Tachycardia : Causes and initial workup

Tachycardia is a condition characterized by an abnormally high heart rate, typically defined as exceeding 100 beats per minute (bpm) in adults. It can arise from various physiological and pathological conditions and is classified based on the underlying cause and the presentation on an electrocardiogram (ECG).

Tachycardias are broadly divided into two main categories based on the QRS complex duration on the ECG:

Narrow Complex Tachycardia: This type is identified by a QRS duration of less than 120 milliseconds. It typically originates from the atria or the atrioventricular (AV) node.
Broad Complex Tachycardia: Characterized by a QRS duration of 120 milliseconds or more, this type generally originates from the ventricles or represents a supraventricular rhythm with aberrant conduction.

Causes and Mechanisms of Tachycardia

Category	Specific Causes	Likely Mechanism
Sinus Tachycardia	Physiological	Increased sympathetic activity (e.g., exercise, stress)
	Pathological	Fever, pain, hypovolemia, anemia, hyperthyroidism, heart failure, pulmonary embolism, sepsis, chronic obstructive pulmonary disease (COPD), acute coronary syndrome, alcohol withdrawal, hypoxia
	Drug-induced	Stimulants (e.g., caffeine, nicotine), medications (e.g., albuterol, epinephrine), illicit drugs (e.g., cocaine, amphetamines)
Narrow Complex Tachycardia	Supraventricular Tachycardia (SVT)	Re-entry circuits in the atria or AV node
	Atrial Fibrillation	Disorganized atrial electrical activity, often with rapid ventricular response...

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