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To what extent may high altitude, and if so at what

altitudes, increase the risk of...
To what extent may high altitude, and if so at what altitudes, increase the risk of a stroke in a person with atrial fibrillation? It is understood that high altitude thickens the blood and increases blood pressure, both of which effects may increase the probability of a stroke;however, the question here is related specifically to strokes attributable to blood clots forming in the heart as a result of the atrial fibrillation
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Answered in 14 minutes by:
3/16/2012
Dr. R. Bora
Dr. R. Bora, Doctor
Category: Medical
Satisfied Customers: 5,233
Experience: Several years of clinical experience in all fields of Medicine.
Verified
At what altitude have you skied till now with aspirin?

You must be knowing that physiologic polycythemia or thickening of the blood starts from 4275 to 5200 meters. So, any altitude higher than this would put you at risk for blood clots and strokes.

I hope my answer is helpful to you.

Please press the "green accept button" to accept this answer and give credit for my work and time.

Positive Feedback and bonus is warmly appreciated.

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Customer reply replied 6 years ago
I am afraid, the "answer" didn't answer my question. I specifically put it in my question that I was aware of polycythemia and blood pressure rising at higher altitudes, and I was ONLY Interested in finding out whether there was any experimental evidence, or at least a reasonable physiological argument that would suggest that the formation of blood clots within the heart - which is presumably the main reason for the increased risk for strokes in people with chronic atrial fibrillation - was more likely at higher elevations where the amount of oxygen is less.
With atrial fibrillation there is always a risk for blood clot / thrombus formation within the heart which can easily get dislodged (known as emboli) and clog an artery in the brain, or neck or even blood clots cab form in the deep veins of the legs which can embolize to the heart.

So, you have to check the INR or the internal normalized ratio which is checked for anyone taking blood thinners and see if the INR is within the normal range (approx. 2.5 to 3.5). If your INR is abnormal, you wil have to see an internist or hematologist and get the drug adjusted to warfarin .

I hope this answers your question.
Please press the "green accept button" to accept this answer and give credit for my work and time.

Positive Feedback and bonus is warmly appreciated.

I hope my answer is helpful to you.

Please press the "green accept button" to accept this answer and give credit for my work and time.

Positive Feedback and bonus is warmly appreciated.
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Customer reply replied 6 years ago
Dear Dr. Bora,

You are not answering my question. You are giving me information that is freely available to anyone and that I have been aware my bself for a long time. I marked the "answer" as "I hate it" because you are talking about having to check my INR : if you read the information I gave you, you must have noticed that I said I was not on warfarin. So, obviously nmy INR would be about 1.

Perhaps, we ought to suspend this exchange. I appears to me that, even if there has been any study carried out or evidence obtained regarding my question, and it is possible that it has not, you are not aware of it. I am terribly sorry, but I cannot accept your answer as anything even remotely useful.
Dr. Owen
Dr. Owen, Board Certified Physician
Category: Medical
Satisfied Customers: 55,754
Experience: Board Certified in 2 Specialities & US Medical Graduate
Verified
Hello, and I am pleased to help, use of my answers are for educational purposes only.
I am also an expert in Aerospace medicine - would you like me to try and answer your question?
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Customer reply replied 6 years ago
It is very clear from his answers that Dr. Bora has not taken the time to understand my question - or worse, was unwilling, or worse still, was unable to. It is quite possible, and I am beginning to suspect that this, indeed, may be the case, that medical science currently has no data or sufficient understanding to provide a meaningful answer to my question. If this be the case, an expert should acknowledge this, rather than reply with facts generally known but which provide no clue to the actual question.

According to the current understanding of medical science, the reason for a higher incidence of ischemic strokes in persons having atrial fibrillation is that the turbulent flow of blood caused by the fibrillation is likely to lead to the formation of blood clots right in the heart. Thus my question was whether this mechanism is or is not exacerbated by a lower oxygen level in the ambient atmosphere, as the case is at higher altitudes, and if so, at what altitudes this effect may become noticeable. A valid corollary point would be whether such an effect may depend upon the person's INR.

If there is a known answer and Dr. Owen is willing to give it to me, I am eager to listen.
Well - let me put my 2 cents in as someone who takes care of astronauts and aviators....
When you expose astronauts to extended stays in low pressure environments which is the space station - they have increased Hemoglobins - increasing red blood cells essentially - but the platelets and clotting factors do not really increase - so this should not affect your atrial fib - I hope that makes sense. If helpful, please click on ACCEPT, thank you
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Customer reply replied 6 years ago
I do not mean to be disrespectful, when I say I "dislike" your answer. (The problem is there is no button that says "incomplete").

Increased hemoglobin in austronauts must be caused by an increased number of red cells - polycythemia - which is known, not only according to my understanding but specifically according to the first response of Dr. Bora - to put people "at risk for blood clots and strokes". However, you are saying that for austronauts "clotting factors do not really increase". That seems to me a contradiction. Also, on space stations they can control not only the pressure but also the ratio of Oxygen to Nitrogen: thus the actual amount of oxygen an austronaut inhales may well be different from the amount a person in open air would inhale at a similar total pressure.
I will opt out too, I do not think I will be able to help you....the physiology is quite complex for what you are asking - and if you want - there is a book called Environmental medicine - take care.
Thank you
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Customer reply replied 6 years ago
I like the answer in that it is honest and says that he has no answer, but I may consult a book. This implies, however, that I can not press the "Accept Answer" button, because I didn't get an answer to my question.
Vakul Aren
Vakul Aren, Doctor
Category: Medical
Satisfied Customers: 4,550
Experience: MBBS,DTM&H,38 years of experience
Verified
Since atrial fib causes clotting at sea level too,which leads to clotting of blood in the atrium,I really cannot understand what difference high altitude will make.Strokes will occur when fragments of the clot will dislodge and enter the cranial/systemic circulation.It would be difficult to predict if high altitude will actually increase the number of strokes.High altitude is a known trigger for atrial fibrillation episodes along with cold beverages,smoking,bronchial inhalants,sumitraptan, and like other triggers should be avoided.Use of Dabigratan,or Plavix/Ticlid and coumadin will reduce the risk of strokes in A -Fib patients by 60-70%.Aspirin is a poor drug as compared to Coumadin and Dabigratan for stroke prevention.The high altitude may increase your dyspnoea and breathlessness and may have the effect of straining a heart pump already under pressure due to the effects of A-Fib.Specifically there is lack of data on the effects of high altitude and strokes in A-fib patients.
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Customer reply replied 6 years ago
Dear Dr. Akul Varen,

The answer I would have liked to hear would come from, unfortunately, precisely such data that you say we don't have: data on the effects of high altitudes on the incidence of strokes in A-fib patients.

Your first sentence would seem to indicate to me that you don't feel that altitude levels should change the probability of blood clot formation in A-fib patients (probably because the clots form right in the heart due to the flow conditions precipitated by the fibrillation and not because of the density of the red cells). Can you verify this for me, please.

The fact that high altitude may act as a trigger for (paroxysmal) atrial fibrillation is of no consequence to me, as I had indicated earlier that I have been in chronic atrial fibrillation for some time - actually some 16 years. However, I managed to regain a good deal of exercise tolerance over the years. I do have to stop to catch my breath during an intense ski run, but this is not prohibitive of my enjoying the sport - more so than I did 16 years ago.

You did point out that the higher altitude would put an increasing load on my heart, which means that I would have to stop more often at, say 9,000 ft than at 3,000 ft (where I normally ski). However, I believe, I could myself be the best judge whether having to stop more often at higher altitudes negates the pleasure of the sport itself.

Thus the question remains only whether this increasing load on the heart, probably particularly at the first day or two during a stay at higher altitude, would actually present a danger of an irreversible effect, stroke or otherwise, to my health in my condition.
In practical terms, the question is the wisdom or otherwise of my driving up to, say, a base elevation of 6,000ft and starting to ski at 9,000 ft on the second or third day to decide whether I should stay longer or simply accept the fact that I am not young any more.
I agree that the atrial clotting of blood ids secondary to the flow conditions and is unlikely to be affected by the viscosity of the blood,hence the question whether higher altitude resulting in increased viscosity of blood need not necessarily increase the clotting.Further,strokes occur due to breakaway from the main clot entering the circulation,whether altitude would really affect this in any is a matter of conjecture.The important factor in stroke formation would be the breaking away of clots rather than clot formation itself.I doubt that the increased load due to high altitude,after getting acclimatised,will have any affect on your circulation is doubtful.this is more so since you exercise regularly and have a good cardiopulmonary reserve.Switching over to coumadin would be advisable(the matter can be discussed with your doctor) as against taking aspirin low dose therapy as the preventive effect of the anticoagulant is definitely better and reduces strokes by as much as 70%.
Vakul Aren
Vakul Aren, Doctor
Category: Medical
Satisfied Customers: 4,550
Experience: MBBS,DTM&H,38 years of experience
Verified
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