What causes tachycardia?

Causes of Tachycardia

Tachycardia (heart rate >100 bpm) is primarily caused by physiological stress, pathological conditions, pharmacologic agents, or arrhythmogenic mechanisms, with the most common pathological causes including fever, hypovolemia, and anemia. 1

Physiological Causes

• Physical exertion/exercise
• Emotional stress and anxiety
• Pain
• Pregnancy

Pathological Causes

Systemic Conditions

• Fever/infection - a common cause of sinus tachycardia 1
• Hypovolemia - due to bleeding, dehydration, or excessive fluid losses 1
• Anemia - reduced oxygen-carrying capacity triggers compensatory increase in heart rate 1
• Hypoxia - inadequate tissue oxygenation 1
• Acidosis - metabolic or respiratory 1
• Thyroid disorders - particularly hyperthyroidism

Cardiac Conditions

• Heart failure - tachycardia can be both a cause and effect of heart failure 2, 3
• Myocardial ischemia/infarction
• Structural heart abnormalities
• Arrhythmogenic mechanisms:
  • Re-entry circuits (most common mechanism in SVT) 4
  • Abnormal automaticity
  • Triggered activity from altered calcium handling 3

Pharmacologic/Toxicologic Causes

• Stimulants:
  • Caffeine 1
  • Alcohol 1
  • Nicotine 1
• Prescribed medications:
  • Salbutamol and other beta-agonists 1
  • Aminophylline 1
  • Atropine 1
  • Catecholamines 1
• Recreational/illicit drugs:
  • Amphetamines 1
  • Cocaine 1
  • Ecstasy 1
  • Cannabis 1
• Anticancer treatments:
  • Anthracyclines (doxorubicin, daunorubicin) 1
• Nerve agent exposure - can cause initial tachycardia followed by bradycardia 1

Types of Tachycardia

Sinus Tachycardia

• Normal sinus node response to physiological or pathological stress 1
• Regular rhythm with normal P wave morphology 1
• Most common tachycardia in critically ill patients 5

Supraventricular Tachycardias

• Atrial fibrillation - irregular rhythm with absence of P waves 6
• Atrial flutter - regular atrial activity with characteristic sawtooth pattern 6
• Atrioventricular nodal re-entrant tachycardia (AVNRT) - most common paroxysmal SVT 6
• Atrioventricular re-entrant tachycardia (AVRT) - including Wolff-Parkinson-White syndrome 6
• Atrial tachycardia - focal or multifocal 6

Ventricular Tachycardias

• Monomorphic VT - regular wide complex tachycardia 7
• Polymorphic VT - irregular wide complex tachycardia 7
• Torsades de pointes - specific form of polymorphic VT associated with QT prolongation 5

Clinical Pearls and Pitfalls

• Diagnostic pitfall: Tachycardia is often misdiagnosed as anxiety or panic disorder, delaying appropriate treatment 4
• Hemodynamic assessment: Tachycardia may be a compensatory mechanism for hypotension or decreased cardiac output; treating the tachycardia without addressing the underlying cause can worsen the clinical situation 1
• Tachycardia-induced cardiomyopathy: Persistent tachycardia can lead to ventricular dilation and systolic dysfunction, which is often reversible when the tachycardia is controlled 2
• Wide complex tachycardia: Always assume ventricular tachycardia until proven otherwise, especially in patients with structural heart disease 7
• Medication interactions: Be cautious with calcium channel blockers in patients with suspected Wolff-Parkinson-White syndrome and atrial fibrillation, as they can accelerate conduction through the accessory pathway 7

Understanding the specific cause of tachycardia is essential for appropriate management and preventing complications such as tachycardia-induced cardiomyopathy or hemodynamic compromise.