A heart murmur is a swooshing sound that occurs with turbulent blood flow in the heart or great vessels. This may result from congenital heart defects or acquired valve defects. Atherosclerosis, hypertension, heart failure, myocardial infarction, rheumatic fever, and infectious endocarditis may stretch, distort, damage, scar, or cause calcification of the heart valves.
The intensity of a murmur is described in terms of six grades:
- Grade i– Barely audible, heard only in a quiet room with difficulty
- Grade ii– Clearly audible, but faint
- Grade iii– Moderately loud, easy to hear
- Grade iv– Loud, associated with a thrill palpable to the chest wall
- Grade v– Very loud, heard with one corner of the stethoscope lifted off the chest wall
- Grade vi– Loudest, heard with entire stethoscope lifted slightly off the chest wall
In addition to grading the murmur, it is important to note the timing of a murmur in relation to the normal heart sounds. S1 is the first heart sound (LUB) caused by the closure of the AV valves signaling the beginning of systole. S2 is the second heart sound (DUB) caused by the closure of the semilunar valves signaling the end of systole. The location is also very meaningful– the point where the murmur is best heard (maximum intensity) should be noted by the valve area or intercostal space.
Let’s take a look at the various types of murmurs and their causes:
Mid-systolic Ejection Murmurs
A mid-systolic ejection murmur results from restricted forward flow through the aortic or pulmonic semilunar valve due to valve calcification. This can be heard as a “LUB-woosh-DUB” upon auscultation with a crescendo-decrescendo effect (increases then decreases in loudness). A murmur resulting from aortic stenosis will be loudest at the second right intercostal space. This will often be accompanied by low blood pressure and a slow, diminished radial pulse and may cause left ventricular hypertrophy as the heart is required to work more to maintain adequate cardiac output. A murmur resulting from pulmonic stenosis will be best heard at the second left intercostal space. Right ventricular hypertrophy commonly develops due to the increased workload on the right ventricle.
Pansystolic Regurgitant Murmurs
A pansystolic regurgitant murmur results from the backward flow of blood from an area of higher pressure to one of lower pressure. This again will be heard as a “LUB-woosh-DUB” upon auscultation except the “woosh” extends steadily from S1 to S2. Mitral regurgitation results from a stream of blood flowing back through an incompetent mitral valve into the left atrium during systole. This murmur is best heard at the apex of the heart and may result in left ventricular dilation and hypertrophy. Tricuspid regurgitation results from the back-flow of blood through an incompetent tricuspid valve– it is best heard at the left lower sternal border. The back-up of pressure may cause engorged, pulsating neck veins and liver enlargement; the extra strain on the right ventricle may cause hypertrophy, as well.
Diastolic Rumbles of AV Valves
Diastolic rumbles of the AV valves are due to filling murmurs at low pressures. This is best heard by lightly touching the bell of the stethoscope against the skin. Mitral stenosis results from a calcified mitral valve not opening properly. This impedes the forward flow of blood into the left ventricle during diastole causing increased left atrial pressure, left atrial hypertrophy, and pulmonary edema. This creates a low-pitched diastolic rumble best heard at the heart’s apex while the person is in a left lateral position. Tricuspid stenosis results from a calcified tricuspid valve impeding forward flow into the right ventricle during diastole. The rumble is best heard at the left lower sternal border.
Early Diastolic Murmurs
An early diastolic murmur results from semilunar valve incompetence. Aortic regurgitation causes a stream of blood to flow back through an incompetent aortic valve into the left ventricle during diastole. The murmur is best heard at the left third intercostal space (base of the heart) as the person sits up and leans forward. A soft high pitched, decrescendo sound begins simultaneously with S2 (“LUB-DUB-woosh”). Left ventricular dilation and hypertrophy develop due to increased LV stroke volume. Pulmonic regurgitation is caused by a back-flow of blood through an incompetent pulmonic valve from the pulmonary artery to the right ventricle. The timing and characteristics are similar to that of aortic regurgitation and are difficult to distinguish upon physical assessment.
Reference: Jarvis, C. (2012). Physical Examination and Health Assessment, 6th Edition. [Pageburstl]. Retrieved from https://pageburstls.elsevier.com/#/books/978-1-4377-0151-7/