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Narrow Complex Tachycardia

Updated on March 24, 2014

The occurrence of a heart rate that is more than 100 beats per minute is referred to as tachycardia. In narrow complex tachycardia, an ECG QRS complex will be shorter than 120 ms. Narrow complex tachycardia is a common condition.

The electrical signal has to travel forward via the AV node to detect narrow complex tachycardia. It indicates a contract with a broad QRS complex meaning that either the electrical circuit is not correctly including the AV node, or the conducting system is faulty.

Differential diagnosis of narrow complex tachycardia

  • Sinus tachycardia refers to a rapid sinus rate caused as a physiological response to anxiety, exercise, fever, pain, or hyperthyroidism. The P waves are the same as sinus rhythm. Heart rhythm is regular but cardiac rate is more than 100 bpm.
  • Sinus nodal re-entrant tachycardia arises because of a reentry circuit near or within the sinus node. P waves are normal, while heart rate is 100 to 150 bpm.
  • Inappropriate sinus tachycardiarefers to rapid rate of baseline sinus despite no physiological stress. It can arise due to sinus node anomaly or its autonomic response, or elevated sensitivity of the sinus node to the autonomic response. P waves are same as sinus rhythm. The condition is usually observed in young women without any structural cardiac disease.
  • Atrial tachycardiarefers to a type of narrow complex tachycardia that accounts for 10 percent of SVTs. It affects people of all ages, but is more common in individuals with atrial defects or abnormalities.The condition can be caused due to ischaemic heart disease, digoxin toxicity, rheumatic heart disease, cardiomyopathy, and sick sinus syndrome. It is identified by reentrant activities or focal automatic activities.
    • Multifocal atrial tachycardiais rare condition often noticed in older adults with pulmonary disorders. It consists of three or more p-wave forms. The ECG reports generally show irregular rhythm comparable to atrial fibrillation, with heart rate readings that are higher than 100 bpm. Treatment includes correction of the underlying condition. Doctors may prescribe beta blockers, magnesium, diltiazem, verapamil, amiodarone, or type 1c agents like flecainide.
    • Atrial flutter
    • Atrial fibrillation
    • AV nodal re-entrant tachycardia: This type of narrow complex tachycardia arises due to the occurrence of two pathways which allow the setting up of a circuit within the AV node, thereby causing arrhythmia. It is the most common kind of narrow complex tachycardia or narrow QRS and usually begins in late teens and the twenties.Heart rate is around 180 bpm. Simultaneous depolarization of the ventricles and atria cause P waves to hide in the QRS.Beta blockers, AV node altering drugs, type 1c agents, and adenosine are used for treatment.
    • AV re-entrant tachycardia is linked to congenital cardiac defects and can occur from infancy.The reentry is caused due to an extra atrial tissue piece that crosses the fibrous ring which separates the upper and lower cardiac chambers. This results in development of a big circuit, wherein the heartbeat travels down the AV node, across the ventricle, returning via the pathway, around the atria and back to the AV node. QRS is narrow with a slurred start. The PR interval is shortened.Beta blockers, vagal manoeuvres, type 1a agents, AV node affecting drugs, and type 1c agents are used for treatment.
    • AF with accessory pathwaysis characterized by an atrial rate of about 300 to 600 bpm. The ventricle is guarded by the AV node from experiencing such abnormal heart rates.

Symptoms accompanying narrow complex tachycardia

Some of the signs and symptoms that may accompany narrow complex tachycardia are listed below:

  • Fatigue
  • Palpitations
  • Dyspnoea
  • Dizziness or lightheadedness
  • Angina
  • Discomfort in the chest
  • Loss of consciousness or syncope

Treatment and management of narrow complex tachycardia

Several kinds of narrow complex tachycardia or arrhythmias do not require any treatment. Treatment is aimed at alleviating the symptoms and preventing the onset of complications. Doctors will also correct the aggravating factors such as infection, drug toxicity, etc. Direct current cardioversion is given for narrow complex tachycardia that cause cardiac failure or hypotension.

Initial management of narrow complex tachycardia involves the following:

  • Give IV and oxygen. Follow advanced life support for adults in absence of pulse.
  • Give synchronized DC shock along with sedation in case heart rate is lower than 250 bpm. Detect and treat AF.
  • Occurrence of abnormal symptoms such as low heart rate or low systolic blood pressure also requires synchronized DC shock under general anesthesia.
  • If required, administer 150 mg IV of amiodarone over ten minutes and later 300 mg over one hour. Repeat DC shock.
  • In case of irregular rhythm use digoxin IV, betablocker IV, or amiodarone to control it.
  • In case of regular rhythm opt for vagal maneuvers and/or adenosine injections. The ECG has to be continuously monitored. Seek expert assistance if normal sinus rhythm does not get restored.
  • Check and prevent the development of any complications.


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      Dr Pran Rangan 3 years ago

      Really good write-up.