Tag Archives: AF

Can Ovine Obesity (Fat Sheep) Teach Us About Atrial Fibrillation?

Until the last year or so when patients asked me what they could do to help their atrial fibrillation (AF) I would tell them to avoid excessive alcohol consumption and take their medications as prescribed.

My response has changed because new data suggest that losing weight and exercising can significantly reduce the recurrent rate of atrial fibrillation. Now, in addition to my standard reasons for staying at ideal body weight and exercising regularly I can toss in the fact that atrial fibrillation will be less frequent and troublesome.

I had noted previously that the majority of my patient’s with AF were obese and sedentary (although there are definitely many AF patients who exercise regularly, eat a great diet and stay at their ideal body weight0 but data was lacking to suggest cause and effect.

LAAfat
View of the left atrial appendage (LAA) and posterior aspect of left atrium obtained in a 400 pound woman about to undergo  electrical cardioversion for her atrial fibrillation. The orange arrow points to extensive collection of fat in the walls of the atrium.

In addition, I had noted that when I looked at the left atrium of the vast majority of patients with AF using an imaging tool called trans-esophageal echocardiography they had evidence for fatty infiltration into the area between the atria (atrial septum)  and the wall of the left atrium.

I strongly suspected based on these observations that somehow the fat infiltrating into the walls of the left atrium was triggering AF but I had no way of proving it.  Isolated observations like these can only generate hypotheses on causality.

Science has many different approaches to solidifying or proving hypotheses and one such approach is to induce a disease in an animal similar to humans and make detailed analyses of the cause and consequences.

Australian researchers writing in JACC in July present their observations on the electrical, physiologic and structural changes that result when sheep get fat.

How Do You Make Sheep Fat?

Apparently you just let them eat as many pellets made of energy-dense soybean oil (2.2%) and molasses–fortified grain as they want.

After 36 weeks the 10 sheep given ad libitum pellets weighed twice as much as the sheep who were restricted and kept lean

After 36 more weeks of obesity the sheep were studied extensively. All sheep underwent “electrophysiological and electroanatomic mapping; hemodynamic and imaging assessment (echocardiography and dual-energy x-ray absorptiometry); and histology and molecular evaluation”.

The investigators found

“Sustained obesity results in global biatrial endocardial remodeling characterized by LA enlargement, conduction abnormalities, fractionated electrograms, increased profibrotic TGF-β1 expression, interstitial atrial fibrosis, and increased propensity for AF. Obesity was associated with reduced posterior LA endocardial voltage and infiltration of contiguous posterior LA muscle by epicardial fat, representing a unique substrate for AF”

The fat sheep developed AF and had multiple abnormalities in the left atrium, the source of AF, that made them more likely to develop atrial fibrillation.
Screen Shot 2015-09-01 at 4.32.32 PM In fact, the investigators believe it was fat collecting around the heart and specifically around the posterior left atrium that was triggering all these changes.

The pictures to the left show a heart from one of the fat sheep. The arrow points to the extensive amount of fat collecting posterior to the left atrium.

When the posterior left atrial wall was viewed microscopically, fat cells could be seen infiltrating between the muscle cells in the fat sheep (right, blue arrow) but not in the lean sheep. Screen Shot 2015-09-01 at 4.33.06 PM

In the fat sheep, fat cells (adipocytes)  were enlarged and infiltrated between the muscle cells of the left atrium, presumably disrupting the normal electrical activity and contributing to the development of atrial fibrillation.

More Reasons To Stay At Your Ideal Body Weight!

If you were previously unmotivated to avoid obesity perhaps this will motivate you.

Think about fat cells gathering around your heart and pouring their evil humours into the tissues of your left atrium and making it more likely that you will develop AF. With AF comes increase risk of stroke, heart failure and death.

-unadipocytically yours

-ACP

AliveCor Smartphone App Detects Atrial fibrillation: Potential for Stroke Prevention

Atrial fibrillation (AF)  is a common abnormal rhythm of the heart which causes 1 in 4 strokes. Those afflicted with AF may lack any symptoms or only have a vague sense of irregularity of their heartbeat and thus the first symptom of AF can be stroke.

The gold standard for diagnosing AF has long been the electrocardiogram (ECG or EKG) and typically the ECG involves placing 12 electrodes on the chest/arm/legs and recording the electrical activity of the heart on an expensive device.

I’ve been checking out a device made by Alive Cor which works with your smart phone to record a single channel ECG and is capable of accurately diagnosing if you are in the normal (sinus) rhythm or in AF.
Screen Shot 2015-07-12 at 8.45.49 AMYou can purchase the third generation (significantly smaller then earlier versions) AliveCor Mobile ECG from Amazon or from AliveCor directly for 74.99$ and it works with an app with both iOS and Android devices.

I used mine with my iPhone 6. At first I carried it separately, fearing the added bulk when stuck on to my iPhone case but after a while I realized that it was never with me when I wanted to use it and that there was a huge risk of losing it and so I used the backing adhesive to attach it to my case.

After pairing the device with the app you put two fingers on each of the metal pads and the smartphone screen displays the recording. After 30 seconds of recording it then interprets the rhythm.

Screen Shot 2015-07-12 at 8.56.47 AM
Typical recording in normal sinus rhythm. The red arrow indicates the small p waves which are the electrical signal of the upper chambers (the atria) depolarizing , the blue arrow indicates the electrical depolarization of the ventricles (QRS). The orange arrow indicates that the time interval between the QRS complexes is the nearly the same for each beat, indicating the regularity that we expect when in NSR compared to AF.

Above is a typical recording I made in my office on a patient who had a history of AF. The quality is good and I can clearly see that he is in normal sinus rhythm. The app correctly made the diagnosis of NSR and calculated his heart rate at 68 beats per minute.

One day I had most of my patients record their ECG’s using AliveCor and compared it to the standard 12-lead ECG we normally record. The device correctly identified the two patients with AF out of this group and correctly identified the normals.

Screen Shot 2015-07-12 at 9.26.42 AM
AliveCor recording of patient with AF with heart rate of 70 beats per minute. Note the absence of p waves before the QRS complexes and note the beat to beat variation in the RR interval (orange arrow)

This recording is from a patient with persistent AF which had recurred two weeks earlier. The device correctly identified AF.

Studies have documented that AliveCor Mobile ECG can accurately diagnose AF in a screening setting and the FDA approved the device for AF screening in 2014.

Given the high prevalence of silent AF, the strong association of AF with stroke and the availability of anticoagulants which reduce AF associated stroke by 70%, screening for AF with devices like AliveCor holds the promise of preventing large numbers of stroke.

(For my comments on taking the pulse and stroke prevention see here and on the inadvisability of a routine 12-lead ECG see here)

AliveCor allows physicians utilizing the Mobile APP and ECG to have a “dashboard” into which their patients can transmit their AliveCor ECG recordings.

I will be discussing this remarkable new device with my AF patients  who are smartphone enabled. I think it will advance our ability to more efficiently and quickly diagnose AF in them.

My standard approach if a patient with AF calls and says that they feel like they are out of rhythm is to have them come into the office for a full 12-lead ECG. If they are AliveCor enabled, they could make their own recording, and we could review that remotely and make a diagnosis without the office visit.

Let me know your thoughts on smartphone ECGs.

fibrillatorily yours,

-ACP