Cognitive impairment in patients with atrial fibrillation
Researchers at the Baker IDI Heart and Diabetes Institute in Melbourne are calling for changes in the assessment of patients with chronic atrial fibrillation, the most common cardiac arrhythmia. Their research highlights the need for high-risk patients to be screened for mild cognitive impairment.
Norman Swan: Research from the Baker Institute in Melbourne has found that a common and often missed abnormal heart rhythm is associated with damaged thinking ability. The condition's called atrial fibrillation.
Here's Professor Simon Stewart who heads Preventative Cardiology at the Baker.
Simon Stewart: Atrial fibrillation is an irregular chaotic heartbeat that impacts on the ability of the heart to produce enough blood around the body and is associated with an increased risk of dying in the future by having heart attacks and strokes.
Norman Swan: And this is where the top two chambers of the heart quiver really rather than beat properly.
Simon Stewart: That's right. So the top two chambers of the heart, the atria, are really passive vessels for collecting the blood down into the more important bottom part of the heart, but when they do go wrong they can impact on the ability of the heart to pump properly quite radically.
Norman Swan: You've kind of outlined them already, but in more detail what are the problems that atrial fibrillation causes?
Simon Stewart: Atrial fibrillation influences the ability of the heart to coordinate itself. So if the top of the heart is quivering at a rapid rate it actually is counter productive against the pumping action of the bottom of the heart. It means that the heart is not receiving all of the blood it needs to pump around the body. And so atrial fibrillation itself provides a scenario where people are at increased risk of developing clots, particularly in the brain, and also at increased risk of developing heart failure, so a failing of the heart.
Norman Swan: Because the heart is beating too fast and chaotically and it just gets knackered.
Simon Stewart: That's right. So the scientific term would be 'flogged'. So if the heart is being overrun, imagine revving your engine too much, you use the engine at high speeds for a long time, naturally enough the natural life of that car will actually be shorter than one that has been cared for, and it's the same with the heart.
Norman Swan: And the clots come from basically stagnating blood in pockets of these atria.
Simon Stewart: We know that the atrial fibrillation does indeed cause clots because of that stasis, as it were. So there is pooled blood sitting in the top of the heart. But we also know that atrial fibrillation itself has some sort of mechanism whereby the blood is intrinsically more likely to clot. So there's a mechanical cause of the clots but there is also a physiological cause that's probably a combination of some really complex processes.
Norman Swan: Simon Stewart.
While atrial fibrillation becomes commoner as we age, plenty of people experience it when they're quite young. Like John Cochrane, who got his first attack when he was 43.
John Cochrane: I was at work. I'd just had my morning coffee and I started noticing a sensation, a dull feeling in my chest. At first I thought it was the coffee and I thought it might have been very strong. I didn't pay a lot of attention to it at first but it developed over about the next half hour or so and the feeling got more intense but very slowly. So not being a totally macho guy I thought even I have to confront this. So after about an hour or so…
Norman Swan: So you wondered if it was a heart attack or something like that?
John Cochrane: I don't know if those thoughts were actually going through my mind and if they were I was putting them somewhere in my mind towards the back.
Norman Swan: So what did you do next?
John Cochrane: I rang my doctor. It was a Wednesday and he closes up his surgery at midday, so I was the last person to see him. He confirmed fairly quickly that my heart was in fibrillation and drove me up to the public hospital nearby.
Norman Swan: Bang went his half-day.
John Cochrane: Bang went his half-day, that's right.
Norman Swan: And after that?
John Cochrane: Well, once I got to the hospital of course—male, early 40s, pain in chest—I was fairly quickly on my back with all sorts of things plugged into my…
Norman Swan: Because they reasonably thought that maybe what caused the atrial fibrillation would have been a heart attack.
John Cochrane: Yes, they were taking a number of blood samples to confirm it wasn't a heart attack.
Norman Swan: So what had caused the atrial fibrillation?
John Cochrane: We never found out. I was described as being a lone fibrillator.
Norman Swan: Did they shock you out of it or what?
John Cochrane: Yes, that's right. I had a number of tests. One was to determine the size of the chambers, that there was no leaking in the heart, that there was no blocked arteries, and I got a clear bill of health on all of those.
Norman Swan: So you truly were a lone fibrillator with no obvious causes for it. So they shocked you out of it, they zapped you and shocked you into normal rhythm.
John Cochrane: That's right.
Norman Swan: But that wasn't the end of it.
John Cochrane: No, that's right, I had the cardioversion, it worked, then I went back into sinus rhythm, regular rhythm, and then I was in sinus rhythm for five years. So all was going well…
Norman Swan: On no medication?
John Cochrane: When I first went into fibrillation I was on sotalol and warfarin, the blood thinner, and then when I went into sinus rhythm after the cardioversion, after about three months I went off all the medication. So I was effectively back to normal.
Norman Swan: So you weren't on anticoagulation to prevent clots or anything like that. And what happened five years later?
John Cochrane: I was working in Sri Lanka and I was bitten by a mosquito and I contracted dengue in Colombo, which put the heart straight back into fibrillation.
Norman Swan: How long did that take to fix up?
John Cochrane: I think about a fortnight.
Norman Swan: And the same thing, zap, back to normal?
John Cochrane: I had a zap, back to normal, about three weeks later back into fibrillation, and he said, look, we'll do it again if you want to but this is diminishing returns. I had it again, I was back into sinus rhythm for a week or two, then into fibrillation and I've been there ever since.
Norman Swan: In fibrillation?
John Cochrane: Yes.
Norman Swan: So what treatment are you on?
John Cochrane: I'm taking warfarin and sotalol.
Norman Swan: Sotalol is a beta-blocker to slow your heart rate down.
John Cochrane: That's right.
Norman Swan: What symptoms do you get now?
John Cochrane: None.
Norman Swan: So you're in the lucky position, unlike most people with atrial fibrillation, your heart risk factors are pretty low.
John Cochrane: I guess so, that's right.
Norman Swan: John Cochrane, who in fact makes all the promos you hear on Radio National, and will hitherto be known around the office as the lone fibrillator.
Back to Professor Simon Stewart now at the Baker Institute.
Simon Stewart: The majority of people with atrial fibrillation probably won't know that they have it, so it's a silent epidemic, as it were. The likelihood of having it below the age of 45 is very low, but as we get older, by the time you reach the age of 80, for example, maybe one in 10, maybe two in 10 individuals will have atrial fibrillation. But if you do feel it you would have flutterings in the chest, you might get short of breath, and you might just feel a general weakness.
Norman Swan: And it's often said that it's under-diagnosed, that doctors miss it, they don't do ECGs or they rely too much on feeling the pulse and the irregularities in the pulse.
Simon Stewart: Yes that's right. So the definitive test for atrial fibrillation would be an ECG. But imagine your typical ECG lasts 12 seconds, so if you had an irregular pulse one minute, your GP decided to take a static ECG, as it were, they might miss that episode, particularly if you have what's called paroxysmal atrial fibrillation which is bursts of atrial fibrillation maybe when you are exercising and then settles down. So the definitive test would be a longer term ECG but that takes time and resources.
Norman Swan: And what are the risk factors for…what causes atrial fibrillation?
Simon Stewart: Like everything else to do with cardiovascular disease, there are some really well known causes of atrial fibrillation. So we can tick them off I guess, we can say that if you are hypertensive particularly, you have elevated blood pressure, you are more likely to get stretching of the heart, so the heart structure itself is affected and that more likely begets atrial fibrillation. If you've had a heart attack previously, that tends to increase your risk of atrial fibrillation. Having diabetes. Also if you're overweight in itself. And the biggest predictor is age. So the older the heart gets, the more likely it is going to develop a problem.
Norman Swan: And of course heart surgery can cause it too.
Simon Stewart: Heart surgery is one of the ones I forgot to mention. So if you do, for example, have heart surgery, a lot of people do develop it in the short term. Thankfully it's very well monitored so that most people are picked up, treated, and you can avoid the long-term consequences thereafter.
Norman Swan: So what is the treatment? Because you hear of people needing to go on warfarin, which is a major anticoagulant, to stop the clotting, but not everybody does. It seems to be a complicated story in terms of what's the right treatment for atrial fibrillation.
Simon Stewart: Yes, the clinical conundrums around the treatment of atrial fibrillation are many, and we talk about this benefit to risk ratio which in a lot of patients is hard to define and to decide upon, and what you tend to get is a sort of stasis where no one makes a definitive decision about treatment. So let's just go through the options. If you did present with atrial fibrillation you might be subject to what's called electrical cardioversion, that's a very successful treatment…
Norman Swan: So they shock you back into action.
Simon Stewart: They shock it back into action, into sinus rhythm, which is the normal rhythm where the atria pumps at a regular beat in time with the ventricles, the bottom of the heart. You may have what's called a pharmacological cardioversion which means you get drugs that slow the heart down and try to get it back into rhythm, or indeed the newer procedures people may have heard of is ablation where in actual fact they can map the electrical conductance of the heart, find where the particular spot is that the atrial fibrillation is coming from and actually sort of eradicate it.
Norman Swan: You've been doing this study called the safety study and made this recent finding on the effect on people's thinking and memory, but just tell us about this study you've been doing.
Simon Stewart: Yes, the safety study is a world first, hopefully. So this is part of a suite of studies we've been undertaking at the Baker Institute trying to determine if there are ways and means for us to structure healthcare better for particularly high risk individuals. And the idea is we are testing a nurse-led home-based intervention with multidisciplinary (these are all the buzzwords)…multidisciplinary coordinated care. But essentially what it's designed to do is visit people in the home, determine the best treatments and pathways to keep them healthy and to see if that particular strategy prevents hospitalisations and even deaths compared to the usual care.
Norman Swan: And do you have results for that study get?
Simon Stewart: We are still in the midst of the study. I'm hoping to report on the study early next year but we have got these fascinating findings about mild cognitive impairment, so mental capacity, and we've also got some fascinating data on heart rhythms, whether or not we can control the heart rhythm, because in atrial fibrillation if you control the heart rate you may not even decide to put a person back into sinus rhythm.
Norman Swan: So let's talk about this finding that people do seem to have damaged thinking ability and whether or not it's the cart or the horse, is it just an association or is the atrial fibrillation causing it? First of all tell us what the observation has been?
Simon Stewart: The observation is compared to the normal population, if you get up to the age of 65 you might expect about 5%, one in 20 people have some form of impaired form of thinking, so the ability to work through problem solving. As you get older this naturally increases. In the safety study we examined hospitalised patients with atrial fibrillation and found that two-thirds of these patients, these individuals with atrial fibrillation had impaired mental capacity.
Norman Swan: And is that just because the plethora of risk factors that lead to atrial fibrillation are also the ones that lead to impaired thinking, or do you think the atrial fibrillation is throwing off clots and damaging the brain?
Simon Stewart: I think we are pretty secure in stating that we think there is an underlying what you might say a basal risk of this problem because of those risk factors that do it, and then it's completely exacerbated by the atrial fibrillation because atrial fibrillation does engender these small clots, what we call micro-emboli, that will in actual fact clog the small arteries, the small blood vessels in the brain. And so this is an issue because we are asking these patients to undertake some really quite complex tasks to look after themselves and keep themselves well in the future.
Norman Swan: And has this been missed, do you think, in the past?
Simon Stewart: We certainly know that there are calls around the world, and UK-based clinicians are starting now to screen for this problem in atrial fibrillation, and I think I'd like to see the same in Australia because we are missing these cases, for sure.
Norman Swan: Is there any evidence that when you treat the atrial fibrillation the thinking ability gets better?
Simon Stewart: At this stage no, we don't have that definitive evidence. This is a pathway of research that needs to be examined, and it is certainly one of the things we are examining in the safety study to see whether the stability of this particular observation stays or whether you actually get better control, does that equate to better capacity. But I think it might be a case of damage done. Prevention is always better than cure, of course.
Norman Swan: And is there a higher rate of Alzheimer's disease or what they call vascular dementia where the blood vessels are at fault?
Simon Stewart: Yes, there are. People have probably heard about vascular dementia. The important point though is it tends to be…when you have these early stages you tend to be very stable for a number of years and then you sort of decant into this state of dementia. There is potentially still a window of opportunity to stabilise someone's risk of developing dementia.
Norman Swan: So you've kind of got mild cognitive impairment due to your blood vessels going wrong and then you fall off the cliff, in a sense.
Simon Stewart: Yes.
Norman Swan: How does vascular dementia differ from Alzheimer's in the way somebody appears to their relatives?
Simon Stewart: With this sort of vascular cognitive impairment it really is decision-making that is a difference and short term memory rather than a longer term memory, and these are far more subtle changes and may not be picked up without a screening tool.
Norman Swan: In summary then, people who are getting older, with atrial fibrillation, this is something that family, friends and doctors need to be aware of because people may need some extra help, and also it might provide some extra motivation to get your heart risk factors in order.
Simon Stewart: Yes, I think there is two key messages from this. The first one is prevention is better than cure. I don't know how many times we can say this more, but atrial fibrillation can be predicted on the basis of your risk factors, so get them under control early.
Norman Swan: And what have you found about heart rhythm?
Simon Stewart: Most of the trials now suggest that if you get it under control, who cares what rhythm you are in as long as you're not running fast, you're not being flogged. We've been putting monitors on people for a whole 24 hours and we've found that there are three distinct groups of patients, and this may have a really important impact on how we manage patients in the future. That is, there is a group that really are under control and that may be up to two-thirds of patients, but one-third of patients are clearly out of control or are clearly very labile. What I mean by that is their heart rate goes up and then it bursts of right out of control, and this is something we don't know about when we discharge these patients from hospital and make that decision.
And we think that unstable group are the ones that would concern us most because the person who is uncontrolled and goes back to his outpatient appointment probably will get picked up and would probably do something about it. But maybe the person who is labile, that is out of control at periods of times, may be missed, and these may be the highest risk patients and maybe they're the ones who have the cognitive impairment, they are the ones who have the higher rates of hospitalisation and death. And so we are just following these patients up at the moment
Norman Swan: Simon Stewart is Professor of Preventative Cardiology at the Baker IDI Heart and Diabetes Institute in Melbourne.
Clearly John Cochrane fits into the stable group and certainly doesn't have any thinking problems, apart from the usual ones associated with working at Radio National.
But he is glad he went to see his GP.
John Cochrane: On the day it happened, despite the fact that it took me an hour, an hour and a half before I decided to go to the doctor and thought, you know, this could be something serious, I think if I went to my doctor and I didn't get an appointment that day, I most probably wouldn't have gone back, thinking this is okay, it's just a pain in the chest, it'll go away. In fact maybe I had a pain in the chest beforehand. I think the cardiologist was surprised that I didn't get any stabbing pain when it came on. So I could have gone some time before it was actually diagnosed. I don't take my own pulse, and in those days I was seeing my doctor about once every one, one and a half, two years. I was in pretty good health, I had no reason to see him.
Norman Swan: So it could have been missed.
John Cochrane: It could have been missed quite easily, that's right, yes.
Ball J et al. Mild cognitive impairment in high-risk patients with chronic atrial fibrillation: a forgotten component of clinical management? Heart first published Online January 12, 2013, doi: 10.1136/heartjnl-2012-303182
- Professor Simon Stewart
- Head of Preventative Health
Baker IDI Heart and Diabetes Institute
- John Cochrane
- Dr Norman Swan
- Brigitte Seega