Physiology, Cardiovascular Murmurs

Article Author:
Seth Thomas
Article Editor:
Amgad Makaryus
Updated:
6/3/2019 12:21:34 PM
PubMed Link:
Physiology, Cardiovascular Murmurs

Introduction

A cardiac murmur is a critical physical exam finding that reinforces the importance of an adequate physical examination. Murmurs are almost always closely associated with a disease. However, benign murmurs can be auscultated commonly in children and can also occur in adults in a few situations. Murmurs are graded on the Levine scale from 1 to 6 in intensity. They are dynamic findings that can be altered with specific maneuvers for a more accurate diagnosis. According to multiple major guidelines, further evaluation with an echocardiogram is indicated when any concerning murmur is auscultated. It is essential to understand all of these topics as well as the specific murmurs and their more common etiologies.[1][2][3]

Development

Cardiac murmurs arise from turbulent blood flow around the structures of the heart. Murmurs are often described regarding the location on the thoracic cage in which it is auscultated, its pitch and volume, and in which phase of the cardiac cycle it was heard. Unique characteristics of the murmur should also be documented. For example, the murmur heard from aortic stenosis is usually described as a high pitched mid-systolic murmur that radiates to the carotid arteries. It is heard loudest at the right second intercostal space.

Most cardiac murmurs are closely associated with specific diseases. However, a minority of cardiac murmurs are benign, mostly found in pregnant women and children. Murmurs develop from a multitude of mechanisms. Some typical examples include low blood viscosity from anemia, septal defects, failure of the ductus arteriosus to close in newborns, excessive hydrostatic pressure on cardiac valves causing valve failure, hypertrophic obstructive cardiomyopathy, and disease of one of the cardiac valves themselves. These all involve the creation of turbulent blood flow that defines a murmur.[4][5][6]

Related Testing

When combined with an accurately identified murmur, a patient history can provide critical details that lead to a diagnosis. Intravenous drug use, a history of untreated streptococcal pharyngitis or scarlet fever, valve replacement history, and a family history of cardiovascular disease or genetic disease are all significant historical items to be aware of in a patient with a murmur.[7][8][9]

In addition to patient history, obtaining a detailed cardiovascular physical examination is paramount in identifying a murmur and its associated disease. Begin by auscultating the four cardiac listening posts to determine the cardiac murmur's location and allow for its characterization. Murmurs are described using the thoracic cage position where they are auscultated, pitch, volume, and in which phase of the cardiac cycle they occur. Auscultating other locations such as the axilla and carotid arteries also helps accurately diagnose the murmur. It should be performed on any patient with suspicion of a murmur. More severe murmurs are associated with thrills, which are palpable vibrations. Murmurs are graded in intensity from 1 to 6 using the Levine grading scale.[10]

Maneuvers

Most murmurs will increase or decrease in volume when the patient performs certain maneuvers. This dynamic quality of murmurs is used as a clinical tool during the patient’s physical exam to aid in diagnosing a specific murmur. Some examples of how maneuvers change the intensity of specific murmurs include:

  • Hand grip: Increases afterload. Hand gripping increases the strength of aortic regurgitation, mitral regurgitation, and ventricular septal defect murmurs. It decreases the intensity of murmurs due to hypertrophic obstructive cardiomyopathy and mitral valve prolapse.
  • Squatting: Increases preload. Squatting increases the intensity of aortic stenosis, mitral stenosis, aortic regurgitation, and mitral regurgitation. It decreases the strength of murmurs due to hypertrophic obstructive cardiomyopathy and mitral valve prolapse.
  • Valsalva: Decreases preload. Valsalva increases the strength of murmurs due to hypertrophic obstructive cardiomyopathy and mitral valve prolapse. It decreases the intensity of aortic stenosis, mitral stenosis, aortic regurgitation, mitral regurgitation, and ventricular septal defects.
  • Standing abruptly: Decreases preload and has the same effects as Valsalva. Sudden standing increases the intensity of murmurs in hypertrophic obstructive cardiomyopathy and mitral valve prolapse. It decreases the strength of aortic stenosis, mitral stenosis, aortic regurgitation, mitral regurgitation, and ventricular septal defects.
  • Amyl nitrate: Decreases afterload. Amyl nitrate increases the intensity of aortic stenosis, hypertrophic obstructive cardiomyopathy, and mitral valve prolapse. It decreases the severity of aortic regurgitation, mitral regurgitation, and ventricular septal defects.

Imaging

Symptomatic patients presenting with new murmurs are always investigated with imaging. An echocardiogram is preferred to evaluate cardiac structure and function because of its practicality, sensitivity, and specificity for detecting valvular diseases. It also dynamically evaluates the heart, allowing for diagnosis of a disease otherwise unseen on nondynamic imaging. Echocardiography is recommended by several major organizations such as the American College of Cardiology, the American Heart Association, and the European Society of Cardiology as the first imaging study to be performed, along with a chest X-ray, in a patient with a symptomatic murmur.

Several types of echocardiography are available. The least invasive is trans-thoracic echocardiography. Trans-thoracic echocardiography allows for the accurate diagnosis of valvular diseases, embolism, endocarditis, and aortic dissection. It is the simplest echocardiographic method, but in some patients, images may be obstructed by the rib cage or from excess tissue in obese patients. For these patients, another more invasive method called trans-esophageal echocardiography may be appropriate. Trans-esophageal echocardiography eliminates the issue of image obstruction by visualizing the heart via a transducer introduced into the esophagus.

Pathophysiology

Common Murmurs and Cardiac Disease States

Murmurs have been closely linked to a multitude of diseases throughout the centuries. There are several common murmurs and cardiac disease states from which each specific murmur develops.

Aortic stenosis

Aortic stenosis is the narrowing of the aortic valve. It is the most common valvular heart disease in the developed world. The condition is described as a harsh crescendo-decrescendo systolic murmur heard best at the right upper sternal border, with radiation of the murmur to the carotid arteries. It may arise from valve calcification over time due to aging or to having a congenital bicuspid aortic valve. Chronic rheumatic heart disease is also a cause of aortic stenosis.

Aortic regurgitation

Also known as aortic insufficiency, aortic regurgitation is a diastolic murmur. It develops due to aortic valve failure during diastole, causing blood to leak back into the ventricles from the aorta in a turbulent manner. The most common causes of aortic regurgitation in the developed world are aortic root dilation, bicuspid aortic valve, and calcific valve disease. Aortic regurgitation is described as a decrescendo blowing diastolic murmur heard best at the left lower sternal border.

Innocent or flow murmur

This type of murmur is usually mid-systolic and arises from increased blood flow due to increased cardiac output. It occurs in children and patients with anemia or thyrotoxicosis. It is also present in up to 80% of pregnant women. A flow murmur may also be called a Still murmur. Both of these are benign and are also known as innocent murmurs. Crucially, a murmur is only genuinely innocent if it has no associated symptoms. Any murmur auscultated in diastole cannot be a benign murmur. Innocent or flow murmurs usually resolve during childhood. Any concern by medical professionals or the presence of any symptomology warrants further investigation of the murmur.

Pulmonary stenosis

Pulmonary stenosis is a systolic murmur best heard at the upper left sternal border. Its causes include Tetralogy of Fallot, where a congenitally stenotic pulmonary valve is present; carcinoid syndrome, where a carcinoid tumor secretes serotonin and causes vegetation growth on the pulmonary valves; congenital rubella syndrome, a multi-organ congenital syndrome; and Noonan syndrome, an inherited genetic disease.

Tricuspid stenosis

Tricuspid stenosis is a diastolic murmur best heard at the lower left sternal border. It is often associated with intravenous drug abusers that present with symptoms of infective endocarditis and in carcinoid syndrome patients. Prolonged tricuspid stenosis will lead to right atrial enlargement and possibly arrhythmias.

Tricuspid regurgitation

This type of murmur is systolic. It is best appreciated at the lower left sternal border. Tricuspid regurgitation may be auscultated due to vegetative growth both in intravenous drug abusers that present with infective endocarditis and in patients with carcinoid syndrome.

Mitral stenosis

Mitral stenosis is a diastolic murmur best heard at the apex. Worldwide, mitral stenosis is most commonly caused by chronic rheumatic heart disease. It is also observed in cases of infective endocarditis and chronic rheumatic heart disease.

Mitral regurgitation

This type of murmur is systolic and is best heard at the apex with radiation to the left axilla. Mitral regurgitation is observed in patients with infective endocarditis, chronic rheumatic heart disease, degenerative valve disease, Ehlers-Danlos syndrome, Marfan syndrome, and systemic lupus erythematosus. The sudden onset of acute, severe mitral regurgitation occurs in some patients that have suffered an inferior wall myocardial infarct. This effect is due to the rupture of the chordae tendineae after the myocardial infarct has weakened the tissue structure.

Mitral valve prolapse

This valvular disease occurs most commonly due to idiopathic myxomatous valve degeneration. Mitral valve prolapse can also be caused by acute rheumatic fever, chronic rheumatic disease, endocarditis, and Ebstein’s anomaly. It presents as an early systolic click heard best at the apex. It often is accompanied by a late systolic murmur indicative of mitral regurgitation occurring after mitral valve prolapse. As with other valvular diseases, mitral valve prolapse is only definitively diagnosed with imaging.

Pulmonic stenosis

Pulmonic stenosis is the main murmur auscultated in infants with Tetralogy of Fallot. It is described as a crescendo-decrescendo systolic ejection murmur heard loudest at the upper left sternal border. Pulmonic stenosis is most commonly a congenital finding. However, it may also arise in a patient with a chronic rheumatic disease.

Austin Flint murmur

This type of murmur is a mid-diastolic rumbling murmur heard best over the apex. It is speculated to occur due to an aortic regurgitant jet causing the anterior mitral valve leaflet to close prematurely. Austin Flint murmurs may be mistaken for mitral stenosis.

Atrial septal defect

An atrial septal defect is congenital. It is located between the left and right atria that allows blood to flow freely between them. It will present as a loud S1 and a wide, fixed split S2 heart sound, and will be loudest at the upper left sternal border. Large atrial septal defects are quieter, while small ones are louder and have a harsh quality. The sound is different because blood will flow with much less turbulence through a larger, unrestrictive space. Atrial septal defects are usually detected in utero or early in childhood through either ultrasound or physical examination.

Ventricular septal defect

This type of murmur is holosystolic. Similarly to atrial septal defects, smaller ventricular septal defects are louder and have a harsher quality, while large ones are quieter but more symptomatic. In a child, a closing atrial or ventricular septal defect will get progressively louder until it closes. A distinguishing trait of ventricular septal defects is the location of the murmur. This type of murmur is loudest at the apex, while an atrial septal defect is loudest at the upper left sternal border.

Hypertrophic obstructive cardiomyopathy

Hypertrophic obstructive cardiomyopathy is an inherited myocardial disease in which the myocardium undergoes hypertrophic changes. These changes cause a systolic ejection murmur due to the mitral valve hitting the thickened septal wall during systole. The murmur is heard best between the apex and the left sternal border. It becomes louder with any maneuver that decreases preload or afterload, such as Valsalva or abrupt standing. This effect occurs because the lower ventricular blood volume from reduced preload or afterload allows for closer approximation of the mitral valve to the hypertrophied septal wall, causing more turbulent blood flow.

Chronic rheumatic heart disease

Chronic rheumatic heart disease is a sequela of untreated streptococcal pharyngitis and acute rheumatic fever. Chronic auto-immune attack of cardiac tissue causes it due to the molecular similarity between the tissue and streptococcal M protein. Mitral stenosis, mitral regurgitation, aortic stenosis, and aortic regurgitation can develop because of this chronic valve inflammation.

Turners syndrome

This inherited disease often presents with a murmur in young women, most commonly due to the presence of a bicuspid aortic valve or coarctation of the aorta. A bicuspid aortic valve will present as a systolic murmur best heard at the right second intercostal space. Coarctation of the aorta will present in both systole and diastole and is heard over the thoracic spine. The continuous harsh systolic component of coarctation of the aorta is due to turbulent blood flowing through the small diameter section of the aorta. Its diastolic component is due to aortic regurgitation. Other causes of murmurs in these patients include hypoplastic left heart or aortic dissection.

Tetralogy of Fallot

The murmur in Tetralogy of Fallot will present in an infant and is usually due to pulmonic valve stenosis. Another possible source of murmur in these patients is from the ventricular septal defect. However, this is less likely because the ventricular septal defect is often large in Tetralogy of Fallot patients. Pulmonic valve stenosis is characterized as an early systolic click with a harsh systolic crescendo-decrescendo ejection murmur. It is heard best at the left upper sternal border. Unlike aortic stenosis, this murmur will not radiate to the carotids.

Carcinoid syndrome

Carcinoid syndrome causes thickening of the tricuspid and pulmonary valves, which leads to either stenosis or regurgitation murmurs from the valves. This thickening arises from high amounts of serotonin released from the carcinoid tumor after the tumor has metastasized to the liver.

Infective endocarditis

The murmur from infective endocarditis is due to the growth of bacterial vegetations on the heart valves, most commonly the tricuspid valve. Tricuspid valve vegetations usually occur in intravenous drug users with infective endocarditis, leading to the development of tricuspid stenosis and tricuspid regurgitation.

Patent ductus arteriosus

Patent ductus arteriosus will present with a continuous machine-like murmur in a newborn that is loudest at the upper left sternal border. If the newborn has no other comorbidities, it may be closed with NSAIDs such as indomethacin. However, if the patient has other cardiac abnormalities, the patent ductus arteriosus may be critical to the patient’s survival and should not be closed.

Prosthetic valve leaks

Murmurs may develop from a leak in any of the prostheses available for the four cardiac valves.

Clinical Significance

Murmurs are critical physical examination findings in many patients. Many diseases have an associated murmur. Fortunately, each murmur often has enough distinguishing qualities that, when combined with patient history, allows the physician to create a concise list of possible diagnoses. Imaging such as an echocardiogram is essential for a definitive diagnosis of any underlying cardiac disease.

The skill of accurately describing a murmur is just as important as gathering a patient’s history. For example, the ability to accurately report whether a murmur is heard in systole or diastole in a healthy-appearing child is essential. The difference will determine whether or not to refer the patient to a pediatric cardiologist for further evaluation.


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