What we call normal rhythm is stimulated by a group of cells in the upper chamber of our heart called the atrium. This group of cells is in an area of the atrium called the sinus node and functions as a “natural pacemaker” stimulating the atria and then the ventricles of our heart to contract.
In normal function (what doctors call normal sinus rhythm, generally with rates from 50 to 90 beats per minute in the resting individual), these cells can increase the rate due to activity (running, jumping, etc), increases in temperature, or many other things such as coffee or medicines.
Sometimes however, a different area of the atria is irritable and escapes from the usual order of things, causing faster and less regulated rhythms. This sometimes causes us to notice "extra beats" or "skips" when we take our pulse. This is quite benign and doesn’t cause any problems.
When the conditions are right for a problem however, these extra beats can "string together" and cause rapid regular fast heart rates that doctors call paroxysmal (meaning an episode of sudden onset) atrial tachycardia (meaning fast heart rate).
In such a case, there seems to be a racing heart, as if you were running, that starts all of a sudden, despite the absence of an obvious cause. This is often described as a "palpitation" or an "anxiety attack".
Paroxysmal atrial tachycardia, also called PAT or PSVT, most often stops as quickly as it starts. Episodes of PAT can be triggered by alcohol, caffeine containing beverages, stimulants (especially amphetamines and cocaine), smoking, gallstones, fevers and respiratory infections. PAT can also be associated with the hormonal excesses caused by an overactive thyroid gland.
It is quite common to observe palpitations during other hormonal surges such as during puberty, pregnancy and menopause. Often if the triggering cause is stopped, the arrhythmias will disappear. Thus, childbirth may end the palpitations of pregnancy, or wearing off of the stimulants may end those triggered by stimulants.
Most palpitations are self limited and benign. If PAT lasts for a longer period, however, it may be associated with other symptoms such as chest, shoulder, neck or arm pain, shortness of breath or dizziness or fainting are reasons to seek health care. Palpitations that are increasing in severity, duration or frequency are a good reason to see your physician.
What should you do if you have PAT at an inconvenient time (has anyone had it at a "convenient time)?
There is a nerve in the body called the vagus nerve. When we stimulate it the heart rate slows down and blood pressure drops. Attempts to stimulate this reflex are called Valsalva maneuvers.
The easiest way to stimulate this reflex is to attempt to exhale with the nostrils, mouth or glottis closed. This equalizes pressure in the middle ear and chest. If this is difficult to understand, just think of what you do when bracing to lift heavy objects.
Another variety of this maneuver is to squeeze down on your abdominal muscles as if trying to move your bowels, or to push out your abdominal muscles against your hand. Yes, your face may turn a bit red, but you will often stop the PAT. Not sure if you are doing it right? It also works when you are not having palpitations. If you are doing it and your heart rate slows, you’ve got it right. Don’t worry, it will speed up afterward.
Interesting fact: the same slowing of the heart rate and dropping of the blood pressure can be the reason that some people faint. We say that these people have vagal episodes. Show some people blood, or a syringe and needle, and down they go. Treatment: lie them down and raise their legs. If they haven’t fallen, putting the head down between the knees works well. Again, don’t worry - the heart will speed up afterward.