Saturday, December 31, 2011

The Risks of Missing Dialysis

Hemodialysis patients have an elevated risk of death - and it's even higher for patients on scheduled dialysis during their "weekend."

Most scheduled plans are every other day Mon-Wed-Fri or Tue-Thu-Sat, which leads to a two-day interval between dialysis - resulting in an extra day of fluid retention and electrolyte abnormalities.  Bad hearts + extra fluid results in a much higher incidence of essentially any kind of mortality or morbidity associated with cardiovascular causes - significantly more myocardial infarction, congestive heart failure, stroke, and dysrhythmia.  Overall, there were 22.1 vs. 18.0 deaths per 100 person-years on the long-interval days than the others.  Retrospective registry data-mining, but it probably illuminates a logical truth.

This particular article caught my eye because we have a significant population at our county facility that comes for "compassionate dialysis".  Non-U.S. citizens that do not qualify for scheduled dialysis, they "live" a tortured existence in which they can only receive "emergency dialysis", as in, we routinely wait until they're at the precipice of death - with strict criteria of pulmonary edema, K+ > 6.0, bicarbonate less than 10, etc. - before pulling them back a small increment and sending them home to repeat the cycle in another week.  Barbaric.  I can't even imagine what their outcomes are like....

"Long Interdialytic Interval and Mortality among Patients Receiving Hemodialysis"
http://www.ncbi.nlm.nih.gov/pubmed/21992122

Thursday, December 29, 2011

Yet Another Highly Sensitive Troponin - In JAMA

...peddling the same tired phenomenon of magical thinking regarding the diagnostic miracle of highly sensitive troponins.  However, this one is different because it's been picked up by the AP, CBS News, Forbes, etc. saying: "Doctors are buzzing over a new blood test that might rule out a heart attack earlier than ever before" and other such insanity.  Yes, our hearts are in atrial flutter around the water cooler about a new assay that changes sensitivity from 79.4% to 82.3% at hour 0 and 94.0% to 98.2% at hour 3.


Unless you actually read the article.

Somehow, contrary to every other high-sensitivity troponin study, this particular highly-sensitive troponin had increased specificity as well - which simply doesn't make sense.  If you're testing for the presence of the exact same myocardial strain/necrosis byproduct as a conventional assay, it is absolutely inevitable that you will detect a greater number of >99th percentile values in situations not reflective of acute coronary syndrome.  The only way to increase both sensitivity and specificity is to measure something entirely different.

Or, if it suits your study aims, you can manipulate the outcomes on the back end.  In this study, the final diagnosis of ACS "was adjudicated by 2 independent cardiologists" whose diagnostic acumen is enhanced by financial support including Brahms AG, Abbott Diagnostics, St Jude Medical, Actavis, Terumo, AstraZeneca, Novartis, Sanofi-Aventis, Roche Diagnostics, and Siemens.

I am additionally not impressed by their results reporting - sensitivity and specificity, followed by the irrelevant positive predictive and negative predictive values.  Since the PPV and NPV are determined by the incidence of disease in their cohort, they're giving us numbers that are potentially not externally valid.  Rather, they should be reporting positive and negative likelihood or odds ratios - which are relatively cognitively unwieldy, but at least not misleading, but conceptually facile, like PPV and NPV.

And this is from JAMA.  Oi.

"Serial Changes in Highly Sensitive Troponin I Assay and Early Diagnosis of Myocardial Infarction"

Tuesday, December 27, 2011

How Frequently Is The Cath Lab Cancelled?

In North Carolina - a fair bit, actually.

This is a 14-hospital registry of cardiac catheterization activations for which the authors retrospectively evaluated how many were subsequently cancelled after activation.  They don't delve into a great deal of detail regarding specific findings that accounted for the cancellation - they simply observe the broad categories of cancellation.

Of all cath lab activations, it was judged that 15% were "inappropriate", with the gold standard being the consulting cardiologist opinion.  Of the cancellations, 40% were based on the EMS ECG, 31% were ED ECG, and the remainder were "not cath lab candidates".  The author's main focus in their conclusion is on the difference between EMS ECG cancellation and ED ECG cancellation due to ECG reinterpretation following activation.

What's more interesting from the paper, however, is when they break it down to the precise cohorts of activation and arrival - and note that 24.7% of EMS activations were subsequently judged inappropriate.  It is also interesting that 13% of non-PCI center activations were inappropriate vs 8% of PCI center activations.  Reading between the lines, there's probably some experiential component to the differences in activation rates, but this study doesn't specifically look at volume and training.

"Rates of Cardiac Catheterization Cancelation for ST Elevation Myocardial Infarction after Activation by Emergency Medical Services or Emergency Physicians: Results from the North Carolina Catheterization Laboratory Activation Registry (CLAR)"
http://www.ncbi.nlm.nih.gov/pubmed/22147904

Sunday, December 25, 2011

Happy Holidays!

Holiday break - intermittent and ineloquent blogging will be the norm.  I count 209 blog posts for the year - more than enough to keep anyone busy reading the archives.

But, if you're done with those, Life In The Fast Lane has a lovely Christmas-themed blog post with great articles including:

"What was wrong with Tiny Tim?"
http://www.ncbi.nlm.nih.gov/pubmed/1340779

"Children’s Nomenclatural Adventurism and Medical Evaluation study"
http://www.ncbi.nlm.nih.gov/pubmed/20415998

"No poinsettia this Christmas"
http://www.ncbi.nlm.nih.gov/pubmed/16866065