Tachycardia (from Greek "tachy" meaning "rapid", and "kardia" meaning "heart", aka tachyarrhythmia) is HR>normal resting rate.

• Dependent on age, including:
  • <3 days, >159bpm
  • <7 days, >166bpm
  • <4 weeks, >182bpm
  • <3 months, >179bpm
  • <6 mo, >186bpm
  • <1yo, >169bpm
  • <3yo, >151bpm
  • <5yo, >137bpm
  • <8yo, >133bpm
  • <12yo, >130bpm
  • <15yo, >119bpm
  • In >15yo (adults), HR>100bpm
• Also depends on the clinical picture, e.g. in sepsis >90bpm is considered tachycardia

Source: RNCeus

• Physiological, with:
  • Exercise
  • Fear
• Electrical problems within the heart
• Anemia
• Atrial fibrillation
• Atrial flutter
• Atrial tachycardia
• AV nodal reentrant tachycardia
• Exercise
• Fever
• Hypoglycemia
• Hypovolemia
• Hyperthyroidism
• Hyperventilation
• Infection
• Junctional tachycardia
• Multifocal atrial tachycardia
• Nicotin
• Pacemaker mediated
• Pain
• Pheochromocytoma
• Sinus tachycardia
• Ventribular fibrillation
• Ventricular flutter
• Wolff-Parkinson-White syndrome
• Drugs, including:
  • Amphetamine
  • Antiarrhythmic agents
  • Caffeine
  • Cocaine

Based upon the width of the QRS complex (ventricular contraction) on an ECG:

• Narrow complex, which tend to originate in the atria:
  • Sinus tachycardia, which originates from the SA node (near base of the SVC). Upper normal rate of sinus tachycardia is (220-age) bpm. It occurs due to:
    • Reflex to decreased BP, blood volume (through dehydration or bleeding), unexpected changes in blood flow (through orthostatic hypotension)
    • Increase in metablic demands, due to fever, hyperventilation, diarrhea, and severe infections
    • Increased sympathetics, both via sympathetic nerve fibers on the heart, and release of adrenaline which has similar effects. This thus includes endocrine disorders (e.g. pheochromocytoma and hyperthyroidism)
  • Supraventricular, which originates from the atria. It includes:
    • Atrial fibrillation, one of the most common arrhythmias. It may be difficult to determine the rhythm's regularity when the rate >150bpm. It can cause heart rates between 50-250bpm, but when new onset tends to be between 100-150bpm
    • Atrial flutter
  • ​AV nodal reentrant tachycardia
  • Accessory pathway mediated tachycardia
  • Atrial tachycardia
  • Multifocal atrial tachycardia
  • Junctional tachycardia
• Wide complex, which tend to originate in the ventricles:
  • Ventricular tachycardia, any tachycardia that originates in the ventricles. It is potentially life threatening. It is a rate between 120-250bpm. It normally lasts only for a few seconds to minutes, but if persistent can lead to ventricular fibrillation
  • Supraventricular tachycardia with aberrancy, which is any narrow complex tachycardia combined with a problem with the conduction system of the heart
  • Supraventricular tachycardia with pre-excitation, which is a narrow complex tachycardia with an accessory conduction pathway, e.g. Wolff-Parkinson-White syndrome
  • Pacemaker-tracked or pacemaker-mediated tachycardia

Tachycardia can be further classified as regular or irregular.

Depends on type (wide complex vs narrow complex), whether the Pt is stable/unstable (i.e. whether other important organ functions are affected, or cardiac arrest is about to occur), whether the instability is due to the tachycardia, but includes:

• Cardioversion
• IV adenosine, in Pt's who are unstable w/ a narrow complex tachycardia

• Ischemia → heart beats excessively/rapidly, heart pumps less efficiently, and provides less blood flow to the rest of the body, including the heart itself. It also leads to increased work and oxygen demand by the heart, which can cause rate-related ischemia

• Bradycardia (antonym)
• Tachypnea (fast breathing)