What are the causes of tachycardia?

Causes of Tachycardia

Tachycardia results from either physiological responses to appropriate stimuli or pathological conditions, and identifying the underlying cause is essential for proper management and prevention of serious complications. 1, 2

Physiological Causes

Physiological sinus tachycardia occurs when the heart rate exceeds 100 bpm in response to appropriate autonomic influences and resolves with correction of the underlying trigger 1:

Metabolic and Systemic Conditions

• Fever and infection - common triggers that increase metabolic demand 1, 2
• Dehydration - reduces circulating volume and triggers compensatory tachycardia 1, 2
• Anemia - decreases oxygen-carrying capacity, requiring increased cardiac output 1, 2
• Hyperthyroidism - increases metabolic rate and sympathetic tone 1, 2
• Pain - activates sympathetic nervous system 1, 2
• Acid-base disturbances - alter cardiac electrophysiology 2

Cardiovascular Conditions

• Heart failure - compensatory mechanism for reduced cardiac output 1, 2
• Hypovolemia - triggers reflex tachycardia 1

Physiological States

• Physical activity or exercise - normal response to increased oxygen demand 2
• Emotional stress or anxiety - appropriate autonomic response 2, 3

Exogenous Substances and Medications

Multiple substances can trigger tachycardia through sympathetic stimulation or direct cardiac effects 2:

Common Substances

• Caffeine - stimulant effect 1, 2
• Alcohol - can trigger arrhythmias 2
• Nicotine - sympathetic stimulation 2

Medications

• Beta-agonist drugs (albuterol, salmeterol) - direct sympathetic effect 1, 2
• Aminophylline - methylxanthine with cardiac stimulant properties 2
• Atropine - anticholinergic effect 2
• Catecholamines - direct sympathetic stimulation 2
• Anthracycline chemotherapy - cardiotoxic effects 2

Illicit Drugs

• Amphetamines - potent sympathetic stimulation 1, 2
• Cocaine - blocks catecholamine reuptake 1, 2
• Cannabis - can trigger tachycardia 2

Pathological Cardiac Causes

Primary Arrhythmias

Supraventricular tachycardias represent intrinsic cardiac rhythm disturbances 2, 4:

• Atrioventricular nodal re-entrant tachycardia (AVNRT) - most common SVT 2, 4
• Atrioventricular re-entrant tachycardia (AVRT) - involves accessory pathways 2, 4
• Atrial tachycardia - ectopic atrial focus 2
• Atrial flutter - macro-reentrant circuit 2
• Sinus node reentry tachycardia - reentry within sinus node region 2

Inappropriate Sinus Tachycardia (IST)

IST is a diagnosis of exclusion characterized by unexplained sinus tachycardia with resting heart rates >100 bpm and 24-hour average rates >90 bpm 1, 2. The mechanisms include:

• Dysautonomia - autonomic nervous system dysfunction 1, 2
• Neurohormonal dysregulation - abnormal hormonal control 1, 2
• Intrinsic sinus node hyperactivity - primary sinus node abnormality 1, 2

Structural Heart Disease

• Cardiomyopathies - can precipitate tachyarrhythmias 2

Neurological and Autonomic Causes

Autonomic dysfunction can manifest as tachycardia 2:

• Anxiety disorders - can trigger physiological sinus tachycardia or coexist with IST 1, 3
• Postural orthostatic tachycardia syndrome (POTS) - excessive heart rate increase (>30 bpm or >120 bpm) within 10 minutes of standing, predominantly affecting females aged 15-50 years 1, 5
• Autonomic dysfunction - generalized dysautonomia 2

Critical Diagnostic Distinctions

When evaluating tachycardia, systematically assess the following 2:

Essential Evaluation Steps

• Distinguish supraventricular from ventricular origins - determines treatment approach 2
• Identify regular versus irregular rhythm - narrows differential diagnosis 2
• Determine QRS width (narrow vs. wide complex) - indicates origin above or below AV node 2
• Evaluate for structural heart disease - affects prognosis and treatment options 2
• Rule out secondary causes including hyperthyroidism, anemia, dehydration, pain, and exogenous substances 1, 2

Important Clinical Pitfall

Anxiety-triggered physiological sinus tachycardia must be distinguished from IST - treating physiological tachycardia as IST leads to overtreatment with medications that may be ineffective or poorly tolerated 3. IST is diagnosed only after excluding all physiological and pathological causes 1.

POTS Distinction

POTS must be differentiated from IST - patients with POTS have predominant postural symptoms, and treatment to suppress sinus rate may cause severe orthostatic hypotension 1. Overlap between conditions can occur within individual patients 1.