Clinical Overview

Ventricular preexcitation is the ECG signature produced when an accessory pathway — most often the bundle of Kent, an extra strand of muscle connecting atrium and ventricle outside the AV node — lets part of the ventricle activate earlier than the AV node’s normal conduction delay would allow (StatPearls, Wolff-Parkinson-White Syndrome, 2023; LITFL, Pre-excitation Syndromes, reviewed 2026). The finding is a short PR interval, a slurred initial QRS upstroke called a delta wave, and a widened QRS. Clinicians and this product’s own WPW page call the identical resting ECG finding “WPW pattern” when it occurs on its own; “WPW syndrome” is reserved for that same pattern plus a documented, symptomatic tachyarrhythmia (Cleveland Clinic, Wolff-Parkinson-White Syndrome; StatPearls, 2023; ACC, Asymptomatic Ventricular Preexcitation, 2022). This page covers the pattern by itself — the ECG finding, not the syndrome diagnosis. The distinction also separates preexcitation from this site’s Shortened PR Interval (SPRI) page: SPRI covers a short PR interval with a normal, narrow QRS and no delta wave, produced by a different substrate (accelerated AV-nodal conduction or a low-atrial/junctional pacemaker); the moment a delta wave and QRS widening appear alongside the short PR interval, the correct read moves from SPRI to this finding. In this product’s own dataset, no record carries both the VPE and WPW labels, and none carries both VPE and SPRI — each strip is annotated under exactly one of the three, consistent with preexcitation, syndrome, and isolated short-PR being tracked as separate labels rather than overlapping ones (search-index.json record data, this dataset).

The accessory pathway forms congenitally, from incomplete separation of atrial and ventricular muscle during fetal development, and unlike the AV node it conducts without the node’s normal rate-dependent slowing (StatPearls, 2023). Impulses reach part of the ventricle early through this pathway while the rest of the ventricle is still activated normally through the His-Purkinje system, and the surface QRS is a fusion of the two wavefronts — the early, slurred delta-wave component plus the normally timed component (LITFL, reviewed 2026; StatPearls, 2023). The same pathway is the substrate for atrioventricular reentrant tachycardia (AVRT): during orthodromic AVRT the impulse travels down the AV node and back up the pathway, and the delta wave temporarily disappears because the ventricle is no longer being preexcited. Preexcitation itself is only the resting-ECG signature of that substrate, not the arrhythmia.

Preexcitation is uncommon in the general population, affecting roughly 0.1-0.3% of people (StatPearls, 2023), and most who carry it never develop a symptomatic arrhythmia: roughly 65% of adolescents and 40% of adults over 30 with the pattern remain asymptomatic, and progression from pattern to a symptomatic arrhythmia runs around 1-2% per year (StatPearls, 2023). Reported estimates of sudden cardiac death risk vary by how the question is framed — a meta-analysis cited by the American College of Cardiology puts overall lifetime risk in asymptomatic patients at 3-4%, mostly between ages 10 and 40, while a 2024 cohort study in EP Europace reports an annual incidence of roughly 0.5-2 per 1,000 patient-years (ACC, 2022; EP Europace, Risk assessment in patients with symptomatic and asymptomatic pre-excitation, 2024) — but the two do not disagree, since a small annual rate compounded over decades is broadly consistent with the higher lifetime figure. That risk is why the field’s management approach has shifted in the past few years: a 2024 EP Europace study and a 2025 ACC-summarized pediatric practice algorithm both report that invasive electrophysiology study (EPS) should now be considered for risk evaluation regardless of symptoms, since exercise-testing loss of preexcitation has poor discriminatory power (40% sensitivity in one cohort) and asymptomatic patients show inducible arrhythmias almost as often as symptomatic ones (61% vs. 69% in the same cohort) (EP Europace, 2024; ACC, Clinical Practice Algorithms For Wolff-Parkinson-White Pattern in Pediatric Patients, 2025). High-risk EPS findings include a shortest preexcited R-R interval of 250 ms or less during induced atrial fibrillation and an accessory-pathway effective refractory period of 250 ms or less (EP Europace, 2024; ACC, 2022).

By definition, the ECG pattern alone produces no symptoms — it is an electrical finding, not a rhythm disturbance. When a patient does report palpitations, lightheadedness, dyspnea, chest discomfort, or syncope, that reflects an associated tachyarrhythmia (most often AVRT, or atrial fibrillation conducted rapidly down the pathway), and the presentation has crossed from an isolated pattern into what this site’s WPW page covers as the full syndrome (StatPearls, 2023; ACC, 2022).

The pathway itself is congenital and its cause is unknown in most patients. A minority of cases are familial, linked to PRKAG2 gene mutations, and preexcitation is also associated with congenital structural heart disease, most notably Ebstein anomaly of the tricuspid valve, and less commonly hypertrophic cardiomyopathy (StatPearls, 2023). Reported risk factors for progressing from an isolated pattern to a dangerous arrhythmia include male sex, age under 35, multiple accessory pathways, a septal pathway location, and a pathway capable of rapid antegrade conduction (StatPearls, 2023; ACC, 2022).

Interpretation Guide

Key Features:

• Rate: not itself altered by preexcitation — reflects whatever the underlying rhythm happens to be; in this dataset’s matching records, atrial fibrillation and sinus tachycardia are the most common underlying contexts, with sinus bradycardia, supraventricular tachycardia, and plain sinus rhythm each appearing in a smaller number of records (search-index.json record data, this dataset)
• Rhythm: regular when the underlying rhythm is sinus-based; irregularly irregular when the underlying rhythm is atrial fibrillation — this label describes the ECG pattern itself, not a fixed rhythm origin
• P waves: normal upright morphology when the underlying rhythm is sinus-based; absent, replaced by fibrillatory activity, when the underlying rhythm is atrial fibrillation
• PR interval: short, under 120 ms (0.12 s) — a defining feature together with the delta wave below
• QRS complex: widened to 120 ms or more, with a slurred, slowly rising initial upstroke — the delta wave — that gives the complex its fused, “smeared-on” appearance; this is the finding’s other defining feature
• ST segment: secondary changes, discordant to the QRS/delta-wave vector, are common and reflect the abnormal depolarization sequence rather than ischemia
• T waves: secondary changes, also discordant to the QRS/delta-wave vector, commonly accompany the ST changes above
• QT interval: not a primary diagnostic feature of this pattern
• Other findings: negative delta waves can produce pseudo-infarct Q waves, present in up to 70% of patients with this pattern, most often in the inferior leads (II, III, aVF) or anteroseptal leads, that can be mistaken for a prior myocardial infarction — and can also mask a genuine one in a patient who has both (LITFL, reviewed 2026)

Key Leads

• Leads V1-V6 — Delta-wave polarity across the precordial leads separates two patterns: Type A, a dominant positive delta wave/R wave in V1-V3 that can mimic right ventricular hypertrophy, and Type B, a delta wave predominantly negative in the right precordial leads with a dominant S wave in V1 that can mimic left ventricular hypertrophy or inferior infarction (LITFL, reviewed 2026).
• Leads II, III, aVF — Worth checking specifically for pseudo-infarct Q waves before assuming an old inferior infarct, since a negative delta wave here is a normal consequence of preexcitation, not necrosis.

Differential Diagnosis

• Wolff-Parkinson-White Syndrome (WPW) — the identical short-PR-interval-plus-delta-wave ECG pattern, but with a documented, symptomatic tachyarrhythmia added on top; a strip showing this pattern with no history of palpitations, syncope, or a captured tachycardia episode belongs here, while the same pattern plus a documented arrhythmia moves it to WPW.
• Shortened PR Interval (SPRI) — a short PR interval without a delta wave or QRS widening; a strip with a short PR and a normal, narrow QRS belongs there, while a slurred QRS upstroke on top of the short PR moves it to this finding.
• Atrioventricular Reentrant Tachycardia (AVRT) — the reentrant tachycardia this same accessory pathway can produce; during orthodromic AVRT the delta wave disappears and the strip instead shows a regular, narrow-complex tachycardia around 150-250 bpm, so a fast, narrow, delta-wave-free rhythm in a patient known to have this pattern is the same pathway operating in a different mode, not a separate structural finding.
• Right Ventricular Hypertrophy (RVH) — a Type A delta pattern’s dominant R wave in V1 can mimic RVH’s own R/S-ratio-above-1 criterion in that lead; the giveaway is the short PR interval and slurred delta-wave upstroke, neither of which is part of RVH’s voltage-based criteria.
• Complete Right Bundle Branch Block (CRBBB) — both produce a widened QRS with an abnormal terminal or initial deflection, but CRBBB starts from a normal PR interval and its RSR’ pattern comes from a late, slurred second half of the QRS, not the short PR interval and early slurred upstroke that mark preexcitation.

Treatment Brief

Confirm lead placement and capture a full 12-lead strip to characterize the delta wave and rule out a genuine pseudo-infarct pattern before treating any Q waves as old infarction, and correlate the finding with the patient’s history and vital signs. An isolated pattern found incidentally in an asymptomatic patient is not itself an emergency; notify the provider so that further risk stratification (echocardiography, and increasingly an electrophysiology study regardless of symptoms) can be arranged rather than treating the strip as one requiring immediate intervention. If the patient reports or is found to have palpitations, syncope, or a captured tachyarrhythmia, treat the presentation per this site’s WPW page instead: vagal maneuvers and adenosine are typical first-line responses to a stable, narrow-complex tachycardia under provider direction, while a wide, irregular tachycardia consistent with preexcited atrial fibrillation is a medical emergency that should not receive AV-nodal-blocking agents (adenosine, calcium channel blockers, beta-blockers, or digoxin), since these can paradoxically push more of the fast atrial rate down the accessory pathway; escalate immediately and prepare for synchronized cardioversion if the patient decompensates.