What are the causes of tachycardia?

Causes of Tachycardia

Tachycardia is caused by a wide range of physiological, pathological, and pharmacological factors, with treatment directed at the underlying cause whenever possible. 1

Classification of Tachycardias

Tachycardias can be broadly categorized into:

1. Sinus Tachycardia

• Physiological Sinus Tachycardia: Results from appropriate autonomic influences 1

  • Physical activity/exercise
  • Emotional responses (fear, anxiety, stress)
  • Pathological causes:
    • Infection with fever
    • Dehydration
    • Anemia
    • Heart failure
    • Hyperthyroidism
  • Exogenous substances:
    • Caffeine
    • Beta-agonist medications (albuterol, salmeterol)
    • Illicit stimulant drugs (amphetamines, cocaine)

• Inappropriate Sinus Tachycardia (IST): Unexplained by physiological demands 1, 2

  • Characterized by:
    • Resting heart rates >100 bpm
    • Average rates >90 bpm in a 24-hour period
    • Associated symptoms: weakness, fatigue, lightheadedness, palpitations
  • Proposed mechanisms:
    • Dysautonomia
    • Neurohormonal dysregulation
    • Intrinsic sinus node hyperactivity

2. Supraventricular Tachycardias (SVTs)

SVTs involve tissue from the His bundle or above, with rates exceeding 100 bpm at rest 1:

• Atrioventricular Nodal Reentrant Tachycardia (AVNRT)

  • Most common SVT
  • Characterized by "shirt flapping" or "neck pounding" sensations 1
  • Regular, rapid tachycardia with abrupt onset/termination

• Atrioventricular Reciprocating Tachycardia (AVRT)

  • Involves accessory pathways
  • Includes Wolff-Parkinson-White syndrome

• Atrial Tachycardia (AT)

  • Focal AT: Arises from localized atrial site
  • Sinus node reentry tachycardia: Microreentry from sinus node complex
  • Multifocal atrial tachycardia (MAT): ≥3 distinct P-wave morphologies

• Atrial Flutter

  • Cavotricuspid isthmus-dependent (typical)
  • Non-cavotricuspid isthmus-dependent (atypical)

• Junctional Tachycardia

  • Originates from AV junction

3. Ventricular Tachycardias

• Ventricular Tachycardia (VT)
  • Originates from ventricular tissue
  • Can be identified by specific ECG criteria 1:
    • QRS complex characteristics (R-S interval >100 ms in precordial leads)
    • Initial R or Q wave >40 ms in aVR
    • AV dissociation
    • Concordant QRS complexes in precordial leads

Common Underlying Causes of Tachycardia

Cardiac Causes

• Myocardial ischemia/infarction
• Cardiomyopathies
• Valvular heart disease
• Congenital heart defects
• Post-cardiac surgery

Systemic Causes

• Metabolic/Endocrine:

  • Hyperthyroidism
  • Pheochromocytoma
  • Electrolyte abnormalities (hypokalemia, hypomagnesemia)

• Respiratory:

  • Hypoxemia
  • Pulmonary embolism
  • COPD exacerbation
  • Pneumonia

• Hematologic:

  • Anemia
  • Hypovolemia/hemorrhage

• Infectious:

  • Sepsis
  • Systemic inflammatory response syndrome

Pharmacological/Toxicological

• Sympathomimetics (beta-agonists, decongestants)
• Anticholinergics
• Caffeine
• Alcohol withdrawal
• Illicit drugs (cocaine, amphetamines, MDMA)
• Medication side effects

Neuropsychiatric

• Anxiety disorders
• Pain
• Autonomic dysregulation
• Postural orthostatic tachycardia syndrome (POTS)

Diagnostic Approach

When evaluating tachycardia, assess:

1. QRS duration (<120 ms suggests supraventricular origin)
2. Rhythm regularity
3. P-wave presence and morphology
4. Relationship between P waves and QRS complexes

Management Considerations

Management depends on the specific type of tachycardia and underlying cause:

• Physiological Sinus Tachycardia: Treat the underlying cause 1

• Inappropriate Sinus Tachycardia: 1, 2

  • Beta blockers (e.g., metoprolol 25-50 mg twice daily)
  • Ivabradine (inhibits "If" channel in sinus node)
  • Combination therapy may be considered in resistant cases

• SVT Management: 1, 2

  • Acute: Vagal maneuvers, adenosine, calcium channel blockers, beta blockers
  • Long-term: Catheter ablation (95% success rate), antiarrhythmic medications

• Ventricular Tachycardia: 2

  • Acute: IV amiodarone, procainamide, or sotalol
  • Long-term: ICD placement, antiarrhythmic therapy

Important Caveats

• Always rule out secondary causes of tachycardia before diagnosing IST 1, 2
• Beta blockers like metoprolol can cause depression of myocardial contractility and may precipitate heart failure in susceptible patients 3
• Abrupt discontinuation of beta blockers in patients with coronary artery disease can lead to severe exacerbation of angina, myocardial infarction, and ventricular arrhythmias 3
• In patients with bronchospastic disease, cardioselective beta blockers like metoprolol may be used cautiously at the lowest effective dose 3

By identifying and addressing the underlying cause of tachycardia, clinicians can effectively manage this common clinical presentation and improve patient outcomes.