What are the causes of tachycardia?

Causes of Tachycardia

Primary Physiological Causes

Tachycardia results from multiple physiological and pathological factors, with the most common being infection with fever, dehydration, anemia, heart failure, hyperthyroidism, and exogenous substances including caffeine, beta-agonist drugs, and illicit stimulants. 1

Normal Physiological Responses

• Physical activity or exercise represents the most common cause of physiological sinus tachycardia, reflecting appropriate autonomic responses 1, 2
• Emotional stress and anxiety trigger normal catecholamine-driven increases in heart rate 1, 2
• Pain induces appropriate sympathetic activation leading to tachycardia 1, 2

Pathological Medical Conditions

Metabolic and Endocrine Disorders

• Hyperthyroidism is a critical reversible cause that must be excluded in all cases of persistent tachycardia 1, 2
• Fever and infection/sepsis commonly precipitate tachycardia and require immediate assessment 1, 2
• Acid-base disturbances can trigger tachyarrhythmias 1

Cardiovascular Causes

• Heart failure produces compensatory tachycardia 1, 2
• Cardiomyopathies can directly cause tachycardia 1
• Myocardial ischemia precipitates tachyarrhythmias in critically ill patients 3

Hematologic and Volume Status

• Anemia reduces oxygen-carrying capacity, triggering compensatory tachycardia 1, 2
• Dehydration and hypovolemia/shock are common reversible causes requiring immediate correction 1, 2
• Hypoxemia represents one of the most common reversible causes of sinus tachycardia 2

Life-Threatening Causes

• Pulmonary embolism must be considered as a potentially fatal cause of tachycardia 2

Exogenous Substances and Medications

Stimulants and Recreational Substances

• Caffeine, alcohol, and nicotine commonly trigger tachycardia 1
• Illicit stimulant drugs including amphetamines and cocaine cause tachycardia 1, 2
• Cannabis can precipitate tachyarrhythmias 1

Therapeutic Medications

• Beta-agonist medications (e.g., albuterol) increase heart rate through sympathetic stimulation 1, 2
• Aminophylline, atropine, and catecholamines directly increase heart rate 1, 2
• Anthracycline anticancer compounds can cause tachycardia 1
• Antiarrhythmic drugs paradoxically can induce ventricular tachycardia through proarrhythmic effects, particularly class IA, IC agents, sotalol, and bepridil 4
• Digitalis toxicity causes ventricular tachycardia 4
• Psychotropic agents including phenothiazines and imipramine can induce tachycardia 4

Electrolyte Abnormalities

• Hypokalemia and hypomagnesemia frequently precipitate both supraventricular and ventricular tachycardias in critically ill patients 3
• Hyperkalemia can cause bradycardia but also complex arrhythmias 3

Primary Cardiac Arrhythmias

Supraventricular Tachycardias

• Atrioventricular nodal reentrant tachycardia (AVNRT) is a common reentry mechanism producing accelerated heart rates 5, 1, 6
• Atrioventricular reentrant tachycardia (AVRT) involves accessory pathways 5, 1
• Atrial tachycardia (focal and multifocal) arises from localized atrial sites 5, 1
• Atrial flutter represents macroreentrant atrial tachycardia 5, 1
• Sinus node reentry tachycardia causes abrupt onset and termination 5, 1

Inappropriate Sinus Tachycardia

• Inappropriate sinus tachycardia (IST) is defined as sinus tachycardia unexplained by physiological demands, with resting heart rate >100 bpm and average 24-hour rate >90 bpm 1, 2
• Possible mechanisms include dysautonomia, neurohormonal dysregulation, and intrinsic sinus node hyperactivity 1
• IST is a diagnosis of exclusion requiring elimination of all secondary causes 2

Ventricular Arrhythmias

• Ventricular couplets, triplets, and non-sustained ventricular tachycardia always require investigation as markers for underlying cardiac pathology 5
• Premature ventricular contractions (PVCs) are present in <1% of athletes but may indicate underlying heart disease, particularly when ≥2 PVCs appear on ECG 5
• Among athletes with ≥2,000 PVCs per 24 hours, up to 30% have underlying structural heart disease 5

Neurological and Autonomic Factors

• Anxiety disorders can precipitate tachyarrhythmias, though this diagnosis should not be made prematurely as it often leads to delayed recognition of true cardiac arrhythmias 1, 6
• Autonomic dysfunction contributes to inappropriate tachycardia 1
• Postural orthostatic tachycardia syndrome (POTS) must be excluded before diagnosing IST 1, 2

Age-Specific Considerations

• In athletes ≥30 years of age, coronary artery disease (CAD) becomes the most common cause of sudden cardiac death and should be considered when evaluating tachycardia 5

Critical Pitfalls to Avoid

• Do not diagnose anxiety or panic disorder without first excluding cardiac causes, as this commonly delays appropriate diagnosis 6
• Do not assume tachycardia is "inappropriate" without systematically excluding all physiological and secondary causes 2
• Always assess for hemodynamic instability including altered mental status, ischemic chest discomfort, acute heart failure, hypotension, or shock before pursuing diagnostic workup 2
• Resting sinus tachycardia >120 bpm warrants repeat ECG after rest, as recent exercise or anxiety may be responsible 5