Atrial fibrillation (AF) with slow ventricular rate
Fine fibrillary waves are seen throughout the baseline, indicating fine atrial fibrillation. When the fibrillary waves are more than 1 mm in amplitude, they can be considered as coarse atrial fibrillation. Coarse atrial fibrillation usually indicates larger re-entrant circuits and hence larger atria. Coarse atrial fibrillation is classically seen in mitral stenosis with large left atrium.
In this case with fine atrial fibrillary waves, the ventricular rate is not high as in usual atrial fibrillation, in which ventricular rates are over 120/minute. The QRS complexes are narrow and there is a slight rightward deviation of axis, with small negative complexes in aVL. Tall R waves are noted in V5 and poor r waves in V1 and V2. There is no significant ST segment or T wave abnormality seen.
Slow ventricular rate in atrial fibrillation indicates that the atrial fibrillary signals are mostly blocked at the atrioventricular node (AV node) and prevented from being conducted to the ventricles. This can happen if the AV node is diseased due to ischemia or degenerative disease. In acute inferior wall myocardial infarction, atrial fibrillation is often associated with slow ventricular rate due to ischemia of the AV node, which often recovers after the acute phase. But the atrial fibrillation also usually disappears by that time. Another situation for slow ventricular rate in atrial fibrillation is with sick sinus syndrome having structural nodal disease of binodal variety. Slow ventricular rate in atrial fibrillation can occur if the AV node is suppressed by drugs like digoxin, beta blockers or nondihydropyridine calcium channel blockers.