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The differential diagnosis of a heart murmur begins with a careful assessment of its major attributes and response to bedside maneuvers. The history, clinical context, and associated physical examination findings provide additional clues by which the significance of a heart murmur can be established. Accurate bedside identification of a heart murmur can inform decisions regarding the indications for noninvasive testing and the need for referral to a cardiovascular specialist. Preliminary discussions can be held with the patient regarding antibiotic or rheumatic fever prophylaxis, the need to restrict various forms of physical activity, and the potential role for family screening.
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Heart murmurs are caused by audible vibrations that are due to increased turbulence from accelerated blood flow through normal or abnormal orifices, flow through a narrowed or irregular orifice into a dilated vessel or chamber, or backward flow through an incompetent valve, ventricular septal defect, or patent ductus arteriosus. They traditionally are defined in terms of their timing within the cardiac cycle (Fig. 10-1). Systolic murmurs begin with or after the first heart sound (S1) and terminate at or before the component (A2 or P2) of the second heart sound (S2) that corresponds to their site of origin (left or right, respectively). Diastolic murmurs begin with or after the associated component of S2 and end at or before the subsequent S1. Continuous murmurs are not confined to either phase of the cardiac cycle but instead begin in early systole and proceed through S2 into all or part of diastole. The accurate timing of heart murmurs is the first step in their identification. The distinction between S1 and S2 and, therefore, systole and diastole is usually a straightforward process but can be difficult in the setting of a tachyarrhythmia, in which case the heart sounds can be distinguished by simultaneous palpation of the carotid upstroke, which should closely follow S1.
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Duration and character
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The duration of a heart murmur depends on the length of time over which a pressure difference exists between ...