Tachycardia
| Tachycardia | |
|---|---|
| Specialty | Cardiology  |
Tachycardia comes from the Greek words tachys (rapid or accelerated) and kardia (of the heart). Tachycardia typically refers to a heart rate that exceeds the normal range. A heart rate over 100 beats per minute is generally accepted as tachycardia. A heart rate under 60 beats per minute is generally accepted as bradycardua. [1] Tachycardia can be caused by various factors which often are benign. However, tachycardia can be dangerous depending on the speed and type of rhythm.
Definition
The upper threshold of a normal human heart rate is based upon age. Tachycardia for different age groups is as listed below:[2]
- 1–2 days: >159 beats per minute (bpm)
- 3–6 days: >166 - bpm
- 1–3 weeks: >182 - bpm
- 1–2 months: >179 - bpm
- 3–5 months: >186 - bpm
- 6–11 months: >169 - bpm
- 1–2 years: >151 - bpm
- 3–4 years: >137 - bpm
- 5–7 years: >133 - bpm
- 8–11 years: >130 - bpm
- 12–15 years: >119 - bpm
- >15 years – adult: >100 - bpm
When the heart beats excessively rapidly, the heart pumps less efficiently and provides less blood flow to the rest of the body, including the heart itself. The increased heart rate also leads to increased work and oxygen demand by the heart, which can lead to rate related ischemia.[3]
Differential diagnosis
An electrocardiogram (ECG) is used to classify the type of tachycardia. They may be classified into narrow and wide complex based on the QRS complex.Cite error: A <ref> tag is missing the closing </ref> (see the help page). The upper limit of normal rate for sinus tachycardia is thought to be 220 bpm minus age.
Ventricular
Ventricular tachycardia (VT or V-tach) is a potentially life-threatening cardiac arrhythmia that originates in the ventricles. It is usually a regular, wide complex tachycardia with a rate between 120 and 250 beats per minute. Ventricular tachycardia has the potential of degrading to the more serious ventricular fibrillation. Ventricular tachycardia is a common, and often lethal, complication of a myocardial infarction (heart attack).
Exercise-induced ventricular tachycardia is a phenomenon related to sudden deaths, especially in patients with severe heart disease (ischemia, acquired valvular heart and congenital heart disease) accompanied with left ventricular dysfunction.[4]
Both of these rhythms normally last for only a few seconds to minutes (paroxysmal tachycardia), but if VT persists it is extremely dangerous, often leading to ventricular fibrillation.
Supraventricular
This is a type tachycardia that originates from above the ventricles, such as the atria. It is sometimes known as paroxysmal atrial tachycardia (PAT). Several types of supraventricular tachycardia are known to exist.
Atrial fibrillation
Atrial fibrillation is one of the most common cardiac arrhythmias. It is generally an irregular, narrow complex rhythm. However, it may show wide QRS complexes on the ECG if a bundle branch block is present. At high rates, the QRS complex may also become wide due to the Ashman phenomenon. It may be difficult to determine the rhythm's regularity when the rate exceeds 150 beats per minute. Depending on the patient's health and other variables such as medications taken for rate control, atrial fibrillation may cause heart rates that span from 50 to 250 beats per minute (or even higher if an accessory pathway is present). However, new onset atrial fibrillation tends to present with rates between 100 and 150 beats per minute.
AV nodal reentrant tachycardia
AV nodal reentrant tachycardia (AVNRT) is the most common reentrant tachycardia. It is a regular narrow complex tachycardia that usually responds well to the Valsalva maneuver or the drug adenosine. However, unstable patients sometimes require synchronized cardioversion. Definitive care may include catheter ablation.
AV reentrant tachycardia
AV reentrant tachycardia (AVRT) requires an accessory pathway for its maintenance. AVRT may involve orthodromic conduction (where the impulse travels down the AV node to the ventricles and back up to the atria through the accessory pathway) or antidromic conduction (which the impulse travels down the accessory pathway and back up to the atria through the AV node). Orthodromic conduction usually results in a narrow complex tachycardia, and antidromic conduction usually results in a wide complex tachycardia that often mimics ventricular tachycardia. Most antiarrhythmics are contraindicated in the emergency treatment of AVRT, because they may paradoxically increase conduction across the accessory pathway.
Junctional tachycardia
Junctional tachycardia is an automatic tachycardia originating in the AV junction. It tends to be a regular, narrow complex tachycardia and may be a sign of digitalis toxicity.
Management
The management of tachycardia depends on its type (wide complex versus narrow complex), whether or not the person is stable or unstable, and if the instability is due to the tachycardia.[5] Unstable means that either important organ functions are affected or cardiac arrest is about to occur.Cite error: A <ref> tag is missing the closing </ref> (see the help page). and <reference /> tags
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- ^ Understand Tachycardia
- ^ Custer JW, Rau RE, eds. Johns Hopkins: The Harriet Lane Handbook. 18th ed. Philadelphia, PA: Mosby Elsevier Inc; 2008. Data also available through eMedicine: Pediatrics, Tachycardia.
- ^ Harrison's Principles of Internal Medicine, 17th Edition
- ^ "Ventricular tachycardia and ST segment elevation during Exercise". Archived from the original on 2007-10-14. Retrieved 2007-07-21.
- ^ Neumar RW, Otto CW, Link MS; et al. (2010). "Part 8: adult advanced cardiovascular life support: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care". Circulation. 122 (18 Suppl 3): S729–67. doi:10.1161/CIRCULATIONAHA.110.970988. PMID 20956224.
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