Heart murmur overview

# Overview
A cardiac murmur is an abnormal heart sound produced as a result of turbulent blood flow, which is sufficient to produce audible noise, defined as a relatively prolonged series of auditory vibrations of varying intensity (loudness), frequency (pitch), quality, configuration, and duration. Murmurs are not characteristic of normal cardiac physiology and may warrant further evaluation, particularly if they occur during diastole.  However, murmurs are sometimes "innocent" or benign if they are only due to increased flow across a normal heart structure.

# Historical Perspective
A heart murmur is an unusual sound heard between heartbeats, physicians performed auscultation of the heart by placing their ear directly on the patients chest, a technique called immediate auscultation. The heart murmurs clearly described in detail by Allan Burns (17811813).

# Classification
Heart murmurs can be classified by seven different characteristics such as their "quality" (blowing, harsh, rumbling, musical), their "pitch" (high, low, or medium), their "intensity" or loudness, their "timing" in the heart cycle (diastolic or systolic), their "shape" or the variation in their intensity over time, their "location" or spot where they are heard best, their "radiation" or where the sound is transmitted to. An example would be the classification of a murmur as "a harsh, rough, low pitched 3/6 systolic ejection murmur at the right upper sternal border that radiates to the carotids" which is consistent with aortic stenosis.

# Pathophysiology
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.

# Causes

# Epidemiology and Demographics
The prevalence of heart murmur among neonates varies among different studies, ranging from as low as 0.9 % to 77.4%. According to one study involving 7204 neonates, a murmur was detected in less than 1 % of the neonates.  Half of the neonates with heart murmur had cardiovascular malformation. The prevalence of heart murmur among neonates varies among different studies, ranging from as low as 0.9 % to 77.4%. there is a (42.5%) chance that the murmur is due to underlying structural defects.

# Natural History, Complications, and Prognosis
heart murmur may present as innocent murmurs in one particular area of the precardium or as a pathological murmur, the majority of murmurs in children are innocent and found incidentally. Complication of heart murmur depend on the cause of the murmur for example MR may lead to development of pulmonary edema, pulmonary hypertension, and right heart failure,and in case of aortic valve stenosis can lead to angina, syncope, congestive heart failure, atrial fibrillation, endocarditis, and sudden cardiac death.

# History and Symptoms
Many times, the person experiencing heart murmur may not be aware of anything. But heart murmur can be associated with other things such as tightness in the chest, shortness of breath, dizziness or lightheadedness. Depending on the cause of the murmur, these symptoms may be different.

# Heart murmur physical examination
The physical examination is the initial step to identify the cause and the severity of the valvular pathology causing a heart murmur. Provocative maneuvers such as handgrip (which increases systemic vascular resistance), the Valsalva maneuver (which reduces the return of blood to the right side of the heart), and inspiration (which increase blood return to the right side of the heart) may help to identify the underlying valvular pathology.

# Laboratory Findings
In a patient with a heart murmur, a complete blood count (CBC) may be useful in evaluating anemia as a contributing condition, thyroid function tests may be checked to rule out hyperthyroidism, blood cultures may be helpful in excluding endocarditis, and a pregnancy test to exclude pregnancy.

# Echocardiography
An echocardiogram is the diagnostic study of choice in a patient with a murmur, and should be obtained in asymptomatic patients with diastolic murmurs, continuous murmurs, holo-systolic murmurs, late systolic murmurs, murmurs associated with ejection clicks or murmurs that radiate to the neck or back as well as a grade 3 or louder midpeaking systolic murmur. An echocardiogram should also be obtained in patients with evidence of myocardial infarction or ischemia, heart failure, congenital heart disease, syncope, endocarditis. Echocardiographic evaluation is not recommended in some murmurs, such as a grade 2 or softer mid-systolic murmur, which can be an "innocent", "benign" or "functional".

# Treatment
Treatment of a murmur depends upon its underlying cause, the pace of its progression and the associated hemodynamic abnormalities, if any, associated with it.