This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'P wave is absent in \nSelect and explain. \nA. Atrial fibrillation, B. CCF, C. Atrial flutter, D. PSVT', 'role': 'user'}, {'content': 'Answer: A \nExplanation: It is characterized by totally irregular and rapid rateThere are no recognizable P waveRef: Medical Physiology for Under Graduate students Indu Khurana 2015 pg no: 202', 'role': 'assistant'}]