When it comes to diagnosis, the clinical presentation will be important. There will often be key diagnostic factors like central crushing chest pain as well as other symptoms like dyspnoea or nausea/vomiting. But there will also be an assessment of the patient’s atherosclerotic risk factors, which were discussed last week. For example, the physician will consider if the patient has hypertension, dyslipidaemia, diabetes, if they are a smoker, if they have a family history of heart disease, and so on.

Once all of that has been considered, the key investigations that follow will be an electrocardiogram (ECG) and a blood test that includes an order for cardiac biomarkers (i.e., a high-sensitivity troponin assay).

The Electrocardiogram (ECG)

As soon as an acute coronary syndrome is suspected (even if there is only a tiny bit of suspicion that the patient might be having an acute coronary event), the patient will receive a 12-lead ECG. That will be reviewed by an experienced physician within 10 minutes of the patient’s presentation to an emergency department.

The ECG will be repeated every 10-15 minutes generally until the patient is pain-free and a cardiologist has approved cessation of the ECG monitoring. Telemetry may be an alternative to serial ECG monitoring. Telemetry is continuous monitoring of a patient’s heart rate and rhythm.

The most important ECG change that ED physician is looking for is ST segment elevation. This is so important because it plays a large role in dictating the treatment protocol the patient receives. For example, for patients with ST elevation, there is a proven benefit associated with using immediate reperfusion therapy (either by fibrinolytic medication or by percutaneous coronary intervention with stenting). In contrast, fibrinolytic medication is not used if there is no ST-segment elevation on the ECG. This will be discussed more later on.

_{Source: https://www.cvphysiology.com/uploads/images/CAD012%20ST%20elevation.png}

Cardiac Troponins

Troponin is a protein that lives in myocardial cells. There are different types (TnC, TnI, and TnT), but TnI is most commonly used for diagnosing ACS. Raised levels of troponin in the blood signifies myocardial injury.

In October 2018, Queensland Health Hospitals introduced a new high-sensitivity cardiac troponin assay. This new assay can reliably detect circulating troponin at lower levels.

Historically, troponin levels were checked on presentation and then again 6 hours later (i.e., at 0 and 6 hours).  Now, troponin levels are checked on presentation and then again 3 hours later (i.e., at 0 and 3 hours). If troponin levels return normal on both occasions, it is unlikely that the person has had a myocardial infarction.

• If a patient has had a myocardial infarction, after approximately 3 hours have elapsed, you would expect troponin levels to be higher than they were at the initial presentation. This is because TnI leaks out of myocardial cells slowly. TnI also persists in the bloodstream for anywhere between 4 and 7 days, which makes it difficult for us to use TnI to diagnose a second myocardial infarction within 7 days of the first one!
• It is also important to note that the turn-around time (the time it takes for the troponin result to be returned from the laboratory) can be variable (up to approximately 50 minutes). So…. if there is ST elevation on the ECG, troponin will be tested and it will be positive, but we don’t wait for the blood to be collected and for the troponin results to return from the lab before reacting to the ST elevation seen on the ECG trace. That is to say, cardiac biomarkers are not necessary to confirm the diagnosis of STEMI. Troponin levels are, however, necessary to differentiate the NSTEACS (i.e. NSTEMI vs. unstable angina). Raised troponin levels will confirm the diagnosis of NSTEMI.

Time is heart muscle (and mortality) !! First steps:

• Seek medical help, call an ambulance!
• Paramedics will:
  • Notify hospital emergency department of impending arrival
  • 12 lead ECG
  • Monitor vital signs
  • E.g. blood pressure, heart rate, respiratory rate, oxygen saturation, temperature, etc.
  • Give aspirin 300mg orally (chewed or dissolved) unless contraindicated
  • Give sublingual GTN spray 400micrograms every 5 minutes if pain persists
  • Up to a total of 3 doses if tolerated
  • Give an intravenous opioid if necessary for persistent chest pain, e.g., morphine 2.5 – 5mg IV every 5 – 10 minutes if necessary (monitor sedation score and blood pressure)
  • Give oxygen (only if necessary, i.e., if the patient’s oxygen saturation is less than 94%).

🎞️ Video 3: Watch the following lecture video, “ACS Part 2″ ⏲️9:06 mins

There are important differences when it comes to the management of a STEMI and the NSTEACS (unstable angina or NSTEMI). These are directly related to the aims of treatment.

 

For patients with a confirmed STEMI who have presented to the emergency department within 12 hours of symptom onset, emergency reperfusion therapy is indicated.

• Note that ‘percutaneous coronary intervention’ is commonly abbreviated to ‘PCI’. This is synonymous with ‘percutaneous transluminal coronary angioplasty’ or ‘PTCA’ that was introduced in week 1 on the possible surgical management of stable angina.

🎞️ Video 4: Watch the video below for a reminder about what this is referring to. ⏲️1:08 mins

Fibrinolysis is the use of an intravenous medication (Tenecteplase, Reteplase, or Alteplase) that works to dissolve the clot that has formed in the coronary artery. The pharmacology of these thrombolytics will be discussed in the week 5 lecture on anticoagulation.

“For the purposes of reperfusion therapy, PCI is preferred over fibrinolysis if it can be performed within 90 minutes of the first medical contact. Otherwise, fibrinolytic therapy is preferred for those without contraindications.” Source: National Heart Foundation of Australia & Cardiac Society of Australia and New Zealand. Australian Clinical Guidelines for the Management of Acute Coronary Syndromes 2016.

Note the following contraindications to fibrinolytic therapy (not an exhaustive list, consult product information, and note that each patient requires individual assessment with regards to risk vs benefit of proceeding with thrombolysis).

• Known hypersensitivity (allergy) to the active ingredient or to gentamicin (a trace residue from the manufacturing process)
• Active bleeding (excluding menses) or significant bleeding disorder
• Severe thrombocytopenia
• Prior intracranial or subarachnoid haemorrhage
• A structural cerebrovascular lesion (e.g., arterial aneurysm or arteriovenous malformation)
• Malignant intracranial neoplasm (primary or metastatic)
• Ischaemic stroke or transient ischaemic attack (TIA) within the previous 6 months
• Severe uncontrolled hypertension (i.e., BP >180/110mmHg)
• Trauma or major surgery (especially involving the head and/or face) within the previous 3 months
• Non-compressible vascular punctures in the past24 hours (e.g., lumbar puncture)
• Suspected aortic dissection
• Severe hepatic dysfunction, including hepatic failure, cirrhosis, portal hypertension, and active hepatitis
• Active peptic ulcer within the previous 3 months
• Prolonged or traumatic CPR (> 2 minutes) within the previous 10 days
• Current therapeutic anticoagulation for another indication

Early management of a STEMI also includes adjuvants to reperfusion therapy.

Management of the NSTEACS is a little bit more complicated than management of STEMIs.  It can help to remember the aims of treatment.

Unstable angina and the NSTEMI are considered a continuum and both are treated under the overarching term that is NSTEACS. The chosen treatment regimen depends on an initial risk assessment. Patients with confirmed NSTEACS are classified as having either a very high, high, or intermediate acute risk of a recurrent cardiovascular event and mortality.

Very high-, high-, and intermediate-risk criteria are listed in the table below.

_{Table source: Chew DP, Scott IA, Cullen L, et al. Guideline Summary National Heart Foundation of Australia & Cardiac Society of Australia and New Zealand. Australian Clinical Guidelines for the Management of Acute Coronary Syndromes 2016. MJA. 2016;205(3):128-133. Available at: https://www.mja.com.au/system/files/issues/205_03/10.5694mja16.00368.pdf}

Specifically, this risk assessment determines when a patient with confirmed NSTEACS should undergo invasive management with PCI or CABG. Remember that fibrinolytic therapy is NEVER used to treat NSTEACS.

• Very high risk = PCI or CABG recommended within 2 hours of presentation
• High risk = PCI or CABG recommended within 24 hours of presentation
• Intermediate risk = PCI or CABG recommended within 72 hours of presentation, but angiography may be delayed and completed post-discharge if this is deemed clinically and logistically appropriate by the cardiologist in consultation with the patient and their family

Note that the GRACE score is an estimate of mortality after NSTEACS or STEMI. If you are interested, you can access an online GRACE score calculator at https://www.mdcalc.com/grace-acs-risk-mortality-calculator or at https://qxmd.com/calculate/calculator_262/grace. There is no need for you to have a comprehensive understanding of the GRACE score.

A summary of NSTEACS management is outlined in the table below: