Definition of "tachycardia"

The heart becomes irritable, there is nervous palpitation, or attacks of paroxysmal tachycardia.

1896 June, E[dwin] M. Hale, “The Heart at the Beginning and Ending of the Menstrual Life: Reprinted from the Hahnemannian Monthly, June, 1896”, in The Hahnemannian Monthly, Philadelphia, Pa.: Homœopathic Medical College of Pennsylvania, page 1

Tachycardias of all types reduce the cardiac output if the rate is high enough. […] The main difference between the tachycardias as regards the reduction of cardiac output is the rate at which they cause a significant reduction of cardiac output, and this depends on the type of tachycardia.

1988, G.M. Woerlee, “Cardiac Arrhythmias – General”, in Common Perioperative Problems and the Anaesthetist (Developments in Critical Care Medicine and Anaesthesiology), Dordrecht: Kluwer Academic Publishers, page 123

Tachycardia is defined as a FHR [fetal heart rate] above 160 bpm that lasts for at least 10 minutes. Tachycardia represents increased sympathetic and decreased parasympathetic autonomic tone and, therefore, is generally associated with a normal loss of FHR baseline variability […].

2003, Rebecca L. Cypher, Donna Adelsperger, Keiko L. Torgersen, “Interpretation of Fetal Heart Rate Patterns”, in Nancy Feinstein, Keiko L. Torgersen, Jana Atterbury, editors, Fetal Heart Monitoring: Principles and Practices, 3rd edition, Dubuque, Iowa: Kendall Hunt, page 117

With atrial tachycardia, the atria of the heart beats abnormally fast. Though often unpleasant for the patient, an atrial tachycardia is typically not fatal. However, some tachycardia, particularly ventricular tachycardia, can trigger ventricular fibrillation wherein the heart beats chaotically resulting in little or no net flow of blood from the heart to the brain and organs.

2013, “Therapies and Treatments”, in Q. Ashton Acton, editor, Tachycardia: New Insights for the Healthcare Professional, Atlanta, Ga.: ScholarlyEditions, published 2013, page 235