This is the term used by the medical profession to describe a fast heart rate of greater than 100 per minute. Tachy¬cardias include:
1. Sinus tachycardia
2. Paroxysmal atrial tachycardia (PAT)
3. Atrioventricular nodal reentrant tachycardia (AVNRT)
4. Atrial fibrillation
5. Atrial flutter
6. Wolff-Parkinson-White syndrome (WPW)
7. Ventricular tachycardia
These tachycardias are usually differentiated for diag¬nostic purposes into narrow QRS and wide QRS and then into regular or irregular tachycardias (see Fig. 5).

A. Sinus Tachycardia
When the fast beat arises from the normal sinus node pacemaker, it is called a sinus tachycardia. This is a normal physiologic occurrence during exercise, infections causing fever, anxiety states, loss of blood, dehydration, and thyroid overactivity. This is one of the most common abnormal tachycardias occurring in young healthy adults.
B. Paroxysmal Atrial Tachycardia
Those who have episodes of very fast heart beat, usually 150–190 beats per minute, may have a condition known as PAT. If episodes are frequent, drug treatment may be necessary. The term paroxysmal atrial tachycardia was introduced more than 50 years ago and was formerly used to include AVNRT, but these two conditions have subtle differences. Most cases called PAT are truly AVNRT.

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