<s>[INST] context: Periodic fainting spells is known as Adams Stokes syndrome Reason: Fluctuating third degree AV block in heas with borderline ischemia of conductive system. Complete AV block -Brain cannot remain active for more than 4-7 sec without blood supply -fainting episode - ventricular escape from overdrive suppression occurs in 5-30 sec - rapid recovery from the faint and then to sustain the person. AV block types: 1. First degree block: prolonged P-Q or P-R interval >0.20, not actual blockage but delay of conduction. 2. Second degree block: a. Wenckebach or Mobitz type 1: progressive P-R prolongation followed by a dropped beat. Abnormality in AV node. b. Mobitz type 2: A fixed number of non-conducted P waves for every QRS complex. P-R interval constant. Ex: 3:1, 3:2, 2:1. Abnormality in bundle of His-Purkinje system. 3. Third degree hea block: Complete AV block. SA and AV node dissociation leading to idioventricular rhythm (ventricular escape as Purkinje fibres becomes new pacemaker, 15-40 beats/min). [/INST] question: A 50-year-old man has been having fainting "spells" for about 2 weeks. During the episodes, his ECG shows a ventricular rate of 25 beats/min and 100 P waves per minute. After about 30 seconds of fainting, a normal sinus rhythm recurs. What is his likely diagnosis? | options: A: First-degree A-V block B: Second-degree A-V block C: Third-degree A-V block D: Stokes-Adams syndrome | answer: D </s>