Ans. (a) Bradycardia-tachycardia syndrome.ECG shows runs of tachycardia interspersed with long sinus pauses.The sinus rate is slow to level that it looks like an arrest.Sinus beats are followed by paroxysms of junctional tachycardia at 140 bpmNone of the definitions of Mobitz I and II blocks discussed above are satisfied.