Category Archives: Cardiac Electrophysiology

Cardiac Electrophysiology

Long Q-T Syndrome

Today, while looking for blog posts about ICDs and cardiac arrhythmias, I came across the Long Q-T Syndrome Blog. The first story I found was by a woman with long Q-T syndrome who had recently had her ICD replaced in Norway.

Once I checked out the blog itself, I found that it’s done by a group of contributors, and is associated with a long Q-T site, QTsyndrome.ch, which has apparently been around for 10 years! In the past I’ve focused rather narrowly on computational cardiac electrophysiology, and had been frustrated by the lack of other bloggers covering the same field. However, I’m starting to find that while cardiologists may not be predisposed to blogging, patients are! Below are two YouTube videos, found via the Long Q-T Syndrome Blog, on long Q-T syndrome. Neither of them does a great job of explaining what the syndrome is caused by at a low level, but there’s a good FAQ on it here, as well as a short history of the disease and some background on the genetics of inherited long Q-T syndrome.

Those videos also don’t do a good job of explaining what the Q-T interval is. In a somewhat-simplified explanation, it’s the time between when your heart’s ventricles (the major pumps) start contracting, and when they stop contracting and rest. A more detailed explanation of the different parts of an ECG trace, including the Q-T interval, is available on the ECG Learning Center.

And now, the videos:

Anatomical Reentry – 1/10th Speed

This video shows an example of simulated anatomical reentry. The view is of a sheet of simulated tissue with a hole in the middle. A wave of electrical activity continuously circles the hole. This is a stable phenomenon, particularly in this simulation. It should go on indefinitely, as long as I let the simulation keep going. Even in experimental set-ups (such as animal models) these can run for more than an hour.

In the video, black is tissue at rest, white/yellow tissue is activated, and red marks activation (at the front) and re-polarization (at the tail of the wave). If this happened around an obstacle in your heart, it would result in atrial flutter (if it occurred in your atria) or ventricular tachycardia (if it occurred in the ventricles). I’ll do a more extensive post in my “CEP Basics” pages later, but for now, here’s the video. The quality was great until YouTube crappified it.

“Aftershocks” – why we try to better understand arrhythmias

Today while looking for other cardiac electrophysiology blogs (let me know if you find any — I cannot), I came across an article called “Aftershocks” by Elizabeth Ann Bartlett. Here are some excerpts:

In the four years I lived with an automatic implantable cardioversion defibrillator (AICD) while waiting for a heart transplant, I had only a few episodes of being shocked. But in each I was fully conscious and shocked multiple times. My experiences, some of which are described below, were horrific. I learned well the power of electricity not only to heal, but to harm.

I should note, however, that my experience with an AICD, although not unique, is not typical either. [ This is a bit of an edge case, sort of a worst-case scenario, and as she mentions, technology has improved since this was written. –Brock ]
…
Lub dub, lub dub, lubdub, lubdub. Faster and faster and faster. Boom boom boom boom POW! What was that? It nearly threw me to the floor. POW! again. It threw me to the bed. POW! What was this pain, this devil, this evil tormentor, in my chest? And then it stopped. Finally, it dawned on me that my defibrillator had gone off.

My heart had slowed a bit but was still racing. My husband called 911 and my neighbor, Nancy, a cardiac nurse. As paramedics struggled to get IV lines in, I felt myself slipping away. I’m going now, I thought, but no, BAM! There it was again. A stretch of calm, into the ambulance. BAM! BAM! Calm again. BAM!

BAM! Make it stop! Make it stop! BAM! I pleaded with God to end the torment, one way or the other.

I was shocked 16 times on the way to the hospital. Shocked into submission. I found myself begging for amiodarone.

This is truly terrifying to read. Every time her device was set off, it not only caused her pain, but damaged her already failing heart by literally blowing holes in the cells (electroporation). As highlighted by this slide from my CEP basics page, even in non-edge-case patients the psychological aftereffects of defibrillation are a real problem:

Psychological aftereffects of defibrillation
The paper mentioned in the slide is here.

Even eight years after the device was removed, says Bartlett,

the shocks, at least the physical sensations of them, still come on occasion. During the time the AICD was implanted, I was diagnosed with post-traumatic stress disorder from the shocking episodes; but I could not be treated with the normal therapy of removing myself from the situation—the perpetrator lived inside my body. I have suffered from flashbacks and nightmares, though these episodes have lessened over time.

Actual physical sensations of being shocked have hit me out of the blue—standing in a grocery line, teaching a class, in my early waking moments. A bright flash of lightning will bring it all right back. Other AICD patients I’ve known have experienced the same phenomenon.

She describes a defibrillator as a “torture device that [she] came to fear almost more than the death from which it supposedly was saving [her].”

It was almost certainly saving her. The fact that she has lived to be picked up by the paramedics in both episodes recounted in the article is good evidence of that. Nonetheless, the devices need to improve. Device manufacturers have pushed the envelope of improvement given the current knowledge of the heart and its problems. We have to better understand the problems and how to circumvent or eliminate them before the devices can improve much more.

And that’s what we’re working on.

Tools of the Trade

I’ve been thinking back on my trials and tribulations when working on the ischemia paper. One thing that tripped me up all along was a lack of knowledge of the techniques for analyzing cardiac electrophysiology data. Something that said, “if you want to find out why X is happening, first try Y and look for this, then try Z and look for that.”

Rather than whine about the lack of a list of such things, I’ve decided to start my own. I’ve added (or will shortly) a Page (on the right) called “Tools of the Trade”. There, I hope to document useful methodologies that I have used and that I use in the future.

Do you have any suggestions for analyzing electrical activity in the heart?