Describe the normal mitral valve.
Left atrium - left ventricle
Two leaflets with chordae tendinae attached to papillary muscles
Describe the normal tricuspid valve.
Right atrium - right ventricle
Three leaflets
Chordae tendinae attached to papillary muscles
Describe the normal aortic valve.
Left ventricle to aorta
Semilunar valve
3 cusps (posterior)
Describe the normal pulmonary valve
Right ventricle - pulmonary artery
Semilunar valve, 3 cusps (anterior)
List the valve pathology types.
Stenosis
Regurgitation
Both stenosis and regurgitation
Functional
Define stenosis of valve pathology.
Narrowing.
Failure of a valve to open completely leading to obstruction to blood flow (pressure overload)
Define regurgitation of valve pathology.
Incompetence
Failure of a valve to close completely leading to reversed/retrograde blood flow (volume overload).
Define both stenosis and regurgitation in valve pathology.
Both pressure and volume overload
Define functional issues in valve pathology.
Example: dilation of the right or left ventricle can pull on the papillary muscles down and outwards, preventing proper closure of structurally normal valves.
What murmur does mitral stenosis produce?
Diastolic murmur (trouble moving blood from atria to ventricles)
What murmur does mitral regurgitation produce?
Systolic murmur
What are the complications of valve pathology due to volume and pressure overload?
Chamber hypertrophy (with pressure overload), later failure and dilation
Chamber dilation (with volume overload)
Atrial fibrillation (AF) secondary to atrial dilation
AF predisposes thrombosis and embolism
Leads to HF
Susceptibility to IE
What are possible causes of valve disease?
Congenital e.g. aortic stenosis Degenerative (aging) - calcific aortic stenosis Hereditary - mitral valve prolapse Immunological - RF Infective - IE
What is acute RF?
Acute, immunologically mediated, multisystem inflammatory disease that occurs a few weeks following a Group A Streptococcal (GAS) pharyngitis
How does a GAS infection cause RF?
Cross reactivity to group A streptococci with self antigens in the heart - molecular mimicry (forms antibodies which attack the heart)
What is the cardiac morphology of RF?
Pancarditis (inflammation of all 3 layers of the heart)
- endocarditis, myocarditis, pericarditis
How does RHD (chronic) occur?
Active phase of RF may progress over time to become chronic rheumatic disease.
What characterizes RHD?
Permanent valve deformities due to healing by fibrosis after RF
Which valve is most commonly affected by RHD?
Mitral valve with mitral stenosis
Aortic valve can be affected as well
Valve deformities lead to stenosis/regurgitation
Where is RF and RHD in high incidence?
Amongst Maori and Pasifika mostly in north island
Children aged 5-15
High frequency of recurrence unless prophylactic antibiotics given
What are the risk factors for rheumatic fever?
Crowded housing conditions Cold damp housing SE deprivation Barriers to primary healthcare access Higher burden of untreated strep sore throat infections
Describe the pathogenesis behind RF.
Antibodies against M proteins of Group A beta hemolytic strep and CD4+ T cells specific for streptococcal peptides cross react with self antigens/proteins in the heart.
This leads to a combination of antibody-mediated and CD4+ T cell mediated inflammation
What type of hypersensitivity is antibody mediated inflammation?
Type II
What type of hypersensitivity reaction is CD4+ T cell mediated inflammation?
Type IV hypersensitivity
Describe the antibody mediated-inflammation involved in RF.
Deposition of antibodies in tissues lead to complement activation.
Complement components result in leukocyte recruitment and vasodilation and increase in vascular permeability.
Release of substances from leukocytes such as lysosomal enzymes which causes tissue damage.
What does the CD4+ T cell mediated inflammation entail?
T cells produce cytokines that recruit and activate macrophages
Are streptococci still present in the throat by the time RF develops?
No
Streptococci are completely absent from the inflammatory lesions of RF!
How do we detect if a person had a GAS infection prior to RF?
Antibodies against streptococcal antigens can be detected in the plasma.
IMPORTANT TO NOTE: disease is not due to the infection of the heart by GAS bacteria! It is an immunologically mediated disease.
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What are the clinical features of RF?
Pancarditis
Migratory polyarthritis of the large joints
Subcutaneous nodules
Erythema marginatum of the skin
Sydenham chorea ( a neurologic disorder with involuntary rapid, purposeless movements )
What is the morphology of endocarditis?
Inflammation of the mural and valvular endocardium on the left side of the heart.
What is the morphology of myocarditis?
Causes heart failure that may rarely lead to death in 1% of cases
Soft and flabby myocardium leading to dilation of heart chambers
Mostly left ventricle
What is the morphology of pericarditis?
Pericardial friction rub can be heard
Describe the morphology of rheumatic endocarditis.
Inflammation of the valvular endothelium (valvulitis) of the mitral and aortic valves.
Results in foci of endothelial injury and necrosis within the cusps or along the chordae tendinae.
Overlying these foci, small (1-2mm) platelet-fibrin thrombi form vegetations = verrucae
Verrucae are sterile and adherent to lines of closure of the valves so do not embolize.
Describe the morphology of rheumatic myocarditis.
Foci of inflammation = Aschoff bodies.
Consist of central necrosis surrounded by lymphocytes (mainly T cells), occasional plasma cells and plump activated macrophages - Antischkow cells
Chromatin in the nuclei of macrophages is condensed into long, wavy ribbons = caterpillar cells
Describe the morphology of rheumatic pericarditis.
Inflamed pericardial surface has a shaggy fibrin rich exudate on top = bread and butter pericarditis
What are the outcomes of RF?
After initial attack = increased vulnerability to recurrence with subsequent GAS infections
Damage to valves is cumulative (over months/years) with fibrosis increasing with every recurrent attack
What is the hallmark of RHD?
Valvular scarring and deformity
Describe the valve leaflets in RHD.
Fibrosed, thickened and distorted.
Commissures are fused: “button-hole” or “fish-mouth” appearance.
Chordae tendinae are thickened and shortened
Leads to valve dysfunction - stenosis/regurgitation
Greatly increases the risks of infection of deformed valves = IE
Which valve is mainly affected by RHD?
Mitral valve is affected alone in 2/3 of cases with aortic in additional 25% of cases
What is the characterization of IE.
A serious infection - colonization of the heart valves by an organism, usually bacteria.
Leads to formation of vegetations composed of thrombotic debris, organisms and inflammatory cells.
Destruction of the valve can occur.
Possible break off of vegetations and embolization to distant sites.
What is the clinical presentation of IE?
Stormy onset with rapidly developing fever and chills.
What is the cause of the subacute type of IE.
Low virulence organisms can affect previously damaged valves (e.g. RHD), artificial ones, or those with congenital defects.
What happens in the subacute type of IE?
Endothelial injury occurs and formation of microthrombi that can easily be colonized later even by low virulence organisms should bacteremia occur.
This can occur following a minor dental or surgical procedure = need prophylactic antibiotic if predisposing valve pathology is known.
Which valves are most commonly affected in the subacute IE?
Aortic and mitral valves.
What is the cause for acute IE?
High virulence organisms on previously normal valves
How do highly virulent organisms gain access in acute IE?
IV access (contaminated needle shared by IV drug users)
How do highly virulent organisms gain access in acute IE?
IV access (contaminated needle shared by IV drug users)
What valve is commonly affected in acute IE?
Tricuspid valve (IV injection reaching the right side of the heart)
Name the organisms involved in acute IE.
Staph aureus
Strep pyogenes
Occasionally fungi
Name the organisms involved in subacute IE.
Oral flora including streptococcus viridans, enterococci, haemophilus
Name the organisms involved in subacute IE.
Oral flora including streptococcus viridans, enterococci, haemophilus
List the differences between acute and subacute IE.
Acute - high virulence orgnanism, previously normal valves, destructive/rampant infection, 20-40% fatality
Subacute - low virulence, diseased valve, low grade infection
What are the clinico-pathological features of IE.
- big, bulky, friable vegetations: containing bacteria, fibrin and inflammatory cells
- ulceration/destruction of the valve
- deterioration of valve function
- possible embolization by septic emboli to the brain, kidneys, may cause abscesses or septic infarcts
- less valvular destruction occurs in the subacute form
Everything in a nutshell.
GAS infection –> RF –> RHD –> IE