Today, while doing this, I noticed that there’s an “Export comments to Data File” option in the Comments menu. “Hmm,” I thought, “I wonder how easy it would be to read this data file?” It turns out that it’s just some ASCII text with a bunch of (to me) useless information, and the highlighted comments in parseable “Contents([highlighted text here])” containers.

I wrote a quick and dirty Perl script that pulls the comments into a text file. I can then just copy and paste that file into FreeMind, and it creates all of the leaves for me. This will save me hours carpal-tunnel-syndrome-inducing mousing and frustration. The perl script, for your perusal (improvements welcome) is available here: extract_comments.pl.

Kindly Let me know if you get any use out of this, and if you find any parsing bugs. It’s in the public domain.

The Cite-U-Like page is here. The rest is below the fold.

Jones 1986

• Internal Cardiac Defibrillation Threshold: Effects of Acute Ischemia

• Authors
  • Jones, Douglas

  • Sohla, Anand
  • Klein, George J.
• Topics
  • internal DFT

  • lead orientation
  • acute ischemia 1B
• Parameters
  • n = 30
    • 15 normal

    • 15 occluded
  • pigs
  • distal 1/3 of LAD ligated
  • began investigation 30 min post-ligation
• Notes

  • Figure 1: Dotted area reperesents ischemic zone produced by ligation of distal LAD

    significant improvement in number of successful defibs using an epicardial plaque (vs. transvenous catheter) [duh]

    Regardless of electrode configuration, no difference in success b/w normal and acutely ischemic pig hearts

    relatively small and distinct ischemic zone produced by ligation of distal third of the left anterior descending artery

    • larger insults resulted in death

• Conclusions

  • Regardless of electrode configuration, no difference in success b/w normal and acutely ischemic pig hearts

    Key: SMALL ISCHEMIC ZONES don’t affect DFT

Becker 1973

• Mapping of left ventricular blood flow with radioactive microspheres in experimental coronary artery occlusion

  Authors

  • Becker, LC

  • Ferreira, R
  • Thomas, M

  Topics

  • radiomarking

  • morphology of infarction

  Parameters

  • 15 micron microspheres

  • n = 10
  • dogs
  • LAD occlusion
    • silk ligatures

    • all major FW diagonal branches (3-5)
    • branches rather than main vessel to reduce immediate mortality
  • FW cut into strips 1-2 cm wide, apex-base
  • epi/endo divisions made
  • 30-60 minutes post-occlusion

  Notes

  • margins of cyanosis sharp at basal and lateral aspects

  • maximal flow reduction in center of lesion
  • concentric areas of intermediate flow
  • region of hyperperfusion around infarct
    • possibly artifact of method?

Ouyang 1981

• Ischemic Ventricular Fibrillation: The Importance of Being Spontaneous

• Authors
  • Ouyang, Pamela

  • Brinker, Jeffrey
  • Buckley, Bernadine
  • Jugdutt, Bodh
  • Varghese, Paul
• Topics
  • defibrillation threshold
    • spontaneous vs. induced VF

    • regional ischemia vs. normal
• Parameters
  • n = 10

  • canine
  • occlusion
    • sites
      • around LAD just distal to first septal perforator artery

      • midway along LAD in anterior interventricular groove
      • around left circumflex coronary artery near its origin
    • duration
      • 10 min or until spontaneous vfib

    • DFT measured if reperfusion fib occurred
  • vfib
    • induced by current during t-wave

    • allowed to continue 10s
  • defib
    • electrodes
      • venous catheter where VC meets right atrium

      • apical cup
    • waveform
      • trapezoidal with exponential delay

      • 1-30 watt seconds with increments
        • Progressively increased until DFT reached

        • 1
        • 2
        • 5
        • 15
        • 20
        • 25
        • 30
    • DFT
      • lowest energy that successfully defibrillated

      • no change noticed over two minutes
      • determined for every episode of fib
  • data on extent of ischemic zone
    • mass of risk region for each occlusion

    • percent of LV mass in risk region
• Notes
  • vfib episodes
    • 32 induced in normal hearts

    • spontaneous vf in 13/25 ischemic episodes
    • induced vf in 12/25 ischemic episodes
    • 19/25 reperfusions resulted in vf
      • 12/13 instances of occlusion w/ sponteneous vfib

      • 7/12 instances of occlusion w/ induced vfib
  • difference b/w DFT in spontaneous vs. induced fib not related to mass of occluded bed
• Conclusions
  • when ischemia was present, DFT rose significantly

  • DFT greatest in ischemia when vfib spontanous
  • DFT twice as high for spontaneous (vs. induced) vfib

When reading a technical paper containing equations, there will be text, and there will be equations. Usually the equations come somewhere in the middle. However, when you come to the equations, you must understand the equations thoroughly before proceeding to the rest of the text.

I used to think that I could still get something important out of the paper without putting the time into understanding the equations, but in my experience that is simply not true.

Be ye warned.

The Hubmed page for today’s article is here: Unpinning of a Rotating Wave in Cardiac Muscle by an Electric Field by Alain Pumir and Valentin Krinsky

Tachycardia (fast heart beat) is commonly caused by a rotating wave of activation in the heart. The study of rotating waves of this type has years of legacy in theoretical and chemical dynamics studies. Today’s article covers rotating waves pinned to anatomical obstacles such as valve openings in the heart. Rotating waves circle a core, which can be functional (a property of the wave shape and dynamics) or anatomical (an obstacle). In the case of an anatomical obstacle, the wave can be eliminated by ablation, which is commonly used in the atria, electrical defibrillation, or possibly unpinning / antitachycardia pacing (ATP). Ablation is typically invasive, requiring catheterization, and defibrillation requires an external shock, or surgery to implant an ICD. Defibrillation, either externally or internally, damages the heart, is painful, and often causes loss of consciousness. Antitachycardia pacing and electrical unpininning open the possibility of elimination of tachycardia with small shocks.

The principle of electrical unpinning, proposed by Huyet et al. (1998) and Krinsky et al. (1995), is that when a localized stimulus is applied in a certain part of the wave tail, it may move the core of the rotating wave. It’s difficult to place a stimulus in a particular place at a particular time in a patient’s heart, but it turns out that when an electrical field is applied over an obstacle, areas of depolarization (positive change) and hyperpolarization (negative change) manifest on the borders of the obstacle.

The paper by Pumir and Krinsky details how a small electrical field may be applied at a specific timing relative to wave rotation in order to create such a depolarization on an obstacle that will unpin a wave attached to that same obstacle. They used simplified models of cardiac action potentials, including the Beeler-Reuter and Fitzhugh models. Since the method deals with the dynamics of a spiral wave, and not with particulars of ionic currents, it’s a safe bet that the methods will apply in more complex models and cardiac tissue.

I won’t repeat the article’s simple and logical explanation of how it works — go read it. It’s only 9 pages, the figures are clear, and the math is mercifully simplified in a way that (ostensibly) doesn’t undermine the results.

Hubmed Page: Role of Cardiac ATP-Regulated Potassium Channels in Differential Responses of Endocardial and Epicardial Cells to Ischemia

This 8-page article quantifies in great detail the ATP sensitivity of ATP-regulated potassium channels, often referred to as I_K(ATP). As the article shows by many references, it’s known that the epicardium of the heart is more sensitive to lack of oxygen (and therefore metabolic energy in the form of adenosine triphosophate — ATP) than then endocardium of the heart. The authors of this study first measured currents from ATP-regulated potassium channels in the presence of CN^- (cyanide, which blocks the generation of ATP), and then more directly pulled off patches of cell membrane with ATP-regulated potassium channels, and tested them in the presence of varying concentrations of ATP. In both cases, action potentials (the way in which cardiac cells ‘fire’ to initiate contraction and signal each other) were shortened more in the epicardial patches than in those from the endocardium. The degree to which this shortening occurred and at what concentrations is well-documented in the article.
The results of this study are clear, well-presented, and extremely useful in modeling ischemia in the heart. It’s a long read, with a ton of experimental detail, but the results are worth slogging through all of that. This fundamental article on ATP-regulated potassium channels is a must-read for anyone wanting to study ischemia and infarction in the heart.

Hubmed Page: What can nonlinear dynamics teach us about the development of ventricular tachycardia/ventricular fibrillation?

This short article (3 pages) describes in a very readable way how nonlinear dynamics may be applied to understand beat-to-beat alternans of action potential duration and amplitude. While the actual methods used are not written, the concept is well-conveyed. I’ve not yet had a course in nonlinear dynamics, so some of the terminology was a bit beyond my understanding. I don’t know anything about eigenmodes, for example.

After providing a brief background of nonlinear dynamics, the authors elaborate on how they used nonlinear dynamics to develop a realistic model of calcium cycling and alternans in the canine myocardium. All-in-all, it’s not a terribly informative paper. Like many articles that mention fibrillation and tachycardia, it comes up short of actually linking the found mechanisms to clinical application and human disease. It is, however, a nice introduction to the topic, and the references look promising. If you have an interest in cardiac arrhythmias, and aren’t very familiar with this sort of analysis, I recommend you read it over and consider further study of the topic.

If you know why this is, kindly leave a comment. In the mean time I’ll be puzzling over it.