Setting: ED
CC: “I have a fever.”
VS: BP: 110/70 mm Hg; P: 90 beats/minute; T: 102°F; R: 14 breaths/minute
HPI: A 43-year-old man with a history of injection drug use (IDU) comes to the ED with fever for the past several days. The last time he injected drugs was several days prior to coming to the ED. He had been sober for 2 years when he relapsed. He denies chest pain or shortness of breath.
PMHX:
Alcoholism: 2 years of sobriety
Three-month residential rehabilitation in past
Medications: none
What valve would be involved most often with endocarditis secondary to IDU?
a. Mitral
b. Aortic
c. Tricuspid
d. Pulmonic
Answer c. Tricuspid
Because of continuously exposing the right side of the heart to infected material you should expect to have an infection of the right side of the heart. The tricuspid valve is most vulnerable. Right-sided endocarditis can spread infection to the lungs with septic emboli.
PE:
Cardiovascular: 3/6 systolic murmur heard best at the lower left sternal border
Extremities: splinter hemorrhages found in some fingernails; no Janeway lesions, no Osler nodes
Which lesion will increase on inhalation?
a. Mitral stenosis
b. Aortic stenosis
c. Tricuspid regurgitation
d. Mitral regurgitation
Answer c. Tricuspid regurgitation
Right-sided lesions increase with inhalation. Left-sided lesions increase with exhalation.
Inhalation Mechanism
• It expands the volume of the chest.
• The phrenic nerve stimulates the diaphragm.
• Negative intrathoracic pressure is present.
• It pulls more blood into the thorax.
The patient’s murmur increases with inhalation. The lower left sternal border is the location of the tricuspid valve.
Initial Orders:
Blood cultures
CBC
CHEM-7
Sensitivity of Blood Cultures
1. 70% to 80%
2. 90% to 95%
3. 95% to 99%
Move the clock forward 5 to 10 minutes and repeat the cultures.
On CCS, the only way to get multiple blood cultures is to move the clock forward and repeat the test. For acute endocarditis, such as from IDU, do not wait for the results of cultures or echocardiography to give the antibiotics.
Three cultures are standard when excluding endocarditis.
Mechanism of Blood Cultures
1. Media contains labeled carbon.
2. Bacteria ingest labeled carbon as they grow.
3. Labeled carbon excreted as labeled carbon dioxide (CO2) by bacteria.
4. Machine samples air in the bottles by needle.
5. Labeled CO2 above the cutoff indicates growth of bacteria.
After the third blood culture is obtained, start antibiotics. Waiting 15 to 30 minutes between cultures is acceptable. Sustained or continuous bacteremia is a strongly suggestive of endocarditis.
Reports:
CBC: normal
CHEM-7: normal
You check the patient’s chemistry to guide dosing of medications. It does not matter that dosing is not possible on CCS. It matters that you know you need to estimate glomerular filtration rate (GFR) so as not to kill your patient’s kidneys.
Subacute endocarditis is associated with anemia in >90% of patients.
A normal CBC in this situation suggests acute endocarditis.
Orders:
Vancomycin IV
Gentamicin IV
All initial laboratory tests and treatments should be ordered while in the ED before transferring the patient to the hospital ward. Never just shoot the patient to the floor or intensive care unit (ICU) without doing something for them.
Native valve endocarditis: Viridans group streptococci is the most common cause.
IDU: S. aureus or epidermidis is the most common cause.
What is the mechanism of aminoglycoside antibiotics such as gentamicin, tobramycin, and amikacin?
a. DNA gyrase
b. RNA polymerase
c. Cell wall
d. Ribosome
e. Unknown
Answer d. Ribosome
Aminoglycoside antibiotics inhibit messenger RNA (mRNA) translation at the ribosome. This is not the same as inhibiting the production of mRNA. Gentamicin stops the production of protein from mRNA at the ribosome. There is no difference in the mechanism or aminoglycosides.
Beta-Lactam Antibiotics
• Penicillins
• Cephalosporins
• Carbapenems
• Monobactam (aztreonam)
Why are beta-lactam antibiotics and gentamicin synergistic in effect?
a. Blocking excretion raises blood level.
b. Gentamicin increases tissue penetrance of penicillin.
c. Different mechanisms of action are complementary.
d. Gentamicin affects the cell wall when used with beta-lactam antibiotics.
Answer c. Different mechanisms of action are complementary.
Beta-lactam antibiotics inhibit the cell wall. This literally puts a hole in the bacterial cell wall. The aminoglycoside can enter the hole in the wall and disrupt the work or production of the ribosome.
Synergism = Two Drugs with Different Mechanisms of Action
Two beta-lactam antibiotics are never synergistic when used together!
Do not forget to order a diet for all admitted patients. The CCS does not expect you to starve your patient!
Why are splinter hemorrhages potentially important in this patient?
a. Changes dose of antibiotics
b. Changes duration of antibiotics
c. Establishes diagnosis of endocarditis if cultures are negative
d. Changes which echocardiogram to use
e. Antiquated and never relevant
Answer c. Establishes diagnosis of endocarditis if cultures are negative
Blood cultures are falsely negative in 1% to 5% of patients with endocarditis. This form of “culture-negative” endocarditis is diagnosed with the presence of vegetations on an echocardiogram and the presence of at least three minor criteria. Splinter hemorrhages are one of the minor criteria.
Minor criteria:
• Risk: IDU or prosthetic valve
• Fever
• Embolic or vascular phenomena: splinter hemorrhages, Osler nodes, Roth spots, Janeway lesions
This type of patient can have the clock moved forward at long intervals, for example, 12 hours is okay for a hospitalized patient. Blood culture results take 1 to 2 days to become positive.
Report:
Blood cultures: S. aureus in all three cultures
What microbiologic feature of S. aureus allows it to cause acute endocarditis?
a. Routine feature of gram-positive organism
b. Coagulase
c. Absence of coagulase
d. Plasmid
e. Mutation of penicillin-binding protein
Answer b. Coagulase
Coagulase is present in the cell surface of S. aureus. This organism is synonymous with the term “coagulase positive staphylococci.” Coagulase literally “melts” its way through intact tissue. This is why IDU causes acute endocarditis. Coagulase makes the organism able to aggressively penetrate normal tissue. Viridans group streptococci and enterococcus are relatively much less virulent. They generally can only invade damaged tissue such as prosthetic valves or those underlying native valvular disease such as mitral stenosis or regurgitation. Staphylococcus epidermidis is one of more than 30 types of less virulent staphylococci that are coagulase negative.
Coagulase penetrates normal tissue.
Orders:
Transthoracic echocardiogram (TTE)
Repeat vital signs
Report:
Repeat temperature 100.8°F at 2 days after start of antibiotics
Make sure fever resolves with endocarditis.
TTE has same sensitivity for right-sided endocarditis as transesophageal echocardiography (TEE).
The right ventricle covers 75% of the anterior surface (front) of the heart.
Strongest indication for valve replacement:
• Ruptured chordae tendineae
Move the clock forward to get the sensitivity of the organism and the TTE results.
Reports:
Sensitivity report: sensitive to oxacillin
TTE: tricuspid valve vegetation (Figure 10-2)
Switch vancomycin to a beta-lactam antibiotic if it is Staphylococcus sensitive.
Orders:
Stop vancomycin
Start oxacillin (or nafcillin)
Chest x-ray
Figure 10-2. Vegetations (arrows) due to viridans streptococcal endocarditis involving the mitral valve. (Reproduced with permission from Longo DL, et al. Harrison’s Principles of Internal Medicine, 18th ed., Vol. 2. New York: McGraw-Hill; 2012.)
Check for septic emboli to the lungs in patients with right-sided endocarditis.
Report:
Chest x-ray: normal
Coagulase creates lung abscesses by tissue penetrance into the lungs.
Move the clock forward to day 5 of treatment. Gentamicin is only needed for synergy with the beta-lactam antibiotic for the first 3 to 5 days of therapy.
Orders:
Stop gentamicin
Continue oxacillin (or nafcillin or cefazolin) for 4 weeks
When the patient’s treatment is finished, what will the patient need for endocarditis prophylaxis with dental procedures in the future?
a. Nothing
b. Amoxicillin with fillings
c. Amoxicillin with dental extraction
d. Quinolones with colonoscopy if biopsied
Answer c. Amoxicillin with dental extraction
Previous endocarditis is an indication for endocarditis prophylaxis if undergoing a potentially bacteremia-causing procedure. Dental extraction or cutting the mouth needs prophylaxis. Dental fillings and any form of endoscopy of either the lungs or gastrointestinal (GI) tract do not need prophylaxis.
Lesions needing prophylaxis with dental extractions:
• Previous endocarditis
• Prosthetic valves
• Unrepaired cyanotic heart disease
• Cardiac transplant recipients