What are the possible causes of tachycardia?

Causes of Tachycardia

Physiological Causes

Tachycardia results from physiological stressors including physical exertion, emotional stress, fever, dehydration, anemia, pain, and hyperthyroidism—all of which appropriately activate autonomic responses. 1

• Physical activity or exercise triggers normal sinus tachycardia through increased metabolic demands 1
• Emotional responses and anxiety disorders are extremely common non-cardiac causes, often misdiagnosed and leading to unnecessary cardiac testing 1
• Fever and infection elevate heart rate proportionally to temperature elevation 1
• Dehydration reduces preload and triggers compensatory tachycardia 1
• Anemia decreases oxygen-carrying capacity, requiring increased cardiac output 1
• Pain activates sympathetic nervous system responses 1

Exogenous Substances and Medications

Stimulant substances and specific medications directly trigger tachycardia through sympathetic activation or direct cardiac effects. 1

• Caffeine, alcohol, and nicotine are common dietary triggers 1
• Beta-agonist medications (albuterol, terbutaline) and aminophylline cause direct sympathetic stimulation 1
• Atropine and catecholamines increase heart rate through anticholinergic and sympathomimetic mechanisms 1
• Illicit stimulant drugs (cocaine, methamphetamine) and cannabis trigger tachycardia 1
• Anthracycline chemotherapy compounds can cause cardiotoxicity manifesting as tachycardia 1

Metabolic and Endocrine Disturbances

Electrolyte abnormalities and hormonal imbalances are reversible causes that must be identified early. 1, 2

• Hyperthyroidism increases metabolic rate and cardiac contractility 1
• Hypokalemia and hypomagnesemia precipitate both supraventricular and ventricular tachycardias in critically ill patients 2
• Acid-base disturbances alter cardiac electrophysiology 1
• Hyperkalemia more commonly causes bradycardia but can precipitate arrhythmias 2

Cardiac Pathological Causes

Primary Arrhythmias

After excluding reversible triggers, primary supraventricular and ventricular arrhythmias become the leading diagnostic considerations. 1

Supraventricular tachycardias include:

• Atrioventricular nodal reentrant tachycardia (AVNRT) is the most common reentry mechanism 1
• Atrioventricular reentrant tachycardia (AVRT) involves accessory pathways 1
• Atrial tachycardia (focal and multifocal) arises from localized atrial sites 1
• Atrial flutter represents macroreentrant atrial tachycardia 1
• Sinus node reentry tachycardia causes abrupt onset and termination 1

Ventricular arrhythmias include:

• Premature ventricular contractions (PVCs) occur in over two-thirds of the population; ≥2 PVCs on ECG warrant investigation for structural heart disease 1, 3
• Ventricular couplets, triplets, and non-sustained ventricular tachycardia always require investigation as markers for underlying cardiac pathology 1
• Among patients with ≥2,000 PVCs per 24 hours, up to 30% have underlying structural heart disease 1

Inappropriate Sinus Tachycardia

This diagnosis requires resting heart rates >100 bpm and average rates >90 bpm over 24 hours, unexplained by physiological demands. 1

• Mechanisms include dysautonomia, neurohormonal dysregulation, and intrinsic sinus node hyperactivity 1

Structural Heart Disease

Underlying cardiac pathology must be excluded through echocardiography in unexplained tachycardia. 1

• Heart failure causes compensatory tachycardia from reduced cardiac output 1
• Cardiomyopathies (dilated, hypertrophic, restrictive) alter cardiac electrophysiology 1
• Valvular disease creates hemodynamic stress 1
• Myocardial ischemia precipitates tachyarrhythmias in critically ill patients 2
• In patients ≥30 years, coronary artery disease becomes the most common cause of sudden cardiac death and must be considered 1

Autonomic and Neurological Causes

Autonomic dysfunction represents a distinct category requiring specific diagnostic evaluation. 1, 4

• Postural orthostatic tachycardia syndrome (POTS) is defined by heart rate increment ≥30 bpm within 10 minutes of standing without orthostatic hypotension; standing heart rate often ≥120 bpm 4, 5
• POTS pathophysiology includes impaired sympathetically mediated vasoconstriction, excessive sympathetic drive, volume dysregulation, and deconditioning 4
• Anxiety disorders with somatic hypervigilance contribute to symptom chronicity 1, 4
• Autonomic dysfunction from various causes precipitates tachyarrhythmias 1

Critical Pitfalls to Avoid

• Resting sinus tachycardia >120 bpm warrants repeat ECG after rest, as recent exercise or anxiety may be responsible 1
• Do not repeatedly order cardiac testing in patients with multiple negative evaluations; instead, refer for cognitive-behavioral therapy 1
• Never initiate class I or III antiarrhythmic drugs without documented arrhythmia due to proarrhythmic risk 1
• Tachycardia during anesthesia is frequently associated with simultaneous changes in blood pressure, requiring assessment of hemodynamic status to guide management 6
• Frequent PACs, previously considered benign, are now recognized as associated with developing atrial fibrillation 3

Diagnostic Approach

Obtain a 12-lead ECG during tachycardia to distinguish supraventricular from ventricular origins and assess QRS width. 1

Essential diagnostic steps include:

• Distinguish between supraventricular and ventricular origins 1
• Identify if the tachycardia is regular or irregular 1
• Determine if the QRS complex is narrow or wide 1
• Evaluate for underlying structural heart disease with echocardiography 1
• Rule out secondary causes: hyperthyroidism, anemia, dehydration, electrolyte abnormalities 1, 3
• In unexplained syncope or presyncope where non-invasive investigations are nondiagnostic, invasive electrophysiology study may identify occult arrhythmic substrates 1