1. Bradycardias and atrioventricular conduction block
Scott Ewing, D.O.
November 3, 2005

2. Sinus Bradycardia
Common in normal individuals during sleep and high vagal tone (athletes and young healthy adults)
P wave before every QRS complex and normal P axis
PR interval is at least 0.12 s
Most common pathological cause acute MI
Particularly associated with inferior MI as the inferior myocardial wall and the SA and AV nodes are usually supplied by the RCA

3. Sick Sinus Syndrome
SSS - dysfunction of the sinoatrial node, with impairment of its ability to generate and conduct impulses
Usually idiopathic fibrosis of the SA node but is also associated with myocardial ischaemia, digoxin, and cardiac surgery
EKG features include
persistent sinus bradycardia
periods of sinoatrial block
sinus arrest
junctional or ventricular escape rhythms
tachycardia­bradycardia syndrome
paroxysmal atrial flutter
atrial fibrillation
Most common EKG feature is an inappropriate, persistent, and often severe sinus bradycardia

4. Tachycardia­Bradycardia Syndrome
Common in sick sinus syndrome
Characterised by bursts of atrial tachycardia interspersed with periods of bradycardia
Paroxysmal atrial flutter or fibrillation may also occur, and cardioversion may be followed by a severe bradycardia

5. Sinoatrial Block
Characterised by a transient failure of impulse conduction to the atrial myocardium, resulting in intermittent pauses between P waves
The pauses are the length of two or more P­P intervals

6. Sinus Arrest
Transient cessation of impulse formation at the sinoatrial node
Manifests as a prolonged pause without P wave
Pause is unrelated to the length of the P­P cycle

7. Escape Rhythms
Result of spontaneous activity from a subsidiary pacemaker, located in the atria, atrioventricular junction, or ventricles
Takes over when normal impulse formation or conduction fails and may be associated with any profound bradycardia
Junctional escape beat has a normal QRS complex shape with a rate of 40­60 beats/min
Ventricular escape rhythm has broad complexes and is slow (15­40 beats/min)