tachycardia
Meaning of tachycardia: A fast heart is usually the body responding correctly to something else, and the real question is what that something else is.
Definition of tachycardia
Tachycardia is a heart rate faster than the expected range. In a resting adult that usually means more than one hundred beats per minute, though the threshold depends on age, since children and infants normally run faster. It describes a rate rather than a diagnosis, and the cause behind it is frequently ordinary.
Why does the heart speed up?
Most tachycardia is an appropriate response rather than a fault. The heart raises its rate to deliver more blood each minute when the body needs it, driven by nerve signals and circulating adrenaline acting on its natural pacemaker. Exercise, fever, pain, fear, dehydration, blood loss, anemia, an overactive thyroid, low oxygen levels and infection all either raise demand or reduce supply, and a fast rate is the correct answer to each of them. Caffeine, nicotine, withdrawal from alcohol, decongestants, stimulants and some inhaled medications raise it directly. A fast rate arising this way is called sinus tachycardia, since the impulse still starts in the normal place, and it settles once whatever prompted it settles.
When is the rhythm itself the problem?
| Type | Where the fast signal starts | Character |
|---|---|---|
| Sinus tachycardia | The heart's normal pacemaker | Rises and falls gradually with its trigger |
| Supraventricular tachycardia | Above the ventricles, often a short circuit | Starts and stops abruptly, frequently very fast |
| Atrial fibrillation | Disorganized activity across the upper chambers | Irregular, with no steady pattern |
| Ventricular tachycardia | The ventricles themselves | Serious, since the main pumping chambers are involved |
These are separated by an electrical tracing of the heart rather than by how fast a pulse feels, because rate alone does not reveal the mechanism. A tracing captured while symptoms are happening is far more informative than one recorded afterward, which is why monitors worn over a period are used when episodes come and go.
What does a sustained fast rate do?
A faster rate shortens the time the heart spends relaxed between beats, and it is during that pause that the chambers fill and that the heart's own arteries receive their supply. Very fast rates therefore reduce the volume pumped with each beat while reducing the muscle's own blood supply at the same time, which is why palpitations, breathlessness, chest discomfort, lightheadedness and occasionally fainting accompany them. Someone with coronary heart disease or congestive heart failure tolerates that combination less well, having less reserve to absorb it. A rate held high for weeks or months can itself weaken the heart muscle, a change that often improves once the rhythm is brought under control.
Also known as
Used in a sentence
Fever and dehydration contributed to the patient's tachycardia.
Good to know
Exercise, fever, stress, dehydration, medicines and abnormal heart rhythms can all cause tachycardia, so a fast rate is a finding to be explained rather than a diagnosis in itself.
Word origin
Where “tachycardia” comes from
From Greek tachys, meaning swift, and kardia, meaning heart.