Chemistry Tests to Guide Therapy During Cardiac Crises

Objective: To identify biochemical tests that have been reported to influence diagnosis, prognosis, and therapy during five cardiac crises: arrhythmia, heart failure, acute myocardial infarction (AMI), cardiac arrest, and heart surgery. Method: Review of the literature. Observations: For each of the five crises, a basic set of tests helps to ensure that myocytes have access to adequate oxygen (PO2, Hct, lactate); adequate, but not excessive fuel (glucose); a balance of electrolytes to support conduction and contraction (K+, ionized calcium, and ionized magnesium [iMg]); and acid-base balance (pH, PCO2). Having this basic set of tests available at points of care (POCs)-the emergency room (ER), the operating room, and the intensive care unit (ICU)-has the potential to improve clinical outcomes. Additional tests, having merit in the ER and the ICU, include troponin (detecting myocyte damage) and brain natriuretic peptide (detecting heart failure). Kidney markers (creatinine and blood, urea, nitrogen) support emergency therapy by ensuring that kidneys are healthy enough to excrete potentially toxic substances (eg, contrast media, Mg), and that the kidneys are not progressing toward acute failure. Examples in the literature of testing for cardiac crises include (1) the importance of monitoring iMg for patients who have been on diuretics for heart failure and who have developed ventricular ectopic beats (arrhythmia), (2) why iMg measurement is important for patients receiving digoxin for heart failure, (3) how lactate measurement may prove valuable for ruling out AMI in the ER with the promise of early patient release, (4) how resuscitation efforts for cardiac arrest may be supported by having lactate and electrolyte values available rapidly, and (5) how measurement of lactate, iMg, and glucose may contribute to better outcomes from coronary artery bypass grafting.