徐脉

Bradycardia is a condition wherein an individual has a slow heart rate, typically defined as a heart rate of under 60 beats per minute (BPM) in adults. Bradycardia typically does not cause symptoms until the rate drops below 50 BPM. When symptomatic, it may cause fatigue, weakness, dizziness, sweating, and at very low rates, fainting.During sleep, a slow heartbeat with rates around 40–50 BPM is common, and is considered normal. Highly trained athletes may also have athletic heart syndrome, a very slow resting heart rate that occurs as a sport adaptation and helps prevent tachycardia during training.The term relative bradycardia is used in explaining a heart rate that, although not actually below 60 BPM, is still considered too slow for the individual's current medical condition.心跳过慢（Bradycardia）也称心动过缓、心跳过缓、心动徐缓、徐脉。是指心脏跳动速度低于正常水平，达到每分钟50次以下的现象。心跳过慢可能是由迷走神经亢奋、窦房结病变、窦房结的冲动波遭到阻挡等原因引起，常见于老年人、心脏病患者