6th March 2024

Investigations

The two most important investigations that will lead to the diagnosis are ECG and cardiac enzymes (high sensitivity troponin). ST segment elevation in at least two contiguous leads or new left bundle branch block and raised troponin will confirm diagnosis of STEMI. 

The distinguishing feature between unstable angina and NSTEMI is the presence of elevated troponin in NSTEMI which implies cardiac damage. Both will have non-ST segment changes (ST segment depression or inverted T waves) or nonspecific changes on ECG. 

The correlation between ECG changes and coronary territories are explained in the table below: 

Troponin I serum levels will usually be elevated 2-3h after the onset of chest pain and reach their peak levels around 12-48h. Levels will normalise 4-10 days post event. They have the highest sensitivity and specificity compared to other cardiac markers. 

CK-MB (creatine kinase myocardial band) are less sensitive and specific than troponin but will normalise 48-72h post MI. Continued rise of CK-MB after 72h is diagnostic of myocardial reinfarction.