Complex sentence: The most important is the "Background Tachycardia" (BKT) which is a focal reentrant tachycardia caused by "Fractal Micro-Reentry" that exists even during AF, keeping the AFNs in high frequency activation.
Split into simpler sentences: The most important is the "Background Tachycardia" (BKT) which is a focal reentrant tachycardia caused by "Fractal Micro-Reentry". This special tachycardia exists even during AF, keeping the AFNs in high frequency activation.