10 www.japi.org © SUPPLEMENT OF JAPI • APRIL 2007 • VOL. 55 Supplement WPW and Preexcitation Syndromes KK Sethi*, A Dhall**, DS Chadha**, S Garg**, SK Malani**, OP Mathew** Abstract Wolff–Parkinson–White syndrome is a disorder characterized by presence of an accessory pathway which predisposes patients to tachyarrhythmias and sudden death. Among patients with WPW syndrome, atrioventricular reentrant tachycardia (AVRT) is the most common arrhythmia, accounting for 95% of re-entrant tachycardias. It has been estimated that one-third of patients with WPW syndrome have atrial fibrillation (AF). AF is a potentially life-threatening arrhythmia. If an accessory pathway has a short anterograde refractory period, then rapid repetitive conduction to the ventricles during AF can result in a rapid ventricular response with subsequent degeneration to ventricular fibrillation (VF). The accessory pathway may be located anywhere along the atrioventricular valve Most of the patients are young and do not have structural heart disease hence it is important to risk stratify these patients so as to prevent the sudden death. Management of asymptomatic patients with WPW syndrome has always remained controversial Catheter ablation of accessory pathways has become an established mode of therapy for symptomatic patients and asymptomatic patients employed in high-risk professions. © ventricular septal defects, coronary-sinus diverticula, and corrected transposition of the great vessels. 7 Thus, the Wolff–Parkinson–White syndrome is an embryonic defect in which processes that electrically insulate the atria from the ventricles go awry. Frequency Delta waves detectable on an ECG have been reported to be present in 0.15% to 0.25% of the general population. 6 A higher prevalence of 0.55% has been reported in first-degree relatives of patients with accessory pathways. Wolff–Parkinson–White syndrome is more commonly diagnosed in men than in women, although this sex difference is not observed in children. Among those with the Wolff–Parkinson–White syndrome, 3.4 percent have first-degree relatives with preexcitation. 8 The familial form is usually inherited as a mendelian autosomal dominant trait. 7-11 Classification Accessory pathways can be classified on the basis of their location along the mitral or tricuspid annulus. Current nomenclature for the atrioventricular (AV) junctions derives from a surgically distorted view, placing the valvar rings and the triangle of Koch in a single plane with antero-posterior and right-left lateral coordinates. Although this nomenclature has served its purpose for the description and treatment of arrhythmias dependent on accessory pathways it is less than satisfactory for the description of atrial and ventricular mapping. To correct these deficiencies, a consensus document has been *Delhi Heart and Lung Institute, New Delhi. **Army Hospital (Research and Referral ), New Delhi. IntrODuCtIOn W olff–Parkinson–White syndrome has attracted cardiologists’ attention not only because of its clinical importance but also because of the opportunity it provides to learn about electrical conduction in the heart. 1 The diagnosis of WPW syndrome is reserved for patients who have both pre-excitation and tachyarrhythmias. Historically, the possibility of the existence of atrioventricular accessory pathways was first raised by Stanley Kent 2 in 1913. In 1930, Wolff, Parkinson, and White reported on 11 young patients with paroxysms of tachycardia or atrial fibrillation that had a functional bundle branch block and an abnormally short PR interval on electrocardiograms recorded during sinus rhythm. 1 In 1933, Holzmann and Scherf 3 reported that the mechanism in Wolff-Parkinson-White syndrome consisted of an acceleration of passage of the impulse from the atria to the ventricles and not a block, as had been proposed by Wolff, Parkinson, and White. In 1944, Ohnell 4 introduced the term “preexcitation” to the medical literature, and along with Wood et al, 5 confirmed the presence of accessory pathways by histologic studies. Among patients with WPW syndrome, atrioventricular reentrant tachycardia (AVRT) is the most common arrhythmia, accounting for 95% of re-entrant tachycardias. Atrial fibrillation (AF) is a potentially life-threatening arrhythmia in patients with WPW syndrome as it can degenerate to ventricular fibrillation (VF). Pathophysiology The anomaly in WPW syndrome is accessory connections between the atrium and ventricle. This accessory connection which is also called bypass tract may be atriofascicular, fasciculoventricular, intranodal, or nodoventricular, the most common being atrioventricular (AV) pathway otherwise known as a Kent bundle. Conduction through a Kent bundle can be anterograde, retrograde, or both. Accessory pathways that are capable of only retrograde conduction are referred to as ‘concealed’, whereas those capable of anterograde conduction are ‘manifest’, demonstrating pre-excitation on a standard ECG. Manifest accessory pathways usually conduct in both anterograde and retrograde directions. 6 Most patients with the Wolff–Parkinson–White syndrome have otherwise normal hearts, but some have concomitant congenital heart disease. Approximately 10 percent of patients with Ebstein’s anomaly have the Wolff–Parkinson–White syndrome 6,7 (Fig. 1). Other congenital heart diseases associated with the syndrome include atrial and Fig. 1 : Atrioventricular pathway in Ebstein’s disease: baseline ECG without preexcitation and disclosing RBBB with normal PR interval. During atrial pacing manifest preexcitation with LBBB, QRS 160 msec wide with a slurred initial r wave in V1.