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Troponin, troponinaemia, troponinitis, troponin leaks - distinguishing type 1 MI from type 2 or nonischaemic myocardial injury. Increased demand for a limited supply of evidence...
Troponin, troponinaemia, troponinitis, troponin leaks - distinguishing type 1 MI from type 2 or nonischaemic myocardial injury. Increased demand for a limited supply of evidence...
Cardiac isoforms of Tn are expressed in cardiac muscle and released in various fragments on necrosis. Some troponin is unbound in cytoplasm – there is some disagreement over whether these free fragments ‘leak’ across the cell membrane under stress. heart.bmj.com/content/92/7/9…
The advent of high sensitivity troponins in 2010 increased sensitivity for detection and allowed earlier testing in low risk individuals but could also detect troponin in normal individuals.
And so the definition of myocardial infarction was updated in 2007 to take into account of the emerging issue that not all elevations in troponin seemed to be directly related to plaque rupture events. ahajournals.org/doi/abs/10.116…
In general, a type 2 MI is due to a mismatch between supply and demand of oxygen to myocardium, although a working clinical definition of this has yet to be made. Saaby proposed a research definition in 2013: amjmed.com/article/S0002-…
However, this shows us one of the problems with studying this group: a lack of definition and a variety of study populations means that attempts to look at them have been heterogeneous and varied over who they did or did not include.
But there are also patients who do not fit into a neat supply/demand model – those with sepsis, critical illness or low-grade ongoing myocardial injury. Alpert proposed the term ‘nonischaemic myonecrosis’ for these patients: amjmed.com/article/S0002-…
The mechanisms here become diverse – for instance in sepsis where fever/tachycardia and anemia/hypoxaemia lead to supply/demand mismatch, inflammatory mediators with cytotoxic effects and microcirculatory thrombosis or a an impaired kidney faiing to clear larger troponin fragment
Most interesting are studies which report troponin elevation following strenuous exercise – the precise mechanism for which appears unknown. ncbi.nlm.nih.gov/pubmed/25755058
Alpert went on to suggest that the definition of MI should be narrowed and the term of ‘myocardial injury’ introduced encompassing type 2 MI and other types of myocardial injury should be introduced to reduce confusion jamanetwork.com/journals/jamac…
Experienced clinicians will say that a comprehensive history and use of serial ECG will help differentiate these patients but following the troponin values over time can be helpful ncbi.nlm.nih.gov/pubmed/22105197
But we do know (thanks to @chapdoc1 in ncbi.nlm.nih.gov/pmc/articles/P… ) that this is a high risk population. Identifying and differentiating the patient with a plaque rupture event is key as these are the ones for whom we have valid therapies; these have not been validated in type 2 MI
The problem with troponin is it identifies injury to the myocardium rather than plaque rupture. A new biomarker is needed – perhaps blood based, although imaging based approaches are seeming promising, for instance viewing pericardial fat to find inflamed plaques
As for treating other myocardial injuries, more research is needed but therapy must be tailored to the patient, aimed at the underlying causes of the illness creating the injury and not based on the assumption that aspirin is always good… ncbi.nlm.nih.gov/pmc/articles/P…
Thanks for reading! Why not check out amjmed.com/article/S0002-… or heart.bmj.com/content/92/7/9… or of course jamanetwork.com/journals/jama/… from @JJheart_doc
ncbi.nlm.nih.gov/pubmed/14691043 for the reference on the renal stuff
See stm.sciencemag.org/content/9/398/… for Charalambous Antonaides' great work on this; picture credit to pubs.rsna.org/doi/10.1148/ra…
