What causes tachycardia (increased heart rate)?

Causes of Increased Heart Rate (Tachycardia)

Tachycardia results from physiological responses to metabolic demands, pathological cardiac and systemic conditions, exogenous substances, and autonomic nervous system dysfunction. 1

Physiological Causes

Normal sinus tachycardia (heart rate >100 bpm) occurs as an appropriate response to increased metabolic demands and resolves when the underlying trigger is addressed. 1

Common physiological triggers include:

• Physical activity and exercise - the most common cause of transient tachycardia 2
• Emotional stress and anxiety - though anxiety can trigger tachycardia, it does not explain pathological forms like POTS 1, 3
• Fever and infection - increases metabolic rate and sympathetic tone 1, 2
• Pain - stimulates sympathetic nervous system activation 1, 2
• Dehydration - reduces circulating volume, triggering compensatory tachycardia 1, 2

Pathological Medical Conditions

Endocrine Disorders

• Hyperthyroidism - causes persistent tachycardia through direct cardiac effects and catecholamine release; can lead to high-output heart failure if untreated 1
• Pheochromocytoma - excess catecholamine secretion 1

Cardiovascular Conditions

• Heart failure - compensatory mechanism to maintain cardiac output 1, 2
• Anemia - reduced oxygen-carrying capacity triggers increased heart rate 1, 2
• Cardiomyopathies - structural heart disease can precipitate tachyarrhythmias 1, 2

Electrolyte and Metabolic Disturbances

• Acid-base disturbances - metabolic acidosis or alkalosis 2

Exogenous Substances and Medications

Multiple substances directly stimulate cardiac rate through sympathomimetic effects or autonomic modulation. 2

Stimulants

• Caffeine - causes tachycardia, restlessness, and increased cardiovascular stimulation 2, 4
• Nicotine - releases catecholamines from adrenal medulla, causing tachycardia and palpitations 2, 5
• Illicit stimulants - amphetamines and cocaine produce marked tachycardia 1, 2
• Alcohol - can trigger tachyarrhythmias 2
• Cannabis - documented cause of tachycardia 2

Medications

• Beta-agonist drugs (albuterol, salmeterol) - direct sympathetic stimulation 1, 2
• Aminophylline and theophylline - bronchodilators with cardiac stimulant effects 2
• Atropine - anticholinergic effect increases heart rate 2
• Catecholamines - direct adrenergic stimulation 2
• Anthracycline chemotherapy - can cause tachycardia as cardiotoxic effect 2

Primary Cardiac Arrhythmias

Inappropriate Sinus Tachycardia (IST)

IST is defined as persistent sinus tachycardia (resting >100 bpm, 24-hour average >90 bpm) unexplained by physiological demands, accompanied by debilitating symptoms including weakness, fatigue, lightheadedness, and palpitations. 1

• Proposed mechanisms include dysautonomia, neurohormonal dysregulation, and intrinsic sinus node hyperactivity 1, 2
• Predominantly affects young women (90% female), mean age 38 years, with high proportion being healthcare professionals 1
• This is a diagnosis of exclusion - must rule out hyperthyroidism, anemia, dehydration, pain, anxiety disorders, and exogenous substances 1
• Must distinguish from postural orthostatic tachycardia syndrome (POTS), where symptoms relate to postural changes 1

Supraventricular Tachycardias

• Atrioventricular nodal re-entrant tachycardia (AVNRT) 2
• Atrioventricular re-entrant tachycardia (AVRT) - including Wolff-Parkinson-White syndrome 2
• Atrial tachycardia, atrial flutter, and atrial fibrillation 1, 2
• Sinus node reentry tachycardia 1, 2

Autonomic Dysfunction

Elevated heart rate reflects increased sympathetic and decreased parasympathetic tone, which clusters with metabolic abnormalities and increases cardiovascular risk. 6, 7, 8

• Postural orthostatic tachycardia syndrome (POTS) - excessive heart rate increase (>30 bpm) with standing, not caused by anxiety but by physiological response to venous pooling 2, 3
• Dysautonomia - generalized autonomic nervous system dysfunction 1, 2

Clinical Significance and Risk Stratification

Persistent tachycardia is not merely a marker of underlying pathology but independently contributes to cardiovascular damage. 6, 7

• Tachycardia associates with hypertension, insulin resistance, dyslipidemia, and increased hematocrit 7, 8, 9
• Fast heart rate predicts all-cause and cardiovascular mortality (hazard ratios 1.3-2.0 in hypertensive men) 6
• Increases arterial wall stress and promotes atherosclerosis development 6, 7
• May cause tachycardia-induced cardiomyopathy with prolonged rapid rates 1

Diagnostic Approach

When evaluating tachycardia, systematically exclude secondary causes before diagnosing primary arrhythmias. 1, 2

Essential evaluation steps:

• Rule out hyperthyroidism, anemia, dehydration, and medication effects first 1, 2
• Obtain 12-lead ECG to distinguish supraventricular from ventricular origins and assess QRS width 1
• 24-hour Holter monitoring to document heart rate patterns and arrhythmia burden 1
• Echocardiogram to exclude structural heart disease 1
• Exercise stress testing to assess heart rate response and arrhythmia inducibility 1

Common pitfall: Attributing tachycardia solely to anxiety without excluding organic causes, particularly in young women where IST and POTS are frequently misdiagnosed as anxiety disorders. 1, 3