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Understanding Heart Murmurs

Heart | January 23, 2015 | Author: The Super Pharmacist

heart

Understanding Heart Murmurs

A heart murmur is a blowing, whooshing, or rasping sound heard during a heartbeat. Heart murmurs are most often caused by defective heart valves. A heart murmur can be heard if a heart valve is narrowed and interferes with the outflow of blood (stenosis) or a valve leaks and allows a backflow of blood (regurgitation or insufficiency). The sound is caused by turbulent blood flow through the defective valve.

Basic Heart Anatomy

There are two sides to the heart, each of which acts as a separate pump. The two sides are further divided into two chambers, giving four chambers in total. The upper chambers are called the atria. Their basic function is to collect blood. The lower chambers are known as the ventricles. Their function is to contract and pump blood out of the heart. One-way valves within the heart separate the right atrium and the right ventricle (tricuspid valve), the left atrium and the left ventricle (mitral valve), the right ventricle and the pulmonary circulation (pulmonic valve), and the left ventricle and the arterial circulation (aortic valve)1

The Cardiac Cycle

The Cardiac CycleThe cardiac cycle describes all the activities of the heart through one complete heartbeat—that is, through one contraction and relaxation of both the atria and ventricles. The period of contraction of the ventricles of the heart is called ‘systole’. During systole, blood from the left ventricle is ejected into the arterial circulation (via the aorta) and blood from the right ventricle is ejected into the pulmonary circulation.

Left ventricular contraction begins with closure of the mitral valve (to prevent backflow into the left atrium) and ends with closure of the aortic valve (to prevent backflow from the aorta into the left ventricle). The left side of the heart is responsible for sending newly oxygenated blood from the lungs out to all the body organs and tissues.

Right ventricular contraction begins with closure of the tricuspid valve (to prevent backflow into the right atrium) and ends with closure of the pulmonic valve (to prevent backflow into the pulmonary circulation).

The right side of the heart receives oxygen depleted blood from the body and directs it to the lungs to release carbon dioxide and reabsorb oxygen. The period of relaxation of the ventricles is called ‘diastole’. During diastole, the ventricles relax and fill with blood in preparation for the next heartbeat.

Heart Sounds

When blood flows normally through the heart valves, it makes a two-beat “lub-lub” sound. The “lub” is the first heart sound (called S1) and is produced by closure of the mitral and tricuspid valves at the start of systole. The second sound,” dub” (called S2), is caused by closure of the aortic and pulmonic valves, marking the end of systole. Thus the time period elapsing between the first heart sound and second sound defines systole (ventricular ejection) and the time between the second sound and the following first sound defines diastole (ventricular filling).

The causes of Heart Murmurs

Heart murmurs can be innocent or abnormal. Innocent heart murmurs, also called normal, benign flow, functional, or physiologic murmurs, occur when blood flow moves quickly through the heart or there is extra blood flow in the heart. Innocent heart murmurs affect 40–45% of children and about 10% of adults at some point during their lifetimes. Innocent heart murmurs can be caused by:

  • Exercise
  • Pregnancy
  • Fever
  • Anemia
  • Hyperthyroidism

Abnormal heart murmurs in children are most commonly caused by congenital heart defects. In adults and older children, heart murmurs are typically caused by heart valve abnormalities related to infections, illness, or aging.

Heart Murmurs in Children

Heart Murmurs in ChildrenBenign Heart Murmurs in Children

Benign heart murmurs are relatively common in children and do not require any treatment or change in daily lifestyle or physical activity. In fact, there are no noticeable symptoms. Many heart murmurs in children become harder to hear with age and eventually disappear altogether.

Abnormal Heart Murmurs in Children

Most abnormal heart murmurs in children are due to congenital heart disease. Examples of congenital heart defects include:

Holes in the heart (Septal defects): The septum is the wall that separates the chambers on left and right sides of the heart. The wall prevents blood from mixing between the two sides of the heart. Some babies are born with holes in the septum. These holes allow blood to mix between the two sides of the heart.

Atrial septal defect: An atrial septal defect is a hole in the part of the septum that separates the atria—the upper chambers of the heart. The hole allows oxygen-rich blood from the left atrium to flow into the right atrium, instead of flowing into the left ventricle as it should. Many children who have atrial septal defects have few, if any, symptoms.

Ventricular septal defect: A ventricular septal defect is a hole in the part of the septum that separates the ventricles—the lower chambers of the heart. The hole allows oxygen-rich blood to flow from the left ventricle into the right ventricle, instead of flowing into the aorta and out to the body as it should.

Patent Ductus Arteriosus: Patent ductus arteriosus is a fairly common heart defect that can occur soon after birth. In patent ductus arteriosus, abnormal blood flow occurs between the aorta and the pulmonary artery. Before birth, these arteries are connected by a blood vessel called the ductus arteriosus. This blood vessel is an essential part of fetal blood circulation. Within minutes or up to a few days after birth, the ductus arteriosus closes. In some babies, however, the ductus arteriosus remains open (patent). The opening allows oxygen-rich blood from the aorta to mix with oxygen-poor blood from the pulmonary artery. This can strain the heart and increase blood pressure in the lung arteries.

Valvular defects. Congenital heart defects can also involve the heart valves (eg, stenosis or insufficiency).

Heart Murmurs in Adults

In adults and older children, heart murmurs are typically caused by damage to the heart valves related to infections, illness, or aging. These conditions include the following:

  • Rheumatic fever
  • Endocarditis
  • Mitral valve prolapse
  • Valve calcification
  • Hypertrophic cardiomyopathy

There are two general types of cardiac valve defects: stenosis and insufficiency. Valvular stenosis results from a narrowing of the valve orifice that is usually caused by a thickening and increased rigidity of the valve leaflets, often accompanied by calcification. When blood is forced through a tight area, turbulent blood flow ensues causing a murmur. Valvular insufficiency results from the valve leaflets not completely sealing when the valve is closed so that regurgitation of blood occurs (backward flow of blood). In valvular insufficiency, blood travels backward through an incompetent valve causing turbulence when it meets normal, forward blood flow and results in a murmur.

Diagnosing Cardiac MurmursĀ Diagnosing Cardiac Murmurs 

A cardiac murmur is first suspected on auscultation of the heart. Auscultation is the method of listening to the sounds of the heart using a stethoscope during a physical examination.

Cardiac Auscultative Findings

Certain findings on auscultation of the heart help to determine the exact nature of a murmur. These descriptive findings include intensity of the murmur, timing of the murmur in the cardiac cycle as well as its location, duration, character, pitch, radiation and configuration.

Intensity: The intensity of the murmur depends on the volume of blood flow across the valve. The louder the murmur, the more likely it is to be pathologic. Functional, benign, or innocent murmurs are usually soft (grade I or II) and usually occur in systole. The grade of the murmur is important, as any murmur above grade II/VI in severity warrants echocardiographic evaluation as per ACC/AHA (American College of Cardiology/American Heart Association) guidelines. Intensity is graded as follows:

  • Grade I: Barely audible
  • Grade II: Soft, but easily audible
  • Grade III: Moderately loud, but not accompanied by a thrill
  • Grade IV: Louder and associated with a thrill
  • Grade V: Audible with the stethoscope barely on the chest
  • Grade VI: Audible with the stethoscope off the chest

Timing: The timing of a murmur is crucial to accurate diagnosis. A murmur is either systolic, diastolic, or continuous throughout systole and diastole. Remember that systole occurs between the S1 and S2 heart sounds while diastole occurs between S2 and S1. Certain valvular abnormalities are known to cause systolic murmurs; others are known to cause diastolic murmurs or continuous murmurs. Identifying a murmur as systolic or diastolic is critical to localising the diseased cardiac valve and determining if it is stenotic or incompetent. Stenosis of the aortic or pulmonic valves will result in a systolic murmur (systole is when the ventricles contract and eject blood through the narrowed valve). On the other hand, if the aortic valve or pulmonic valve is incompetent or ‘leaky,’ blood will flow backward across the valve when the ventricles relax resulting in a diastolic murmur. Inversely, stenosis of the mitral valve or tricuspid valve will result in a diastolic murmur (diastole is when the atria contract and transfer blood into the ventricles). Incompetence of the mitral valve or tricuspid valve will result in a systolic murmur as blood flows backward across the valves during ventricular contraction.

Location: where the murmur is heard the loudest

Character: harsh, blowing, rumbling, musical, or cooing

Pitch: high or low pitched depending on frequency

Radiation: the direction in which the sound of the murmur travels

Configuration: plateau, decrescendo, crescendo-decrescendo, or crescendo

Dynamic Cardiac Auscultation

Certain dynamic maneuvers are performed to purposely accentuate and/or diminish cardiac murmurs to further aid in their characterisation.

Positional changes: The murmur should be auscultated and compared when the patient is supine and then sitting or standing. Most murmurs will decrease when transitioning from supine to sitting or standing as preload decreases.

Respiration: Right-sided murmurs usually increase with inspiration, and left-sided murmurs usually increase with expiration.

Valsalva: The patient is instructed to forcibly exhale while keeping the mouth and nose closed. Most murmurs decrease in length and intensity.

Exertion: Isometric exercise, such as hand squeezing, can be used to enhance murmurs due to valvular stenosis or regurgitation and ventricular septal defect.

Tests and Procedures

Tests and ProceduresEchocardiography is the main test for diagnosing heart valve disease. An electrocardiogram (EKG) and chest x-ray are also commonly used to reveal certain signs of the condition. Additional diagnostic studies which may be warranted include cardiac catheterisation, stress testing, and cardiac magnetic resonance imaging (MRI).  

Management and Treatment of Cardiac Murmurs

Treatment for heart valve disease depends on the type and severity of valve disease. An important consideration in a patient with a cardiac murmur is the presence or absence of symptoms. Many asymptomatic children and young adults with grade 2/6 midsystolic murmurs and no other cardiac physical findings need no further cardiac workup after the initial history and physical examination. Staging for different diseases, in different valves, is broken down into four categories: at risk (stage A), progressive (stage B), asymptomatic severe (stage C), and symptomatic severe (stage D). Pharmacologic management of heart valve disease has four goals:

  • Decrease workload on the heart
  • Restore normal heart rhythm
  • Prevent blood clots and strokes
  • Prevent further damage to the valve

The following information is obtained from the 2014 AHA/ACC guideline for the management of patients with valvular heart disease.

Infective endocarditis prophylaxis

Only those patients at the highest risk of developing infective endocarditis (ie, those with prosthetic heart valves) should be treated. These patients should receive antibiotics one hour before dental procedures or operations on the mouth, throat, gastrointestinal genital, or urinary tract.

Aortic stenosis (AS)

Hypertension in patients at risk for developing AS (Stage A) and in patients with asymptomatic AS (stage B and C) should be treated.

  • Cautious use of digitalis, diuretics, and angiotensin-converting enzyme (ACE)inhibitors (eg, captopril, lisinopril, enalapril) in patients with pulmonary congestion
  • Vasodilators (ie, hydralazine, nitroglycerin, nifedipine) in the acute management of severely decompensated aortic stenosis (stage D)
  • Statin therapy is not indicated for prevention of hemodynamic progression of AS in patients with mild-to-moderate calcific valve disease (stages B to D).
  • Aortic valve replacement is indicated in symptomatic patients with severe AS (stage D).

Aortic regurgitation (AR)

Treatment of hypertension (systolic BP >140 mm Hg) is recommended in patients with chronic AR (stages B and C).

  • Dihydropyridine calcium channel blockers (eg, felodipine, nifedipine, amlodipine)
  • ACE inhibitors or angiotensin-receptor blockers (ARBs) (eg, losartan, valsartan, olmesartan)
  • ACE inhibitors/ARBs and beta blockers in patients with severe AR (stages C and D) who are not candidates for surgery because of severe co-occurring medical conditions
  • Aortic valve replacement (AVR) in symptomatic patients with severe AR (stage D)

Mitral stenosis (MS)

Mitral stenosis (MS)The goals of medical treatment for MS are to reduce recurrence of rheumatic fever, reduce symptoms of pulmonary congestion (eg, difficulty breathing), slow the heart rate in order to give the heart more time to fill, and prevent thromboembolic complications. Because rheumatic fever is the primary cause of mitral stenosis, secondary prophylaxis against group A beta-hemolytic streptococci is recommended. For many years, surgical open heart mitral commissurotomy was the only available method to correct MS.

The development of balloon valvotomy techniques has revolutionized the surgical management of MS.

  • Penicillin (for secondary prophylaxis of rheumatic fever)
  • Diuretics, nitrates and beta-blockers for pulmonary congestion
  • Beta-blockers, calcium channel blockers, amiodarone, or digoxin to control the heart rate in patients who have atrial fibrillation
  • Heart rate control may also be beneficial in patients with normal sinus rhythm who are symptomatic during exercise.
  • Anticoagulation (vitamin K antagonist or heparin) is indicated in patients with atrial fibrillation or who have a history of a prior embolic event, or in patients with evidence of a left atrial thrombus (clot).
  • Percutaneous mitral balloon valvuloplasty (a procedure where a catheter is guided through a blood vessel to the valve and a balloon is inflated at its tip to widen the mitral valve) is recommended for symptomatic patients with severe MS (stage D).
  • Mitral valve surgery (repair, open heart commissurotomy, or valve replacement) is indicated in severely symptomatic patients with severe MS (stage D) who are not high risk for surgery and who are not candidates for or who have failed previous percutaneous mitral balloon valvuloplasty.

Mitral regurgitation (MR)

MR is either primary or secondary. In primary MR, it is the valve itself which the origin of the problem. In secondary MR, it is the left ventricle that has sustained previous damage due to a myocardial infarction or dilated cardiomyopathy that has caused mitral valve insufficiency. Medical therapy has no role in treating primary MR whereas it is the mainstay of treatment in patients with secondary MR.

Primary MR

Mitral valve surgery is recommended for symptomatic patients with chronic severe primary MR (stage D). The management primary MR is focused on deciding the appropriate timing of surgery, before the development of irreversible left ventricular dysfunction.

Secondary MR

Patients with chronic secondary MR (Stages B to D) and heart failure should receive standard guideline-determined medical therapy for heart failure, including:

  • Diuretics to remove excess fluid in the lungs.
  • Beta-blockers, ACE inhibitors, ARBs or calcium channel blockers.
  • Cardiac resynchronization therapy with biventricular pacing is recommended for symptomatic patients with chronic severe secondary MR (stages B to D) who meet the indications for device therapy.

Tricuspid regurgitation (TR)

For patients in whom TR is secondary to left-sided heart failure, treatment is focused on adequate control of fluid overload and heart failure symptoms (eg, diuretic therapy). The main therapy is treatment of underlying cause. In most cases, surgery is not indicated since the root problem lies with a dilated or damaged right ventricle.

  • Diuretics for signs of right-sided heart failure.
  • Tricuspid valve surgery is recommended for patients with severe TR (stages C and D) undergoing left-sided valve surgery.

Tricuspid stenosis (TS)

TS is an uncommon valvular abnormality that typically occurs in association with other valvular lesions.

  • Tricuspid valve surgery is recommended for patients with severe TS at the time of operation for left-sided valve disease.
  • Percutaneous balloon tricuspid valvuloplasty might be considered in patients with isolated, symptomatic severe TS without accompanying TR.

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References

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File:Blausen 0039 AorticRegurgitation.png. http://commons.wikimedia.org/wiki/File%3ABlausen_0039_AorticRegurgitation.png.             Wikiversity Journal of Medicine. Blausen.com staff. "Blausen gallery 2014". Wikiversity Journal of Medicine. DOI:10.15347/wjm/2014.010. ISSN 20018762. (Own work) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons.

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