Tachycardia is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal (such as with exercise) or abnormal (such as with electrical problems within the heart).
Tachycardia can be harmful in two ways. First, when the heart beats too rapidly, it may perform inefficiently. Second, the faster the heart beats, the more oxygen and nutrients the heart requires. This can be especially problematic for patients suffering from ischaemic heart disease.
An electrocardiogram (ECG) is used to classify the type of tachycardia (Pic. 1). They may be classified into narrow and wide complex based on the QRS complex (Pic. 2).
The management of tachycardia depends on its type (wide complex versus narrow complex), whether or not the person is stable or unstable, and whether the instability is due to the tachycardia. Unstable means that either important organ functions are affected or cardiac arrest is about to occur.
Tachycardia may be associated with several diseases including:
Hyperthyroidism is the condition that occurs due to excessive production of thyroid hormone by the thyroid gland. An increased rate of metabolic activity in hyperthyroidism may be associated with tachycardia occurence.