has part has part has_part occurs in occurs in characteristic of has modifier cardiac muscle contraction fibrillation atrial fibrillation Atrial fibrillation shows no distinct P waves and is characterized by chaotic, erratic electrical impulses causing the atria to quiver. Do not confuse with atrial flutter which is characterized by rapid but organized electrical activity in the atria, often presenting as a "sawtooth" pattern on an ECG. MPheno.ontology MP:0008543 asynchronous contraction or quivering of individual cardiac muscle fibers in the atria atrial arrhythmia abnormal asynchronous cardiac atrium