Wolff-Parkinson-White pattern or ventricular preexcitation - When this ECG pattern is seen without the tachycardia.
First described in 1930 in an article by Louis Wolff, Sir John Parkinson, and Paul Dudley White in 11 patients.
• Accessory bypass tracts detectable on an ECG - reported in 0.15 to 0.25 %.
• Familial association - 0.55 %.
• 2:1 male: female predominance.
• Tachyarrhythmia - depends on the population studied and varies from 13% in a healthy outpatient population to 80% in the hospital setting.
• Incidence of sudden death in the 0-4% range.
• Approx. 5–10% of patients with documented bypass tracts have concomitant structural heart disease.
o Ebstein anomaly is the most common, accounting for 25–50%,
o Corrected transposition of the great arteries (levo-TGA), and
o Hypertrophic cardiomyopathy.
• Association of right-sided accessory pathways with structural heart disease is strong. 45% of patients with right-sided vs 05% of those with left-sided.
• Most common bypass tract is an accessory atrioventricular (AV) pathway called Kent bundle.
• Another common preexcitation syndrome, Lown-Ganong-Levine (LGL), has an accessory pathway - James fibers, which connect the atria serially to the His bundle.
• Pathways can cross the AV groove anywhere in its course to connect the left or right atrium to its respective ventricle except the region between the aortic and mitral valves. The distribution of accessory pathways,
- 46–60% are located in the left free wall,
- 25% within the posteroseptal space,
- 13–21% in the right free wall, and
- 2% in the anteroseptal space.
ECG
Each location produces a distinct ECG pattern but in the 13% of patients with two or more bypass tracts the ECG tracing can be confounding and show multiple QRS morphologies. During sinus rhythm, an atrial impulse will reach the ventricles via both the AV node and the accessory AV pathway. The latter conducts the atrial impulse to the ventricles before the AV node, resulting in ventricular pre-excitation and a short PR interval. On reaching the ventricles, the pre-excitation impulse is not conducted via the specialised conducting system. Hence, early ventricular activation will be slowed, resulting in a slurred upstroke of the QRS complex, the so-called delta (d) wave.The abnormal ventricular activation also gives rise to secondary S-T segment and T-wave abnormalities. d-wave polarity in a 12-lead ECG may help localise the anatomical position of the accessory pathway.
In type A WPW the accessory pathway is usually situated on the left with pre-excitation of the left ventricle. Positive R waves in the right precordial leads, short PR & a delta wave giving rise to wide QRS complex
Type B WPW has a dominantly negative QRS complex in V1 and the accessory pathway tends to be on the right with pre-excitation of the right ventricle.
CLINICAL - AVRT or AF can occur with WPW.
During AVRT, the re-entry impulse usually travels down the AV node and back up the accessory pathway. Ventricular activation is via the normal conducting pathways and the QRS will be narrow. This is called orthodromic conduction.
Occasionally, the re-entry impulse may pass in the opposite direction (down the accessory pathway and up the AV node), resulting in a wide QRS-complex tachycardia due to abnormal slow ventricular activation. This is antidromic conduction. Treatment is the same as for AVRT.
AF is common in WPW 11-38%, and may be life-threatening. Most impulses are conducted via the accessory pathway, leading to wide QRS complexes. The ECG of WPW with AF usually shows rapid, irregular QRS complexes with variable QRS width. Ventricular response is very rapid, leading to hypotension or cardiogenic shock. This arrhythmia may degenerate to VF.
Symptoms range from palpitations to syncope, episodes of tachycardia may be associated with dyspnea, chest pain, decreased exercise tolerance, anxiety, dizziness, or syncope.
ELECTROPHYSIOLOGIC TESTING
•To confirm the presence of an AP
•To differentiate this condition from other forms of SVT
•To find the pathway participating in the tachycardia and aid in ablative therapy
TREATMENT
Treatment usually involves synchronised DC shock.
Antiarrhythmic drugs may be used when patients are haemodynamically stable and the ventricular rate is not excessively rapid.
•Drugs that prolong the refractory period of the accessory pathway are useful (e.g. sotalol, amiodarone, flecainide and procainamide).
•Drugs that shorten the refractory period (e.g. digoxin) are contraindicated as they may accelerate ventricular rate.
•Verapamil and lidocaine may increase the ventricular rate during AF, and are also best avoided.
•b-Adrenergic blockers have no effect on the refractory period of the accessory pathway.
Catheter Ablation of APS
In conjunction with a diagnostic EP test. Once the AP is localized to a region of the heart, precise mapping and ablation is performed using a steerable electrode catheter. The largest prospective, multicenter clinical trial to evaluate the safety and efficacy of radiofrequency ablation was reported by Calkins and colleagues. This study involved analysis of 1050 patients, of whom 500 had APs. Overall success curing APs was 93 percent. Following an initially successful procedure, recurrence of AP conduction is found in approximately 5 percent of patients.
Complications
•Obtaining vascular access (hematomas, DVT, perforation of the aorta, AV fistula, PTx),
•Catheter manipulation (valvular damage, microemboli, perforation of the coronary sinus or myocardial wall, coronary dissection and/or thrombosis), or
•Delivery of RF energy (AV block, myocardial perforation, coronary artery spasm or occlusion, transient ischemic attacks, or cerebrovascular accidents).
Calkins and coworkers reported the incidence of
•major complications - 3 %
•minor complications - 8 %.
•procedure-related mortality - 0 - 0.2 %.
The two most common types of major complications reported during catheter ablation of APs are inadvertent complete AV block and cardiac tamponade.
Cryoablation has become available as an alternative energy source for creation of myocardial lesions. The main advantage of cryoenergy, compared to radiofrequency energy, is that the risk of heart block appears to be lower.
Aymptomatic Preexcitaion
Mostly have a good prognosis. Because of the small but real risks associated with invasive procedures, EPS is not routinely recommended for risk stratification and/or ablative therapy. ACC/AHA/ESC Guidelines for Management of Patients With Supraventricular Arrhythmias gives catheter ablation a 2a classification for treatment of patients with asymptomatic preexcitation.
The detection of intermittent preexcitation—which is characterized by an abrupt loss of the delta wave, normalization of the QRS complex, and an increase in the P-R interval during a continuous ECG recording—is evidence that an AP has a relatively long refractory period and is unlikely to precipitate VF. The loss of preexcitation after administration of antiarrhythmic drugs like procainamide has also been used to indicate a low-risk subgroup. These noninvasive tests are generally considered inferior to EPS testing in the assessment of risk of sudden cardiac death. Because of this, they play little role in patient management at present.
Studies have identified markers that identify patients at increased risk –
(1) a short preexcited RR interval <250 msec during spontaneous or induced AF (2) a history of symptomatic tachycardia, (3) multiple APs, and (4) Epstein anomaly.
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