Fever in NSTEMI Patients: Non-Infectious Etiology
The available evidence does not provide specific percentages for non-infectious febrile episodes in NSTEMI patients, but fever is recognized as a potential secondary cause of myocardial ischemia that warrants evaluation during the acute presentation.
Clinical Context of Fever in NSTEMI
Fever in NSTEMI patients should be evaluated as both a potential precipitating factor for ischemia and as a complication requiring investigation. 1
Fever as a Precipitating Factor
- Temperature measurement is a mandatory component of the initial vital signs assessment in all patients with suspected acute coronary syndrome 1
- Fever increases myocardial oxygen demand and can provoke or exacerbate ischemia in patients with underlying coronary artery disease, potentially triggering NSTEMI in the setting of pre-existing coronary stenosis 1
- The evaluation should specifically assess for conditions causing increased cardiac oxygen demand, including fever from any source, signs of hyperthyroidism, sustained tachyarrhythmias, or markedly elevated blood pressure 1
Post-MI Inflammatory Response
While the provided evidence focuses primarily on STEMI, relevant insights include:
- Post-myocardial infarction inflammation follows a biphasic pattern, with fever during different phases having distinct prognostic implications 2
- In STEMI patients, fever during the second phase (days 4-10) was strongly associated with worse long-term cardiac outcomes, whereas fever during the first phase (within 3 days) was not 2
- The inflammatory response differs between STEMI and NSTEMI, with NSTEMI patients showing lower levels of most inflammatory markers at admission except for CD40 ligand 3
Differential Diagnosis Approach
Non-Infectious Causes to Consider
The guidelines emphasize evaluating multiple non-infectious causes of fever in critically ill patients, which apply to NSTEMI patients: 1
- Cardiac causes: Acute myocardial infarction itself, Dressler syndrome (pericardial injury syndrome), acute pericarditis 1
- Thrombotic complications: Pulmonary infarction, venous thrombosis 1
- Drug-related: Drug fever from medications commonly used in ACS management 1
- Other systemic causes: Gout, pancreatitis, adrenal insufficiency 1
Infectious Complications
- Serious infections occur in approximately 2.4% of STEMI patients treated with primary PCI, with median time to diagnosis of 3 days 4
- The most commonly identified organism is Staphylococcus aureus, with bloodstream being the main location of infection 4
- Infections are associated with markedly worse 90-day outcomes (adjusted hazard ratio for death: 5.6) 4
Clinical Implications
Initial Assessment
- Every NSTEMI patient should have body temperature measured as part of the initial vital signs assessment 1
- The physical examination should specifically evaluate for evidence of increased cardiac oxygen demand, including fever, which may have precipitated the ischemic event 1
- A complete evaluation should include assessment for secondary causes of unstable angina, with measurement of body temperature being a key component 1
Monitoring Strategy
- Fever occurring in ICU patients (including those with NSTEMI) occurs in 26-88% depending on the definition used and patient characteristics 1
- Not all febrile episodes require investigation—those with obvious non-infectious etiology (such as immediately post-operative) may not warrant extensive workup 1
- When investigation is warranted, a thorough history and physical examination should guide diagnostic studies rather than reflexive ordering of all possible cultures 1
Key Caveats
- The specific percentage of NSTEMI patients developing non-infectious fever is not established in the current literature
- The distinction between fever as a precipitating factor versus a complication of NSTEMI requires careful clinical assessment 1
- Given the high mortality associated with serious infections post-MI (>60% in some series), infectious causes must be systematically excluded even when non-infectious etiologies are suspected 4