Enhanced cardiac enzyme profile.

Abstract

A protocol for an enhanced Cardiac Enzyme Profile is proposed based on an admission, or initial, serum specimen and a second specimen 16 hours after onset of symptoms as minimal baseline serum samples in order to accomplish several simultaneous goals: 1. Detecting CK2MB at its average peak for maximal assurance of diagnosis when release is small and for prognosis in all cases of increased serum CK2MB 2. Detection of laboratory evidence of myocardial injury when admission is delayed after onset by the collection of an admission sample for declining CK2MB, and for assays of other enzymes with longer time curves after myocardial injury such as LD isoenzymes and ASAT/ALAT activities and ratio 3. Establishment of decision limits and criteria for the determination of laboratory evidence of myocardial injury 4. Providing cost-effective procedures other than limitation of the number of samples; these include establishing thresholds and criteria for total CK, total LD, and ASAT so that isoenzymes and ALAT are only performed when thresholds are exceeded and criteria are met; performing only CK and, if the threshold is exceeded, CK isoenzymes on the 16-hour sample; collecting additional samples after the first two only when indicated by positive or suspicious (borderline) results and only on routine morning or afternoon rounds rather than specifically timed specimens (except in cases involving thrombolytic therapy); and termination of the protocol once peak positive CK2MB activity and requisite diagnostic consensus confirmation (such as positive LD isoenzymes) is obtained whether or not thrombolytic therapy is involved. Tissue localization of the enzymes has been outlined in some detail with particular reference to the amount of CK2MB in skeletal muscle. Pathophysiological factors discussed in more depth in a previous article have been amplified here with particular reference to the role of increased synthesis as a response to myocardial injury by surrounding prehypertrophic and hypertrophic myocardium as a possible major source of increased serum enzymes in myocardial infarction. ASAT and especially the ASAT/ALAT ratio are useful tests in the protocol, particularly in cases tested late after onset of symptoms when CK2MB has declined into the borderline or usual range, and ASAT/ALAT may be helpful in evaluating LD isoenzyme results. Codes for interpretive comments are provided to serve as guidelines.