V2 demonstrating characteristic findings in<unk> . A characteristic delta wave (above the blue bar), a short PR interval (red bar) of 80 ms, and a long QRS complex (blue bar plus green bar) at 120 ms are visible.<unk>  is commonly diagnosed on the basis of the electrocardiogram in an asymptomatic individual. In this case, it is manifested as a delta wave, which is a slurred upstroke in the QRS complex that is associated with a short PR interval. The short PR interval and slurring of the QRS complex are reflective of the impulse making it to the ventricles early (via the accessory pathway) without the usual delay experienced in the AV node. If a person with<unk>  experiences episodes of atrial fibrillation, the ECG shows a rapid polymorphic wide-complex tachycardia (without torsades de pointes). This combination of atrial fibrillation and<unk>  is considered dangerous, and most antiarrhythmic drugs are contraindicated. When an individual is in normal sinus rhythm, the ECG characteristics of<unk>  are a short PR interval (less than 120 milliseconds in duration), widened QRS complex (greater than 120 milliseconds in duration) with slurred upstroke of the QRS complex, and secondary repolarization changes (reflected in ST segment-T wave changes). In individuals with<unk> , electrical activity that is initiated in the SA node travels through the accessory pathway, as well as through the AV node to activate the ventricles via both pathways. Since the accessory pathway does not have the impulse slowing properties of the AV node, the electrical impulse first activates the ventricles via the accessory pathway, and immediately afterwards via the AV node. This gives the short PR interval and slurred upstroke of the QRS complex known as the delta wave. In case of type A pre-excitation (left atrioventricular connections), a positive R wave is seen in V1 ("positive delta") on the precordial leads of the electrocardiogram,<unk>  in type B pre-excitation (right atrioventricular connections), a predominantly negative delta wave is seen in lead V1 ("negative delta"). People with<unk>  may have more than one accessory pathwayin some cases, as many as eight abnormal pathways have been found. This has been seen in individuals with Ebstein's anomaly.<unk>  is sometimes associated with Leber's hereditary optic neuropathy, a form of mitochondrial disease. Risk stratification electrocardiogram of an individual with<unk> <unk>  carries a small risk of sudden death, presumably due to rapidly conducted atrial fibrillation causing ventricular fibrillation.<unk>  the overall risk is approximately 2.4 per 1000 person years, the risk in an individual is dependent on the properties of the accessory pathway causing pre-excitation. A higher risk accessory pathway may be suggested by a history of syncope, but risk stratification is best performed by assessing how frequently a pathway can conduct impulse to the ventricles, usually via programmed electrical stimulation (PES) in the cardiac electrophysiology laboratory. This is an invasive but generally low-risk procedure during which the atria are stimulated to try to induce tachycardia. If a tachycardia involving the accessory pathway can be triggered, the cardiologist can then assess how rapidly the accessory pathway is able to conduct. The faster it can conduct, the higher the likelihood the accessory pathway can conduct fast enough to trigger a lethal tachycardia. High-risk features that may be present during PES include an effective refractory period of the accessory pathway less than 250 ms, multiple pathways, septal location of pathway, and inducibility of supraventricular tachycardia (AVRT, atrial fibrillation). Individuals with any of these high-risk features are generally considered at increased risk for SCD or symptomatic tachycardia, and should be treated accordingly (i.e.: catheter ablation). It is unclear whether invasive risk stratification (with PES) is necessary in the asymptomatic individual.<unk>  some groups advocate PES for risk stratification in all individuals under 35 years old, others only offer it to individuals who have history suggestive of a tachydysrhythmia, since the incidence of sudden cardiac death is so low (less than 0.6% in some reports). Other methods of risk stratification include observing the ventricular rate during spontaneous atrial fibrillation on a 12-lead ECG. RR intervals of less than 250 ms suggest a higher risk pathway. During exercise testing, abrupt loss of pre-excitation as heart rate increases also suggest a lower risk pathway. However, this approach is hampered by the normal improvement in AV node conduction during exercise which can also mask pre-excitation despite ongoing conduction down the accessory pathway.
Wolff–Parkinson–White syndrome
Lown–Ganong–Levine syndrome
Catel–Manzke syndrome
Parkinson-plus syndrome
De Barsy syndrome
Dravet syndrome
Benedikt syndrome
Stratton Parker syndrome