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ECG Interpretation

Patient/Technical Details
  • Date: 01-06-2026, recorded at Valluvanad Hospital
  • Settings: 25 mm/s paper speed, 10 mm/mV gain, 0.67-25 Hz filter, AC50
  • Machine-printed diagnosis: Sinus Arrhythmia + Ventricular Pre-excitation Type A

Measured Intervals (from printout)

ParameterValue
HR98 bpm
PR76 ms (short - normal is 120-200 ms)
QRS119 ms (widened - normal <100 ms)
QT/QTc364/467 ms
P/QRS/T axis36/40/0 degrees
RV5/SV10.83/4.0/0.000 mV

Key ECG Findings

1. Short PR Interval (76 ms) This is the hallmark of antegrade accessory pathway conduction. The normal AV node with its decremental conduction produces a PR of 120-200 ms. Here, the sinus impulse bypasses the AV node via the accessory pathway and reaches the ventricle almost immediately, producing this dramatically short PR.
2. Delta Wave + Widened QRS (119 ms) Because the accessory pathway inserts directly into ventricular myocardium (which conducts slowly, cell-to-cell), the initial part of the QRS is a broad, slurred upstroke - the delta wave. Once the AV node conduction catches up, the His-Purkinje system rapidly activates the rest of the ventricle, creating an inflection point in the QRS. The result is a fusion beat - part preexcited (slow myocardial), part normal (fast Purkinje).
3. Type A WPW Pattern Type A means the dominant QRS deflection in V1 is positive (tall R or R' in V1-V2). This indicates a left-sided accessory pathway (posteroseptal or left free wall), as the accessory pathway depolarizes the left ventricle first, generating a rightward/anterior initial vector that appears positive across V1-V2. This is confirmed by the machine-printed delta wave transition between V1 and V2 noted in the report.
  • V1-V3: positive dominant R waves with slurred upstroke (delta waves)
  • Inferior leads (II, III, aVF): upright complexes with delta waves
  • aVR: negative delta waves (reciprocal)
4. Sinus Arrhythmia The varying R-R intervals visible on the tracing reflect normal respiratory variation in sinus node firing rate - faster on inspiration, slower on expiration. This is a normal variant, especially common in younger patients.
5. Secondary ST-T Changes ST depression and T-wave changes visible in left precordial leads are "secondary" changes - they result from the abnormal ventricular depolarization order, not from ischemia. Do not interpret these as ischemic.

Diagnosis

Wolff-Parkinson-White (WPW) Syndrome - Type A (Left-sided accessory pathway)
This is a manifest accessory pathway (conducts antegradely), producing the classic triad:
  1. Short PR interval (<120 ms)
  2. Delta wave (slurred QRS upstroke)
  3. Widened QRS (>100 ms)

Clinical Significance and What to Do Next

ConcernDetails
Risk of AVRTOrthodromic AVRT (narrow QRS, most common) or antidromic AVRT (wide QRS) can occur
Risk of AF with rapid conductionUp to 30% of WPW patients develop AF. If AF conducts down the accessory pathway, ventricular rates can reach 200-300 bpm and degenerate into VF - potentially fatal
Avoid AV nodal blockers in AFDigoxin, verapamil, diltiazem, beta-blockers are contraindicated if AF with WPW occurs - they can unmask rapid accessory pathway conduction and cause VF
Definitive treatmentRadiofrequency catheter ablation of the accessory pathway is curative (>95% success rate) and is the first-line recommendation for symptomatic patients
Risk stratificationElectrophysiology (EP) study to assess the effective refractory period (ERP) of the accessory pathway - a short ERP (<250 ms) indicates higher risk for sudden death
Acute tachycardiaOrthodromic AVRT: adenosine/vagal maneuvers. Antidromic or pre-excited AF: procainamide or electrical cardioversion. Never give AV nodal blockers for wide-complex tachycardia in WPW

Reference: Classic WPW ECG from Braunwald's Heart Disease

WPW ECG reference showing preexcited atrial fibrillation with wide-complex tachycardia and asterisks marking very short R-R intervals consistent with high-risk pathway
Reference ECG from Braunwald's Heart Disease showing WPW with preexcited AF - asterisks () indicate dangerously short R-R intervals (~240 ms). Your patient's tracing shows resting sinus rhythm with preexcitation, not tachycardia at this point, which is the favorable finding.*
Bottom line: This ECG shows classic WPW Type A in sinus rhythm. The patient should be referred to a cardiologist/electrophysiologist for risk stratification and likely catheter ablation, even if currently asymptomatic. The left-sided pathway localization guides the ablation approach (typically transseptal or retrograde aortic).
Sources: Braunwald's Heart Disease 12e, p.511-512; Rosen's Emergency Medicine 10e, p.1058
Disclaimer: This interpretation is for educational purposes. Clinical decisions must be confirmed by a qualified physician reviewing the original tracing in the context of the patient's full clinical picture.
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