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The Science Behind Pre-Syncope


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Following a cardiac ablation for concealed WPW I have been diagnosed as having "autonomic dysfunction".

By far the most pronounced symptom of mine is what I presume to be episodes of pre-syncope. A very sudden feeling of faintness or dizzyness, sometimes falling, lasts seconds. Naturally a feeling of panic or sudden HR increase is associated with it once the feeling is acknowledged. There is no clear trigger.

My arrhythmia(AVRT/SVT/AF) has returned following the ablation, however having had a holter my EP thinks these episodes of pre-syncope are not due to a rouge cardiac arrhythmia.

So my question is, what's the mechanism behind Pre-syncope? Taking in to consideration HR and BP is normal(e.g 115/68). I had always thought pre-syncope would be due to one or the other. Or is there more to it?

Having just seen an Endo for 24 hour urine and blood tests she's mentioned Diabetes insipidis as a possible cause. I suspect Hyperadrenergic POTS but i'm not sure if these results fit in the norm:

sodium 146 (normal range 135-145)

plasma osmolality 298 (normal range 285-295)

urine osmolality 118 (normal range 80-1200)

urine volumes of 7.39 litres and 6.45 litres

noradrenaline 391 and 252 (normal range 90-500)

liver function tests normal apart from a marginally elevated ALT at 56 (normal range 9-52)

urine dopamine 3355 and 2576 (normal range 300-3000)

ACTH 19.7, cortisol 421, plasma renin activity 12.1 (upright range 2.64-27.7).

Any thoughts appreciated.

Thanks!

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Were your urine/serum osmolality tests done after fasting? Mine look like that almost every afternoon, but I do concentrate my urine under extreme conditions. I have a questionable diagnosis of partial diabetes insipidus, some others of us do as well. If you do a water deprivation test, do it under strict protocol and get a serum copeptin level drawn as well. There is a new study that should release its findings soon that shows that serum copeptin is a better marker of true DI than serum ADH levels.

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Thanks for your reply Firewatcher.

No urine/serum osmolality tests were taken at the hospital, and i presume from 24 hour urine. I have dehydration test scheduled to take place in hospital in a couple of weeks so I'll mention serum copeptin. Thank you for the heads up.

I had searched for DI before and saw your posts. What was it that finally got you your H POTS Diagnosis if you dont mind me asking? I really want to get a firm diagnosis asap to get meds so i can get life back on track.

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"What was it that finally got you your H POTS Diagnosis if you dont mind me asking?"

My ANS tests at Vanderbilt were very suggestive of hyperadrenergic POTS. Basically, my HR and BP both went way up on testing instead of "normal" responses. My presentation was also fairly life-long without a viral or postpartum "trigger." I have the tremor and cold, sweaty hands and feet with no palpable, wrist pulse when upright.

As for the DI dx, I don't have the posterior pituitary "bright spot" on MRI and have no detectible ADH on testing (even at a serum Osm of 304.) Like I mentioned before, I do concentrate my urine under extreme dehydration: serum Osm of 304, with a standing BP of 80/nothing.***this is the part to be aware of!*** A BP that low should have voided my test results because a BP drop is a potent release trigger for whatever ADH your body can produce. They never took my BP before my water deprivation test, and it should have been done before my serum Osm got above 295. When I walked into the lab, I was already at 304 and had only done overnight fasting...that really isn't normal.

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So my question is, what's the mechanism behind Pre-syncope? Taking in to consideration HR and BP is normal(e.g 115/68). I had always thought pre-syncope would be due to one or the other. Or is there more to it?

This is the question you had, right? I pasted this below from one place I have bookmarked. Just not enough oxygen in the brain, we all know how that is. Syncope happens so your brain can get oxygen when you faint or lie down. When the level is not good enough, the brain tells us thank goodness! Then we sit or lie down. BP varies, doesn't have to be high or low.

The brain is the most metabolically active organ in the body and requires a steady supply of oxygen and glucose to maintain healthy function. Although the brain represents only 1-2% of the body's mass, it utilizes 20% of the body's oxygen consumption and 15% of cardiac output. Our brains are thus highly dependent on adequate blood circulation to maintain our sense of health and well being. The thought process, regulation of body temperature, hormone release, and many autonomic systems can be impaired by loss of proper blood pressure control. Our survival is as dependent on adequate blood pressure regulation as on the fundamental process of breathing.

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Sarah,

In a normal pituitary MRI, the posterior pituitary will be hyperintense, aka: a "bright spot" due to the presence of ADH. In central DI, that bright spot is absent. Mine is absent, there is no difference between the anterior and posterior pituitary on imaging, with or without contrast. This is why my dx is "iffy." With partial DI, people can concentrate their urine under extreme conditions, but only for a limited time...this is why I think my formal water deprivation test was inconclusive; normal people don't have a serum Osm of 304 after overnight fasting or a BP of 80/nothing (it was 50/"I can't hear anything" while supine.)

pituitary disorders

If you scroll down to the bottom of this page, there is an MRI image of a normal pituitary bright spot.

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Presyncope in POTS can potentially be caused by:

1.Abnormal cerebro vascular autoregulation - blood flow to the head and brain is normal, but the brain buffer that keeps it maintained at a steady level seems faulty in POTS.

2. Excessive angiotensin II mediated or norepinephrine mediated cerebral vasospasm - too much cerebral vasoconstriction.

3. selective vasomotor abnormalities

4. reduces stroke volume alone

5. hypovolumia - either whole body and absolute or related to leaky veins in the thoratic or splanchnic circulation.

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So my question is, what's the mechanism behind Pre-syncope? Taking in to consideration HR and BP is normal(e.g 115/68). I had always thought pre-syncope would be due to one or the other. Or is there more to it?

This is the question you had, right? I pasted this below from one place I have bookmarked. Just not enough oxygen in the brain, we all know how that is. Syncope happens so your brain can get oxygen when you faint or lie down. When the level is not good enough, the brain tells us thank goodness! Then we sit or lie down. BP varies, doesn't have to be high or low.

The brain is the most metabolically active organ in the body and requires a steady supply of oxygen and glucose to maintain healthy function. Although the brain represents only 1-2% of the body's mass, it utilizes 20% of the body's oxygen consumption and 15% of cardiac output. Our brains are thus highly dependent on adequate blood circulation to maintain our sense of health and well being. The thought process, regulation of body temperature, hormone release, and many autonomic systems can be impaired by loss of proper blood pressure control. Our survival is as dependent on adequate blood pressure regulation as on the fundamental process of breathing.

Thanks Sally. I am still learning and researching this conditions so understanding the fundamentals of what's causing this fainting feeling is paramount for me.Appreciate the info.

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"What was it that finally got you your H POTS Diagnosis if you dont mind me asking?"

My ANS tests at Vanderbilt were very suggestive of hyperadrenergic POTS. Basically, my HR and BP both went way up on testing instead of "normal" responses. My presentation was also fairly life-long without a viral or postpartum "trigger." I have the tremor and cold, sweaty hands and feet with no palpable, wrist pulse when upright.

As for the DI dx, I don't have the posterior pituitary "bright spot" on MRI and have no detectible ADH on testing (even at a serum Osm of 304.) Like I mentioned before, I do concentrate my urine under extreme dehydration: serum Osm of 304, with a standing BP of 80/nothing.***this is the part to be aware of!*** A BP that low should have voided my test results because a BP drop is a potent release trigger for whatever ADH your body can produce. They never took my BP before my water deprivation test, and it should have been done before my serum Osm got above 295. When I walked into the lab, I was already at 304 and had only done overnight fasting...that really isn't normal.

Thanks. I did wonder if the diagnostic tests or tools were different for H Pots as opposed to normal POTS. Will ensure BP is closely monitored at my dehydration test.

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Presyncope in POTS can potentially be caused by:

1.Abnormal cerebro vascular autoregulation - blood flow to the head and brain is normal, but the brain buffer that keeps it maintained at a steady level seems faulty in POTS.

2. Excessive angiotensin II mediated or norepinephrine mediated cerebral vasospasm - too much cerebral vasoconstriction.

3. selective vasomotor abnormalities

4. reduces stroke volume alone

5. hypovolumia - either whole body and absolute or related to leaky veins in the thoratic or splanchnic circulation.

Thanks Ramakentesh.

For those that experience sudden pre-syncope can I ask what meds have helped alleviate this feeling? Florinef, any SSRI's? In my case i'm not sure that salt alone is having enough effect. The high salt and fluid intake just seems to cause an even greater urine output.

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licorice at the time used to help. You can spike your BP with caffeine as well that might help for five minutes but you might feel worse later potentially.

Thanks for your response, I shall try the licorice. That's a great tip!

And for those who actually faint. Have you noticed that your BP stoops exceptionally low when you do faint, or has anyone experienced fainting when there BP was "normal"?

I ask because POTs in new onset for me, and although i haven't fainted, i'm come pretty close even when my BP is normal.

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licorice at the time used to help. You can spike your BP with caffeine as well that might help for five minutes but you might feel worse later potentially.

Rama, can you help me with the caffeine question? I had avoided it for a long time because my heartrate was just too fast and it made me feel unpleasant, but now that my symptoms have settled a little, a bit of caffeine in the AM seems to give me a temporary boost at a time of day when I struggle most with OI.

What might it be doing that could make me feel worse later?

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