Figure 17

EKG findings Associated with Atrioventricular-Conduction Disturbances.
1) First-degree atrioventricular block: PR interval of >0.2 second. Every P wave followed by a QRS complex.
2) Second-degree atrioventricular block, Mobitz type I (Wenchebach block): Progressive lengthening of PR interval and shortening of RR interval until a P wave is blocked. PR interval after blocked beat is shorter than preceding PR interval.
3) Second-degree atrioventricular block, Mobitz type II: Intermittently blocked P waves. PR interval on conducted beats is constant.
4) Second degree, high-grade atrioventricular block: Conduction ratio of 3:1 or more. PR interval of conducted beats is constant.
5) Third-degree atrioventricular block: Dissociation of atrial and ventricular activity. Atrial rate is faster than ventricular rate, which is of junctional or ventricular origin.

Mangrum, J.M., Dimarco, J.P., The Evaluation and Management of Bradycardia, NEJM 2000; 342, No. 10, 703-709