Good morning everyone,
We’ve come across the paper on ‘Impact of Periprocedural Myocardial Biomarker Elevation on Mortality Following Elective Percutaneous Coronary Intervention’ from Garcia-Garcia et al published in JACC: Cardiovascular Intervention and scratched our heads as to the overall results and interpretation. The paper is available here: http://interventions.onlinejacc.org/content/12/19/1954
The authors have pooled 5 coronary stent trials and 1 large registry - all patients were stable, with ‘normal’ baseline biomarkers (notably CK-MB and cTn); different cut-offs were compared to assess the prognostic significance of biomarker elevation following coronary intervention. The authors concluded that CK-MB was a better predictor of mortality after 1 year than cTn.
The conclusion was based on, as far as I can tell, two main findings:
- Figure 1 depicts one-year mortality rates depending on the biomarker range, categorised into ratios of CK-MB/cTn ratios of ULN.
- The Cox models: As per their methods section, the biomarkers were forced into two models - model A using CK-MB at ≥10 x ULN, model B using cTn ≥70 x ULN. The ratios are derived from the SCAI or Universal Definition of MI definitions.
I feel this analysis could have been improved dramatically to provide more granularity. A major limitation is that two biomarkers with different release kinetics are compared at the same timepoint - cTn only peaks somewhere between 24-36 hours, and you would not expect elective patients to still be in hospital for a ‘peak sample’; CK-MB rises faster and peaks earlier.
The ULN ratios are rather arbitrary, and whilst they are ‘as good as it gets’ currently, when it comes to guideline-endorsement, afaik they were not derived based on a biological concept (or equivalence, for that matter).
With respect to the Cox models, it’s odd to see different variables entered into the two multivariate models - model A uses age, prior MI, lesion complexity, CK-MB ratio, hyperlipidaemia and DM. I would have expected model B to just swap CK-MB for cTn ratio, but the model has also ‘gained’ prior CABG and sex - surely, based on the univeriate analysis, both of them should have been entered into both models? Can somebody think of a genuine reason as to why not?
An interesting detail is that having a diagnosis of hyperlipidaemia appears to lower your risk by almost half - I don’t see that mentioned in the discussion either.
Would be keen to hear your opinions on the points raised above.