Author Affiliations: Department of Surgery, University of Texas Medical Branch, Galveston (vconti@utmb.edu).
To the Editor: Dr Domanski and colleagues1 reviewed 7 studies correlating creatine kinase (CK-MB) levels early after coronary artery bypass graft (CABG) surgery with survival. They concluded “mortality is an increasing function of CK-MB ratio” and “no threshold exists in the response relationship.” However, review of the individual studies suggests there is a threshold effect beyond which an increased risk of mortality exists. Figure 2 does not depict a linear relationship between CK-MB and 30-day mortality rate. Rather, the plot shows a quadratic or perhaps a threshold effect. The authors stated, “a linear term was used for the CK-MB ratio because this provided a better fit using a Cox model with covariates.” They did not state whether they tested for a nonlinear functional form of the CK-MB ratio, either by including polynomial functions or using a nonparametric method such as splines. The extreme CK-MB values may be driving the observed relationship between the continuous CK-MB variable and 30-day mortality rates.
In addition, other sources of CK-MB enzyme release should be considered. Atrial tissue contains as much CK-MB per gram of tissue as does ventricular muscle.2 Chest wall musculature has a higher percentage of CK-MB than peripheral skeletal muscle.2 Any suturing of the atrium,3 such as atrial cannulation for bypass and placing of pacing wires, leads to a background amount of CK-MB elevation. The expected elevations should have no relationship with short- or long-term survival. The authors did not mention any source of CK-MB elevation other than from ventricular muscle injury. Taking such sources into account could alter their conclusion regarding low levels of enzyme elevation.
Conflict of Interest Disclosures: All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported.
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
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