Preexcitation Syndromes (WPW And LGL Syndrome) – Causes, Diagnosis And Treatment
Ventricular pre-excitation activity is defined as a premature activity of a part or of the entire ventricular myocardium, through a supraventricular impulse, occurred through connections or accessories pathways, which are short-circuiting the normal way of impulse conduction. Pre-excitation syndromes are caused by a defect in embryonic development of the atrioventricular ring. Accessory pathways are composed of myocardial fibers with conduction velocity and refractory period lower than the structures of His bundle and of atrioventricular node.
These pathways can lead the excitation both anterograde and retrograde, which allows a reentry circuit. Therefore, in people with pre-excitation syndromes, occur frequently paroxysmal supraventricular tachycardia crises, which are usually initiated by a atrial extrasystole or by ventricular extrasystole, which is lead through the way with shorter refractory period and with a faster velocity conduction.
Pathways by which the ventricular myocardium is early depolarized are:
- Kent atrioventricular bundle, which makes a connection between the right atrium and right ventricle or between the left atrium and left ventricle.
- James bundle, connecting atrial myocardium with the lower third of the atrioventricular node or His bundle.
- Mahaim bundle, which makes the connection between the bottom of the atrioventricular node and the interventricular septum.
Wolff-Parkinson-White Syndrome (WPW syndrome):
Wolff-Parkinson-White syndrome is produced by the presence of Kent bundle and has a frequency in general population of 1-4‰. Clinically, patients may present paroxysmal tachyarrhythmia in 20-40% of cases.
Diagnosis of Wolff-Parkinson-White syndrome is based on the ECG interpretation:
- PR interval <0.12 seconds, P waves of normal appearance;
- QRS complex is wide, with a longer duration than 0.12 seconds;
- The presence of delta waves. Slow enrollment or thickening of the initial portion of the QRS complex (delta wave) is the most important criterion for diagnosis of Wolff-Parkinson-White syndrome. Delta wave length range between 0.02-0.07 seconds;
- Secondary changes of ST segment and T wave, which are showing a opposite direction from the QRS complex and delta wave.
Treatment of Wolff-Parkinson-White syndrome:
Asymptomatic patients, showing only ECG changes do not require treatment.
Arrhythmic chronic treatment, designed to prevent crisis of ventricular tachycardia and to control ventricular rate in case of atrial fibrillation is realized by the administration of class IC antyarrhythmics (flecainide, propafenone), class III antiarrhythmics (amiodarone, sotalol), drugs that are increasing the refracted period in Kent bundle.
Elective treatment of Wolff-Parkinson-White syndrome, in the patients with symptoms, is the ablation of the accessory bundle with radiofrequency current.
Treatment of supraventricular tachycardia access is done by: vagal maneuvers, intravenous administration of adenosine and verapamil. After administration of adenosine can occur an episode of atrial fibrillation with rapid ventricular rate, which necessitate, sometimes, electrical defibrillation.
Lown-Ganong-Levine Syndrome (LGL syndrome)
Lown-Ganong-Levine syndrome is produced by the presence of James bundle and has a frequency, in general population, of 0.5%. Clinically, patients with this syndrome may present ventricular tachycardia.
The diagnosis of Lown-Ganong-Levine syndrome is based on ECG interpretation:
- PR interval with a duration of less than 0.12 seconds, with normal P waves;
- The QRS complex duration is normal;
- The absence of delta waves;
- Episodes of paroxysmal supraventricular tachycardia.