What cardiac enzymes should be assessed in an elderly patient with a probable old inferior infarct and low QRS voltage on electrocardiogram (EKG)?

Cardiac Enzyme Assessment in Elderly Patients with Suspected Cardiac Pathology

Measure cardiac troponin I or T at presentation and repeat at 3-6 hours after symptom onset; do not use CK-MB or myoglobin for diagnosis of acute coronary syndromes with contemporary troponin assays. 1

Primary Biomarker: Cardiac Troponin

Troponin is the sole recommended cardiac biomarker for diagnosing acute coronary syndromes in contemporary practice. 1

Measurement Protocol

• Obtain cardiac troponin (I or T) at initial presentation 1
• Repeat troponin measurement 3-6 hours after symptom onset to identify the pattern of values 1
• If symptom onset timing is unclear, use time of presentation as the reference point for serial troponin measurements 1
• Obtain additional troponin levels beyond 6 hours in patients with initially normal serial troponins who have ECG changes or intermediate/high-risk clinical features 1

Prognostic Value

• Troponin elevations provide both short-term and long-term prognostic information 1
• In elderly patients specifically, troponin levels measured with high-sensitive assays are strong predictors of all-cause mortality (HR: 1.44) and cardiovascular mortality (HR: 1.66) 2
• Consider remeasuring troponin on day 3 or 4 in confirmed MI patients as an index of infarct size and dynamics of necrosis 1

Special Considerations in Elderly Patients

Baseline Troponin Elevations

Be aware that mild troponin elevations are common in elderly patients without acute MI. 3

• Among elderly patients without AMI, baseline troponin levels are elevated above the 99th percentile in 51% with high-sensitive troponin T assays 3
• Despite higher baseline levels, sensitive troponin assays maintain high diagnostic accuracy in elderly patients (AUC 0.94-0.95) 3
• Optimal cut-off levels for troponin are substantially higher in elderly compared to younger patients 3

Age-Related Changes

• Troponin levels increase over time in elderly populations, with median levels rising by 45% over 5 years 2
• Nearly all elderly subjects (96.4%) have detectable troponin levels when high-sensitive assays are used 2

Biomarkers NOT Recommended

CK-MB and Myoglobin

With contemporary troponin assays, CK-MB and myoglobin are not useful for diagnosis of acute coronary syndromes (Class III: No Benefit). 1

Limited Exceptions for CK-MB

CK-MB has only two specific remaining clinical roles: 4

• Detecting early reinfarction when troponin levels remain elevated from the initial event (CK-MB returns to normal within 36-48 hours vs. troponin remaining elevated 5-14 days) 4
• Diagnosing periprocedural myocardial infarction following cardiac interventions 4

Additional Biomarkers for Risk Assessment

BNP/NT-proBNP

BNP or NT-proBNP may be considered for additional prognostic information (Class IIb recommendation). 1

• Very high NT-proBNP levels disproportionate to the degree of heart failure, combined with elevated troponin, are strongly suggestive of infiltrative cardiomyopathy (such as cardiac amyloidosis) in patients with echocardiographic hypertrophic phenotype 1
• NT-proBNP is elevated early in cardiac amyloidosis before cardiac symptoms appear 1

Clinical Context: Low QRS Voltage and Old Inferior Infarct

Low QRS voltage on ECG combined with increased left ventricular wall thickness should raise suspicion for infiltrative cardiomyopathy, particularly cardiac amyloidosis. 1

• Low QRS voltage occurs in approximately 25% of patients with ATTR amyloidosis and 50% of patients with AL amyloidosis 1
• The combination of low ECG voltage with LV septal thickness >12 mm is particularly useful for increased clinical suspicion of ATTR cardiac amyloidosis 1
• Elevated troponin levels in this context carry grave prognostic implications, with in-hospital mortality of 8.0% for troponin-positive patients versus 2.7% for troponin-negative patients 5

Common Pitfalls

• Do not order CK-MB, myoglobin, LDH, or transaminases for routine cardiac evaluation in contemporary practice 1, 4
• Do not interpret mildly elevated troponin in elderly patients as automatically indicating acute MI; consider chronic elevations and use serial measurements to identify rising patterns 3, 2
• Do not use a single troponin measurement; serial measurements are essential to identify the dynamic pattern characteristic of acute injury 1