What is the recommended protocol for monitoring cardiac biomarkers, such as troponin (T or I) and creatine kinase-MB (CK-MB), in the Cardiovascular Intensive Care Unit (CVICU)?

Cardiac Biomarker Monitoring Protocol in CVICU

For patients in the Cardiovascular Intensive Care Unit (CVICU), troponin T or I should be measured on admission and repeated 6-12 hours later, with additional measurements guided by clinical presentation and suspected cardiac events. 1, 2

Initial Biomarker Assessment

• Troponin T or I is the preferred cardiac biomarker for detecting myocardial damage in CVICU patients due to its high specificity for cardiac injury and superior diagnostic accuracy compared to other markers 1
• An initial troponin measurement should be obtained at admission, with a repeat measurement 6-12 hours later, even if the initial value is normal 1, 2
• A single troponin test on arrival is insufficient, as 10-15% of patients with myocardial damage may have undetectable troponin levels initially 1

Timing of Serial Measurements

• For patients with suspected acute coronary syndromes, cardiac troponin should be measured at presentation and 3-6 hours after symptom onset to identify a rising and/or falling pattern 2
• If the time of symptom onset is unclear, the time of presentation should be considered the starting point for timing subsequent troponin measurements 2
• Additional troponin measurements beyond 6 hours are warranted in patients with normal initial values but with ECG changes or high clinical suspicion 2

Special Considerations for Post-PCI Monitoring

• All patients who have signs or symptoms suggestive of myocardial infarction during or after PCI and those with complicated procedures should have CK-MB and troponin measured after the procedure 1
• Routine measurement of cardiac biomarkers (CK-MB and/or troponin) in all patients undergoing PCI is reasonable 8-12 hours after the procedure 1

Biomarker Selection and Complementary Testing

• Contemporary troponin assays are the preferred markers for diagnosis of ACS; CK-MB and myoglobin should not be routinely ordered alongside troponin 2
• For patients with very recent symptoms (<6 hours), myoglobin and/or CK-MB mass may be measured as early markers of myocardial infarction 1
• In patients with recent infarction (<2 weeks) and recurrent ischemia, CK-MB or myoglobin measurements are preferred for detecting re-infarction, as troponin may remain elevated for 1-2 weeks after the initial event 1

Monitoring Protocol for Specific Scenarios

• For post-operative cardiac surgery patients, obtain baseline troponin and CK-MB before surgery, then at 8-12 hours post-procedure, and daily for 2-3 days 1, 2
• For patients with recurrent chest pain during CVICU stay, obtain troponin measurements at the onset of symptoms and 6-12 hours later 1
• For patients with confirmed MI, it may be reasonable to remeasure troponin once on day 3 or day 4 as an index of infarct size 2

Interpretation of Results

• Troponin elevations should be interpreted in clinical context, as non-MI related elevations can occur in conditions such as heart failure, myocarditis, pulmonary embolism, and renal dysfunction 3
• The presence and magnitude of troponin elevations are useful for both short-term and long-term prognosis 2
• High-sensitivity assays can detect troponin in 50-90% of healthy individuals, making serial measurements and delta changes crucial for diagnosis 3

Common Pitfalls to Avoid

• Failing to repeat troponin measurements in patients with high-risk features despite initially negative results 2
• Relying solely on troponin without considering the clinical context and ECG findings 2, 3
• Using outdated biomarkers like CK-MB and myoglobin as primary tests when contemporary troponin assays are available 2
• Attributing troponin elevation in renal dysfunction solely to impaired clearance, when cardiac conditions often contribute 3