurs.
- Grade I: Faint murmur audible only on auscultation in a quiet room by an expert.
- Grade 2: Slight murmur
- Grade 3: Moderate intensity murmur
- Grade 4: Loud murmur
- Grade 5: Very loud murmur
- Grade 6: Loudest murmur. It is mentioned that grade 6 murmurs are audible with the stethoscope close to the chest without actual contact.
Systolic murmurs: A murmur which extends through out the systole is called pansystolic murmur (Also known as holosystolic murmur). Important pansystolic murmurs are those due mitral and tricuspid regurgitation and that of a ventricular septal defect. Mid systolic murmur starts a short period after the onset of systole. Typical mid systolic murmur is that of mitral valve prolapse. Late systolic murmur could also be there in mitral valve prolapse. Ejection systolic murmurs of pulmonary and aortic stenosis start a short while after the onset of systole (S1) and is preceded by the ejection click. They are crescendo-decrescendo murmurs or diamond shaped murmurs. The length of these murmurs are directly related to the severity of stenosis. In ventricular septal defect, a loud murmur usually indicates a small defect with large pressure gradient across the defect. In large ventricular septal defect, due to the large left to right shunt, pressure in the right ventricle increases (hyperdynamic pulmonary hypertension) so that pressure in the two ventricles are nearly equal. This results in a soft murmur.
Diastolic murmurs: Early diastolic murmur starts with the second heart sound. Typical early diastolic murmurs are those of aortic regurgitation and pulmonary regurgitation due to pulmonary hypertension (Graham steel murmur). They are decrescendo murmurs. In pulmonary regurgitation without pulmonary hypertension (non-hypertensive pulmonary regurgitation), the murmur starts a short while after the second heart sound (delayed diastolic murmur). In mitral and tricuspid stenosis, there is a mid-diastolic murmur. The mitral diastolic murmur heard in severe aortic regurgitation (Austin Flint murmur) could be either mid diastolic or late diastolic murmur (pre-systolic murmur).
Continuous murmurs: Continuous murmurs start in systole and continue through the second heart sound into a variable part of the diastole. Some of these murmurs are heard throughout the cardiac cycle. The classical continuous murmur is that of patent ductus arteriosus (Gibson’s murmur). The place where this murmur is best heard below the left clavicle is known as Gibson’s area. The murmur of patent ductus arteriosus peaks over the second heart sound. Another cause of continuous murmur is the rupture of sinus of Valsalva into the right atrium or right ventricle. The continuous murmur of rupture of sinus of Valsalva into right ventricle typically produces a murmur which peaks in diastole. This is because the track which passed through the right ventricular muscle gets compressed during systole, reducing the intensity of the murmur in diastole.