I have had supraventricular tacchyarrhythmias (try saying that three times in a row), usually supraventicular tacchycardia, both known as SVTs, myself. I also sometimes feel like I am going to pass out when I bend from the waist. I also have been told by a doctor it was "all in your head," only it wasn't.
The extremely fast heartbeat does not in itself interfere with the heart's ability to circulate blood throughout the body, but you can feel like you are about to die. Your heart can pound so hard and fast it feels like it is about to jump out of your chest. You can feel like you just can't catch your breath. You can have chest pain (more like the chest pain from running really hard than the chest pain from a heart attack, but I can say that because I've had a heart attack, and not everyone who has SVT has or will). You can pass out, plunk, right down to the floor in the middle of normal activity.
What's going on with an SVT is basically a short circuit in the heart. The heart is a muscle that powers the flow of blood to the rest of the body by top to bottom coordinated movement. The sinoatrial node (SA) at the top of the heart generates an electrical signal that is passed from cell to cell to make the top two chambers of the heart, the atria, beat in sequence. The electrical charge is passed on in just thousandths of a second, so we are not consciously aware of it, but it moves from cell to cell to cell in order.
When the impulse has moved through the top two chambers of the heart, it continues to the atrioventricular (AV) node. This junction starts a new impulse that moves through the bottom two chambers of the heart, the ventricles, so that their motions are coordinated.
The problem in SVT is that some electrical signals from the atria to the ventricles "jump" the "gate" at the AV node. In addition to the regular electrical stimulation the ventricles are supposed to receive, they also receive "stray" electrical signals from the atria. The ventricles beat faster than they are supposed to, still moving as much blood, if they are healthy, as if they were normally stimulated. The heart beats too fast, but it can still do its job. When there is injury to the heart, however, this same general process can result in atrial fibrillation (A-fib), in which the atria can beat as fast as 600 beats per minute, or atrial flutter. What a cardiologist diagnoses as "flutter" and what you or I experience as flutter are usually different things, but SVT and flutter-like feelings have a way of forecasting more serious disease.
- Emotional stress. SVT may be what is happening when people pass out cold on hearing bad news.
- Use of stimulants. Caffeine, nicotine, and some street drugs (cocaine, in particular) can trigger SVT.
- Heart attack can induce SVT, as can cardiomyopathy, slow degeneration of the heart muscle.
- Bending at the waist, especially with a full stomach.
Other physical activities usually don't trigger SVTs, just bending at the waist, especially on a full stomach. The likely reason for this is a more generalized "jump" of an electrical signal from the vagus nerve. The vagus nerve is a long nerve that extends from the back of the head to the stomach. It acts as a "brake" on the speed of the heartbeat. When pressure from food (or belly fat) interfere with the conduction of impulses through the vagus nerve, any other influences that cause SVT are temporarily unchecked, and the result can be rapidly accelerating heartbeat. This isn't something you will get from the medical books, but it is something that makes good anatomical and experiential sense.
What can you do about SVTs? First of all, you don't have to wear a monitor for a couple of days to know you have them. They are easy to detect on an EKG, and since anything you do on your own is treating symptoms, not the disease itself, you can go ahead and try these on your own.
- Doctors typically recommend the Vasalva maneuver as a treatment for SVTs. Press down your lower abdomen to imitate the sensation you have during a bowel movement. (This can cause an actual bowel movement.) Within a couple of minutes, your pulse rate should go down.
- If you have a queasy stomach, simply lie down, on your left side. This relieves pressure on your heart that can stimulate your pulse.
- Splash yourself in the face with cold water. Your body slows down your heart rate as if you were drowning, to conserve oxygen.
- Slow down your breathing, prolonging exhalations so that you breathe out longer than you breathe in. Your body interprets this as oxygen deprivation, and slows down heart rate to conserve oxygen, even though all you have to do to get enough oxygen is to breathe normally.
Doctors usually treat SVT with either beta-blockers (metoprolol is the drug of choice in the USA) or calcium channel blockers (typically verapamil). There is a radiofrequency ablation procedure that a cardiologist can perform to reduce the possibility of "jumping" electrical impulses in the heart. The procedure is done through a catheter, inserted through a three millimeter incision in the groin, with only local anesthetic. However, not everyone who has SVTs is a candidate for the procedure.
The good news is, the right beta-blocker can make a huge difference in symptoms, provided you get it in the right dose. When I started metoprolol for SVTs I had a problem with waking up in the middle of the night with rapidly beating heart, but adding a second dose of the beta-blocker at night stopped the problem.
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