Monthly Archives: May 2006

Almost time to write

I have four papers and several abstracts left to read. I’m losing my motivation to read because I feel like I can already answer the questions posed. However, I acquired these papers because they are relevant, and so they must be read.

Soon, the writing will begin.

Also, I’m antsy because our new server came in. We need it badly, and I want to set it up, but I have to do a bunch of other stuff, including the qualifier, first.


Round 1 of Reading Complete

I’ve read the latest and greatest papers on heart resynchronization therapy. Now it’s time to read their interesting references, many of which (thankfully!) overlap. In particular, there have been a few major studies in the last few years, and for a complete picture of the existing HRT knowledge, I must read these studies.

By the way, Guidant has funded the majority of the HRT studies I’ve read. I wonder if they’re doing more research on it than anyone else, or if they’re just hiring more academics to do it rather than doing studies in-house. Hmm.

ADDENDUM 2006-05-25 @ 10:17 CDT: I have 168 references to check out. Not all of them are unique, and not all of them are likely to be interesting enough to look up (by the title), but they were all referenced in an interesting way in the papers I’ve already read.

ADDENDUM 2006-05-25 @ 13:33 CDT: After pruning, 72 articles to acquire and read. On my mark, get set, go!.

The Many Things I Don’t Know (yet)

I’ve only read through ten papers on bi-ventricular pacing and heart-resynchronization therapy so far, and I have more, but it’s clear that before I continue I need to look a bunch of things up, including but not limited to:

  • What are “active fixation” leads? – This seems to refer to leads that screw in or are otherwise actively attached to the heart, versus leads with knobs and so on to keep them from wiggling.
  • What’s a “transvenous Bi-Ventricular ICD”? Particularly the transvenous part. – Apparently it means passed into the heart through a vein.
  • What is the drug “amiodarone”? What are its indications? – Class III (what’s that mean?) antiarrhythmic, works by prolonging AP with actions on sodium and potassium channels (from Wikipedia.
  • What specifically is “transatrial placement”? – I’m guessing it means “through the atria” but that’s neither for certain nor very helpful.
  • What’s “percutaneous”? – A procedure performed through a small opening made in the skin. from ehealthmd. Seems most appropriate to ICD implantation.
  • How does one get any useful information out of a fluoroscopic picture, which basically just shows some leads floating in space? I know clinicians can decode these things… – No luck so far, this is probably something people learn in residency…
  • What are Class I and Class II indications for ICD therapy? I’ve already looked up the classes of heart failure in the previous post. – For ICD therapy classes, look here.
  • What is VDD pacing mode? – Seems to mean “Dual chamber ventricular pacing” but I haven’t figured out the acronym yet
  • What is the drug “spironolactone”? – Treats hypokalemia, low-renin hypertension, etc. See Wikipedia.
  • What is “secondary prevention”? – Secondary prevention refers to patients that have survived sudden cardiac death (5% survival!), while primary prevention refers to people who are likely to suffer SCD but have not yet had an episode. (From Wake Forest University Baptist Medical Center article here.
  • What is “patency”? (already looked this up. For my purposes, it means “the state of being not blocked, or open”).
  • What are “thebesian veins”? What are their compensatory abilities with regard to adequacy of blood flow? – Defined here, still not sure about the compensatory stuff.
  • What is “minitoracotomy”? – There are only 29 instances of this word on the entire internet, and I suspect it may be another way of referring to minithoracotomy which is a small hole in the chest (methinks).
  • What are “DDD Pacemakers”? – A DDD pacemaker can sense intrinsic activity in the atrium and ventricle, pace either or both chambers when not inhibited by native activity, and thereby maintain atrioventricular synchrony over a wide range of heart rates. DDD units are noncommitted employing an atrial blanking period following atrial stimuli to avoid sensing of such events on the ventricular channel. All such pacemakers have upper rate characteristics and blocking modes to prevent 1:1 conduction during atrial arrhythmias such as flutter and fibrillation. Virtually all such devices are extensively programmable, and most have the ability to telemeter both programmed and real-time parameters. One of the major initial problems encountered with DDD pacing is pacemaker-mediated tachycardia, which is where the pacemaker acts as one limb of a re-entrant circuit. However, this has been solved by the ability to program the interval at which atrial sensing resumes after a ventricular sensed or paced event. from here, not sure how credible it is.
  • What does “chagasic” mean? – Relating to chagas disease, relevant issue is that it commonly includes right bundle branch block (RBBB), from Biology Online. More info on Chagas Disease on Wikipedia.
  • How about “idiopathic”? – Means cause unknown. Thanks, Wikipedia
  • What’s “myocardial scintigraphy”? – Looking at the heart using unsealed radioactive substances
  • What is “endocavitary access”? – Not much luck with this, but from the roots it looks like it means “inside the cavity (read: ventricle).
  • What’s the technical definition of “cardiomyopathy”? – A weakening of the heart muscle. From here.
  • What is the “buddy wire technique”? – Article on this here.

I’m sure to have more questions as I dig into the other papers, the patents, and the references, but these should keep me busy for a little while. I have access to some physiology books here, but I’ll probably need to borrow my (medical student) girlfriend’s “Stedman’s Concise Medical Dictionary” or some such title to answer some of these.

Stages of Heart Failure

As I read academic articles, I mark things that I don’t know or haven’t heard of as a reminder to look them up.

One thing that’s been popping up in paper after paper about heart resynchronization therapy is the New York Heart Association (NYHA) heart failure classification system. The Heart Failure Soceity of America (HFSA?) has a summary of the classes with their symptoms on this page.

I’m already learning about the ways in which patients are evaluated for treatment based on their NYHA classification, and finding out that some of the “best practices” employed by physicians are being revealed as incorrect.

Once I get through the first round of papers and patents (yes, patents), it’s time to dig into the references. I have about 5 more initial papers and maybe 8 patents to read, and then I start pulling more. Overlaps notwithstanding this can be a very deep and wide search. Imagine if I start with five papers, and each has five interesting references. Then I’m up to 30 papers. You might guess that the next generation would bring the total to around 180 papers, but by the time you get back three generations things usually start to narrow again. I’m guessing I’ll probably have to consider around 30-50 papers for the purpose of this exam.