Category Archives: Cardiac Electrophysiology

Cardiac Electrophysiology

Article Review: Reentry in heterogeneous cardiac tissue described by the Luo-Rudy ventricular action potential model by K.H.W.J. Ten Tusscher and A.V. Panfilov

Hubmed Page: Reentry in heterogeneous cardiac tissue described by the Luo-Rudy ventricular action potential model (with abstract)
The primary focus of this article is the effect of a gradient of action potential duration (APD) on spiral wave dynamics. The authors ran several simulations of a spiral wave using the Luo-Rudy I ionic model, and tracked the drift of the spiral wave’s phase singularity with respect to a gradient of APD. As the abstract says, spiral wave drift was in the direction of longer rotation period (analogous to longer APD, in this case), which is right in line with what should be expected. Higher-frequency rotation should push the spiral wave center (phase singularity) away, regardless of the phenomenon underlying that higher frequency. The article is a medium-length read at six pages. While it seems somewhat redundant, in that every test yielded approximately the same results, this leant strong support to the conclusions of the paper — no caveats or qualifications were necessary. The conclusions of this article are important to the study of arrhythmias in regional disease, where gradients of electrophysiological disease exist along the borders between normal and diseased tissues.
The paper does not, unfortunately, delve into the details of why high-frequency rotation pushes away low-frequency rotation. A similar phenomenon was explained to me this past fall by Dr.Valentin Krinski with regard to two interacting spiral waves or periodic sources. I’m currently struggling to find the bridge — the relationship between different frequencies in different parts of the same spiral wave, and different frequencies in different spiral waves.

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

Article Review: A Chilling Tale by J.H. Indik

Hubmed Page: A Chilling Tale

This is an article about a clinical case of a man who went to an emergency room for diarrhea, and ended up having a heart attack. It goes on to analyze the odd ECG recordings he produced, describe how hypothermia was induced to minimize damage, and elucidate the origin of the problem. It’s a quick read at 3 pages, two of which consist primarily of ECG plots.

As a basic scientist who does mostly simulation work, I’m not very good at reading pathology from ECG readouts. However, I’m trying to read more clinical literature to become more familiar with the way cardiologists look at a heart’s electrophysiological function. This article points out a number of odd features of the subject’s ECG readout, and explains the sources of them. It’s a little over my head, but it should be valuable information as I try to learn more about this form of diagnosis.

New Articles on Virtual Electrode Polarization

Virtual Electrode Polarization (VEP) is an effect seen when an electrical field is applied across cardiac tissue. Large regions of positive and negative polarization manifest on the tissue surfaces, and sometimes within the depths of the heart. I’d link to the Wikipedia article on the term, but there is none. Perhaps I should write one.

Here are some recently-published articles on the subject:

  • N.H. Kuijpers et al. found that tissue irregularity increased the number of virtual electrodes in simulation. Given that VEP appears strongly at tissue borders, this is not surprising. It’s good to see a methodic investigation on the subject, though.
  • D.L. Beaudoin et al. investigated the arrhythmogenic effect of plunge recording electrodes in real cardiac tissue. They found that in some cases, the VEP caused by plunge electrodes could induce reentry. This encourages optical mapping studies of surface activity, and points to simulation as even more advantageous for studying electrical activity withinthe heart.
  • Fujian Qu and others from the Efimov lab found that ascending ramp defibrillation waveforms produce more pronounced VEP, thereby more effectively eliminating reentry. I had the pleasure of meeting Fujian this past fall, during our lab’s Post-Katina stay at Washington University. This approach promises to decrease the necessary defibrillation energy, which implies less damage on the heart from defibrillation shocks.

There are some other articles in my queue, but they are from 2004 and earlier. I’ll post more as they roll in.

Heart Disease Blog Disappears

The heart disease news blog that I linked to not long ago has mysteriously disappeared. Luckily, I still have the last few news items in my aggregator. Unluckily, they pretty much lack references now. Those that I can rediscover references for, I will post below:

  • High intake of vegetable protein linked with lower blood pressure – A recent epidemiological study found that a high intake of vegetable protein correlated with low blood pressure.
  • Low blood pressure might not be good if you already have some heart failure – where the article in the previous bullet points out what is normally considered advantageous — low blood pressure in a healthy system — it turns out that low blood pressure in heart failure is associated with higher mortality, per this American Heart Journal article.

That’s it. If you know why that blog was shut down, please comment or send me an email.