Heart murmur pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Turbulent flow is responsible for most murmurs. Turbulent flow occurs when the velocity of blood flow becomes critically high because of a high volume of flow, the flow goes through an irregular or narrow area, the flow empties into a dilated vessel or chamber, or if the flow goes backward through an incompetent valve, septal defect, or patent ductus arteriosus. Frequently, a combination of these factors is operative.
Characteristics of Heart Murmurs
Heart murmurs can be classified by seven different characteristics as:
- Timing: Whether the murmur is a systolic or diastolic murmur. There is seldom any difficulty distinguishing between systole and diastole, because systole is considerably shorter at normal heart rates. At rapid heart rates, the examiner can usually time the murmur by simultaneous palpation of the lower right carotid artery or can rely on the fact that the S2 is usually the louder sound at the base. Once S2 is identified, murmurs can be located properly in the cardiac cycle as systolic or diastolic. The inching technique, popularized by Harvey and Levine, consists of slowly moving the stethoscope down from the base to the apex while repeatedly fixing the cardiac cycle in mind, using S2 as a reference point. In sinus tachycardia, carotid sinus pressure can temporarily slow the rate and make it possible to differentiate systole from diastole.
- Shape: Shape refers to the intensity over time; murmurs can be crescendo (increasing), decrescendo (diminishing), crescendo-decrescendo (increasing-decreasing or diamond shaped) and plateau (unchanged in intensity).
- Location: Location refers to where the heart murmur is auscultated best. There are 6 places on the anterior chest to listen for heart murmurs; the first five out of six are adjacent to the sternum. Each of these locations roughly correspond to a specific part of the heart. The locations are: 2nd right intercostal space, 2nd to 5th left intercostal spaces, and 5th mid-clavicular intercostal space.
- Radiation: Radiation refers to where the sound of the murmur radiates. The general rule of thumb is that the sound radiates in the direction of the blood flow.
- Intensity: Intensity refers to the loudness of the murmur, and is graded on a scale from 0-6/6.
- Pitch: The pitch of a murmur is either low, medium or high and is determined by whether it can be auscultated best with the bell or diaphram of a stethoscope.
- Quality: Some examples of the quality of a murmur are: blowing, harsh, rumbling or musical.