What causes tachycardia?

Causes of Tachycardia

Tachycardia is caused by multiple physiological and pathological factors including infection with fever, dehydration, anemia, heart failure, hyperthyroidism, and exogenous substances such as caffeine, beta-agonist drugs, and illicit stimulants. 1

Physiological Sinus Tachycardia

Physiological sinus tachycardia occurs in response to appropriate autonomic influences and can be caused by:

• Physical activity or exercise 1
• Emotional responses or stress 1
• Fever and infection 1
• Dehydration 1
• Anemia 1
• Heart failure 1
• Hyperthyroidism 1
• Pain 1, 2

Exogenous Substances and Medications

Several substances can trigger tachycardia:

• Caffeine 1
• Alcohol 1
• Nicotine 1
• Beta-agonist medications (e.g., albuterol, salmeterol) 1
• Aminophylline 1
• Atropine 1
• Catecholamines 1
• Illicit stimulant drugs (e.g., amphetamines, cocaine, "ecstasy") 1
• Cannabis 1
• Anticancer treatments, particularly anthracycline compounds (e.g., doxorubicin, daunorubicin) 1

Pathological Causes of Tachycardia

Inappropriate Sinus Tachycardia (IST)

IST is defined as sinus tachycardia unexplained by physiological demands, with:

• Resting heart rates >100 bpm and average rates >90 bpm in a 24-hour period 1
• Possible mechanisms include dysautonomia, neurohormonal dysregulation, and intrinsic sinus node hyperactivity 1

Supraventricular Tachycardias (SVTs)

Common types of SVT include:

• Atrioventricular nodal re-entrant tachycardia (AVNRT) 1, 3
• Atrioventricular re-entrant tachycardia (AVRT) 1, 3
• Atrial tachycardia (focal and multifocal) 1
• Atrial flutter 1, 4
• Sinus node reentry tachycardia 1

Ventricular Tachycardias

• Ventricular tachycardia (VT) 1, 4
• Ventricular fibrillation (VF) 4
• Torsade de pointes 4

Electrolyte and Metabolic Disturbances

• Electrolyte abnormalities (particularly hypokalemia and hypomagnesemia) 2, 4
• Acid-base disturbances 1

Structural Heart Disease

• Cardiomyopathies 1, 4
• Myocardial ischemia 4
• Valvular heart disease 4

Neurological Factors

• Anxiety disorders 1
• Autonomic dysfunction 1, 5
• Postural orthostatic tachycardia syndrome (POTS) 1
• Various neurologic conditions can precipitate tachyarrhythmias 5

Clinical Presentation

Patients with tachycardia may experience:

• Palpitations 1, 6
• Chest pain 6, 3
• Lightheadedness or dizziness 1, 3
• Dyspnea 6, 3
• Weakness and fatigue 1
• Syncope in severe cases 3, 5

Diagnostic Approach

When evaluating tachycardia, it's important to:

• Distinguish between supraventricular and ventricular origins 1, 4
• Identify if the tachycardia is regular or irregular 4, 5
• Determine if the QRS complex is narrow (<120 ms) or wide (≥120 ms) 1, 4
• Evaluate for underlying structural heart disease 1, 2
• Rule out secondary causes such as hyperthyroidism, anemia, and dehydration 1

Common Pitfalls and Caveats

• Misdiagnosis of anxiety or panic disorder when the underlying issue is a tachyarrhythmia 6
• Failure to identify Wolff-Parkinson-White syndrome, which requires expedient referral to a cardiologist 6
• Not recognizing that frequent premature atrial contractions (PACs) are associated with developing atrial fibrillation 2
• Overlooking medication side effects as a cause of tachycardia 1
• Failing to distinguish inappropriate sinus tachycardia from postural orthostatic tachycardia syndrome 1