Makindo Medical Notes

Related Subjects: |Atherosclerosis |Ischaemic heart disease |Assessing Chest Pain |ACS - General |ACS - STEMI |ACS - NSTEMI |ACS - GRACE Score |ACS - ECG Changes |ACS -Cardiac Troponins |ACS - Post MI arrhythmias |ACS: Right Ventricular Infarction

Troponins begin to be released within minutes of myocardial damage. Take a troponin at time 0 and at 6-12 hours.

About

• Troponin is a component of thin filaments (along with actin and tropomyosin) and is the protein to which calcium binds to accomplish this regulation and has three subunits, TnC, TnI, and TnT which are found in skeletal and cardiac muscle.
• When calcium is bound to specific sites on TnC, the structure of the thin filament changes in such a manner that myosin (a molecular motor organised in muscle thick filaments) attaches to thin filaments and produces force and/or movement.
• In the absence of calcium, tropomyosin interferes with this action of myosin, and therefore muscles remain relaxed. Troponin C is non-cardiac so not used.

Testing and uses

• cTnT and cTnI are not usually detected in the normal circulation and so any rise may be significant. One common cause is that cardiac troponins (cTnI or cTnT) are the biomarker of choice for the assessment of ACS.
• They are the most specific and sensitive laboratory markers of myocardial cell injury. Troponin is released with as little as 1gram of myocardial cell death and it is therefore now possible to diagnose a myocardial infarction of a much smaller size, so small that it does not cause ST-segment elevation.
• It has been estimated that, since the 2001 guidelines were introduced, the number of patients leaving the hospital with a diagnosis of MI has increased by more than 50%.

Definition

• According to the fourth universal definition of MI, acute MI (AMI) requires a rise and/or fall in cardiac troponin (cTn) with at least one value above the 99th percentile upper reference limit.
• Cardiac troponin I (cTnI) and cardiac troponin T (cTnT) are the preferred biomarkers in acute coronary syndrome

Interpretation: Patient with chest pain and normal or equivocal ECG

• For patients presenting with ischaemic sounding chest pain and a normal or equivocal ECG, they should have cardiac biomarkers performed on admission and at 3 and 6 hours.
• If the initial troponin T concentration is > 14 ng/L and the 3-hour troponin increases by over 7 ng/L, the patient should be treated for NSTE-ACS.
• If the initial troponin T concentration is < 14 ng/L and the 3-hour troponin > increases by over 7 ng/L and is > 14 ng/L, the patient should be treated for NSTE-ACS.
• If the initial troponin T is > 14 ng/L with no significant increase at 3-hours, then review the clinical history and consider other clinical conditions (e.g. trauma, heart failure, pulmonary embolus, aortic valve disease, hypertrophic cardiomyopathy, renal failure, hypotension, sepsis) and investigate and manage as appropriate.
• If the initial 3 and 6-hour troponins are < 14 ng/L then the patient should be assessed with the GRACE score. Patients with a high GRACE Score or unstable symptoms should be considered for in-patient assessment (review by ACS practitioner or Cardiologist). Patients with a low-intermediate GRACE Score (<140) and stable symptoms should be suitable for out-patient assessment ( e.g. Rapid Access Chest Pain Clinic RACPC).

Assessing Troponin

• Normal (hs Troponin T < 14ng/l) A result of <14ng/L more than 6 hours after symptoms rules out MI.
• Possible MI (hs Troponin T 14-30 ng/l) especially if there is +7ng/L rise 3 hrs later
• Probable MI (hs Troponin T > 30 ng/l)

Causes of elevated Cardiac troponins

• When to test
  • Requesting troponin only when ACS was suspected such as chest pain, shortness of breath, collapse/syncope, and palpitations
• High sensitivity Troponin
  • NICE has assessed 3 assays that measure cardiac troponin levels in the blood. These can detect rises earlier and so can allow patients with negative tests to be discharged earlier.
  • High-sensitivity cardiac troponin (hscTn) assays have the ability to rapidly rule in or rule out acute coronary syndrome with improved sensitivity, and they are increasingly being used.
• Significance
  • Chest pain with normal CK-MB but elevated troponins is called minor myocardial damage and micro infarction
  • Troponin levels are prognostic for patients with ACS at risk of poorer outcomes
  • CK-MB, cTnT, or cTnI can be done at 12 hours as maximal then and may be elevated up to 10-14 days
  • Has meant that many more people have been diagnosed with Myocardial infarction

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