..is characterized by attacks of abnormally high (2 - 4 or more times normal speed) heart rate, which can last for hours or even days. It's caused by spontaneous impulses in the upper chamber of the heart that play havoc with your body's "natural pacemaker". It can cause chest pain and heart palpitations, and fainting spells and shortness of breath. Attacks can be stopped with drugs or by straining (as when constipated) with mouth and nose blocked, though this is dangerous and can cause a stroke, but sometimes the only effective method is electric cardioversion. (done with the defibrillator (the thing with paddles) you always see on TV)

The straining mentioned above is the Valsalva manoeuvre.

Intravenous adenosine given by fast intravenous infusion is the drug of choice for SVTs and works by causing heart block for a split second following injection - though it is contraindicated in asthma. Another drug that can be used is verapamil, a beta blocker, though this is contraindicated if other beta blockers have already been given or if there is a broad QRS complex on ECG.

What having SVT means in real life to an otherwise healthy person is this:

I found out that I had SVT when I was 16. I had already been swimming for 4 years, and lived on warm pepsi. I was told I could take drugs to combat it, but the side effects were worse than the cure. Now, I hold my breath and strain mildly when my heart starts flipping a shit. I rarely have more than 2 drinks, and I try to stick with caffeine free coke. (It tastes just like the real thing.) It scares my boyfriend more than it scares me - he won't rest his head on my chest because of my irregular heartbeat.
There are several methods that have been recommended to me by doctors/websites to 'naturally' convert episodes of PSVT back to a normal heart rhythm. Here they are, along with any comments/successes I have had with them:

1. Vagal maneuvers...

Holding your breath, coughing, tensing your stomach muscles (as if bearing down on a bowel movement), having someone press down on your stomach while holding your breath, standing on your head while holding your breath. These are called Vagal maneuvers because they do something to the vagus nerve on your heart which releases substances to decrease your heartrate.

This has proven to be the most successful 'natural' (non-emergency room) method of converting my tachycardia. Usually holding my breath, breathing in and out slowly, sometimes while leaning forward in a sitting position, other times lying on my back will get rid of the tachycardia after a few minutes. When it doesn't, I will usually get up (slowly so as to avoid fainting), walk around for a couple minutes, then lay down and try again.

2. Massaging the carotid artery in the neck...

This is another way to tell your heart to slow down. I do not employ this method regularly myself. While it does tend to slow down my heartrate, the tachycardia always remains and never converts as a result of carotid massage for me. I have also read that this can be dangerous for older people by putting them at risk for a stroke (I am only 23, but would rather not take my chances).

3. Dunking your head in cold water...

This brings about what is known as the 'dive reflex' and can stop the tachycardia. I heard once that this method is used on young babies who experience PSVT (just hold them upside down, dunk, splash, all done). I've tried this on a few occasions when the vagal manouvers would not work. The first couple times I dunked my head into large sinks filled with cold water, the third time I tried a cold shower. It hasn't worked for me yet. I always ended up drying off my hair, returning to the vagal maneuvers, and eventually converting it that way.

4. Nerves?

This was never recommended to me, but has worked on a couple occasions so I feel it bears mentioning. There have been a couple times where my tachycardia lasted frighteningly long periods of time. The first time I was actually scared was when it started in the morning during one of my university lectures, and lasted until bedtime almost 12 hours later. It was the longest spell I had ever had without being able to convert it. I finally built up the courage to go tell my parents (I had to wake them up). I went and knocked on their bedroom door (which I never do), woke them up, and then as I was telling them it finally stopped. I was sure it had to do with the fact that I was so nervous to be bugging my parents about something like that.

Another time I was having trouble converting an episode right after it started, so I went to my room to lay down. As soon as I did, my 60 lb dog ran around the corner at top speed, leapt into the air, landed 1 inch from my face, and started licking my mouth. This surprised me so much that my tachycardia stopped cold.

5. Drugs...

Yay!! Drugs!!!

In most cases, I am able to convert my tachycardia, or it will simply stop on its own, within the first 5-10 minutes, and if it goes longer than that, rarely for over 45-60 minutes. The first time it went longer I've described above. The second time it had been going for a good 2-3 hours. This was at a time when my then-girlfriend (now-wife) was living with me and my parents while we waited for my fiance visa to be approved by the US Immigration and Naturalization Service. Because we have a strict honesty policy between us, I let her know as soon as it started. Normally even after the first few hours I would have simply sat it out, but my girlfriend was frightened and eventually convinced me to let her tell my parents. After a few more hours with no luck converting it, my dad decided to drive me to the emergency room.

Upon arrival, my pulse was taken, confirmed to be way too fast (190-200 beats per minute), and I was told to wait until called. We waited for about 20 minutes, and then I was directed to a bed in the back where I was hooked up to a heart monitor and an IV. Eventually a doctor came and explained to me what PSVT is, told me that it was fairly common in the emergency room, and then went through some of the more common methods of converting it I've mentioned above (he had me try a few of them with no positive result).

He said since it had been going for so long (5-6 hours by then) that he would simply push a drug called adenosine into my IV. He explained (quite accurately) that I would feel a flushed sensation in my face, and a pressure on my chest when he did so. Apparently, adenosine stops all electrical activity in the heart for a brief moment. It felt WEIRD!!! But it immediately stopped my tachycardia.

Apparently it's good to stop about 90% of cases, and has no real negative side effects at the dosage level required to convert PSVT (other than the brief discomfort/disorientation after it's pushed). My doctor seemed to feel that it should be made available by prescription for people with PSVT, but gave me some reason why it was not (I forget the reason now -- probably that it had to be administered through IV).

5. Surgery...

I was told that there is an operation that can cure PSVT, but that at this time the risks of the surgery were slightly high to justify curing a condition that is little more than a nuisance to those who have it.

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