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Baseline is irregular and lead V1 shows coarse fibrillary waves suggestive of atrial fibrillation. But the unusual feature about this ECG is the grouped beating, which is unusual in atrial fibrillation. The QRS complexes appear to be in a bigeminal rhythm. Since a long rhythm strip is not available, we cant be sure about the group beating. Here all the beats are having a narrow QRS complex. If it was one narrow and one wide, it could have been called a ventricular ectopic bigeminy. But since both QRS complexes are narrow, more complex explanations will have to be sought, provided this pattern is confirmed in a long rhythm recording. QRS complexes can be regular in atrial fibrillation if there is complete heart block. Theoretically there can be bigeminal rhythm if there are two levels of block – complete blockage of atrial impulses at a higher level and second degree exit block with 3:2 conduction ratio for the subsidiary pacemaker focus at a lower level.