Definition of Tachycardia
Tachycardia is defined as an arrhythmia with a heart rate greater than 100 beats per minute. 1, 2
Core Definition
The American Heart Association establishes this threshold of >100 bpm as the universal cutoff for defining tachycardia, regardless of the underlying mechanism 1, 2. This definition applies to both:
- Sinus tachycardia: Heart rate >100 bpm originating from the sinus node 1, 2
- Tachyarrhythmias: Pathologic rhythms exceeding 100 bpm involving tissue from the His bundle or above 1
Clinical Context and Significance
The rate threshold alone does not determine clinical significance or need for treatment. 1, 2 Several important clinical considerations modify how you should interpret tachycardia:
Age-Related Upper Limits
- The upper limit of physiologic sinus tachycardia is approximately 220 bpm minus the patient's age in years 1, 2
- This calculation helps distinguish appropriate physiologic responses from pathologic arrhythmias 1
Hemodynamic Significance Thresholds
- Heart rates <150 bpm rarely cause hemodynamic instability unless ventricular function is impaired 1, 2
- Rates ≥150 bpm are more likely to represent primary tachyarrhythmias requiring specific treatment 1
- When cardiac function is poor, rapid heart rate may be compensatory—normalizing the rate can paradoxically worsen cardiac output 1, 2
Critical Distinction: Primary vs. Secondary Tachycardia
You must determine whether tachycardia is the primary problem or a physiologic response to an underlying condition. 1, 3, 2 This distinction fundamentally changes management:
- Physiologic sinus tachycardia results from appropriate responses to fever, dehydration, anemia, pain, hypotension, or hypoxemia—treat the underlying cause, not the heart rate 1, 3, 2
- Primary tachyarrhythmias (SVT, atrial fibrillation, ventricular tachycardia) require rhythm-specific interventions 1
Common Pitfall
Sinus tachycardia is the most common tachycardia in critically ill patients, and inappropriately treating the rate rather than the underlying cause can be harmful 1, 2, 4. Always identify and correct precipitating factors (hypoxemia, hypovolemia, pain, fever, thyrotoxicosis) before considering rate-control interventions 3, 2.