Adenosine is the first-line medication for supraventricular tachycardia (SVT). The standard initial dose is 6 mg given as a rapid IV push, followed by a 12 mg dose if the first attempt doesn’t work. Before any medication, though, physical techniques called vagal maneuvers are typically tried first.
Vagal Maneuvers Come Before Medication
The first thing attempted for a stable SVT episode isn’t a drug at all. Vagal maneuvers, particularly the Valsalva maneuver (bearing down as if straining), stimulate the vagus nerve and can slow the heart enough to break the abnormal rhythm. The standard version works only about 5 to 20% of the time, but a modified version, where you strain and then immediately lie flat with your legs raised, converts SVT to a normal rhythm in roughly 43% of cases. That’s a meaningful jump from a simple positional change.
When vagal maneuvers fail, adenosine becomes the go-to pharmacological option.
How Adenosine Works
Most SVT episodes involve an electrical signal looping through the AV node, the junction between the upper and lower chambers of the heart. Adenosine temporarily blocks conduction through the AV node, which interrupts that loop and lets the heart reset to its normal rhythm. It also slows the heart’s natural pacemaker cells, giving the entire electrical system a brief pause.
What makes adenosine distinctive is its speed. The drug breaks down in the bloodstream within seconds, which is why it must be pushed rapidly through an IV line followed immediately by a 20 mL saline flush. If the injection is too slow, the drug gets metabolized before it reaches the heart in a high enough concentration to work. That ultrashort half-life is also the reason adenosine’s side effects, while intense, are extremely brief.
What Receiving Adenosine Feels Like
Adenosine is one of those medications that works fast but can feel alarming in the moment. When it hits, many people experience a sudden chest tightness, flushing, lightheadedness, and nausea. Some describe a brief but unsettling sensation of impending doom. A few seconds of pause in the heart’s rhythm is also normal and expected.
These effects are genuinely short-lived, typically lasting under 30 seconds, because the drug clears the body so quickly. Knowing this in advance can make the experience far less frightening. Medical teams routinely warn patients right before the push so they’re prepared for the sensation.
When Adenosine Doesn’t Work
Adenosine can fail for two main reasons. First, its extremely short half-life means it might not reach the heart at a sufficient concentration, especially if the IV site is far from the chest or the flush isn’t fast enough. Second, some types of SVT don’t depend on the AV node at all, so blocking that node won’t interrupt the circuit.
Caffeine and similar compounds (found in coffee, tea, energy drinks, and certain medications) can also blunt adenosine’s effect. They compete for the same receptors in the heart, meaning higher doses may be needed or the drug may not convert the rhythm at all. People with asthma are generally not given adenosine because it can trigger significant airway narrowing.
When adenosine fails, calcium channel blockers are the typical next step. Both verapamil and diltiazem are effective, with conversion rates above 96% in studies. Beta-blockers are another option. These second-line drugs take longer to work and last longer in the body, which means their side effects, particularly drops in blood pressure, stick around longer too.
Dosing for Adults and Children
For adults, the American Heart Association protocol is straightforward: 6 mg IV push followed by a rapid saline flush. If the rhythm doesn’t convert within one to two minutes, a second dose of 12 mg is given the same way.
Children receive weight-based dosing, starting at 0.1 mg per kilogram of body weight. Research shows this initial dose converts SVT in fewer than half of pediatric cases, so repeat doses at 0.2 and 0.3 mg/kg are common. For infants under one year, the starting dose is often bumped to 0.15 mg/kg because the lower dose was effective in only about 35% of cases in one UK study.
Long-Term Management After an SVT Episode
Adenosine is a rescue medication. It stops an acute episode, but it doesn’t prevent future ones. For people who experience recurring SVT, two main paths exist for long-term management: daily medication or catheter ablation.
Daily drugs, typically beta-blockers or calcium channel blockers, reduce the frequency of episodes but have a recurrence rate of about 20% for the most common SVT types (AVNRT and AVRT). That means roughly one in five people on medication will still have breakthrough episodes.
Catheter ablation is a procedure where a specialist threads a thin wire into the heart and destroys the small area of tissue responsible for the abnormal circuit. Success rates are striking: 98% for AVNRT and 99% for AVRT. Because of this gap, ablation is increasingly recommended for people with frequent or bothersome SVT rather than committing to lifelong medication. The procedure carries a small risk of complications, but for most patients it offers a permanent fix.