VARIABLE PR
Type I 2nd degree AV block (Wenckebach periodicity)
- Progressive prolongation of P-R intervals until AV transmission is blocked completely
- Intermittent failure of transmission of the atrial impulse to the ventircles
3rd degree AV block
- Random PR interval length, complete independence of conduction between the aria and ventricles
- Occasionally P-R intervals may vary with fluctuating vagal/adrenergic tone – usually this is associated with marked sinus arrhythmia (OSA, autonomic dysfunction)