Once heart attack is suspected on the basis of symptoms and signs, certain investigations may help to confirm the diagnosis.
- Electrocardiography:- It is a common investigation carried out to confirm the diagnosis. The results may however be normal in the early stages or sometimes difficult to interpret. It can also suggest which portion of the muscle wall has gone into infarction.
- Blood cardiac enzymes estimation:- Certain enzymes contained in heart muscle cells are released in circulation after infarction (heart attack). The increased level of these enzymes can confirm heart attack especially, when ECG is inconclusive. Serial measurement of these enzymes holds more significance than a single value.
- Creatine phosphokinase (CPK-MB):- CPK-MB, the isoenzyme of Creatine phosphokinase, is present in significant amounts only in cardiac muscles and so its rise can be an important indicator of a myocardial episode. Blood levels of CPK-MB may remain elevated for 48-72 hours after a heart attack. It may also be increased in certain heart related procedures (DC cardioversion, cardiac catheterisation).
- Cardiac specific TROPONIN T & TROPONIN I (cTnT & cTnI) :- Rise in levels of these enzymes is very specific for heart attack. This test is considered more sensitive than CPK-MB estimation in detection of small infarcts (small areas of dead tissue). The level of cTnT and cTnI remains elevated for 7-10 days and can be of value in patients of heart attack who seek medical attention very late.
- Aspartate Aminotransferase and Lactate Dehydrogenase (AST & LDH) :- These tests are not commonly done nowadays due to availability of more sensitive and specific tests.
- Echocardiography:- Echocardiography can detect abnormal movements of the infarcted wall and is done to support the diagnosis. It also helps in assessing left ventricular function (ability to eject blood) and detecting complications of myocardial infarction.
- Perfusion scans :- These are very sensitive but not specific for detection of acute infarct. The new as well as old infarcted portion (damaged part of the heart) does not take up the isotope and appears as a “cold spot” (in thallium 201 or technetium 99m sestamibi scans).
- Radionuclide Ventriculography :- This is also not a specific test. It demonstrates the abnormal movements of infarcted portion (new and old) as well as measures the ejection fraction of the ventricles (i.e. the ability to eject blood).