Atrial fibrillation is characterised by the absence of P waves and presence of fibrillatory waves. If the fibrillary waves are more than 1 mm (0.01 mV) it is known as coarse atrial fibrillation and it indicates atrial hypertrophy. In fine atrial fibrillation, the fibrillary waves are less than 1 mm in amplitude and may be hardly visible in certain leads which are perpendicular to the axis of the waves. Slow ventricular response can occur due to the effect of drugs like digoxin, beta blockers and verapamil which suppress the AV nodal conduction so that more impulses are blocked at the AV node. It can also occur in structural nodal disease (sick sinus syndrome) with disease of the AV node.