tachycardia

A 45-year-old male with a history of hypertension presents with recurrent episodes of palpitations and near-syncope. His ECG during an episode shows a wide QRS complex tachycardia with a rate of 220 bpm. There is no evidence of structural heart disease on echocardiography. Which of the following is the most likely underlying mechanism of his arrhythmia?

A 74-year-old lady presents with a 2-hour history of nosebleed. She is pale and clammy with ongoing bleeding despite digital pressure. Her blood pressure is 120/80 mmHg and her heart rate is 120/min. What is the most appropriate next step in management?

A 45-year-old man with a history of hypertension presents to the emergency department with palpitations and lightheadedness. His ECG shows a regular narrow-complex tachycardia at a rate of 180 bpm. There are no visible P waves, and the QRS duration is 0.08 seconds. He is hemodynamically stable. Which of the following is the most appropriate initial management?

A 32-year-old woman presents to the clinic with a 2-week history of palpitations, anxiety, and weight loss despite an increased appetite. She also reports feeling hot and experiencing increased sweating. On examination, she has a fine tremor, warm moist skin, and a diffusely enlarged thyroid gland. Her heart rate is 110 bpm. Blood tests reveal suppressed TSH and elevated free T4. What is the most appropriate initial treatment for her condition?