Atrial fibrillation is an electrical disorder of the upper chambers of the heart in which they are activated in an irregular haphazard fashion at high rate.
Usual cause of thickening of the walls of the heart is an increase in the load which produces a compensatory increase in thickness to overcome added load.
The sinus node is the normal pacemaker of heart which gives out regular electrical signals for the functioning of the heart in response to body's needs.
Defibrillator is a device used to shock the heart back into action when it has stopped due to a life threatening rhythm disorder (ventricular fibrillation).
AIVR is short for accelerated idioventricular rhythm. When the normal pacemaker of the heart (sinus node) slows down, subsidiary pacemakers can take over.
When heart contracts, blood is pushed into the blood vessels through the aorta from the left ventricle. This increases the blood pressure at that time.