Accelerated impulse formation in SA node, leading to a HR of >100 BPM

• Impulse conduction is normal - every P wave followed by a normal QRS complex
• Usually an appropriate response to an underlying condition e.g. exercise, pain, anxiety, fever, drugs, anaemia hypoxaemia, hypovolaemia, PE

Manage the underlying condition - e.g. reduce anxiety, treat anaemia, fever

unexplained sinus tachycardia - consider PE