Answer is A, B, and C Second degree AV block (Type I and /or Type II) may be associated with prolonged conduction time (prolonged PR interval), Atrial rate more than ventricular rate and change in QRS complex morphology (Tipe II). Name Rhythm Rate (beats/minute) P waves (lead II) PR Interval QRS complex First-degree atrio- ventricular (AV) block Regular That of underlying sinus rhythm; both atrial and ventricular rates will be the same Sinus origin: one P wave to each QRS complex Prolonged (more than 0.20 second); remains constant Normal (0.10 second or less) Second-degree AV Atrial: regular Atrial: that of Sinus origin Varies; progressively Normal (0.10 block, Mobitz I Ventricular: irregular underlying sinus rhythm lengthens until a P wave isn't conducted second or less) Ventricular: depends on number of impulses conducted through AV node: will he less than atrial rate (P wave occurs without the QRS cmplex); a pause follows the dropped QRS complex Second-degree AV Atrial: regular Atrial: that of Sinus origin: two or Normal or Normal if block at block, Mobitz II ventricular: usually underlying sinus three P waves prolonged; remains level of bundle of regular, but may be rhythm (sometimes more) constant His; irregular if Ventricular: depends before each QRS conductions ratios vary on number of Impulses conducted through AV node; will be less than atrial rate complex bundle branches Third-degree AV block Atrial: regular Atrial: that of Sinus P waves with Varies greatly Normal if block at Ventricular: regular underlying sinus rhythm Ventricular:40 to 60 if paced by AV junction; 30 to 40 (sometimes less) if paced by ventricles; will be less than atrial rate no constant relationship to the QRS complex; P waves found hidden in QRS complexes and T waves level of AV node or bundle of His; wide if block in bundle branches No constant Relationship between P wave and QRS complex is a feature of Third degree or complete hea block. One P wave to each QRS complex is a feature of First degree block