Infective endocarditis

After studying this note, you will be able to approach a patient with suspected infective endocarditis comprehensively. Remember to always check specific drug doses and local protocols against the Kenya Ministry of Health guidelines and your hospital formulary.

Definition

Infective endocarditis (IE) is an infection of the endocardium, which is the inner lining of the heart chambers and valves. It typically involves the heart valves, but can also affect the mural endocardium, septal defects, or intracardiac devices.

Anatomy and physiology you need

The endocardium is a thin, smooth membrane that lines the heart chambers and covers the heart valves. The heart valves (aortic, mitral, tricuspid, pulmonary) are crucial for ensuring unidirectional blood flow through the heart. Damage to the endocardium, particularly on valve leaflets, creates a surface where bacteria or fungi can adhere and proliferate, forming vegetations. These vegetations can embolize to other organs or cause valve dysfunction.

Causes and risk factors

The causes of IE are primarily bacterial or fungal pathogens. In the Kenyan setting, several factors increase the risk:

• Valvular heart disease:
  • Rheumatic heart disease: This is a significant cause of valvular damage, particularly mitral and aortic regurgitation, creating a substrate for IE.
  • Degenerative valve disease: Common in older adults.
• Congenital heart disease:
  • Ventricular septal defects (VSDs), Atrial septal defects (ASDs), Patent ductus arteriosus (PDA): Abnormal blood flow can damage the endocardium.
• Prosthetic heart valves: Both mechanical and bioprosthetic valves are at increased risk.
• Intracardiac devices: Pacemaker leads and defibrillator leads.
• Intravenous drug use: Direct inoculation of bacteria into the bloodstream.
• Immunosuppression:
  • HIV/AIDS: Increased susceptibility to infections, including IE.
  • Tuberculosis (TB): While not a direct cause of IE, TB can lead to systemic illness and immunosuppression, indirectly increasing risk.
  • Malaria: Severe malaria can cause haemolysis and systemic inflammation, potentially predisposing to IE.
• Other factors:
  • Sickle cell disease: Can lead to increased susceptibility to certain infections and splenic dysfunction.
  • Poor oral hygiene/dental procedures: Can lead to transient bacteraemia.
  • Indwelling catheters: Urinary or vascular catheters.
  • Previous IE: Patients with a history of IE are at higher risk of recurrence.
  • Sepsis: Any source of bacteraemia can lead to IE.

Pathophysiology

Damaged endocardium/valve $\rightarrow$ Turbulent blood flow $\rightarrow$ Endothelial damage $\rightarrow$ Platelet and fibrin deposition (non-bacterial thrombotic endocarditis) $\rightarrow$ Adherence of circulating microorganisms (bacteria/fungi) $\rightarrow$ Vegetation formation $\rightarrow$ Microvascular invasion and inflammation $\rightarrow$ Destruction of valve tissue/endocardium $\rightarrow$ Embolization of vegetations $\rightarrow$ Systemic or focal organ damage.

Clinical features

History questions that matter

• Fever pattern and constitutional symptoms: Ask about persistent, low-grade fevers, drenching night sweats, anorexia, and progressive weight loss (subacute) versus sudden high rigors and prostration (acute).
• Predisposing cardiac lesions: History of childhood sore throats, joint pains, or known rheumatic heart disease (RHD); prior valve repair/replacement; congenital defects.
• Portals of entry: Recent dental extractions or cleaning, skin sepsis, unsafe intravenous drug use, recent abortions, catheterizations, or long-term indwelling lines.
• Embolic and immune symptoms: Sudden focal neurological deficits (stroke), acute flank pain with red urine (renal infarction), painful fingers or toes, or sudden loss of vision.
• Underlying immunosuppression: Known HIV status, advanced immunosuppression, or history of pulmonary tuberculosis.

Examination findings and their mechanisms

• General appearance: Pale (anemia of chronic disease or microangiopathic hemolysis), cachectic, actively febrile, or in respiratory distress.
• Cardiac signs:
  • New or changing murmur: Regurgitant murmurs (mitral or aortic regurgitation) caused by leaflet perforation, tear, or bulky vegetations impeding coaptation.
  • Heart failure signs: S3 gallop, elevated JVP, bilateral basilar crackles, and hepatomegaly due to acute valvular disruption.
• Peripheral vasculitic and immunologic phenomena:
  • Osler nodes: Tender, violaceous, raised subcutaneous nodules on the pulp of fingers and toes; caused by circulating immune complex deposition and localized vasculitis.
  • Roth spots: Pale retinal exudates surrounded by hemorrhage; caused by localized immune complex-mediated retinal vasculitis.
  • Glomerulonephritis: Microscopic hematuria and edema; caused by subendothelial immune complex trapping.
• Peripheral embolic and septic phenomena:
  • Janeway lesions: Non-tender, flat, erythematous or hemorrhagic macules on palms and soles; caused by septic microemboli with microabscess formation.
  • Splinter hemorrhages: Linear, dark red streaks under the proximal nail bed; caused by microemboli damaging nail bed capillaries.
  • Petechiae: Found on palpebral conjunctiva, buccal mucosa, and pretibial areas due to capillary fragility and microembolism.
  • Splenomegaly: Reactive lymphoid hyperplasia from sustained bacteremia or focal splenic infarction from macroemboli.
  • Clubbing: Secondary to prolonged tissue hypoxia and circulating platelet-derived growth factors in chronic/subacute infection.

Differential diagnosis

Investigations

Diagnosis and severity

Diagnostic criteria: Modified Duke Criteria

Diagnosis relies on integrating clinical, microbiological, and echocardiographic findings:

• Definite IE: 2 major criteria; OR 1 major and 3 minor criteria; OR 5 minor criteria; OR pathological confirmation (microorganisms demonstrated in a vegetation or intracardiac abscess).
• Possible IE: 1 major and 1 minor criterion; OR 3 minor criteria.
• Rejected: Firm alternate diagnosis, resolution with antibiotic therapy for ≤4 days, or no pathological evidence at surgery/autopsy.

Major criteria:

1. Positive blood cultures: Typical organisms (S. viridans, S. bovis, HACEK, S. aureus, community-acquired enterococci) from two separate blood cultures; or persistently positive blood cultures drawn >12 hours apart; or a single positive culture for Coxiella burnetii.
2. Evidence of endocardial involvement: Positive echocardiogram (oscillating intracardiac mass, abscess, new partial dehiscence of a prosthetic valve) or new valvular regurgitation (worsening or changing of pre-existing murmur is not sufficient).

Minor criteria:

1. Predisposition (pre-existing cardiac condition or IV drug use).
2. Fever (temperature ≥38.0°C).
3. Vascular phenomena (arterial emboli, septic pulmonary infarcts, Janeway lesions, conjunctival hemorrhages).
4. Immunologic phenomena (glomerulonephritis, Osler nodes, Roth spots, positive rheumatoid factor).
5. Microbiological evidence (positive blood culture not meeting major criteria or serological evidence of active infection).

Severity stratification

High-risk features requiring urgent cardiothoracic surgical consultation and intensive monitoring include:

• Hemodynamic compromise: Acute severe aortic or mitral regurgitation leading to pulmonary edema, cardiogenic shock, or refractory heart failure.
• Uncontrolled infection: Persistent bacteremia or fever lasting >7 days despite optimal antimicrobial therapy; infections caused by difficult-to-eradicate or fungal pathogens.
• Local extension: Conduction block (new PR prolongation or bundle branch block indicating aortic root extension), perivalvular abscess, fistula, or large false aneurysm.
• Embolic risk: Very large, mobile vegetations (especially >10 mm on the mitral valve) or recurrent embolic events despite appropriate therapy.

Management

Immediate Stabilisation

• Assess airway, breathing, and circulation.
• Provide supplemental oxygen if hypoxic; place the patient upright if in acute pulmonary oedema.
• Manage acute heart failure secondary to valvular destruction with intravenous loop diuretics and vasodilators (if blood pressure permits). Avoid beta-blockers in acute severe aortic regurgitation as compensatory tachycardia maintains cardiac output.
• Stabilise septic shock with crystalloid fluid challenges guided by signs of fluid overload; initiate inotropes or vasopressors if refractory.
• Draw three sets of blood cultures from separate venepuncture sites prior to administering antimicrobial therapy.

Definitive Medical Treatment

• Empirical therapy (Native valve): High-dose bactericidal regimens covering staphylococci, streptococci, and enterococci. Typically intravenous ampicillin combined with (flu)cloxacillin and gentamicin, or intravenous ceftriaxone with gentamicin. Vancomycin replaces beta-lactams if MRSA or severe beta-lactam allergy is suspected.
• Empirical therapy (Prosthetic valve): Triple therapy covering resistant staphylococci: intravenous vancomycin plus gentamicin plus oral rifampicin. Rifampicin is added because it penetrates bacterial biofilm on foreign material; it is often introduced a few days after clearing bacteraemia to prevent rapid emergence of resistance.
• Targeted therapy: Narrow antimicrobials once culture isolates and minimum inhibitory concentrations (MICs) are identified. Treat for a prolonged duration (usually 4 to 6 weeks) because vegetations lack a direct microvascular supply, relying on passive drug diffusion into avascular fibrin-platelet meshworks.

Surgical Management (Indications for Early Surgery)

• Heart failure: Severe acute aortic or mitral regurgitation causing refractory pulmonary oedema or cardiogenic shock.
• Uncontrolled infection: Persistent bacteraemia or fever >7 days despite targeted antimicrobial therapy; fungal or multidrug-resistant organisms; local extension (abscess, fistula, pseudoaneurysm, new heart block).
• Embolic prevention: Large mobile vegetations (>10 mm) persisting after one or more systemic embolic events, or very large isolated vegetations (>15 mm).

Monitoring, Follow-up, and Safety

• Monitoring: Daily examination for new murmurs, heart failure signs, and peripheral stigmata. Continuous or daily ECG to detect PR-interval prolongation signalling a perivalvular aortic root abscess. Monitor renal function and serum therapeutic drug levels closely when using aminoglycosides or glycopeptides.
• Safety: Anticoagulation is generally contraindicated or held in active native-valve infective endocarditis due to the high risk of fatal intracerebral haemorrhage from septic embolic infarctions or ruptured mycotic aneurysms.

Complications and Prognosis

Prognosis is poorest with prosthetic valve involvement, Staphylococcus aureus etiology, heart failure, and perivalvular invasive disease.

High-Yield Exam Points

• Common wrong first step: Commencing intravenous antibiotics before drawing blood cultures. Three separate sets taken over at least an hour (unless the patient is in septic shock) are mandatory.
• The look-alike trap: Rheumatic fever reactivation. Both present with fever and a changing murmur in young patients. Infective endocarditis typically produces microhaematuria, splenomegaly, and septic emboli; acute rheumatic fever demonstrates elevated ASO titers, migratory polyarthritis, and Sydenham chorea.
• The PR-interval question: Examiners standing at the bedside will ask: "Why are you ordering a daily ECG?" The correct answer is to monitor for PR prolongation, which indicates extension of infection from the aortic valve into the adjacent atrioventricular node (aortic root ring abscess), demanding urgent surgical intervention.
• Right- vs. Left-sided IE: Right-sided (tricuspid) endocarditis is classically seen with intravenous drug use or indwelling central lines. It presents with septic pulmonary emboli (cough, hemoptysis, cavitating lung lesions) rather than systemic emboli, and rarely causes peripheral peripheral vasculitic stigmata.

Clinical Case

A 24-year-old female with known childhood rheumatic heart disease presents with a 4-week history of low-grade fever, weight loss, night sweats, and progressive exertional dyspnoea. On examination, she is pale and febrile. Cardiovascular examination reveals a displaced apex beat, a new early diastolic murmur at the left sternal border, and splinter haemorrhages under the fingernails. Urinalysis reveals microscopic haematuria.

Question 1

What is the single most critical diagnostic investigation to perform before administering therapy? Model Answer: Obtain three separate sets of blood cultures via distinct peripheral venepunctures, spaced at least 30 to 60 minutes apart, to isolate the causative organism and determine antibiotic sensitivities.

Question 2

Serial ECGs show progressive lengthening of the PR interval. What complication does this indicate, and what is the definitive management step? Model Answer: It indicates a perivalvular aortic root abscess extending into the cardiac conduction system (AV node). This warrants urgent cardiothoracic surgical consultation for debridement and valve replacement.

Question 3

Why must therapeutic anticoagulation be avoided despite the high risk of embolic stroke? Model Answer: Septic emboli cause ischemic infarction with fragile, inflamed neocapillaries or mycotic aneurysms; therapeutic anticoagulation carries an unacceptably high risk of catastrophic haemorrhagic transformation.

Practice Questions

Question 1

A 30-year-old male with a history of intravenous drug use presents with high fever, pleuritic chest pain, and cough productive of blood-streaked sputum. A chest radiograph demonstrates multiple peripheral cavitating nodular opacities. A systolic murmur is audible along the left lower sternal border that accentuates on inspiration. Which organism is most commonly responsible for this presentation?

A. Streptococcus viridans
B. Enterococcus faecalis
C. Staphylococcus aureus
D. Coxiella burnetii

Answer: C. Staphylococcus aureus
Explanation: Right-sided tricuspid valve endocarditis in people who inject drugs is most frequently caused by Staphylococcus aureus and typically manifests with septic pulmonary emboli presenting as cavitating lung infiltrates.

Question 2

A 48-year-old woman being treated for native mitral valve Enterococcus faecalis endocarditis develops sudden-onset left-sided hemiparesis. Non-contrast cranial CT reveals an acute right middle cerebral artery territory ischemic stroke. Her international normalised ratio (INR) is normal. What is the most appropriate next step regarding anticoagulation?

A. Initiate intravenous unfractionated heparin with an activated partial thromboplastin time (aPTT) target of 1.5–2.5.
B. Withhold anticoagulation and manage supportively while monitoring neurological status.
C. Administer low-dose therapeutic low-molecular-weight heparin.
D. Start loading-dose aspirin and clopidogrel immediately.

Answer: B. Withhold anticoagulation and manage supportively while monitoring neurological status.
Explanation: Anticoagulation is withheld in native-valve endocarditis complicated by stroke due to the high risk of fatal intracerebral haemorrhagic transformation within septic infarcts.

Question 3

A 62-year-old man with a mechanical aortic valve replacement performed 6 months ago presents with fever, malaise, and a new regurgitant murmur. Blood cultures grow methicillin-resistant Staphylococcus epidermidis. In addition to vancomycin and gentamicin, which oral antimicrobial must be added to penetrate the prosthetic biofilm?

A. Rifampicin
B. Ciprofloxacin
C. Doxycycline
D. Metronidazole

Answer: A. Rifampicin
Explanation: Rifampicin has unique bactericidal penetration into foreign material and bacterial biofilms, making it an essential component of treatment for prosthetic valve endocarditis caused by staphylococci.

Question 4

A bedside examiner asks a student why an acute severe aortic regurgitation murmur in infective endocarditis is notoriously short, soft, and difficult to auscultate, unlike chronic rheumatic aortic regurgitation. What is the correct explanation?

A. The stroke volume drops to zero during diastole.
B. The left ventricle does not have time to dilate, leading to rapid equilibration of aortic and left ventricular diastolic pressures.
C. Vegetations physically block the acoustic sound transmission across the chest wall.
D. The mitral valve closes prematurely in systole rather than diastole.

Answer: B. The left ventricle does not have time to dilate, leading to rapid equilibration of aortic and left ventricular diastolic pressures.
Explanation: In acute severe aortic regurgitation, a non-compliant left ventricle experiences an abrupt rise in end-diastolic pressure, eliminating the diastolic pressure gradient between the aorta and ventricle early, which shortens the murmur.

Question 5

A 20-year-old patient with native aortic valve infective endocarditis has persistent high-grade fevers despite 5 days of targeted intravenous crystalline penicillin. Transthoracic echocardiography shows a 6 mm vegetation. The patient is haemodynamically stable. A routine ECG demonstrates a new first-degree AV block that was absent on admission. What is the most appropriate next intervention?

A. Switch empirical therapy to broad-spectrum meropenem.
B. Perform an urgent transoesophageal echocardiogram.
C. Implant a temporary transvenous cardiac pacemaker immediately.
D. Discharge on prolonged outpatient intravenous antibiotics.

Answer: B. Perform an urgent transoesophageal echocardiogram.
Explanation: New conduction delay implies local tissue invasion into the atrioventricular node (aortic root abscess); transoesophageal echocardiography is the modality of choice to visualize perivalvular extension and guide prompt surgical debridement.

Drafted with AI assistance from standard references and reviewed for structure. Check details against your lecture notes and the Kenya MoH guideline.