PRE EXCITATION SYNDROME
What is Pre Excitation Syndrome?
It is an abnormal heart rythm in which ventricles of the heart depolarized too early.
Causes of Pre Excitation Syndrome
During foetal development few special strands of myocardial fibres make connections between the atria and ventricular musculature outside the normal conducting system. After birth, these strands either disappear or become functionless:
In Pre excitation syndrome these strands persist. Because these fibres partly or completely bypass the normal conducting system they are called Accessory pathways. These pathways may connect right atrium with the ventricles, left atrium with the ventricle or connect the atrial or ventricular septae on right or left side.
Types of Pre Excitation Syndrome:
There are three main forms of Pre excitation syndrome.
- In Wolff- Parkinson- White or WPW syndrome the connecting pathway is called James Bundle which makes direct connection between atria and ventricle completely bypassing the conduction system. This is the commonest type. Its incidence is 1.5 to 3.1 per thousand individuals. In is common in men than women. 60% to 70% cases will have no heart disease. Main feature is re-entrant Tachyarrhythmia. Though it is congenital yet symptoms do not appear till young or adult stage. PRE EXCITATION SYNDROME
ECG shows normal P wave, a short P-R interval < .12 sec, QRS duration is wide > .12 sec, there is initial slurring of QRS complex called Delta Waves. WPW syndrome is of two types :
(I) Type A where excitation travels along left accessory pathway giving rise to right ventricular enlargement or RBBB pattern in V1 and;
(II) Type B where excitation travels along right lateral accessory pathway producing a pattern of LBBB. This is, however, a crude method of classification.
- In Lown-Ganong-Levine or LGL syndrome the accessory pathways is called James Bundle which connects the atria with the lower portion of the A V node.
ECG shows short P-R but normal QRS duration. This also causes Tachyarrhythmia.
- In another type the pre-excitation occurs through Mahaim fibres which connect the ventricles from below the A V node.
Clinical FIndings of Pre Excitation Syndrome:
About 50% of the patients will have no symptom. Remaining 50% may present with supraventricular tachyarrhythmia such as atrioventricular re-entrant tachycardia, atrial flutter and atrial fibrillation from time to time. Asymptomatic cases are diagnosed during routine ECG check up.
ECG shows (a) short P-R interval, (b) wide QRS duration,
(c) Delta wave. In Lown-Ganong-Levine syndrome (b) and
(c) are absent.
Some cases may develop PAT and one third will develop atrical fibrillation.
In symptomatic cases prophylactic antiarrhythmic therapy may be given which slows the conduction rate and prolong the refractory period of bypass tract. Flecainide, disopyramide or amiodarone may be given. Digoxin and Verapamil should be avoided as they increase the conduction in bypass tract. Radiofrequency transvenous catheter ablation of the bypass tract is the treatment of choice. Atrial fibrillation and flutter should be managed as given before avoiding digoxin, calcium channel blocker and B-blocker. PRE EXCITATION SYNDROME