The Stress Resilient Mind Blog
Heart Rate Variability and Heart Attacks
Publication date: 22 December 2014
This week I read an article by Dr Thomas Cowan, entitled "What's the Real Cause of Heart Attacks?", originally published in the Townsend Letter (a forum for presenting scientific information on alternative medicine topics) and reproduced on Dr Mercola's website. I found it interesting because of what it says about the part played by stress, and how the effects of stress are mediated via the Autonomic Nervous System (ANS) - but not quite in the way you might expect. If Dr Cowan is right then it the importance of heart rate variability (HRV) as a biomarker for stress and ANS balance is amplified, as is the role of HRV biofeedback as a stress reduction tool.
I'll briefly summarise at least some of what Dr Cowan is saying.
It used to be believed that heart attacks were caused by plaques building up in the blood vessels of the heart, and occluding them so that heart cells are starved of oxygen and nourishment. A more recent development is that it's not the "hard plaques" that are dangerous but soft plaques which are liable to dislodge and cause thrombosis (where the dislodged material blocks blood vessels). Soft plaques are linked to the buildup of oxidised LDL cholesterol, which is why LDL has the undeserved reputation as "bad cholesterol". But Dr Cowan reports that less than half of heart attacks involve such a thrombosis, and he believes thrombosis to be an effect of the heart attack rather than the cause.
Dr Cowan further proposes that the Autonomic Nervous System plays a significant role in causing heart attacks. This wouldn't be too surprising because the ANS is the major mediator of stress, and it's known that stress is a risk factor, that so-called "type A personalities" are at increased risk. Type A's tend to be driven, competitive, hostile, agitated and short tempered.
The ANS controls a lot of the automatic or involuntary functions of the body, is divided into two branches, known as sympathetic and parasympathetic. The sympathetic nervous system (SNS) is like the accelerator in terms of body arousal, while the parasympathetic nervous system (PSNS) is the brake - e.g. the SNS speeds up heart rate while the PSNS slows it down. In terms of stress, the SNS classically mediates the "fight or flight" response, while the PSNS mediates the "rest and digest" response.
Since type A's typically show strong sympathetic activation, you might think that the SNS plays a role in heart attacks, but that's not what Dr Cowan is saying. He reports that heart attack patients typically have over a third lower PSNS activity as measured by heart rate variability, and that over 80% of heart attacks are preceded by a strong reduction in PSNS activity. Conversely, abrupt increases in SNS activity do not lead to heart attacks. The PSNS relaxes and slows the heart - it seems it is the withdrawal of this influence that triggers problems.
A couple of years ago, I attended a training seminar by Professor Richard Gevirtz, one of the leading researchers in HRV and especially HRV biofeedback. He presented a modern model of the ANS called polyvagal theory - which I've written about in my ebook, "Mind-Body Intelligence: How to manage your mind with biofeedback and mindfulness".
Professor Gevirtz thinks that maybe the worst kind of stress is the low-level chronic variety, e.g. worrying about your mortgage payments. Classic, short sharp "fight or flight" reactions (mediated by the SNS, which triggers the release of adrenalin) aren't damaging if you can recover from them afterwards - that's how the stress system evolved to work. But chronic low level stress is different - it doesn't necessarily trigger the SNS but a withdrawal of the healing PSNS influence. And it seems this could be damaging - certainly if Dr Cowan is right.
As I've said, HRV is a biomarker for ANS activity, and PSNS in particular (in fact it's not very good for judging SNS activation). HRV is also a very viable biofeedback parameter, and HRV biofeedback is thus a useful tool for training and exercising the PSNS response.
Does that mean that HRV biofeedback may protect against heart disease? I'm aware of at least one study that suggests it might. The Heartmath Institute, who we can thank for the popularization of HRV biofeedback, ran a study of HRV biofeedback for congestive heart failure patients. HRV biofeedback training resulted in functional capacity improvements, as well as gains in measures of stress and depression.
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