Clinical Overview

Supraventricular tachycardia (SVT) is a fast heart rhythm whose driving circuit or focus sits above the ventricles — anatomically, any tachydysrhythmia arising from above the level of the bundle of His (Burns and Buttner, LITFL ECG Library, 2024). Because the impulse still reaches the ventricles through the normal His-Purkinje system, it usually shows up as a regular tachycardia with a narrow QRS complex of less than 120 ms (Patti, Horenstein, and Ashurst, StatPearls, 2025).

This is a genus, not a species — and this page is scoped to the genus. “Supraventricular tachycardia” is explicitly a broad umbrella term (Patti et al., StatPearls, 2025), and the same source library that supplies this page’s dataset label uses it as one of a small set of top-level rhythm categories rather than as a specific diagnosis. The umbrella covers regular atrial rhythms (sinus tachycardia, atrial tachycardia, atrial flutter, inappropriate sinus tachycardia, sinus node reentrant tachycardia), irregular atrial rhythms (atrial fibrillation, atrial flutter with variable block, multifocal atrial tachycardia), and regular atrioventricular rhythms (AVNRT, AVRT, automatic junctional tachycardia) (Burns and Buttner, LITFL ECG Library, 2024). A record labeled “SVT” therefore tells you the tachycardia is supraventricular in origin — it does not tell you which supraventricular mechanism produced it. Naming the species (AVNRT versus AVRT versus focal atrial tachycardia versus junctional tachycardia) usually requires more than a single strip: a baseline tracing in sinus rhythm, the response to adenosine, or an electrophysiology study. [CLINICAL REVIEW NEEDED: this dataset’s per-record “Supraventricular Tachycardia” label is a category label, and there is no way to recover from the label alone whether a given record’s clinician intended the full umbrella or the narrower everyday bedside shorthand — in which “SVT” often means specifically a paroxysmal, AV-node-dependent tachycardia such as AVNRT or AVRT. Individual records should be read as “a supraventricular tachycardia,” not as a specific diagnosis.]

Mechanistically, most of what a monitor tech will see labeled SVT is reentry — a self-sustaining electrical loop, rather than a single focus firing fast. In atrioventricular nodal reentrant tachycardia (AVNRT), the most common form of paroxysmal SVT in adults, the AV node itself contains two functionally distinct pathways: a fast pathway with a longer refractory period and a slow pathway with a shorter one. A well-timed premature atrial beat arrives while the fast pathway is still refractory, is forced down the slow pathway, and by the time it reaches the far end the fast pathway has recovered enough to conduct the impulse back up — closing a loop that then sustains itself (Hafeez and Ahmed, StatPearls, 2026). In atrioventricular reentrant tachycardia (AVRT), the loop is larger and uses an accessory pathway — an extra muscular connection between atrium and ventricle outside the AV node. Orthodromic AVRT, 80% to 87% of AVRTs, conducts down the AV node and back up the accessory pathway, producing a narrow QRS; antidromic AVRT, 5% to 10% of AVRTs, runs the loop the other way and produces a broad QRS that closely resembles ventricular tachycardia (Jabbour, Horenstein, and Grossman, StatPearls, 2024; Buttner, LITFL ECG Library, 2022). Other members of the umbrella are not reentrant at all — focal atrial tachycardia and automatic junctional tachycardia arise from an ectopic focus firing faster than the sinus node, which is why they respond differently to the same interventions.

Clinically, SVT is common and usually survivable but not trivially benign. Paroxysmal SVT has a prevalence of roughly 0.2% in the United States, with an incidence of about 1 to 3 cases per 1,000 patients; AVNRT accounts for over 60% of cases, and women are affected at about twice the rate of men (Hafeez, Quintanilla Rodriguez, Ahmed, and Grossman, StatPearls, 2024). AVNRT specifically affects roughly 2.29 per 1,000 individuals, and SVT is the most common symptomatic arrhythmia in infants and children (Patti et al., StatPearls, 2025). Most episodes are not life-threatening, but they can be in a patient with other cardiac disease, where the consequences include heart failure, loss of consciousness, and cardiac arrest (Cleveland Clinic, 2024). Two situations raise the urgency sharply: hemodynamic instability at a sustained fast rate, and a pre-excited rhythm in a patient with an accessory pathway, where the usual AV-node-blocking drugs are actively harmful (see Treatment Brief). Episodes can last seconds to hours (Cleveland Clinic, 2024).

Symptoms most often reported are palpitations, neck fullness, anxiety, and fatigue, along with dizziness, syncope, nausea, shortness of breath, chest discomfort, and diaphoresis; unusual presentations including tinnitus, seizure-like episodes, and panic attacks have been documented (Hafeez et al., StatPearls, 2024). Some patients have no noticeable symptoms at all despite a markedly elevated rate (Cleveland Clinic, 2024), which is part of why SVT is sometimes first caught on a monitor rather than reported by the patient.

Common triggers and risk factors include physical activity, emotional stress, caffeine, nicotine, alcohol, sleep deprivation, and dehydration, plus hyperthyroidism, myocardial ischemia, infection, hypoxia, and hypovolemia; digoxin toxicity correlates frequently with PSVT, and accessory pathways are associated with congenital heart disease such as Ebstein anomaly (Hafeez et al., StatPearls, 2024; Cleveland Clinic, 2024). Reported risk factors also include female sex, anxiety, tobacco use, intense physical training, lung and heart disease, thyroid disease, diabetes, and pregnancy (Cleveland Clinic, 2024). AVNRT in particular has been associated with myocardial ischemia, rheumatic heart disease, pericarditis, mitral valve prolapse, and stimulants such as caffeine and theophylline, while junctional variants are associated with cardiac ischemia, digoxin toxicity, and cardiac surgery (Nickson, LITFL Critical Care Compendium, 2023).

Interpretation Guide

Key Features:

• Rate: fast and, in the AV-node-dependent forms, often strikingly fast. A typical SVT presentation runs about 150-220 bpm (Patti et al., StatPearls, 2025). AVNRT is quoted more broadly at 140-280 bpm (Burns and Buttner, LITFL ECG Library, 2024), and AVRT at 200-300 bpm (Buttner, LITFL ECG Library, 2022). Treat the rate as supporting evidence, not as the discriminator — the mechanisms overlap heavily in rate.
• Rhythm: regular in the AV-nodal and accessory-pathway forms, which is the presentation most often labeled SVT. Reentrant paroxysmal SVT characteristically starts and stops abruptly rather than accelerating and decelerating gradually (Hafeez et al., StatPearls, 2024). An irregular fast supraventricular rhythm is still inside the umbrella (atrial fibrillation, flutter with variable block, multifocal atrial tachycardia) but points away from AVNRT/AVRT.
• P waves: frequently the hardest part of the strip. P waves may be absent or hidden inside the QRS (Patti et al., StatPearls, 2025). In typical (slow-fast) AVNRT the retrograde P wave lands essentially on top of the QRS, producing a very short RP interval and the classic distortions: a “pseudo-R’” in V1-V2 and a “pseudo-S” in the inferior leads II, III, and aVF (Hafeez and Ahmed, StatPearls, 2026; Burns and Buttner, LITFL ECG Library, 2024). Atypical (fast-slow or slow-slow) AVNRT instead shows a long RP interval with a distinct retrograde P wave after the QRS (Hafeez and Ahmed, StatPearls, 2026). Orthodromic AVRT also shows a distinct retrograde P wave following the QRS, with an RP interval longer than typical AVNRT’s — over 70 ms, versus under 70 ms for typical slow-fast AVNRT (Jabbour et al., StatPearls, 2024).
• PR interval: usually not measurable in typical AVNRT — there is no discrete P wave in front of the QRS to measure from. Where a retrograde P wave is visible after the QRS, the useful measurement is the RP interval, not the PR interval.
• QRS complex: narrow, under 120 ms, in the usual case (Patti et al., StatPearls, 2025). A wide QRS does not rule SVT out: SVT can present with a wide QRS from a pre-existing bundle branch block, from rate-related aberrancy, or from pre-excitation over an accessory pathway (Hafeez et al., StatPearls, 2024), and antidromic AVRT is wide by mechanism (Buttner, LITFL ECG Library, 2022). A wide-complex regular tachycardia should not be assumed to be SVT with aberrancy — see the Differential.
• ST segment: not a defining feature of SVT and not what identifies the rhythm; assess it on a post-conversion tracing rather than trying to read it at rate.
• T waves: not a defining feature. At fast rates the T wave frequently swallows the retrograde P wave, which is precisely why the pseudo-R’/pseudo-S trick matters.
• QT interval: not a defining or diagnostic feature; at these rates the T wave and the following P wave overlap enough that a reliable QT measurement generally has to wait for conversion.
• Other findings: QRS alternans — a beat-to-beat, phasic variation in QRS amplitude with otherwise normal QRS amplitude — is associated with both AVNRT and AVRT and distinguishes them from true electrical alternans (Burns and Buttner, LITFL ECG Library, 2024). Where a baseline sinus-rhythm tracing exists, check it for a delta wave, since pre-excitation reframes the whole rhythm and changes what is safe to give.

Key Leads

• V1 and V2 — the highest-yield leads for typical AVNRT. Look for a small terminal positive deflection at the end of the QRS that is not present on the patient’s baseline tracing: that “pseudo-R’” is the buried retrograde P wave (Hafeez and Ahmed, StatPearls, 2026; Burns and Buttner, LITFL ECG Library, 2024).
• Leads II, III, and aVF — the inferior leads, where the same buried retrograde P wave appears instead as a “pseudo-S” wave notching the terminal QRS (Hafeez and Ahmed, StatPearls, 2026). These are also the leads where atrial flutter’s sawtooth pattern is most visible, so they do double duty in the differential.
• Any lead with a clean, high-amplitude baseline — used to judge regularity, abruptness of onset and offset, and QRS alternans, none of which is lead-specific.
• A comparison tracing in sinus rhythm — not a lead, but the single most useful adjunct. The pseudo-R’ and pseudo-S findings are defined by their absence from the patient’s own baseline QRS, and a delta wave visible only in sinus rhythm identifies pre-excitation. This condition is not lead-agnostic: V1-V2 and the inferior leads carry disproportionate diagnostic weight.

Differential Diagnosis

• Sinus Tachycardia — the most common benign mimic, and a member of the SVT umbrella under the broad anatomic definition, though a regular narrow-complex tachycardia labeled “SVT” clinically usually means something other than sinus. Distinguishing clue: sinus tachycardia has a normal upright P wave preceding every QRS (upright in I, II, and aVF), and its rate builds and falls gradually with activity, fever, pain, or volume status rather than switching on and off abruptly the way reentrant SVT does.
• Atrial Flutter — the classic trap at a ventricular rate near 150 bpm, where 2:1 conduction hides every other flutter wave inside a QRS or T wave. Distinguishing clue: look across the inferior leads and V1 for continuous sawtooth flutter waves with no isoelectric baseline between them; flutter’s atrial rate stays fixed around 300 bpm, and adenosine transiently blocks the AV node to unmask the flutter waves without terminating the rhythm, whereas an AV-node-dependent SVT terminates outright.
• Atrial Fibrillation — also supraventricular and also fast, but a different mechanism entirely. Distinguishing clue: the ventricular response is irregularly irregular with no organized, repeating atrial activity, versus the strict regularity of AVNRT and AVRT. Regularity is the first thing to check before reaching for the P-wave hunt.
• Atrial Tachycardia — a focal, automatic member of the umbrella rather than an AV-nodal reentrant one. Distinguishing clue: discrete P waves of non-sinus morphology, separated by a flat isoelectric baseline, precede the QRS complexes; the atrial activity is visible and organized rather than buried in the QRS as a pseudo-R’ or pseudo-S.
• Paroxysmal Ventricular Tachycardia — the differential that matters most when the QRS is wide, because SVT with aberrancy and VT can look nearly identical. Distinguishing clue: AV dissociation (P waves marching independently of the QRS complexes), capture beats, and fusion beats favor VT, as do a QRS wider than 160 ms and positive or negative concordance across the precordial leads. Electrocardiographic differentiation is not always possible, and the standing safety rule is that a wide-complex tachycardia of uncertain origin is treated as VT until proven otherwise (Burns and Buttner, LITFL ECG Library, 2024).

Treatment Brief

SVT is a rhythm to act on, not merely to document — but the first monitoring priority is capturing enough information that someone can later identify which SVT it was.

• Capture and save a full 12-lead during the tachycardia if at all possible, and another one after it converts. The during-and-after pair is what lets a clinician find the pseudo-R’/pseudo-S, measure the RP interval, and check for a delta wave. A rhythm that self-terminates before anyone prints a strip is a lost diagnosis.
• Assess hemodynamic stability first — blood pressure, level of consciousness, chest pain, signs of poor perfusion. Stability, not the rate number, drives the treatment path.
• Confirm lead placement and rule out artifact before escalating, and note the exact onset and offset times if the monitor captured them; abrupt onset and offset is itself diagnostic information.
• For a stable patient, vagal maneuvers come first — the Valsalva maneuver, with ice to the face described for infants and children — followed by adenosine as the first-line drug, then beta-blockers or calcium channel blockers (Patti et al., StatPearls, 2025). Vagal maneuvers succeed less than 30% of the time; adenosine is 75-95% effective for AV-node-dependent arrhythmias (Hafeez et al., StatPearls, 2024). Adenosine also carries diagnostic value: termination points to an AV-node-dependent circuit, while transient AV block that merely unmasks organized atrial activity points to flutter or atrial tachycardia.
• For an unstable patient, synchronized cardioversion is the treatment, starting around 50-100 J (Patti et al., StatPearls, 2025).
• The pre-excitation exception. In pre-excited atrial fibrillation, digoxin, beta-blockers, diltiazem, verapamil, and amiodarone are not recommended and are potentially harmful (Class III) (2019 ESC Guidelines for the management of patients with supraventricular tachycardia, via ACC Key Points, 2020). Blocking the AV node in that setting forces conduction down the accessory pathway and risks an extremely rapid ventricular rate and cardiac arrest (Buttner, LITFL ECG Library, 2022). This is the single most consequential reason a known or suspected accessory pathway must be flagged to the provider before rate-control drugs are given.
• Longer term, catheter ablation is offered as an initial choice in all reentrant and most focal supraventricular arrhythmias (2019 ESC Guidelines, via ACC Key Points, 2020), with success rates above 95% for slow-pathway ablation in AVNRT (Hafeez and Ahmed, StatPearls, 2026).
• After conversion, keep the patient on the monitor: recurrence is common, and the post-conversion tracing is also where ST-segment and QT assessment finally becomes meaningful.