Narrow complex tachycardia is a fast heart rhythm, over 100 beats per minute, where the electrical signal travels through the heart’s normal conduction system. On an ECG, this produces a QRS complex (the spike representing each heartbeat) that lasts less than 120 milliseconds. Because the signal uses the heart’s built-in wiring rather than taking an abnormal path through the muscle, the QRS stays “narrow,” and the rhythm almost always originates above the ventricles. That’s why these rhythms are also called supraventricular tachycardias.
Understanding what type of narrow complex tachycardia you have matters because the causes, risks, and treatments differ significantly depending on whether the rhythm is regular or irregular, and which specific circuit is driving it.
Regular vs. Irregular Rhythms
The first thing a doctor looks for on an ECG is whether the fast rhythm is regular (evenly spaced beats) or irregular (chaotic spacing). This single observation narrows the possibilities dramatically.
Regular narrow complex tachycardias include three main types: AV nodal reentrant tachycardia (AVNRT), AV reentrant tachycardia (AVRT), and atrial tachycardia. AVNRT is the most common. These rhythms often hit suddenly, with your heart jumping from a normal rate to 150 or 200 beats per minute in seconds, then stopping just as abruptly.
Irregular narrow complex tachycardias have a different set of causes. Atrial fibrillation is by far the most common, affecting roughly 33 million people worldwide. Atrial flutter with variable conduction and multifocal atrial tachycardia round out the list. These tend to feel different from the regular types. Rather than a sudden onset of steady pounding, you may notice a fluttering, skipping, or chaotic sensation in your chest.
How Each Type Works
AVNRT
In AVNRT, two pathways exist within or near the AV node (the electrical relay station between the upper and lower chambers). One pathway conducts slowly, the other quickly. Under the right conditions, an electrical impulse loops between these two pathways in a continuous circle, creating a self-sustaining fast rhythm. This “reentry circuit” keeps firing until something breaks the loop. AVNRT is the single most common cause of regular narrow complex tachycardia and frequently affects otherwise healthy young adults, particularly women.
AVRT
AVRT involves an extra electrical connection between the atria and ventricles, called an accessory pathway. The impulse travels down through the AV node and back up through this extra pathway (or vice versa), creating a larger reentry loop that includes both the upper and lower chambers. Some people with this condition have a pattern on their resting ECG called Wolff-Parkinson-White, but others have a “concealed” pathway that only shows up during the tachycardia itself.
Atrial Fibrillation
In atrial fibrillation, the upper chambers fire chaotically at 400 to 600 times per minute. The AV node filters most of those signals, so the ventricles beat at a fast but lower rate. On an ECG, the telltale sign is an irregularly irregular rhythm with no consistent spacing between beats. Risk increases with age, high blood pressure, heart valve disease, obesity, and obstructive sleep apnea. Acute triggers include alcohol intoxication, an overactive thyroid, infection, and dehydration.
Multifocal Atrial Tachycardia
This rhythm occurs when at least three different spots in the atria fire electrical signals on their own, producing three or more distinctly shaped P waves on the same ECG lead. The heart rate exceeds 100 beats per minute, and the spacing between beats is irregular. It most often shows up in people with severe lung disease or critical illness.
What It Feels Like
The most common symptom is palpitations, a sudden awareness that your heart is beating fast, hard, or irregularly. Many people describe it as a pounding or fluttering in the chest or throat. When the heart rate climbs high enough, the heart doesn’t fill efficiently between beats, which can cause lightheadedness, shortness of breath, chest pressure, or a sense of anxiety.
In more serious cases, the fast rate drops blood pressure low enough to cause near-fainting or actual fainting. Signs that the rhythm is significantly affecting circulation include a systolic blood pressure below 90, confusion, pale or clammy skin, and worsening chest pain. These warrant emergency evaluation.
How Doctors Tell the Types Apart
A 12-lead ECG is the primary tool. Beyond checking whether the rhythm is regular or irregular, doctors look closely at tiny details in the waveform. In typical AVNRT, for example, the electrical signal reaches the atria and ventricles almost simultaneously, so the small P wave (representing the atria) gets buried inside or just at the edge of the QRS complex. This can appear as a subtle notch at the end of the QRS in certain leads. In AVRT, the P wave usually appears after the QRS but with slightly more separation, because the signal takes a longer path back up to the atria.
For irregular rhythms, atrial fibrillation shows chaotic, low-amplitude “fibrillatory” waves with no recognizable P waves and constantly varying intervals between beats. Multifocal atrial tachycardia looks superficially similar but has distinct, identifiable P waves, at least three different shapes, with varying intervals between them. In many cases, the final distinction between regular rhythm types requires an electrophysiology study, where thin catheters are threaded into the heart to map the electrical circuits directly.
Stopping an Episode
For regular narrow complex tachycardias like AVNRT and AVRT, the first step is often a vagal maneuver, a physical technique that stimulates the vagus nerve and briefly slows conduction through the AV node, potentially breaking the reentry loop. The most effective version is the modified Valsalva maneuver: you blow hard against resistance (like straining) for about 15 seconds while semi-reclined, then immediately lie flat with your legs raised. In a study comparing techniques, the modified approach restored normal rhythm in about 48% of patients on the first attempt, compared to only 15% with the standard technique. With repeated attempts, success reached 62%.
If vagal maneuvers don’t work, the next step in a medical setting is adenosine, a medication given as a rapid injection through an IV. It works within seconds by temporarily blocking electrical conduction through the AV node. The effect is brief, lasting only a few seconds, but that’s usually enough to interrupt the circuit. Even when adenosine doesn’t permanently stop the rhythm, the brief pause it creates can reveal the underlying pattern on the ECG, helping doctors identify which type of tachycardia they’re dealing with.
For patients who are hemodynamically unstable, meaning the fast rhythm is causing dangerously low blood pressure, confusion, or signs of organ distress, the treatment is synchronized cardioversion. This is a controlled electrical shock delivered in sync with the heart’s rhythm, typically starting at 50 joules and increasing if needed up to 200 joules.
Long-Term Management
How narrow complex tachycardia is managed over time depends entirely on the type. For AVNRT and AVRT, catheter ablation is highly effective. During this procedure, a catheter is guided to the heart and used to destroy the tiny area of tissue responsible for the extra pathway or the slow pathway in the reentry circuit. Cure rates are high, and most people go home the same day or the next morning.
Atrial fibrillation has a broader management strategy that includes rate control (slowing the heart rate during episodes), rhythm control (attempting to maintain normal rhythm), and blood thinners to reduce stroke risk. The approach depends on how often episodes occur, how symptomatic they are, and your individual stroke risk factors.
For people with infrequent, well-tolerated episodes of AVNRT or AVRT who prefer not to have ablation, a “pill-in-the-pocket” strategy is sometimes used, where you take a medication only when an episode starts. Others learn to reliably terminate their episodes with vagal maneuvers alone and carry on without any regular treatment.