Supraventricular Tachycardias

A 28-year-old woman presents to the emergency department with palpitations and chest discomfort lasting 2 hours. She reports a sudden onset of rapid regular heartbeat while sitting at her desk. On examination, BP is 118/76 mmHg, HR 180/min, regular. Physical examination reveals cannon a waves in the JVP. A 12-lead ECG shows a narrow complex tachycardia with a rate of 180/min; P waves are not clearly visible. Carotid massage is attempted but produces no change in heart rate. An intravenous bolus of adenosine 6 mg is given, resulting in immediate termination of the arrhythmia and restoration of normal sinus rhythm. What is the most likely diagnosis?

A 52-year-old man with hypertension and diabetes presents with a 3-day history of persistent palpitations. Physical examination reveals an irregular pulse at 130–150 bpm. A 12-lead ECG shows a narrow-complex tachycardia with a ventricular rate of 140 bpm and no visible P waves. Which investigation is most specific for confirming the diagnosis of atrial fibrillation with rapid ventricular response?

A 35-year-old man with recurrent episodes of palpitations and a regular narrow-complex tachycardia is diagnosed with atrioventricular nodal reentrant tachycardia (AVNRT) on electrophysiology study. Regarding the management and electrophysiological features of AVNRT, all of the following statements are correct EXCEPT:

A 28-year-old woman with a history of palpitations since childhood presents with a regular narrow-complex tachycardia at 180 bpm. An ECG shows a short PR interval and a delta wave. Regarding the electrophysiological properties of accessory pathways in Wolff-Parkinson-White (WPW) syndrome, all of the following are true EXCEPT:

A 32-year-old woman with known Wolff-Parkinson-White (WPW) syndrome presents to the emergency department with palpitations and dyspnea. On examination, heart rate is 180 bpm, BP 110/70 mmHg, and she is alert and hemodynamically stable. A 12-lead ECG shows a regular narrow-complex tachycardia with a rate of 180 bpm. What is the most appropriate immediate next step in management?