Figure 16

Electrocardiographic Findings Associated with Sinus-Node Dysfunction which include the following.
1) Sinus bradycardia: normal P-wave axis with heart rate of <60 beats per minute. Every P wave followed by QRS complex.
2) Sinus arrest: Normal P-wave axis. Every P wave followed by QRS complex. Pauses of >3 seconds without atrial activity.
3) Sinoatrial exit block: Normal P-wave axis. Progressive shortening of PP interval until one P wave fails to conduct (second degree, type I) or sinus pause is an exact multiple of the base-line PP interval (second degree, type II (shown)).
4) Bradycardia-tachycardia syndrome: Alternating periods of atrial tachyarrhytmias and bradycardia. The P waves have been labled in red. The QRS's are labled R's in red

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