Infective endocarditis: infection on a valve
Infective endocarditis is an infection of the endocardium — the heart's smooth inner lining — and especially of the heart valves, which are made of that same lining. Bacteria (sometimes fungi) circulating in the blood settle on a valve, most readily where its surface is already roughened by prior damage, an artificial valve, or turbulent flow.
Once lodged, the microbes and the body's clotting response build up a [[vegetation|vegetation]] — a fragile clump of bacteria, platelets, and fibrin stuck to the valve. Vegetations cause harm in three ways: they chew up and destroy the valve (causing leaking and a new murmur), they pour bacteria continuously into the bloodstream (causing fever and sickness), and pieces can break off as emboli that lodge in the brain, kidneys, or limbs.
Catching it: cultures, echo, and the Duke criteria
Because endocarditis is sneaky and serious, clinicians use a structured framework — the Duke criteria — to weigh the evidence rather than relying on a hunch. The two pillars are blood cultures growing a typical organism (proving bacteria are in the bloodstream) and an [[echocardiography|echocardiogram]] showing a vegetation on a valve. These are the major criteria; fever, embolic events, and predisposing risk factors count as minor ones.
Duke criteria — combining evidence to reach a diagnosis:
MAJOR criteria
- Positive blood cultures with a typical endocarditis organism
- Echo evidence: a vegetation, abscess, or new valve leak
MINOR criteria
- Predisposing heart condition or injection drug use
- Fever >= 38 C
- Vascular signs (emboli to brain/limbs)
- Immune signs (e.g. glomerulonephritis)
- A single positive blood culture
Diagnosis = DEFINITE if:
2 major OR
1 major + 3 minor OR
5 minor
Worked example:
Strep cultures positive .......... 1 MAJOR
Vegetation on mitral valve ....... 1 MAJOR
-----------------------------------------
2 major -> DEFINITE endocarditisTreatment is a long course — typically several weeks — of intravenous antibiotics chosen to match the cultured organism, sometimes with surgery to replace a destroyed valve or remove a large vegetation at high risk of embolizing. The earlier it is caught, the more of the valve can be saved.
Rheumatic fever: when the body attacks its own valves
Rheumatic fever is a different kind of valve disease — not a direct infection of the heart, but an immune misfire that follows an untreated streptococcal throat infection. A week or two after the sore throat, the immune system, confused by molecules the bacteria share with human tissue, mistakenly attacks the body's own joints, skin, brain, and — most importantly — the heart.
When it hits the heart, acute rheumatic carditis inflames all three layers — lining, muscle, and sac. The lasting damage is to the valves, above all the mitral valve. Repeated attacks scar and deform the valve over years, leading to rheumatic heart disease — a stiffened or leaking valve that may only declare itself decades later. It remains a leading cause of valve disease worldwide, particularly where strep throats go untreated.