Saturday, April 2, 2011

More Sensitive Troponin Assay Saves Lives?

These authors show us something very interesting about "negative" troponin testing in their prospective review.  Like my facility, they had an assay with a certain level of detectability.  I will say, though, that their assay detection level of 0.20 ng/mL is different than our assay, that goes down to 0.02 ng/mL.  But, basically, they implemented a new assay that was sensitive down to 0.05 ng/mL but didn't tell their clinicians any of the newly detectable troponin numbers below 0.20, but they built a database of the cohort in that detectable-but-previously-undetectable range.  Then, they showed clinicians their new detectable numbers and let them do what they wished with it.  It turns out, the population with the 0.05 to 0.20 troponins had similar cardiac morbidity/mortality risk as their >0.20 troponin population - while the truly undetectable did much better over their 1-year follow-up.

Additionally, after the new threshold was introduced, clinicians treated the 0.05 to 0.20 more similarly to the >0.20 group with additional testing, cardiology consultation, and medications - and their outcomes improved 20%.

So, this study really makes you think what it means to have a "negative" troponin and wonder what the disposition and follow-up should be at different points.  At my institution, we've traditionally said 0.10 ng/mL is the cut-off for "positive", and the lesser, yet still detectable troponins, are "negative".  But, this study clearly suggests that a lot of the patients we're labeling "negative" really need to have more aggressive treatment.  This study doesn't tell us whether they need to be inpatient, or have expedited follow-up, or precisely how to manage them in order to improve their outcomes, but it suggests a lot of great new questions to ask regarding how to use the information we receive from our troponin assay.

The Cost-Effectiveness of Cardiac CTA

I was really hoping this would be a great article that convinced me that my hesitancy towards cardiac CTA is unfounded.  I feel, based on the literature, that we're misusing cardiac CTA - or at least, the current generation of technology and reconstruction methods aren't leading us in the right direction.  Angiography, whether radiographic or invasive, describes anatomy, and then we use the anatomy as our basis whether to attribute chest pain to cardiac causes or not.  Many situations, this works - the STEMI goes to the cath lab and the occlusion correlates with symptoms.  But, we're trying to use CTA in our low-risk population to draw conclusions about the etiology of chest pain - and it's much harder to say someone's troponin-negative and EKG non-specific chest pain comes from a stenosis of a certain percentage.

The problem with their article is that they completely underestimate the number of false-positives cardiac CTA is generating.  There are several articles out there showing that the population considered for cardiac CTA is generally a population that just does great in follow-up, and that the number of negative follow-up studies generated after cardiac CTA - nuclear stress and invasive angiography - tend to far outnumber the number of positives.  They base their cost estimates on numbers that just don't reflect reality, and I just can't believe that cardiac CTA is a test that saves money and gives me better answers compared to functional cardiac testing.  If you wanted to use it as a screening tool for identifying a population that needs aggressive secondary-prevention of progressive atherosclerotic coronary disease, it would do great at that - but we know that plenty of ACS comes from ruptured plaque and hemodynamically insignificant disease, and someone who had a "negative" cardiac CTA that morning doesn't preclude them from needing an enzymatic rule-out.

Patient Reported Symptoms in STEMI and NSTEMI

Here's an article with a lot of great numbers to keep you from sleeping well at night.  It's a prospective look at the symptoms patients present with when their eventual diagnosis is STEMI or NSTEMI.  6.4% of their STEMI patients and 5.6% of their NSTEMI patients didn't complain of any chest symptoms (pain, pressure, etc.).  There's a lot of arm pain, epigastric pain, shoulder pain, and then multiple anginal-equivalents on their list of symptoms, but it's a great example showing that if you write off ACS in your patients without chest pain, you're going to get burned - 1 in 16 STEMIs in their cohort.  Even better, only 45.1%/53.9% of their patients thought their symptoms were cardiac related, which probably means there's a population of STEMIs just sitting at home figuring they'll feel better in the morning....