The increased heart rate also leads to increased work and oxygen demand by the heart, which can lead to rate related ischemia. Differential diagnosis
An electrocardiogram (ECG) is used to classify the type of tachycardia. They may be classified into narrow and wide complex based on the QRS complex. Equal or less than 0.1s for narrow complex. Presented order of most to least common, they are:
Narrow complex
Sinus tachycardia, which originates from the sino-atrial (SA) node, near the base of the superior vena cava
Atrial fibrillation
Atrial flutter
AV nodal reentrant tachycardia
Accessory pathway mediated tachycardia
Atrial tachycardia
Multifocal atrial tachycardia
Cardiac Tamponade
Junctional tachycardia (rare in adults)
Wide complex
Ventricular tachycardia, any tachycardia that originates in the ventricles
Any narrow complex tachycardia combined with a problem with the conduction system of the heart, often termed "supraventricular tachycardia with aberrancy"
A narrow complex tachycardia with an accessory conduction pathway, often termed "supraventricular tachycardia with pre-excitation" (e.g. Wolff–Parkinson–White syndrome)
Pacemaker-tracked or pacemaker-mediated tachycardiaTachycardias may be classified as either narrow complex tachycardias (supraventricular tachycardias) or wide complex tachycardias. Narrow and wide refer to the width of the QRS complex on the ECG. Narrow complex tachycardias tend to originate in the atria, while wide complex tachycardias tend to originate in the ventricles. Tachycardias can be further classified as either regular or irregular. Sinus
The body has several feedback mechanisms to maintain adequate blood flow and blood pressure. If blood pressure decreases, the heart beats faster in an attempt to raise it. This is called reflex tachycardia.
It was initially thought to be secreted by the parathyroid gland but was shown by Iain Macintyre and his team at the Royal Postgraduate Medical School, London, to be secreted by parafollicular cells of the thyroid gland. Dr. Copp named the discovered hormone calcitonin because of its role in maintaining normal calcium tone. Medical significance
Calcitonin assay is used in identifying patients with nodular thyroid diseases. It is helpful in making an early diagnosis of medullary carcinoma of thyroid. A malignancy of the parafollicular cells, i.e. Medullary thyroid cancer, typically produces an elevated serum calcitonin level. Prognosis of MTC depends on early detection and treatment. Calcitonin also has significantly impacted molecular biology, as the gene encoding calcitonin was the first gene discovered in mammalian cells to be alternatively spliced, now known to be a ubiquitous mechanism in eukaryotes. Pharmacology
Calcitonin has clinically been used for metabolic bone disorders for more than 50 years. Salmon calcitonin is used for the treatment of:

Postmenopausal osteoporosis
Hypercalcaemia
Bone metastases
Pagets disease
Phantom limb painIt has been investigated as a possible non-operative treatment for spinal stenosis.The following information is from the UK Electronic Medicines Compendium

General characteristics of the active substance
Salmon calcitonin is rapidly absorbed and eliminated. Peak plasma concentrations are attained within the first hour of administration. Animal studies have shown that calcitonin is primarily metabolised via proteolysis in the kidney following parenteral administration. The metabolites lack the specific biological activity of calcitonin. Bioavailability following subcutaneous and intramuscular injection in humans is high and similar for the two routes of administration (71% and 66%, respectively).