IUHS Student-2-Student USMLE Step 1 Recall
Cardiovascular
Heart Valve Defects
Acute
Rheumatic Fever
acute rheumatic fever is triggered by infection with specific strains of group A streptococci which possess antigens that cross-react with human connective tissue, particularly heart valve glycoprotein...
the condition usually affects children or young adults, and there is a familial variation in susceptibility...its prevalance in Western Europe and North America has progressively declined to very low levels, but it remains common in parts of asia, africa and south america, where it is still the most common cause of acquired heart disease in childhood adolescence...
rheumatic fever is a systemic illness typically presenting with fever, anorexia, lethargy and joint pains...
arthritis occurs in approximately 75% of patients and other features include skin rashes, carditis and neurological features...
anti-streptococcal antibody, anti-streptolysin antibody, positive culture for group A streptococcus, recent scarlet fever...
erythema marginatum (the expanding erythematous rash) and sydenham chorea (rapid, purposeless movements) also accompany this disorder...
carditis is the most important manifestation of rheumatic fever...carditis presents as breathlessness, palpitations or chest pain...
other
features consist of tachycardia, cardiac enlargement and new or changed cardiac
murmurs...
a soft systolic murmur is common but non-specific...a soft mid-diastolic murmur is often due to valvulitis, with nodules forming on the mitral valve leaflets...
there is a pericardial friction rub which is often intermittent...cardiac failure may result either from impaired function of ventricular muscle or from mitral or aortic incompetence and tends to occur in a 'fulminant' form of rheumatic fever that is more common in developing countries...
electrocardiographic changes include ST or T wave changes; conduction defects sometimes occur and may cause syncope...
mitral valve becomes thickened with fused chorda tendinea...
aortic regurgitation occurs...
Chronic
Rheumatic Heart Disease
chronic valvular heart disease develops subsequently in at least half of those affected by rheumatic fever with carditis...the predominant valve affected is the mitral (>90%) and less commonly the aortic, tricuspid, and pulmonary...
mitral regurgitation...
the main pathological process in chronic rheumatic heart disease is a progressive fibrosis particulary affecting the heart valves...
this is in contrast to the destructive lytic process of acute rheumatic fever...the condition also affects the pericardium and myocardium and may contribute to heart failure and conduction disorders...
for the mitral valve the result is shortening of the chordae tendineae, fusion of the commissures and a reduction in size of the valve orifice...the haemodynamic result is mitral stenosis with or without regurgitation...
similar disorders of the aortic and tricuspid valves produces distortion and rigidity of the cusps, and in consequence, stenosis and incompetence...once damage has developed on a valve, the altered haemodynamic stresses on the valve perpetuate and extend the damage, even in the absence of a continuing rheumatic process...
Mitral Stenosis
Mitral
Stenosis produces a middiastolic murmur following an opening snap, whereas
aortic regurgitation produces a descrescendo diastolic murmur...
mitral stenosis is almost always rheumatic in origin...however, in the elderly, heavy calcification of the mitral valve apparatus can produce a syndrome similar to mitral stenosis...there is also a rare form of congenital mitral stenosis...
some episodes of rheumatic fever may pass unrecognised and it is only possible to elicit a history of rheumatic fever or chorea in about half of the patients...isolated mitral stenosis accounts for about 25% of all cases of rheumatic heart disease and an additional 40% have mixed mitral stenosis and regurgitation...2/3 of cases occur in women...
in rheumatic mitral stenosis the mitral valve orifice is slowly diminshed by progressive fibrosis and calcification of the valve leaflets, fusion of the cusps and subvalvular apparatus...
the flow of blood from the left atrium to the left ventricle is therefore restricted and left atrial pressure rises, leading to pulmonary venous congestion and breathlessness...
there is dilatation and hypertrophy of the left atrium, and left ventricular filling becomes more dependent on left atrial contraction...
any increase in heart rate shortens diastole (the time the mitral valve is open) and produces a further rise in left atrial pressure; situations that demand an increse in cardiac output will also increase left atrial pressure...exercise and pregnancy are therefore poorly tolerated...
all patients with mitral stenosis are at risk form left atrial thrombosis and systemic thromboembolism, particularly those with atrial fibrillation...
insidious onset of breathlessness, and pulmonary congestion may cause cough...
exercise tolerance may diminish very slowly over many years and patients often do not appreciate the extent of their disability...
eventually symptoms occur at rest...acute pulmonary edema or pulmonary hypertension can lead to haemoptysis...systemic embolism is sometimes a presenting feature...
Mitral
Regurgitation
rheumatic disease is the principal cause of mitral regurgitation in countries where rheumatic fever is common...
chronic mitral regurgitation causes gradual dilatation of the left atrium with little increase in pressure and therefore relatively few symptoms...
however breathlessness and pulmonary edema will supervene if the left ventricle dilates and the left ventricular diastolic and left atrial pressure increase as a result of chronic volume overload...
in contrast, acute mitral regurgitation tends to cause a rapid rise in left atrial pressure (b/c left atrial compliance is normal) and marked symptomatic deterioration...
one of the more common causes of mild mitral regurgitation...it is caused by congenital or degenerative myxomatous changes and is sometimes a feature of connective tissue disorders such as Marfan's syndrome...
in the mildest form of mitral prolapse the valve remains competent but bulges back into the atrium during systole, causing a mid-systolic click but no murmur...
in the presence of a regurgitant valve the click is followed by a late systolic murmur...the murmur lengthens as regurgitation becomes more severe, and the combination of a
clik and late systolic murmur provides the clinical hallmark of mitral prolapse...
mitral prolapse is associated with an increased incidence arrhythmias--these are usually small but a small minority of patients have frequent and bizarre arrhythmias...
too much dermatan sulfate is in the mitral valve, dermatan sulfate is a glycosalminoglycan...
Pansystolic murmur...
Marfan
Syndrome
the Abe Lincoln look alike...loss of microfibrillary protein of elastic tissue...
Tall HAT + lanky person + Dominant Person...
metabolic defect: loosey goosey collagen, myxomatous deposition...
high arched palate, arachnodactyl (spider fingers), tall, dislocated lens (loose zonules), floppy mitral valve (mitral prolapse), loose jointed (loose ligaments)...
dominant inheritiance, delayed onset (dies age 30-40), defect in collagen, differences in expressivity...
marfans syndrome leads to connective tissue weakness in the aorta characterized by cystic medial necrosis that predisoposes to aortic dissection...
abnormal Fibrillin Gene, usually Missense mutations...
mitral valve prolapse...can lead to immediate death b/c of conduction deficits...
Aortic
Stenosis
aortic stenosis is the most frequent of all valvular abnormalities...
acquired aortic stenosis is usually the consequence of either calcification induced by wear and tear of congenitally bicuspid or calcification of aortic valves...
the overwhelming majority of cases represent age-related degenerative calcification...
aortic stenosis comes to clinical attention primarily in individuals in their fifties to sixties with congenitally bicuspid valves but not until the seventies and eighties with previously normal valves having three cusps; hence the term senile calcific aortic stenosis...
the characteristic heart murmur of AS is a crescendo-decrescendo midsystolic ejection murmur that has a paradoxically split S2...
the obstruction to left ventricular outflow leads to a gradually increasing pressure gradient across the calcified valve, which may reach 75 to 100 mm Hg in severe cases...
left ventricular pressure must consequently rise to 200 mm Hg or more in such instances, and cardiac output is maintained by the development of concentric left ventricular (pressure overload) hypertrophy...
eventually as the stenosis worsens, angina or syncope may appear...angina is probably a consequence of impaired microcirculatory perfusion of the hypertrophied myocardium, but the basis of syncope is poorly understood...
eventually, cardiac decompensation with congestive heart failure may ensue...
the onset of such symptoms (angina, syncope, or CHF) in aortic stenosis heralds the exhaustion of compenstory cardiac hyperfunction and carries a poor prognosis if not treated by surgery...
Aortic Regurgitation
the
condition results from congenitally abnormal aortic cusps (bicuspid valves), or
from valve damage due to rheumatic heart disease or infective endocarditis, or
other rarer causes...
when regurgitation is marked, the stroke output of the left ventricle may be doubled or tripled...the major arteries are then conspicuously pulsatile; the left ventricle dilates and hypertrophies and initially compensates for the regurgitation....
the left ventricular diastolic pressure rises, at first only with exercise, and breathlessness develops...in contrast to chronic gradual onset regurgitation, acute regurgitation may result from damage to the aortic leaflets (endocarditis, trauma), and auscultatory signs may be masked by tachycardia and the abrupt rise in LV endodiastolic pressure (shortening or even abolishing the typical murmur)...
descrescendo diastolic murmur that is heard best over the left border of the heart...
until the onset of breathlessness, the only symptom may be an awareness of the heart beat, particulary when lying on the left side...this results from the increased stroke volume...
paroxysmal nocturnal dyspnoea may be the first symptom and peripheral edema, or angina, may occur...although it is usually best heard to the left of the sternum, it is sometimes louder to the right...a thrill is uncommon...
a systolic murmur due to the increased stroke volume is common, and does not necessarily indicate stenosis...when the leak is large the diagnosis is usually easy, with gross pulsation in the large arteries, a collapsing pulse, a low diastolic and an increased pulse pressure...there is usually a thrusting apical impulse and often a presystolic impulse and a fourth heart sound...
the regurgitant jet produces fluttering of the mitral leaflets and a soft mid-diastolic murmur; the latter is called an Austin Flint murmur...