Causes of Tachycardia
Tachycardia results from physiological responses, pathological conditions, exogenous substances, or primary cardiac arrhythmias—with the most common causes being fever/infection, dehydration, anemia, hyperthyroidism, heart failure, and stimulant use. 1, 2
Physiological Causes
Appropriate sinus tachycardia occurs as a normal autonomic response to specific demands 1, 2:
- Physical activity or exercise triggers increased heart rate through sympathetic activation 2
- Emotional stress or anxiety produces physiological tachycardia 1, 2
- Pain stimulates sympathetic nervous system activation 1, 2
These resolve when the underlying stimulus is removed 1
Pathological Medical Conditions
Systemic Disorders
The following conditions cause secondary tachycardia that resolves with treatment of the underlying disease 1, 2:
- Fever and infection increase metabolic demands 1, 2
- Dehydration reduces intravascular volume 1, 2
- Anemia decreases oxygen-carrying capacity 1, 2
- Hyperthyroidism increases basal metabolic rate 1, 2
- Heart failure activates compensatory mechanisms 1, 2
- Acid-base disturbances alter cardiac automaticity 2
Cardiac Structural Disease
- Cardiomyopathies can both cause and result from persistent tachycardia 1, 2
- Tachycardia-induced cardiomyopathy develops when heart rates exceed 100 bpm chronically, with atrial fibrillation being the most common trigger 1
Exogenous Substances and Medications
Stimulants
Multiple substances directly increase heart rate 2, 3, 4:
- Caffeine causes cardiovascular stimulation including tachycardia 2, 4
- Illicit stimulants (amphetamines, cocaine) produce sympathomimetic effects 1, 2, 3
- Alcohol and nicotine trigger tachycardia 2
- Cannabis can precipitate tachyarrhythmias 2
Medications
- Beta-agonist drugs (albuterol, salmeterol) increase heart rate through beta-receptor stimulation 1, 2
- Aminophylline and atropine have chronotropic effects 2
- Catecholamines directly stimulate cardiac receptors 2
- Anthracycline chemotherapy can cause tachycardia 2
Critical warning: Amphetamines and other CNS stimulants cause modest increases in heart rate (3-6 bpm average) but can precipitate serious cardiovascular events including sudden death, particularly in patients with pre-existing structural cardiac abnormalities 3
Primary Cardiac Arrhythmias
Inappropriate Sinus Tachycardia
IST is defined as unexplained sinus tachycardia with resting heart rates >100 bpm and 24-hour average >90 bpm without physiological cause 1, 2. Proposed mechanisms include 1, 2:
- Dysautonomia
- Neurohormonal dysregulation
- Intrinsic sinus node hyperactivity
Supraventricular Tachycardias
Multiple reentrant mechanisms produce SVT 1, 2:
- Atrioventricular nodal reentrant tachycardia (AVNRT) is the most common paroxysmal SVT 1, 2
- Atrioventricular reentrant tachycardia (AVRT) involves accessory pathways 1, 2
- Atrial tachycardia arises from focal atrial sites 1, 2
- Atrial flutter involves macroreentrant circuits 1, 2
- Sinus node reentry tachycardia produces P-waves identical to sinus rhythm 1, 2
Ventricular Arrhythmias
- Frequent premature ventricular complexes can induce cardiomyopathy when persistent 1
- Ventricular tachycardia occurs in both structural heart disease and idiopathic forms 5
Neurological and Autonomic Factors
- Anxiety disorders commonly trigger or exacerbate tachycardia 1, 2
- Autonomic dysfunction disrupts normal heart rate regulation 2
- Postural orthostatic tachycardia syndrome (POTS) causes excessive heart rate increases with position changes 2
Critical Diagnostic Distinctions
When evaluating tachycardia, you must systematically 2:
- Distinguish supraventricular from ventricular origin using QRS width
- Determine regularity (regular vs. irregular rhythm)
- Evaluate for structural heart disease with echocardiography
- Rule out secondary causes including hyperthyroidism, anemia, dehydration, and substance use
- Assess for electrolyte abnormalities that may precipitate arrhythmias
Common pitfall: Anxiety and panic disorder are frequently misdiagnosed when the actual cause is a primary cardiac arrhythmia—patient history revealing abrupt onset and termination suggests true SVT rather than anxiety 6